Antagonistic Effects of Tryptamine and β-Phenylethylamine on the Behaviour of Rodents

Abstract

ACCORDING to Brodie and Shore, the behaviour of higher animals depends on neurohumoral agents produced in the diencephalon. Catecholamines such as noradrenaline and dopamine are said to act as ergotropic agents, whereas serotonin is their antagonistic trophotropic factor^1,2. The essential validity of these concepts has been confirmed many times^3,4. There are, however, some discrepancies concerning the supposed stimulating (ergotropic) effects of catecholamines; some results confirm their alerting action, but others point to a depressing effect^5,6. We found^7–11 that not only catecholamines, but also their amino-acid precursor L-dopa, suppress exploratory behaviour in mice, whereas amphetamine derivatives, as well as β-phenylethylamine and its amino-acid precursor phenylalanine, enhance it; there is a mutual antagonism between the two groups of substances. Serotonin too suppresses exploratory activity in mice and produces a Parkinson-like state in rats, similar to that produced by reserpine. β-Phenylethylamine antagonizes these effects of serotonin¹². We concluded that β-phenylethylamine rather than catecholamines should be considered the ergotropic agent, while serotonin, as proposed by Brodie and Shore, is its antagonistic trophotropic factor. It seems to us that catecholamines may function differently in particular systems, but they do not seem to stimulate motor activity. Amphetamine and its derivatives may act by liberating β-phenylethylamine.