Differential expression of c-fos mRNA in rat prefrontal cortex, striatum, N. accumbens and lateral septum after typical and atypical antipsychotics: an in situ hybridization study

The regional difference in the expression of c-fos mRNA induced by typical and atypical antipsychotics was determined in prefrontal cortex, striatum, N. accumbens and lateral septum in rats by in situ hybridization. Two typical antipsychotics, haloperidol (2 mg/kg) and fluphenazine (2 mg/kg), and three atypical antipsychotics, (-)sulpiride (100 mg/kg), clozapine (20 mg/kg) and OPC-14597 (40 mg/kg), were used. Brains were fixed with 4% paraformaldehyde 45 min after drug administration (i.p.). Brain sections of 30 microns-thickness were made in a cryostat and hybridized with 35S-labelled for c-fos oligonucleotide probe. These sections were apposed to X-ray films and the autoradiograms were semi-quantitatively analysed by computer-assisted densitometry. All antipsychotics used increased c-fos mRNA expression in N. accumbens shell, a region of the forebrain associated with limbic systems. On the other hand, two typical antipsychotics (haloperidol and fluphenazine) that cause a high incidence of acute motor side effects increased the expression of c-fos mRNA in the dorsolateral striatum, an extrapyramidal region primarily involved in motor control. Only clozapine induced c-fos mRNA in the medial prefrontal cortex and lateral septum. These results strongly suggest that the shell region of N. accumbens may be a common site of therapeutic action of antipsychotics.