Increase in the isolation-induced social behavioural deficit by agonists at 5-HT1A receptors

The effect of 5-HT1A agonists was studied in the isolation-induced social behavioural deficit test. The drugs 8-OH-DPAT (0.125 mg/kg), buspirone (16 mg/kg) and ipsapirone (8 mg/kg) further increased the deficit. Unlike 8-OH-DPAT, the other two drugs may act non-specifically since they reduced spontaneous motor activity at 16 mg/kg, as measured in an activity meter. In addition, 8-OH-DPAT (0.25 mg/kg), buspirone (8 mg/kg) and ipsapirone (8 mg/kg) decreased exploratory activity in the open-field test. Since the smallest active doses were very close in the behavioural deficit and in the open-field tests, it is suggested that a common phenomenon, increased emotionality or reactivity, sustained both these reductions in activity. The increase in the behavioural deficit induced by 8-OH-DPAT, was likely to have resulted from stimulation of 5-HT1A receptors, since it was impaired by pretreatment with penbutolol, a beta-adrenergic-blocking drug, also known to bind to 5-HT1 receptors. Since it was previously shown that the behavioural deficit was reduced by agonists at 5-HT1B receptors, it is proposed that the behavioural inhibition, resulting from an isolation-induced increase in reactivity is bi-directionally modulated by serotonergic drugs, where 5-HT1A agonists increase and 5-HT1B agonists decrease this inhibition.