ANXIOLYTIC HOMOPHTHALAZINES INCREASE FOS-LIKE IMMUNOREACTIVITY IN SELECTED BRAIN-AREAS OF THE RAT

Nerisopam, an anxiolytic and antipsychotic homophthalazine induces rap id, intense expression of Fos-like immunoreactivity in the rostral, do rsomedial and lateral parts of the striatum in the rat. Fos-positive c ells also occurred in the globus pallidus, the olfactory tubercle and in the accumbens nucleus (in the cone and shell portions) but the subs tantia nigra, the entopeduncular and the subthalamic nuclei were virtu ally Fos-negative. 5 h after nerisopam application, however, cells in the reticular zone of the substantia nigra showed Fos-like immunoposit ivity. After a daily application of nerisopam for two weeks, relativel y weak Fos-like immunoreactivity was observed in the striatum and the subthalamic nucleus but not in the globus pallidus. Unilateral surgica l transection of the striato-nigral pathway, which depleted tyrosine h ydroxylase immunostaining in the ipsilateral striatum did not influenc e nerisopam-induced Fos-like immunoreactivity in the striatal neurons, either ipsi- or contralateral to the knife cut. Our results suggest t hat the striatal neurons are the primary targets of this anxiolytic an d antipsychotic drug in the central nervous system. (C) 1997 Elsevier Science B.V.