TYPE Original Research PUBLISHED 31 March 2023 DOI 10.3389/fncel.2023.1152248 Neural substrates of cognitive OPEN ACCESS impairment in a NMDAR EDITED BY Yuh-Man Sun, Retired, London, United Kingdom hypofunction mouse model of REVIEWED BY Torfi Sigurdsson, schizophrenia and partial rescue Goethe University Frankfurt, Germany Dennis Kätzel, University of Ulm, Germany by risperidone *CORRESPONDENCE M. Victoria Puig Cristina Delgado-Sallent1 , Thomas Gener1,2,3 , Pau Nebot1 , vickypuig.bcn@gmail.com Cristina López-Cabezón2,3 and M. Victoria Puig1,2,3* SPECIALTY SECTION 1 This article was submitted to Hospital del Mar Medical Research Institute (IMIM), Barcelona Biomedical Research Park, Barcelona, Cellular Neurophysiology, Spain, 2 Catalan Institute of Nanoscience and Nanotechnology, CSIC and BIST, Barcelona, Spain, 3 Institut a section of the journal de Neurociències, Universitat Autònoma de Barcelona, Barcelona, Spain Frontiers in Cellular Neuroscience RECEIVED 27 January 2023 ACCEPTED 10 March 2023 PUBLISHED 31 March 2023 N-methyl D-aspartate receptor (NMDAR) hypofunction is a pathophysiological CITATION mechanism relevant for schizophrenia. Acute administration of the NMDAR Delgado-Sallent C, Gener T, Nebot P, López-Cabezón C and Puig MV (2023) Neural antagonist phencyclidine (PCP) induces psychosis in patients and animals substrates of cognitive impairment in a while subchronic PCP (sPCP) produces cognitive dysfunction for weeks. We NMDAR hypofunction mouse model of schizophrenia and partial rescue by investigated the neural correlates of memory and auditory impairments in mice risperidone. treated with sPCP and the rescuing abilities of the atypical antipsychotic drug Front. Cell. Neurosci. 17:1152248. doi: 10.3389/fncel.2023.1152248 risperidone administered daily for two weeks. We recorded neural activities in the medial prefrontal cortex (mPFC) and the dorsal hippocampus (dHPC) COPYRIGHT © 2023 Delgado-Sallent, Gener, Nebot, during memory acquisition, short-term, and long-term memory in the novel López-Cabezón and Puig. This is an object recognition test and during auditory processing and mismatch negativity open-access article distributed under the terms of the Creative Commons Attribution License (MMN) and examined the effects of sPCP and sPCP followed by risperidone. We (CC BY). The use, distribution or reproduction found that the information about the familiar object and its short-term storage in other forums is permitted, provided the original author(s) and the copyright owner(s) were associated with mPFC→dHPC high gamma connectivity (phase slope are credited and that the original publication in index) whereas long-term memory retrieval depended on dHPC→mPFC theta this journal is cited, in accordance with accepted academic practice. No use, connectivity. sPCP impaired short-term and long-term memories, which were distribution or reproduction is permitted which associated with increased theta power in the mPFC, decreased gamma power does not comply with these terms. and theta-gamma coupling in the dHPC, and disrupted mPFC-dHPC connectivity. Risperidone rescued the memory deficits and partly restored hippocampal desynchronization but did not ameliorate mPFC and circuit connectivity alterations. sPCP also impaired auditory processing and its neural correlates (evoked potentials and MMN) in the mPFC, which were also partly rescued by risperidone. Our study suggests that the mPFC and the dHPC disconnect during NMDAR hypofunction, possibly underlying cognitive impairment in schizophrenia, and that risperidone targets this circuit to ameliorate cognitive abilities in patients. KEYWORDS phencyclidine, atypical antipsychotic drugs, theta and gamma oscillations, neural synchrony, novel object recognition, auditory evoked potentials, prefrontal cortex, hippocampus Frontiers in Cellular Neuroscience 01 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 Introduction (Delgado-Sallent et al., 2022). In healthy mice, acute risperidone had an inhibitory effect on the circuit, reducing spiking N-methyl D-aspartate receptor (NMDAR) hypofunction is a activity and theta-gamma oscillations in both areas, and it also pathophysiological mechanism found in schizophrenia patients disrupted the circuit’s connectivity (Gener et al., 2019). Here, that can be replicated in rodent models by using pharmacological we investigated the neural correlates of memory and auditory agents that block NMDAR, for example phencyclidine or deficits in the sPCP model of schizophrenia and their rescue ketamine (Lee and Zhou, 2019). Sub-chronic administration by chronic risperidone, experimental conditions closer to the of phencyclidine (sPCP, also known as angel dust) to rodents clinical settings. mimics cognitive symptoms in schizophrenia for several months. That is, it impairs executive functions such as recognition memory, cognitive flexibility, and sensorimotor gating, including Materials and methods mismatch negativity (MMN; Rajagopal et al., 2014; Hamilton et al., 2018b; Lee and Zhou, 2019). Moreover, exposure to PCP Animals reduces the density of PV-expressing GABAergic interneurons (PV+ ) in the prefrontal cortex (PFC) and the hippocampus Experiments were performed in C57BL/6J male mice (n = 51) (HPC; Abdul-Monim et al., 2007) of the animals. This is that were 2–3 months old at the start of the experiments. Mice were similar to what is observed in post mortem tissue from patients housed under conditions of controlled temperature (23 ± 1◦ C) with schizophrenia (Lewis et al., 2005; Konradi et al., 2011; and illumination (12 hours light/dark cycle). All procedures were Kaar et al., 2019), further validating subchronic PCP (sPCP) authorized by the Barcelona Biomedical Research Park (PRBB) as a suitable animal model. The reduction in PV+ neuron Animal Research Ethics Committee and the local government. populations impair perisomatic inhibition of pyramidal neurons that likely contributes to a diminished gamma synchronization that is required for most cognitive functions (Lewis et al., 2005). Surgeries However, a comprehensive neurophysiological characterization of prefrontal-hippocampal circuits following sPCP treatment is Mice were induced with a mixture of ketamine/xylazine and missing. placed in a stereotaxic apparatus. Anesthesia was induced with Atypical antipsychotic drugs are effective in reducing the 4% isoflurane and maintained at 0.5–2%. Small craniotomies positive symptoms of schizophrenia patients while showing were drilled above the medial PFC and the HPC. Several micro- modest amelioration of the negative and cognitive symptoms. screws were screwed into the skull to stabilize the implant, The neural substrates underlying these complex behavioral and the one on top of the cerebellum was used as a general effects are poorly understood, which makes the development ground. Three tungsten electrodes, one stereotrode and one of better treatments a difficult endeavor. In rodents, atypical single electrode, were implanted in the prelimbic region of antipsychotic drugs attenuate some of the behavioral effects the medial PFC (mPFC) and two more were implanted in induced by NMDAR antagonists, including sPCP-induced the CA1 area of the dorsal HPC (dHPC). The electrodes cognitive dysfunction (Grayson et al., 2007). They enhance were positioned stereotaxically in the prelimbic cortex (AP: dopamine efflux in the cortex and the HPC, affecting less 1.5, 2.1 mm; ML: ± 0.6, 0.25 mm; DV: −1.7 