5-Hydroxytryptamine synthesis and metabolism in discrete nuclei of the rat brain during surges of prolactin associated with restraint stress or suckling.

5-hydroxytryptamine (5-HT) synthesis [accumulation of 5-hydroxytryptophan (5-HTP) following inhibition of aromatic L-amino acid decarboxylase with NSD 1015] and metabolism [concentration of the primary metabolite of 5-HT, 5-hydroxyindole-3-acetic acid (5-HIAA)] were measured in the suprachiasmatic (SCN), medial preoptic (MPO), and arcuate (AN) nuclei as well as the median eminence (ME) and striatum (ST) of the rat brain and correlated with changes in serum prolactin resulting from restraint stress (30 min) or the stimulus of acute suckling (30 min, following 4 h pup deprivation). Restraint stress increased serum increased serum prolactin and 5-HT synthesis and metabolism in the SCN and MPO. Acute suckling increased serum prolactin and 5-HT synthesis and metabolism only in the MPO, although 5-HT neuronal activity in the ME of lactating rats was stimulated versus diestrous control values regardless of whether the animals were suckled. These results demonstrate a differential effect on 5-HT synthesis and metabolism in discrete nuclei of the rat brain during two paradigms where the secretion of several hormones, including prolactin, is undergoing a dynamic change.