Repeated treatment with amitriptyline reduces immobility in the behavioural 'despair' test in rats by activating dopaminergic and beta-adrenergic mechanisms.

Seven days of treatment with amitriptyline 10 mg kg-1 day-1, reduced the immobility time in the behavioural 'despair' test in rats. 0.5, but not 0.25 mg kg-1 haloperidol significantly counteracted the reduction of immobility caused by amitriptyline. Its anti-immobility effect was reduced by 50 and 100 mg kg-1 sulpiride, another blocker of dopamine receptors, and 5 mg kg-1 (+/-)-propranolol, a beta-adrenolytic drug. Prazosin, 3 mg kg-1, an antagonist of post-synaptic alpha-adrenoceptors, had no effect. It is suggested that dopaminergic and beta-adrenoceptors mediate the anti-immobility effect of repeated amitriptyline treatment in rats.