mm from the limbic system, whereas classical neuroleptics show the bregma) and the CA1 region (AP: −1.8 mm; ML: −1.3 mm; opposite effect. These actions are mediated by the affinity of DV: −1.15 mm). Neural activity was recorded while the atypical antipsychotic drugs for serotonin receptors, especially electrodes were being lowered down inside the brain to help the 1A (5-HT1A R) and the 2A (5-HT2A R) subtypes, which locate the CA1 region. In addition, three reference electrodes have a widespread expression in the brain and modulate the were implanted in the corpus callosum and lateral ventricles dopaminergic, serotonergic, glutamatergic, and GABAergic (AP: 1, 0.2, −1; ML: 1, 0.8, 1.7; DV: −1.25, −1.4, −1.5, systems. Risperidone is one of the most prescribed atypical respectively). The electrodes were made with two twisted strands antipsychotic drugs. It targets mainly D2R and 5-HT2A R of tungsten wire 25 µm wide (Advent, UK) and were held and is effective at treating the positive symptoms while together using heat insulation. At the time of implantation, also ameliorating certain aspects of cognitive symptoms the electrodes had an impedance that ranged from 100 to in humans and rodents, including executive function, 400 k and were implanted unilaterally with dental cement. attention, learning, and memory (Grayson et al., 2007; Electrode wires were pinned to an adaptor to facilitate their Houthoofd et al., 2008; Rajagopal et al., 2014; Baldez et al., connection to the recording system. After surgery, animals were 2021). allowed at least one week to recover during which they were We have recently reported that acute PCP exerts strong extensively monitored and received both analgesia and anti- influences on prefrontal-hippocampal neural dynamics in freely inflammatory treatments. Prior to the initiation of the experiments, moving mice. The psychosis-like states produced by PCP the animals were handled and familiarized with the implant were associated with hypersynchronization of the medial PFC connected to the recording cable. After the experiments ended, (mPFC), desynchronization of the dorsal HPC (dHPC), and the electrode placements were confirmed histologically by staining disrupted mPFC-dHPC circuit connectivity. Acute risperidone the brain slices with Cresyl violet (Figure 1B). Electrodes reduced cortical hypersynchronization but had limited efficacy in with tips outside the targeted areas were discarded from data restoring hippocampal synchronization and circuit connectivity analyses. Frontiers in Cellular Neuroscience 02 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 Behavioral tests objects, all conditions combined, 4.29 ± 0.13; BAS: 4.5 ± 0.16, sPCP: 4.07 ± 0.25, RIS: 4.29 ± 0.36; [24 h test] Novel objects, Resting states all conditions combined, 3.83 ± 0.12; BAS: 3.84 ± 0.21, sPCP: Recordings during quiet wakefulness were performed in an 3.89 ± 0.12, RIS: 3.7 ± 0.26; Familiar objects, all conditions open field box (50 cm × 40 cm × 20 cm) for 30 min. We harnessed combined, 4.47 ± 0.1; BAS: 4.47 ± 0.15, sPCP: 4.57 ± 0.19, RIS: the accelerometer signals integrated within the Intan RHD2132 4.3 ± 0.15. We also note that we needed to concatenate more visits amplifiers to precisely monitor general mobility of mice. We when they were short to reach five seconds. quantified the variance of the instantaneous acceleration module (ACC; variance (Root square[X2 , Y2 , Z2 ])) that was maximum Auditory evoked potential (AEP) and mismatch during exploration and decreased as the animals were in quiet negativity (MMN) tests alertness (Gener et al., 2019; Delgado-Sallent et al., 2022). Low The auditory tests were conducted consecutively in the home mobility was determined by a defined threshold in the output of cage located inside a soundproof box. We used the Python the accelerometer signals and normal movement was defined as library simpleaudio to generate the sounds in custom scripts that above that threshold. The animals typically rested for brief periods synchronized the sound with the electrophysiological recordings between 2 and 10 consecutive seconds. via an EIB board. Mice were habituated to the environment for 5 min. Next, 100 consecutive clicks separated by 10 s were presented Novel object recognition test (NOR) to the mice for a total of 8 min. A click consisted of 15 ms of white noise (“15ms_whitenoise.wav” function in the simpleaudio We quantified recognition memory in a custom-designed Python library). We next used an auditory oddball paradigm to T-maze as previously reported (Alemany-González et al., 2020, measure MMN. Mice were presented with a series of standard tones 2022). The maze was made of aluminum with wider and (6 or 8 kHz) in which a target tone (8 or 6 kHz) was presented higher arms than the standard mazes (8 cm wide × 30 cm randomly in 75–25% proportions, respectively. The frequencies of long × 20 cm high). The maze was shielded and grounded for the standard and target tones were switched after 500 trials in a flip- electrophysiological recordings and was placed on an aluminum flop design (Hamilton et al., 2018a). Tones lasted 10 ms and were platform. The novel-familiar object pairs were previously validated presented with 500 ms intertrial intervals. The protocol consisted as in Gulinello et al. (2018). The arm of the maze where the in the presentation of 1,000 tones, lasting around 10 min. novel object was placed in each session was randomly chosen across experiments. The task consisted of a habituation phase, familiarization phase, short-term memory test (STM), and long- term memory test (LTM), each lasting ten minutes (Figure 1B). Subchronic PCP model and During the habituation phase, the animals explored the maze pharmacology without objects. Five minutes later, mice were put back in the maze where two identical objects had been placed at the end We used phencyclidine hydrochloride (PCP; Sigma- of the lateral arms for the familiarization phase. Three minutes Aldrich) 10 mg/kg, 5+5 days, as in Rajagopal et al. (2014); and twenty-four hours later, a familiar object and a new object risperidone (RIS; Sigma-Aldrich) 0.5 mg/kg, 14 consecutive days. were placed in the maze for the STM and LTM tests, respectively. PCP was administered subcutaneously (SC) and risperidone Memory acquisition was investigated by comparing the initial intraperitoneally (IP). The following pharmacological groups were (early) and the last (late) visits to the two identical items in the investigated: sPCP (n = 21 mice), sPCP-RIS (n = 9), and their familiarization phase; memory retrieval and novelty seeking were corresponding saline controls: SAL (n = 8), sPCP-SAL (n = 7), investigated during the initial visits to familiar and novel objects, SAL-SAL (n = 8; Figure 1B and Supplementary Figure 1). respectively, during the STM and LTM tests. Exploratory events were timestamped into the recording files by sending TTL pulses to the acquisition system. This allowed us to quantify the number Neurophysiological recordings and data and duration of the visits. We used this information to estimate analyses the neurophysiological correlates of memory performance. The duration of the initial visits and the visits to the novel objects were All the recordings were implemented with the multi-channel typically longer than the last visits of the sessions and to the familiar Open Ephys system at 0.1–6,000 Hz and a sampling rate of 30 kHz. objects (Figure 1E). Because some of the