Serotonin receptor blockade potentiates behavioural effects of beta-phenylethylamine.

The 5-hydroxytryptamine (5HT) receptor blocker, methysergide (10 mg/kg), was found to potentiate the behavioural effects of beta-phenylethylamine (PEA) (at doses between 20 and 60 mg/kg) on food reinforced schedule-maintained behaviour in two separate experiments involving a fixed interval 2 min schedule and a fixed ratio 20 schedule. Potentiation caused a parallel shift to the left in the log dose response curve for suppression of responding induced by phenylethylamine, and was observed in both male and female rats. These data contrast with recent reports indicating that inhibition of functioning of 5HT systems blocks the effects of phenylethylamine in inducing the "Serotonin behavioural syndrome" (Sloviter et al., 1980a: Dourish, 1981). However, the potentiation reported here is compatible with frequent reports indicating that behavioural effects of amphetamine (alpha-methyl-PEA) can be potentiated by reduction in 5HT functioning and are thus compatible with the hypothesis that phenylethylamine is a potential "endogenous amphetamine".