Acute antipsychotic treatments induce distinct c-Fos expression patterns in appetite-related neuronal structures of the rat brain

A number of atypical antipsychotic drugs are known to perturb appetite regulation causing greater hyperphagia in humans and rodents than earlier generation typical agents. However, the neuronal structures that underlie hyperphagic effects are poorly understood. Arcuate nucleus (ArcN), paraventricular hypothalamic nucleus (PVN), paraventricular thalamic nucleus (PVA) and nucleus incertus (NI) have been implicated in appetite regulation. The NI is the principal source of the relaxin-3 (RLN3) peptide, which is reported to have orexigenic effects. Moreover, ArcN, PVN, and PVA receive RLN3 immunoreactive fibers from the NI and express relaxin family peptide type 3 (RXFP3) receptor. The present study was designed to evaluate the acute effects of clozapine (atypical), chlorpromazine (typical) and fluphenazine (typical) on c-Fos expression (a marker of neuronal response) in these appetite-related centers of the rat brain. The numbers of c-Fos expressing neurons in these structures were counted in immunofluorescence stained brain sections. Acute treatment with clozapine, chlorpromazine and fluphenazine differentially influenced c-Fos expression in these brain structures. This study is also the first demonstration that antipsychotics influence the NI. The patterns of the effects of these antipsychotics are related to their reported hyperphagic properties.