mathematical tools Recorded signals from each electrode were filtered offline to extract employed are sensitive to the time window used, we concatenated local field potentials (LFPs) and multi-unit activity (MUA). different visits until the accumulated time reached five seconds. We note that familiarization was considered valid when mice Oscillatory activity visited the objects for at least ten seconds, as in previous studies To obtain LFPs, recorded signals were detrended, notch-filtered (Alemany-González et al., 2020, 2022). The exact number of visits and decimated to 1 kHz offline. The frequency bands considered used for each analysis was the following: [Familiarization phase] for the band-specific analyses included: delta (2–5 Hz), slow theta All conditions and objects combined, early: 3.91 ± 0.17, late: (4–8 Hz), theta (8–12 Hz), low gamma (30–48 Hz), high gamma 4.86 ± 0.05; BAS, early: 3.81 ± 0.25, late: 4.81 ± 0.1; sPCP, early: (52–100 Hz), and HFOs (100–200 Hz). Power spectral density 4.25 ± 0.19, late: 5; RIS, early: 3.54 ± 0.45, late: 4.73 ± 0.14; results were calculated using the multi-taper method. Spectrograms [3 min test] Novel objects, all conditions combined, 3.24 ± 0.2; were constructed using consecutive Fourier transforms. Phase- BAS: 3.07 ± 0.25, sPCP: 3.92 ± 0.25, RIS: 2.29 ± 0.52; Familiar amplitude coupling (PAC) was measured following the method Frontiers in Cellular Neuroscience 03 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 described in Onslow et al. (2011). The parameters used were: DIs. Statistical analyses were implemented in Python with the phase frequencies = [0, 15] with 1 Hz step and 4 Hz bandwidth, Pingouin statistical package (Vallat, 2018). amplitude frequencies = [10, 250] with 5 Hz step and 10 Hz bandwidth. Phase-amplitude coupling quantification results were obtained by averaging the values of selected areas of interest in the Results comodulograms. The exact frequencies used for each analysis are described in the figure legends. Directionality of signals between Chronic risperidone prevented areas (PFC→HPC and HPC→PFC) was calculated with the phase slope index (PSI) with a Python translation of MATLAB’s sPCP-induced short-term and long-term data2psi.m (epleng = 60 s, segleng = 1 s) as in Nolte et al. memory deficits (2008). Briefly, the PSI quantifies the consistency of the phase lag (or lead) as a function of frequency, between two signals. Here, We administered subchronically to mice the NMDAR positive slopes suggested the presence of PFC-to-HPC flows of antagonist phencyclidine (10 mg/kg SC 5 + 5 days; sPCP group) information while negative slopes suggested the opposite signal to model cognitive impairment in schizophrenia. We investigated directionality. The significance of PSI’s deviations was tested via the neural substrates of the well-established memory and auditory surrogate analysis. The surrogate analyses were performed by deficits of this model and their subsequent rescue by chronic randomizing the data of two pairs of channels, one in PFC and one risperidone (0.5 mg/kg IP for 14 consecutive days; sPCP-RIS in HPC, using all the combinations of different pairs of channels. group). We recorded neural activities in the prelimbic medial PFC The data were shuffled across time series and across pair of channels (mPFC) and CA1 region of the dorsal HPC (dHPC), brain regions 1,000 times to obtain the correspondent PSI shuffle. Next, to relevant for cognitive processing and the pathophysiology of remove chance effects, the randomized data were averaged and schizophrenia (Sigurdsson and Duvarci, 2016). The animals’ subtracted from the original data. To establish significance, a t-test behaviors and neural activities were characterized during was performed between the original data and its shuffle (Puig and baseline, after sPCP, after risperidone (sPCP-RIS group), and Miller, 2015; Lancaster et al., 2018). their corresponding saline controls (SAL, sPCP-SAL, and SAL-SAL groups; Figures 1A, B and Supplementary Figure 1). We first examined short-term memory (STM) and long-term Spiking activity memory (LTM) abilities of the different pharmacological groups Multi-unit activity was estimated by first subtracting the raw assessed via the NOR task (Figure 1B), a well validated memory signal from each electrode with the signal from a nearby referencing test that relies on the mice’ innate instinct to explore novel objects electrode to remove artifacts resulting from the animal’s movement. and depends on hippocampal-prefrontal circuits (Warburton and Then, continuous signals were filtered between 450 and 6,000 Hz Brown, 2015; Alemany-González et al., 2020; Wang et al., 2021). with Python and thresholded at -3 sigma standard deviations with Consistent with previous studies, discrimination indices (DIs) for Offline Sorter v4 (Plexon Inc.). We estimated MUA in three- novel versus familiar objects ([time visiting the novel object − time second (quiet alertness) or 10 ms (auditory evoked potentials) visiting the familiar object]/total exploration time) were positive for non-overlapping windows. Spike-LFP coupling was estimated with all the mice during baseline in the 3-min and 24 h memory tests the pairwise phase consistency (PPC) method, which is an unbiased (DIs = 0.35 ± 0.05 and 0.29 ± 0.04; n = 7, 8 mice, respectively). parameter to determine the degree of tuning of the neurons’ That is, mice exhibited good STM and LTM at the beginning of the firing to ongoing network activity at specific frequencies (Vinck experiment. After sPCP, mice explored novel and familiar objects et al., 2011, p. 20; Zorrilla de San Martín et al., 2020). PPC was evenly (DIs = 0.01 ± 0.06 and −0.06 ± 0.06; baseline vs. sPCP: determined using the phases of spikes from MUA in 25 s epochs, p < 0.0005, paired t-test) indicating poor recognition memory. This only considering epochs with at least 250 spikes. was not observed in controls with saline (SAL group, n = 4 mice). Chronic risperidone rescued both STM deficits (DI = 0.42 ± 0.1; n = 4 mice) and LTM deficits (DI = 0.37 ± 0.07; n = 6 mice; Statistical analysis Figure 1C and Table 1), but not their corresponding saline controls (sPCP-SAL group, n = 7 mice; Supplementary Figure 1). Data are represented in boxplots (seaborn function in Python) We next analyzed the number and duration of the visits to each where the median and the quartiles are shown. We used object per session. During baseline and risperidone conditions, paired t-tests, one-way repeated measures ANOVAs to compare mice visited the novel items on more occasions than the familiar behavioral and neurophysiological measures within animals items ([STM: baseline, risperidone]: p = 0.019, 0.038; [LTM: (baseline-sPCP-RIS), and mixed ANOVAS to compare behavioral baseline, risperidone]: p = 0.003, 0.047; paired t-tests) and the and neurophysiological measures between pharmacological groups visits lasted longer, particularly during the STM test ([baseline, (baseline-sPCP-SAL). Two-way ANOVAs were used to compare risperidone]: p < 0.005, 0.056). In contrast, after sPCP the the effects of the sPCP-RIS group with their respective saline mice visited both objects evenly by increasing the number and controls (sPCP-SAL, SAL-SAL). Paired t-tests were used to assess duration of visits to familiar objects, behaving as if they were differences between early and late visits to objects (familiarization novel (Figure 1D). This indicated poor recognition