The Effect of Gonadal Steroids and Altered Tryptophan Metabolism on behaviour

Abstract

Gonedal steroids have been shown to affect tryptophan metabolism in both brain and body, end are thus thought capable of altering the rate of 5-hydroxyptamine synthesis, end consequently, serotoninergic
neuronal activity. Subsequent behavioural changes should result, and a primary aim of the research was to elucidate such changes within specific behavioural
parameters.

In order to discern more exactly the effect of gonadal steroids on behaviour, other, more specific,
alterations in tryptophan metabolism were undertaken
using various pharmacological manipulations. Alterations
in behaviour after such manipulations were then observed,
within the previous behavioural paremeters.

A clinical study was carried out in order to ascertain the effect of gonadel steroids, in the form of
the oral contraceptive, on plasma tryptophan, mood and behaviour in the human female.

The results suggest that gonadal steroids influence behaviour by increasing 5-hydroxytryptamine synthesis. In general, such an effect led to an exhibition of behaviourel depression, manifested as reduced locomotor activity and startle response magnitude.

A paradoxical effect of tryptophan on behaviour was discovered. Increasing doses of l-tryptophan were found to induce heightened startle response magnitude
while reducing spontaneous locomotor activity.

It was concluded that both the contraceptive
effect and changes in behaviour, brought above after the
administration of synthetic gonadal steroids, were caused
by increased serotoninergic neuronal activity. It was
suggested that these gonadel steroids induce changes in
the equilibrium between the catecholaminergic end
serotoninergic neuronal systems, causing the latter to predominate.

The. hyperactivity syndrome, reported efter the
concurrent administration of a monoamine oxidase inhibitor and either l-tryptophan or 5-hydroxytryptophan, was thought to be due to increased brain tryptemine levels, rather than the associated increase in brain 5-hydroxytryptamine levels,

Date of Award	Apr 1979
Original language	English
Awarding Institution	Aston University