Effects of ovarian steroids on serotonin metabolism within grossly dissected and microdissected brain regions of the ovariectomized rat.

Brain serotonin (5-HT) levels and accumulation rate within the dorsal raphe nucleus (DR) were elevated in ovariectomized (OVX) rats after ovarian steroid treatment, which consisted of estradiol benzoate (EB) followed by progesterone (P) 48 hr later. Some animals were also given the monoamine oxidase (MAO) inhibitor pargyline at designated times 10-40 min prior to sacrifice. Decapitation occurred 5 hr following the second steroid injection and 4-6 hr into the dark phase of a 14:10 light/dark cycle. Basal 5-HT levels and the rate of 5-HT accumulation (5-HTr) following MAO inhibition were estimated by radioenzymatic assay of brain tissue punched from frozen sections or dissected freehand. Within the DR, 5-HT levels and 5-HTr rates were respectively 13.8% (p less than 0.001) and 23.2% (p less than 0.025) higher in EB+P treated females compared with oil controls. Differences in basal 5-HT were found within the median raphe nucleus, but these were inconsistent from experiment to experiment. No differences were found in tissue immediately adjacent to these nuclear regions or within other brain regions including the ventral medial nucleus and suprachiasmatic nucleus of the hypothalamus. Increased levels of 5-HT were also found in grossly dissected tissue containing the mesencephalic raphe nuclei.