memory. The test), between visits to novel and familiar objects (3-min and 24 h duration of the visits decreased within a session as the mice became tests), and between PSI and its shuffle. We used Sidak’s correction less interested in the objects, both novel and familiar. A sharp post hoc tests in the ANOVAs. We employed Pearson correlations decrease in duration occurred during the first five visits to the to identify associations between neurophysiological measures and novel objects in the two tests and subsequently the duration of the Frontiers in Cellular Neuroscience 04 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 FIGURE 1 Experimental design and main behavioral results. (A) Experimental protocol and behavioral tests used. S indicates the date of surgery to implant recording electrodes. (B) The novel object recognition test (NOR) in detail. Right and left buttons on a joystick were pressed for the duration of each visit to timestamp the information into the recording files. Representative examples of histological verification of electrode locations within the prelimbic PFC and the CA1 area of the HPC. We recorded neural activities during the surgical implantations to increase the chances of implanting the electrodes within the target areas. At the end of the experiment, before euthanasia, a gentle current was passed through the electrodes to mark the recording areas (arrows). Also shown is a summary table that illustrates the different pharmacological groups of the study and the number of mice used in each group. (C) Discrimination indices (DIs) during the 3-min (STM) and the 24 h (LTM) tests. DIs decreased significantly after sPCP and recovered after chronic risperidone (STM, LTM: F(2,6) = 16.64, 15.15, p = 0.004, <0.0005; one-way repeated measures ANOVA, n = 9 mice; the results including all the mice are shown in Supplementary Figure 1). (D) Number and mean duration of visits to familiar and novel objects during the STM and LTM tests. After sPCP, mice visited both objects evenly by increasing the number of visits to familiar objects, reflecting poor recognition memory (F(1,13) = 15.12, 5.2, p = 0.002, 0.037). (E) The duration of the visits decreased within a session as the mice became less interested in the objects ([baseline STM, LTM]: F(2,26) = 3.52, 3.56, p = 0.005, 0.0006; one-way repeated measures ANOVA with novel and familiar objects combined). A sharp decrease in duration occurred during the first 5 visits to both objects in the two tests, and this was more pronounced for novel objects (first 5 visits to novel objects vs. first 5 visits to familiar objects; [STM, LTM]: F(2,26) = 36.03, 11.57, p < 0.0005, 0.002). These behaviors were not overtly disrupted by sPCP or risperidone. visits declined slowly. These prolonged initial visits did not occur activities during resting states, brief 3-second episodes of low when the mice visited the familiar objects. These behaviors were behavioral activity while the mice explored an open field (see not overtly disrupted by sPCP or risperidone (Figure 1E). section “Materials and methods”). As we reported previously (Delgado-Sallent et al., 2022), during resting states healthy mice exhibited a strong circuit synchronization at theta frequencies Risperidone partially rescued (4–12 Hz): theta oscillations were prominent in the mPFC and sPCP-induced disruptions of theta and there were robust theta oscillations, theta-gamma and spike-theta gamma synchronization in coupling in the dHPC (Figures 2A–C). prefrontal-hippocampal circuits during sPCP disrupted theta and gamma rhythms within mPFC- quiet alertness dHPC circuits that were partially restored by risperidone (n = 21 mice). First, sPCP increased high gamma (52–100 Hz) power in We first aimed to gain insight into the neural dynamics the mPFC that was reduced by risperidone. Concomitantly, sPCP of healthy prefrontal-hippocampal circuits (mPFC-dHPC) during decreased high gamma power in the dHPC, however, this was not quiet alertness and their impact by sPCP and risperidone. To rescued by risperidone (Figure 2A). In addition, sPCP weakened mitigate the effects of the hyperlocomotion produced by sPCP intrinsic theta-gamma coupling both locally in the dHPC and (Mouri et al., 2012; Castañé et al., 2015) we analyzed neural inter-regionally (PFCphase -HPCamp ) that were partially restored by Frontiers in Cellular Neuroscience 05 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 TABLE 1 Summary of main results. sPCP Risperidone Quiet alertness mPFC Increased high gamma power Fully rescued dHPC Decreased high gamma power and theta-gamma coupling Coupling partially rescued Memory acquisition BEHAVIOR – – mPFC Increased theta power Not rescued dHPC Decreased high gamma power and theta-gamma coupling Coupling partially rescued PSI Disrupted mPFC → dHPC high gamma signals during familiar visits Not rescued Short-term memory BEHAVIOR Decreased discrimination index Fully rescued mPFC Increased theta power Not rescued dHPC Decreased high gamma power and theta-gamma coupling Partially rescued PSI Disrupted mPFC → dHPC high gamma signals during familiar visits Not rescued Long-term memory BEHAVIOR Decreased discrimination index Fully rescued mPFC – – dHPC Decreased high gamma power and theta-gamma coupling Partially rescued PSI Disrupted dHPC → mPFC theta signals during familiar visits Not rescued Auditory processing BEHAVIOR Decreased response ratio Partially rescued mPFC-P2 Decreased spiking activity Partially rescued mPFC-P3 Decreased amplitude and spiking activity Partially rescued MMN MMN not present Not rescued risperidone (Figure 2B). We detected strong correlations between compared the neurophysiological signals during the familiarization the reductions of hippocampal high gamma power and the two phase (Figure 1B) between the initial visits to the two (identical) forms of theta-gamma coupling both during baseline ([HPC, objects, which imply novelty seeking, and the last visits of the circuit] Pearson’s R = 0.73, 0.69, p < 0.0005) and after sPCP session, when the animals had just acquired a new memory about (R = 0.81, 0.76, p < 0.0005). These correlations put forward a key the objects. More specifically, we compared neurophysiological role of hippocampal high gamma oscillations in the generation of biomarkers recorded during the first five seconds versus the last theta-gamma coupling within the circuit. Moreover, sPCP tended five seconds of the total accumulated time of the visits, regardless to increase the firing rate of neuron populations (MUA) in the of object (i.e., located in the right or left arms) or number of visits. mPFC that was reduced by risperidone (n = 5 mice; Figure 2C). On average, the 5-second epochs included 3.91 ± 0.2 early visits and In the dHPC, sPCP did not change the firing rate of neurons 4.86 ± 0.06 late visits (see section “Materials and methods”). During but disrupted the coupling of spikes to ongoing theta oscillations normal memory acquisition, theta power (8–12 Hz) increased in (n = 4 mice). Risperidone was unable to restore the spike-theta the mPFC and decreased in the dHPC (early vs. late visits; p = 0.012, synchronization and it increased the locking of spikes to delta 0.024, paired t-test; Figures 3A, B), whereas local and inter-regional oscillations (<5 Hz; Figure 2D). No major changes in power, cross- theta-gamma coupling seemed unchanged (Figures 3C, D). We frequency coupling, and spike-LFP coupling were observed at other note that changes in theta power were not simply due to differential frequencies in either region. Finally, the directionality of signals locomotion of mice during a session, as the animals’ mobility was within the circuit was not overtly affected by sPCP or risperidone low while they were visiting the objects both at the beginning and (Figure 2E). These sPCP-induced alterations were not present in at the end of the sessions. We further investigated whether any saline controls (SAL group, n = 8 mice; Supplementary Figure 2). flow of information emerged within the circuit during memory Together, these findings suggested that risperidone improved acquisition. We focused on theta and gamma frequencies based sPCP-induced disruption of theta and gamma synchronization in on previous work from our group (Alemany-González et al., 2020, mPFC-dHPC circuits (Figure 2F and Table 1). 