Differential induction of Fos-like-immunoreactivity in the extended amygdala after haloperidol and clozapine

The extended amygdala is composed of the central and medial amygdaloid nucl eus which through the sublenticular extended amygdala (SLEA) and the inters titial nucleus of the posterior limb of the anterior commissure (IPAC) merg e into the bed nucleus of stria terminals (BST). Based on anatomical connec tions with limbic areas, the extended amygdala has been proposed to play an important role in cognitive and affective processes. This study examines t he effect of the atypical antipsychotic clozapine and the classical antipsy chotic haloperidol on Fos-like-immunoreactivity (FLI) induction in areas be longing to the extended amygdala. Acute administration of clozapine (10-20 mg/kg) induced FLI in the central amygdaloid nucleus, IPAC, SLEA, and BST l ateral division and, as previously described, in areas connected to the ext ended amygdala, such Its the prefrontal cortex and nucleus accumbens shell. In contrast, acute administration of haloperidol (0.1-1 mg/kg) failed to i nduce FLI in the BST lateral division and SLEA but increased FLI in the IPA C. A small increase in FLI was observed in the central amygdaloid nucleus a fter 0.1 but not after 1 mg/kg of haloperidol. The present results, showing a preferential influence of clozapine, as compared to haloperidol, in the extended amygdala propose a new brain structure involved in the pharmacolog ical effects of atypical antipsychotics. 1999 American College of Neuropsyc hopharmacology. Published by Elsevier Science Inc.