Guided in part by empirical neuropharmacologic studies, neurochemical research on autism has focused on neurotransmitters and neuromodulators [10 , 54]: first, the mesolimbic dopamine system; then, endogenous opioid systems and oxytocin; and, in current research, serotonin, examined because of an identified link between autism and affective disorders [41] and the discovery of some favorable behavioral effects of serotonergic drugs.