Effects of B-HT 920 in the tail-suspension test.

The effect of B-HT 920 on mice subjected to the tail-suspension test (TST), a behavioural tool for gauging depression, was studied. During the test, all the animals had bouts of agitation interspersed with periods of immobility but B-HT 920-treated animals exhibited a differentiated behavioural pattern according to the dose employed: at doses selective for dopaminergic (DA) autoreceptor stimulation (50 and 100 micrograms/kg), the periods of immobility were unaffected, while at higher doses (0.5, 1, 2 and 3 mg/kg), which are also considered to be active on alpha 2-adrenoceptors, they were much shorter, as they are when known antidepressants are administered. Both clonidine (75 and 150 micrograms/kg) and yohimbine (1 and 5 mg/kg), alpha 2-adrenoceptor agonist and antagonist, respectively, increased immobility time, while N-n-propylnorapomorphine, a DA-agonist, at a dose (10 micrograms/kg) specific for DA autoreceptors, was completely ineffective. Since the behavioural effects of B-HT 920 vary according to the dosage employed, discussion centres on what receptors might conceivably underly these effects and on their preclinical relevance.