Anxiolytic-like effects of yohimbine in the murine plus-maze: strain independence and evidence against alpha 2-adrenoceptor mediation.

The influence of alpha 2-adrenoceptor antagonists in animal models of anxiety is quite inconsistent, with results spanning the full range of effect from anxiogenesis to anxiolysis. In the present study, an ethological technique was used to examine the effects of yohimbine (0.5-4.0 mg/kg) on plus-maze behaviour in DBA/2 mice. Results indicated significant anxiolytic-like effects on standard spatiotemporal measures at 2.0-4.0 mg/kg, and on risk assessment measures across the entire dose range. Full-scale follow-up studies with T1 and BALB/c strains confirmed that this action of yohimbine in the murine plus-maze is not peculiar to DBA/2 mice. The more selective alpha 2-adrenoceptor antagonist, idazoxan (0.63-5.0 mg/kg), exerted much weaker behavioural effects in the maze while the alpha 2-adrenoceptor agonist, clonidine (0.01-0.1 mg/kg), produced a profile consistent with non-specific behavioural disruption. Data are discussed in relation to the possible involvement of 5-HT1A receptor mechanisms in the observed anxiolytic-like effects of yohimbine in the murine plus-maze.