2022). We found that mPFC→dHPC high gamma signals tended to emerge during the late visits (Figure 3E). Therefore, memory acquisition was associated with increases of theta power in the mPFC, decreases of theta and gamma power in the dHPC, and Risperidone partially restored the neural mPFC→dHPC high gamma signals (Figure 3F). correlates of sPCP-induced poor sPCP augmented non-specifically theta power in the mPFC and recognition memory in decreased it in the dHPC. In addition, high gamma power also prefrontal-hippocampal circuits declined in the dHPC after sPCP. None of the power changes were consistently recovered by risperidone, although tendencies were We first aimed to understand the neural mechanisms detected in the dHPC (Figures 3A, B). Local and inter-regional underlying memory acquisition in healthy animals (n = 9 mice). We theta-gamma did not change during memory acquisition. However, Frontiers in Cellular Neuroscience 06 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 FIGURE 2 sPCP disrupted theta and gamma synchronization in mPFC-dHPC circuits during quiet wakefulness. Some of these alterations were ameliorated by risperidone. (A) sPCP increased high gamma power in the mPFC (baseline vs. sPCP: p = 0.047, paired t-test; n = 21 mice) and decreased it in the dHPC (p = 0.004). Risperidone rescued aberrant gamma power in the mPFC (F(2,16) = 0.11, p = 0.9; one-way repeated measures ANOVA; no post-hoc differences between BAS and sPCP-RIS), but not in the dHPC (F(2,14) = 6.73, p = 0.01). (B) sPCP weakened local and inter-regional theta-gamma coupling (6–10 Hz with 40–60 Hz; l-PAC; p = 0.008; ir-PAC PFCphase -HPCamp ; p = 0.001; one-way repeated measures ANOVA) that were partially restored by risperidone (F(2,14) = 0.23, p = 0.125; no post-hoc differences between BAS and sPCP-RIS). (C) sPCP promoted the spiking activity of neuron populations (multi-unit activity or MUA) in the mPFC that was reduced by risperidone (F(2,6) = 4.58, p = 0.047). (D) sPCP disrupted the coupling of spikes to theta oscillations in the dHPC that was restored by risperidone (F(2,6) = 19.4, p = 0.002). Risperidone also boosted spike-delta coupling in the dHPC (3–6 Hz, F(2,6) = 5.39, p = 0.046). Spike-LFP coupling was estimated via the pairwise phase consistency method (PPC). (E) sPCP did not significantly affect the directionality of theta and high gamma signals within the circuit, but some tendencies were observed in the high gamma band. Circuit directionality was estimated via the phase slope index (PSI). (F) Proposed neural mechanism for the effects of sPCP and risperidone on mPFC-dHPC circuits during quiet alertness. In red, changes produced by sPCP, in orange sPCP-induced deviations ameliorated by risperidone. See also Supplementary Figure 3. as above, and consistent with the reduction of gamma power in Pearson’s R = 0.7, p = 0.026; Figure 4F). Similar again to memory the dHPC, both types of theta-gamma coupling weakened after acquisition, sPCP increased theta power in the mPFC and reduced sPCP (differences with SAL controls; Supplementary Figure 2). high gamma power in the dHPC (Figures 4A, B). Correspondingly, After risperidone, theta-gamma coupling was partially restored both local and inter-regional theta-gamma coupling were also (Figures 3C, D). Finally, sPCP disrupted the mPFC→dHPC high reduced (Figures 4C, D). Risperidone only partially recovered gamma signals detected during late visits to the objects that were the power and coupling alterations produced by sPCP in the partially corrected by risperidone (Figure 3E). Overall, we found dHPC. The mPFC→dHPC high gamma signals detected during that sPCP disrupted all the biomarkers associated with memory familiar visits when the animals were healthy were also disrupted by acquisition, that were not rescued by risperidone. sPCP further sPCP and were not recovered by risperidone (Figure 4E). Overall, weakened theta-gamma coupling in the dHPC that was partially risperidone attenuated the alterations produced by sPCP in the restored by risperidone (Figure 3F and Table 1). dHPC but was unable to rescue disrupted neural activities in the We next investigated the neural substrates of STM (n = 7 mice). mPFC or the flow of information within the circuit (Figure 4G and We compared the neurophysiological signals recorded during the Table 1). first five seconds of visits to the novel and familiar objects during We further investigated the neural substrates of LTM (n = 8 the 3-min tests (Figure 1B). On average, these included 3.24 ± 0.2 mice). We compared the neurophysiological signals recorded and 4.29 ± 0.13 visits to novel and familiar objects, respectively during the first 5 s of visits to the novel and familiar objects (Figure 1E). Animals with DIs over 0.2 during the baseline were during the 24 h memory tests (Figure 1B). On average, these used in these analyses. Theta power (Figures 4A, B) and theta- included 3.83 ± 0.12 and 4.47 ± 0.1 visits to novel and familiar gamma coupling (Figures 4C, D) did not differ during the visits to objects, respectively (Figure 1E). Again, only animals with DIs novel and familiar objects. However, we detected a mPFC→dHPC over 0.2 during baseline were used. Similar to STM, we did not flow of information at high gamma frequencies during the visits to detect changes in power or theta-gamma coupling between visits familiar objects (Figure 4E), similar to memory acquisition. This to novel and familiar objects in either region (Figures 5A–D). directionality of signals seemed relevant for memory processing Furthermore, dHPC→mPFC theta signals were detected during as it correlated strongly with memory performances (DI with PSI: the visits to familiar objects (Figure 5E) and correlated inversely Frontiers in Cellular Neuroscience 07 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 FIGURE 3 Neural substrates of memory acquisition and effects of sPCP and risperidone. (A) Power spectra showing the effects of sPCP and risperidone in the mPFC and the dHPC during the familiarization phase. Vertical dashed lines mark the first second upon initiation of the visits. (B) Prefrontal theta power increased in healthy animals during the late visits to the objects. sPCP increased non-specifically theta power in the mPFC (baseline vs. sPCP: F(1,10) = 7.46, p = 0.021; mixed ANOVA with time of visits (early vs. late) and treatment (baseline vs. sPCP) as factors) and reduced theta and high gamma power in the HPC (baseline vs. sPCP: F(1,12) = 4.81, 9.59, p = 0.053, 0.011), disrupting the normal neural dynamics of memory acquisition. Risperidone did not