Housing conditions and the anxiolytic efficacy of buspirone: the relationship between main and side effects

Serotonergic anxiolytics yield contradictory results both in the laboratory and clinically. In an attempt to investigate the cause of discrepancies, the anxiolytic effect of buspirone (0, 3 or 10 mg/kg, single treatment) was tested 1 h and 4 h after injection in rats in different housing conditions. At 1 h after drug administration, buspirone increased corticosterone production and decreased locomotor behaviour in both the elevated plus-maze and the social interaction tests. No anxiolytic-like effect was produced in either test. At 4 h after drug injection, no corticosterone or locomotor effects of buspirone were observed. In contrast, anxiolytic effects emerged in this phase. Open arm exploration and social investigation were increased in the plus-maze and social interaction test, respectively. In the plus-maze, the anxiolytic effect was significant in isolated animals only. In the social interaction test, the anxiolytic effect was stronger in isolated than in group-housed animals. When corticosterone secretion was inhibited by adrenalectomy, a full anxiolytic effect of buspirone was observed 1 h after drug administration. It appears that the side effects of buspirone have a shorter duration than the main anxiolytic effect. The buspirone-induced increase in corticosterone may have abolished the anxiolytic effects of the drug shortly after injection. Individual housing enhanced the anxiolytic efficacy of buspirone 4 h after administration.