Regional changes in the rate of brain monoamine synthesis were monitored in male rats exposed to, but prevented from physical contact with, an estrous or an ovariectomized female. The in vivo rate of
tyrosine and
tryptophan hydroxylase activities were estimated by measuring the accumulation of
DOPA and
5-HTP following inhibition of cerebral
aromatic L-amino acid decarboxylase by means of
3-hydroxybenzylhydrazine (NSD-1015) treatment (100 mg/kg i.p.). 5 min upon
NSD-1015 treatment, the males were exposed to an intact estrous female or an ovariectomized female for 20 min before
decapitation and brain dissections. Exposure to an estrous female produced an increased rate of
tyrosine and
tryptophan hydroxylase activity in the medial prefrontal cortex, the dorso-lateral neostriatum and in the ventral neostriatum, in comparison with home-cage controls. By the same comparison, exposure to an ovariectomized female resulted in an increased rate of
tyrosine hydroxylase activity in the medial prefrontal cortex, but not in the neostriatal areas, whereas
tryptophan hydroxylase activity was unaffected. Finally, exposure to the empty test cage, with no stimulus females present, did not produce any statistically significant changes in the rate of
tyrosine or
tryptophan hydroxylase activity in any of the brain areas sampled. Taken together with recent findings from this laboratory, the present results demonstrate that the level of sexual motivation brought about by the olfactory, auditory and/or visual stimulation of a receptive female is associated with an increased demand on
catecholamine and
5-hydroxytryptamine synthesis in the limbic forebrain of the male rat.(ABSTRACT TRUNCATED AT 250 WORDS)