rescue these power changes. (C,D) Intrinsic dHPC theta-gamma coupling (7–10 Hz with 60–80 Hz) did not change with memory acquisition. sPCP disrupted theta-gamma coordination that was partially rescued by risperidone ([l-PAC] F(1,12) = 37.68, p < 0.0005; mixed ANOVAs as above; differences with sPCP-SAL controls: F(1,22) = 6.31, p = 0.02; mixed ANOVA with time of visits (early vs. late) and treatment (SAL vs. sPCP) as factors). Similar results were obtained for inter-regional theta-gamma coupling ([ir-PAC] F(1,12) = 41.09, p < 0.0005; data not shown; differences with sPCP-SAL controls: F(1,22) = 4.62, p = 0.024; mixed ANOVAs as above). (E) In healthy mice, mPFC→dHPC high gamma signals tended to occur during the late visits to the objects (PSI vs. shuffle, p = 0.069; paired t-student; marked with an arrow). sPCP disrupted these flows of information (baseline vs. sPCP, p = 0.096; PSI vs. shuffle, p = 0.49) that were not restored by risperidone (PSI vs. shuffle, p = 0.38). (F) Proposed neural mechanism for memory acquisition and effects of sPCP and risperidone. In red, changes produced by sPCP, in orange sPCP-induced deviations ameliorated by risperidone. with the DIs (Pearson’s R = −0.72, p = 0.01; Figure 5F). As above, alterations were observed across different days. Risperidone sPCP decreased dHPC high gamma power when the animals visited partially rescued some of these disturbances, hippocampal gamma both objects (Figures 5A, B). Also as above, both local and inter- oscillations and theta-gamma coupling in a more consistent way, regional theta-gamma coupling were reduced by sPCP (Figures 5C, suggesting a preferential action on this brain region (Table 1). D). Like during STM, risperidone partially rescued sPCP-reduced gamma power and theta-gamma coupling in the dHPC. However, it was unable to restore dHPC→mPFC theta signals (Figure 5G Risperidone improved the and Table 1). neurophysiological signatures of Together, these results unraveled a contribution of theta and auditory processing in sPCP-treated gamma signals within mPFC-dHPC circuits to normal memory mice but did not reinstate MMN acquisition, STM and LTM processes in the context of object recognition memory. sPCP increased theta power in prefrontal We finally investigated the effects of sPCP and risperidone on microcircuits, disrupted high gamma rhythms in the dHPC and the neural substrates of auditory attention and processing. More the theta-gamma coupling associated with it, regardless of brain specifically, we examined alterations in auditory evoked potentials state and cognitive task. That is, sPCP-induced neurophysiological (AEPs) and mismatch negativity (MMN), as both biomarkers Frontiers in Cellular Neuroscience 08 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 FIGURE 4 Neural substrates of short-term memory and effects of sPCP and risperidone. (A) Power spectra in the mPFC and the dHPC during the 3-minute memory test and effects of sPCP and risperidone. Vertical dashed lines mark the first second upon initiation of the visits. (B) Theta and high gamma oscillations were similar during the visits to familiar and novel objects in both regions. sPCP increased theta power in the mPFC non-specifically interfering with the normal theta dynamics (F(1,7) = 8.26 p = 0.024; mixed ANOVA with object (familiar vs. novel) and treatment (baseline vs. sPCP) as factors). sPCP also reduced dHPC high gamma power (F(1,12) = 8.37, p = 0.023; differences with sPCP-SAL controls: F(1,20) = 6.44, p = 0.022; mixed ANOVA with object (familiar vs. novel) and treatment (SAL vs. sPCP) as factors) that were partially rescued by risperidone. (C,D) Intrinsic hippocampal theta-gamma coupling (7–10 Hz with 60–80 Hz) was similar during visits to familiar and novel objects. sPCP disrupted theta-gamma coordination that was partially rescued by risperidone ([l-PAC] F(1,12) = 10.36, p < 0.009; differences with sPCP-SAL controls; F(1,22) = 19.13, p = < 0.0005; mixed ANOVAs as above). Similar results were obtained for inter-regional theta-gamma coupling ([ir-PAC] F(1,12) = 16.38, p = 0.002, data not shown; differences with sPCP-SAL controls: F(1,22) = 17.5, p < 0.0005; mixed ANOVAs as above). (E) In healthy mice, mPFC→dHPC high gamma signals were detected during the visits to the familiar objects (PSI vs. shuffle, p = 0.004; paired t-student). sPCP disrupted this flow of information (baseline vs. sPCP, p = 0.008; PSI vs. shuffle, p = 0.19) that was not restored by risperidone (PSI vs. shuffle, p = 0.24). (F) mPFC→dHPC PSI at high gamma frequencies during the visits to familiar objects correlated strongly with discrimination indices during baseline (R = 0.7, p = 0.026), but not after sPCP (R = –0.28, p = 0.43) or risperidone (R = –0.39, p = 0.38). (G) Proposed neural mechanism for STM and effects of sPCP and risperidone. In red, changes produced by sPCP, in orange sPCP-induced deviations ameliorated by risperidone. are highly translational between patients and rodent models of The AEP protocol consisted of 100 trials of white noise, schizophrenia (Amann et al., 2010; Nagai et al., 2013; Javitt and each tone lasting 15 ms with an inter-trial interval of 10 s Sweet, 2015; Modi and Sahin, 2017). Briefly, mice were placed (Figure 6A). During baseline, we detected cortical AEPs in 82.3% in a cage surrounded by a sound enclosure with four speakers. of the trials (response ratio: [number of AEPs/number of trials]). The animals were presented with standard auditory stimuli first The response ratio decreased after sPCP to 64.7%, but not after and subsequently the oddball paradigm in 30-min sessions during saline (Supplementary Figure 4). Risperidone partially rescued baseline, after sPCP and after risperidone treatments as above. Only the response ratio to 71.8% (Figure 6B). Concomitantly, sPCP- animals evaluated in the three experiments were included in the treated mice showed abnormal AEPs with respect to the baseline, analyses. Neural activities were recorded both in the mPFC and specifically the P2 and P3 peaks, analogous to the P200 and the dHPC, but hippocampal responses were inconsistent and highly P300 peaks in humans. sPCP attenuated the spiking activity variable between animals, therefore we only present data collected associated with the P2 component (40–70 ms) whereas the P3 from the mPFC. component (200–300 ms) was reduced both in amplitude and Frontiers in Cellular Neuroscience 09 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 FIGURE 5 Neural substrates of long-term memory and effects of sPCP and risperidone. (A) Power spectra in the mPFC and the dHPC during the 24h memory test and effects of sPCP and risperidone. Vertical dashed lines mark the first second upon initiation of the visits. (B) Power in the mPFC and the dHPC was similar during visits to familiar and novel objects. sPCP reduced high gamma power in the dHPC non-specifically (F(1,12) = 15.33, p = 0.006; mixed ANOVA with object (familiar vs. novel) and treatment (baseline vs. sPCP) as factors; differences with SAL controls, F(1,20) = 5.28, p = 0.021; mixed ANOVA with object (familiar vs. novel) and treatment (SAL vs. sPCP) as factors). As above, risperidone partially rescued hippocampal gamma power. (C,D) Intrinsic hippocampal theta-gamma coupling (7–10 Hz with 60–80 Hz) was similar during visits to familiar and novel objects. sPCP disrupted theta-gamma coordination that was partially rescued by risperidone ([l-PAC] F(1,12) = 15.96, p < 0.003; differences