||Diabetic neuropathy (PND) is the most frequent secondary complication of diabetes mellitus (DM). The most important contributors to reduction in the quality of life of patients with DM are neurological pain and foot ulcerations and, ultimately, non-traumatic amputation of the affected limb. The pathogenesis is multifactorial, there are structural changes in the peripheral nerves and current treatments remain largely symptomatic, non-specific and not uniformly effective. Transgenic diabetic RIP/INFβ mice when treated with low doses of streptozotocin (STZ) present with pancreatic β-cell destruction, mimicking autoimmune diabetes in humans. On the basis that mechanisms governing peripheral nerve degeneration and regeneration are controlled by dorsal root ganglion (GAD), the aim of this thesis was to characterize gene expression, and thus the biological processes that take place in the GAD of injured sciatic nerve, of transgenic RIP/INFβ mice treated with multiple low doses of STZ (Tg-STZ). Gene expression in GAD was studied in four different groups of mice: wild type ICR (ICR) as a wild type genetic background control; ICR treated with STZ (ICR-STZ); transgenic RIP/INFβ mice (Tg); and Tg mice treated with STZ (Tg-STZ). Four weeks after diabetes was established in Tg-STZ mice, a left sciatic nerve crush injury was performed in all groups, the right limb was left intact. Four weeks after sciatic nerve injury GAD samples were collected from both hind limbs. GAD RNA was extracted to perform microarray study (Affymetrix GeneChip® Mouse Genome 430 2. 0 Array). Real time PCR (RT-qPCR) was performed to validate some of gene expression values obtained. Comparisons were made between the gene profiles from the different experimental conditions: 1) ICR-STZ injured vs ICR injured, 2) ICR injured vs ICR uninjured, 3) Tg-STZ uninjured vs ICR uninjured and 4) Tg-STZ injured vs ICR injured. Baseline samples were the uninjured limbs from ICR mice with a Fold Change value of 1. Once the compared profiles were obtained, upregulated and downregulated genes were analysed, as well as their related biological process, using different databases (Database for Annotation, Visulaization and Integrated Discovery; Center for Quantitaive Biology; Gene Home). The absence of differences in gene expression between injured limbs GAD from ICR-STZ mice vs ICR mice showed that STZ administration had no toxic effect in GAD. Four weeks after sciatic nerve injury, genes associated with nerve regeneration were still upregulated in ICR mice, particularly those involved in signalling (Gpr151, Nts), synaptic transmission (Npy), neuronal projection and axonal guidance (Sox11, Atf3, Tnc, Sema6a, Sprr1a, Gal). This finding indicates that the lesion was not completely resolved. Transgenic diabetic mice (Tg-STZ) showed downregulation of genes related to metabolic pathways (Vgf) and upregulation of genes implicated in carbohydrate (Car3) and lipid metabolism (Gdpd3), indicating that 8 weeks after DM onset, a sustained hyperglycaemia affects GAD. Transgenic diabetic mice (Tg-STZ) showed, after 8 weeks of sustained hyperglycaemia, downregulation of genes associated with nervous system development (Gal, Bdnf, Erg3), axonal regeneration (Sprr1a, Lingo1), synaptic transmission (Calb1, Snapin), signal transduction (Nts, Rgs2), potassium channel (Kcns1, Kcnq5, Knj13, Kcna6, Kcnt1) and apoptosis (Tfnaip, Ctsb, E2f1, Crh). Reflecting GAD degenerative changes due to PND. Four weeks after sciatic nerve injury, genes associated with nerve regeneration were still upregulated in diabetic transgenic mice (Tg-STZ) such as those involved in axon guidance (Foxd1), axonal regeneration (Sprr1a), neuronal projection (Mapk8), GAD neurons survival and neurite elongation (Gal, Sox11), or signalling (Npy1r, Igf1, Rgs18, Gpr151), synaptic transmission (Gabrb3, Neto1, CcKbr) and apoptosis (Crh). Suggesting ongoing posttraumatic GAD regeneration processes. Four weeks after sciatic nerve injury, several genes were downregulated in diabetic transgenic mice (Tg-STZ) involved in axogenesis (Nptx1, Cxcr4), neuromuscular synaptic transmission (Egr3) and transport (Htr3a, Tnpo, Mlc1, Slc15a2, Slc6a4), evidencing delayed nerve regeneration. Four weeks after sciatic nerve injury, genes associated with nerve regeneration were still upregulated in ICR mice, involved in extracellular matrix (MEC) reorganization and local microenvironment (Mmp16, Col18a1, Col3a1, Col5a2, Loxl2), cell adhesion (Lmo7, Flrt3), transport (Cacna2d1, Slc15a3, Slc15a9, Slc6a4) and apoptosis (Phb, Comp) indicating reorganization and regeneration of the injured site. Transgenic diabetic mice (Tg-STZ) only showed upregulation of 2 genes (Mmp16, Tgfbi) related to MEC reorganization. The remaining genes were barely upregulated. This finding is in accordance with a delayed regeneration, and with the fact that local remodelling is yet to be started. Four weeks after sciatic nerve injury, genes associated with neuropatic pain were upregulated in ICR mice (Npy, Npy2r, Gal). However, in diabetic transgenic mice Tg-STZ, no Npy expression was found and, moreover, Gal was downregulated. This finding could be related to PND loss of pain sensitivity. Our findings regarding genes and biological processes involved in nerve degeneration and regeneration mechanisms in ICR mice and in diabetic transgenic mice Tg-STZ lead to new research lines aimed to understanding PND pathogenesis and to the study of target therapeutic molecules for PND and diabetic pain.