Social instability in female rats: effects on anxiety and buspirone efficacy.

RATIONALE: Buspirone produces inconsistent effects in laboratory rodents. Individual housing increases the efficacy of buspirone in male rats, suggesting that the effects of this (and other) compounds become conspicuous in animals showing anxiety-like states. The effect of individual housing was, however, weak, and evident only when the locomotor suppressive effects of buspirone dissipated (i.e. 4 h after treatment).
OBJECTIVES: The effects of social instability, a recently developed model of social stress in female rats, was investigated on both anxiety and the anxiolytic efficacy of buspirone.
METHODS: Female rats were exposed to alternate days of isolation and moderate crowding for 2 weeks. Group composition was changed for each crowding phase. Basal anxiety and the anxiolytic efficacy of buspirone were assessed by the social interaction test of anxiety 24 h after the last crowding phase.
RESULTS: Crowding appeared stressful, as it increased plasma glucocorticoid levels in less than 1 h. Anxiety-like behaviours were increased by social instability compared with stable group housing. In group housed controls, buspirone markedly suppressed locomotion, without clear effects on anxiety-related behaviours. Social instability attenuated the locomotor suppressive effects of buspirone, but made the anxiolytic effects of the compound more conspicuous. The effects of individual housing (assessed earlier) and social instability (assessed here) on buspirone efficacy appear qualitatively different.
CONCLUSIONS: Buspirone abolishes stress-induced anxiety, but has no anxiolytic effects in controls. This is consistent with clinical findings, as the drug decreases anxiety in anxious patients but not in healthy humans. Laboratory models involving stress-induced anxiety-like states can improve our understanding of drug effects and efficacy.