with sPCP-SAL controls: F(1,22) = 6.31, p = 0.021; mixed ANOVAs as above). Similar results were obtained for inter-regional theta-gamma coupling ([ir-PAC] F(1,12) = 33.19, p < 0.0005; differences with sPCP-SAL controls: F(1,22) = 5.97, p = 0.02; data not shown). (E) In healthy mice, dHPC→mPFC theta signals were detected during the visits to the familiar objects (PSI vs. shuffle, p = 0.031; paired t-student). sPCP disrupted this flow of information (baseline vs. sPCP, p = 0.024; PSI vs. shuffle, p = 0.94) that was not rescued by risperidone (PSI vs shuffle, p = 0.64). (F) dHPC→mPFC PSI at theta frequencies during the visits to familiar objects correlated strongly with discrimination indices during baseline (R = –0.72, p = 0.01), but not after sPCP (R = –0.42, p = 0.17) or risperidone (R = –0.47, p = 0.24). (G) Proposed neural mechanism for LTM and effects of sPCP and risperidone. In red, changes produced by sPCP, in orange sPCP-induced deviations ameliorated by risperidone. spiking activity. Risperidone ameliorated the alterations associated Figure 4). Together, risperidone attenuated the behavioral and with both components (Figure 6C and Table 1). neurophysiological alterations associated with the late components We finally examined the MMN using a passive oddball of the AEPs but failed to rescue the MMN (Table 1). paradigm. Mismatch negativity is a component of event-related potentials that reflects preattentive auditory sensory memory. It emerges following deviant auditory stimuli and has been Discussion well characterized in patients with schizophrenia. We examined whether sPCP-treated mice exhibited reduced MMN and the We found that subchronic PCP impaired STM, LTM, and rescuing abilities of risperidone. Mice were presented with 500 auditory processing in mice that were partially rescued by tones that differed in frequency (6 or 8 kHz) in 25–75% ratios risperidone administered daily for two weeks. The behavioral (target and standard stimuli, respectively; Figure 6D). During deficits were accompanied by disrupted dHPC-mPFC neural baseline and in SAL mice, MMN emerged when the 6–8 kHz dynamics that attenuated after risperidone, preferentially in the target-standard tone combination was presented, but not with dHPC. These findings suggest that risperidone may target this the 8–6 kHz combination. The MMN was abolished by sPCP circuit, at least in part, to elicit its beneficial actions on cognitive and not restored by risperidone (Figure 6E and Supplementary abilities in patients with schizophrenia. Frontiers in Cellular Neuroscience 10 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 FIGURE 6 Neural substrates of auditory processing in the prelimbic cortex and effects of sPCP and risperidone. (A) AEP protocol. (B) Ratio of AEP responses detected in the PFC after the auditory stimuli. The ratio decreased in sPCP-treated animals ([baseline vs. sPCP, sPCP vs. saline]: p = 0.024, 0.024, paired and unpaired t-test, respectively) and was partially recovered by risperidone. (C) Mean AEP and corresponding spiking activity (multi-unit firing rates) at three different timescales. P2 (40-70 ms) was associated with less spiking activity after sPCP ([baseline vs. sPCP, sPCP vs. saline as above]: p = 0.013, 0.068; paired and unpaired t-tests, respectively), whereas P3 (200–300 ms) was reduced in amplitude and spiking activity ([baseline vs. sPCP, sPCP vs. saline as above]: amplitude: p = 0.015, 0.055; firing rate: p = 0.024, 0.06). Risperidone increased the spiking activity associated within P2 with respect to sPCP (F(2,10) = 2.49, p = 0.076; one-way repeated measures ANOVA) and augmented the amplitude and spiking activity associated with P3 component ([amplitude, firing rate]: p = 0.065, 0.097; paired and unpaired t-tests, respectively). (D) Protocol used for the oddball paradigm to assess mismatch negativity (MMN). (E) MMN was detected during the presentation of the 6-8 KHz target-frequent combination (left) but not the 8–6 kHz combination (right). Shown is the subtraction of target-frequent responses. MMN was absent in the sPCP-treated group (baseline vs. sPCP area under the curve; p = 0.021, paired t-test) and not restored by risperidone. Vertical dashed lines mark the start and end of tone presentation. The memory impairments produced by sPCP and their rescue to antipsychotic medication (Castañé et al., 2015; Rajagopal et al., by risperidone are in consonance with previous studies reporting 2016; Cadinu et al., 2018). Despite the novel object recognition that sPCP disrupts recognition memory in rodents that is sensitive task being extensively used as a screening tool for memory Frontiers in Cellular Neuroscience 11 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 abilities in biomedicine, an understanding of its underlying neural realistically the prescription of antipsychotic drugs to patients. mechanisms was missing. Thus, we first investigated whether and Here, the injection of risperidone for two weeks rescued STM how mPFC-dHPC circuits encoded memory acquisition, STM, and LTM impairments and attenuated the neural activity and LTM in this task. Our findings unraveled a relevant role for reductions observed in the dHPC, albeit it was unable to restore the circuit’s communication in the encoding of this task during cortical hypersynchronization or the connectivity of the circuit. baseline, with limited contribution of local power and theta- However, it is plausible that dampening cortical hyperactivity gamma coupling. mPFC→dHPC high gamma signals emerged by more prolonged administration of risperidone restores during memory acquisition and the visits to familiar objects in the circuit’s communication. Therefore, chronic medication the 3-minute memory test and were strongly associated with STM with risperidone may indeed favor healthier dHPC-mPFC performance (R = 0.7). Later, dHPC→mPFC theta signals were neural dynamics in patients with schizophrenia, accounting detected during the visits to familiar objects in the 24 h memory for their better performance in executive function, attention, test, which also correlated with LTM retrieval (R = 0.72). We note learning, and memory (Houthoofd et al., 2008; Baldez et al., that the mPFC sends direct afferents to the dHPC in the mouse 2021). whereas dHPC→mPFC pathways use the nucleus reuniens of the Furthermore, the findings of this study may help reconcile thalamus as a relay (Sigurdsson and Duvarci, 2016). Our findings studies in schizophrenia patients, in which both increases and suggest that the information about the new object (acquisition) decreases of gamma oscillations were found to be key biomarkers and its short-term storage were encoded by direct mPFC→dHPC of the disorder (Uhlhaas and Singer, 2010). Pathological gamma connectivity whereas long-term memory retrieval depended on oscillations in the cortex may originate from disinhibition dHPC→mPFC indirect connectivity. This hypothesis is in line with previous studies showing that novel experiences initiate molecular of cortical pyramidal neurons resulting from deficient PV+ signaling in the PFC that subsequently travel to the HPC (Takehara- interneurons (Sigurdsson, 2016; Guyon et al., 2021; Alemany- Nishiuchi, 2020), where memories are stored (Eichenbaum, 2004). González et al., 2022). In contrast, sPCP reduces PV+ density A key contribution of the circuit’s connectivity to memory extensively in the HPC (Abdul-Monim et al., 2007; Sabbagh processing was evidenced further by the fact that sPCP impaired et al., 2013) that, in turn, down-regulates pyramidal neuron STM and LTM and disrupted dHPC-mPFC communication during activity (Korotkova et al., 2010). This may explain the dampening the three phases of the NOR task. Previous studies from our of gamma oscillations and theta-gamma coupling observed in group have consistently detected that dHPC→mPFC signals are the dHPC of sPCP-treated mice. Consistent with our findings, relevant for long-term memory retrieval in wild-type mice of a abnormal gamma synchrony produced by NMDAR hypofunction different genetic background and altered in a mouse model of in both areas has been linked to cognitive impairment, including intellectual disability (Alemany-González et al., 2020, 2022), further tasks assessing STM and object recognition (Tort et al., 2009; supporting the findings presented here. Conflicting results exist Korotkova et al., 2010; Carlén et al., 2012). Further experiments, on whether recognition memory for objects requires the PFC however, are needed to elucidate the exact neural mechanisms (Spanswick and Dyck, 2012; Morici et al., 2015). Recent studies underlying gamma pathology in schizophrenia. Risperidone using optogenetic interrogation, however, implicate the mPFC in attenuated sPCP-induced gamma and theta-gamma decreases this type of memory and, in fact, identify HPC→mPFC theta in the dHPC very consistently. This antipsychotic drug binds coupling as a major neural mechanism involved (Wang et al., 2021; to serotonin 5-HT2A R with high affinity for which it is Chao et al., 2022). an inverse agonist. Therefore, it is likely that risperidone The differential effects of sPCP on prefrontal and hippocampal modulates gamma synchrony via 5-HT2A R-expressing PV+ microcircuits may explain the disruption of the flow of interneurons, which are present both in the mPFC and the dHPC information within this pathway. sPCP “disconnected” the (Puig et al., 2010; Puig and Gulledge, 2011; Puig and Gener, circuit by causing opposite effects in the two brain regions: 2015). it increased neural synchronization in the mPFC (enhanced We finally investigated the neural correlates of abnormal theta and gamma power) and desynchronized neural networks auditory processing in the frontal cortex of sPCP-treated mice, and in the dHPC (reduced theta, gamma power, and theta-gamma the rescuing abilities of risperidone. As above, we found that sPCP coupling). Prior studies have demonstrated that acute NMDAR impaired auditory processing in the mPFC that was attenuated by hypofunction desynchronizes neural activity in the HPC of risperidone. That is, there was a reduction in the number of AEPs rodents, including oscillatory and cross-frequency coupling after sPCP, which in turn exhibited smaller P2 and P3 late peaks, (Caixeta et al., 2013). Remarkably, we recently reported comparable effects following an acute administration of PCP that generated the mouse components analogous to the P200 and P300 peaks in psychosis-like states in mice (Delgado-Sallent et al., 2022). humans (Amann et al., 2010; Modi and Sahin, 2017). In addition, In that study, acute risperidone attenuated aberrant cortical abnormal P2 and P3 components were associated with decreased hypersynchronization but was unable to restore hippocampal spiking activity. Risperidone partially restored the late components desynchronization. This likely reflects risperidone’s efficacy of the AEPs, as observed in patients (Umbricht et al., 1999). We in containing psychosis but its inefficiency in ameliorating note that we did not detect alterations in the early component cognitive abilities in the short term. While acute risperidone of the AEPs (the P1 and N1), which have been associated with has proven to be effective in restoring cognitive deficits in the positive symptoms (Galderisi et al., 2014), consistent with the lack sPCP mouse model of schizophrenia (Grayson et al., 2007; of psychotic-like symptoms in sPCP-treated animals. However, Meltzer et al., 2011; Cadinu et al., 2018), it was important to electrophysiological recordings in the auditory cortex would be assess the effects of a chronic treatment that mimicked more necessary to confirm these results as the auditory cortex has shown Frontiers in Cellular Neuroscience 12 frontiersin.org Delgado-Sallent et al. 10.3389/fncel.2023.1152248 more consistent alterations in the early components in patients TG, CL-C, and PN analyzed the data. CD-S and MVP wrote the and rodent models (Wang et al., 2020). sPCP-treated mice also first draft of the manuscript. All authors contributed to manuscript showed reduced MMN, however, it was not rescued by risperidone. revision, read, and approved the submitted version. Reduced amplitude of the P200 and P300 peaks and the MMN are robust findings in patients with schizophrenia (Galderisi et al., 2014; Javitt and Sweet, 2015; Turetsky et al., 2015; Hamilton et al., Funding 2019; Fitzgerald and Todd, 2020; Koshiyama et al., 2020) and have also been reported in NMDAR hypofunction animal models This study was financed by grants SAF2016-80726-R and (Ehrlichman et al., 2008, 2009; Amann et al., 2010). Therefore, our PID2019-104683RB-I00 to MVP funded by MCIN/AEI/10.13039/ findings on sPCP- and risperidone-produced alterations of AEPs 501100011033 and by ERDF “A way of making Europe”. CD-S and MMN are highly translational and relevant to human studies. was supported by a FI AGAUR predoctoral fellowship from the In conclusion, sPCP impaired recognition memory that Catalan Government (Generalitat de Catalunya grant number was associated with increased mPFC, decreased dHPC neural 2018 FI_B_00112). network activities, and disrupted mPFC-dHPC communication. Risperidone rescued the memory deficits and attenuated hippocampal desynchronization but did not ameliorate mPFC and circuit connectivity alterations. sPCP also impaired auditory Acknowledgments attention and its neural correlates in the mPFC, which were also ameliorated by risperidone. Our study suggests that the We thank Jose A. Garrido and Amanda B. Fath for scientific mPFC and the dHPC disconnect during NMDAR hypofunction, insight into this study and Patricia Ruiz for administrative support. possibly underlying cognitive impairment in schizophrenia, and that risperidone targets this circuit to ameliorate cognitive abilities in patients. Conflict of interest The authors declare that the research was conducted in the Data availability statement absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation. Publisher’s note Ethics statement All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated All procedures were conducted in compliance with EU organizations, or those of the publisher, the editors and the directive 2010/63/EU and Spanish guidelines (Laws 32/2007, reviewers. Any product that may be evaluated in this article, or 6/2013 and Real Decreto 53/2013) and were authorized by the claim that may be made by its manufacturer, is not guaranteed or Barcelona Biomedical Research Park (PRBB) Animal Research endorsed by the publisher. Ethics Committee and the local government. Supplementary material Author contributions The Supplementary Material for this article can be found CD-S, TG, and MVP contributed to conception and design of online at: https://www.frontiersin.org/articles/10.3389/fncel.2023. the study and wrote the final version of the manuscript. 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