TYROSINE-HYDROXYLASE AND NOREPINEPHRINE TRANSPORTER MESSENGER-RNA LEVELS INCREASE IN LOCUS-COERULEUS AFTER COITUS IN RABBITS

Hypothalamic norepinephrine (NE) plays an important role in the contro l of sexual behavior and in the secretion of gonadotropin. Our previou s study showed that coitus induced simultaneous increases in hypothala mic NE and GnRH releases in female but not in male rabbits. To investi gate the activities in noradrenergic neurons during the coitus-induced process of an LH surge, we measured tyrosine hydroxylase (TH, the rat e-limiting enzyme in NE synthesis) and NE transporter (NET, a key prot ein for NE cellular reuptake) mRNA levels in locus coeruleus (LC) nora drenergic cells in female New Zealand White rabbits. Changes in LC-TH and LC-NET mRNA levels were also measured in males as controls. Female rabbits were killed before coitus and at 15, 30, 60, 120, and 240 min after coitus (n=6-7/time point); males were killed before and at 30, 60, and 120 min after coitus (n=3/time). Individual brainstems were se ctioned, the LC neurons punched, and TH and NET mRNAs were quantified by ribonuclease protection assay (RPA). Rabbit-specific TH (330 bp) an d NET (503 bp) cDNAs were used as probes in the RPA for gene-specific signals. A rabbit 'house-keeping' cDNA (cyclophilin, 158 bp) was also cloned and used as an internal marker for tissue RNA content. Trunk bl ood was collected to determine serum LH levels. In female rabbits, ser um LH levels rose by 15 min after coitus, reached peak concentrations at 1-2 h, and declined thereafter. The time interval for changes in TH and NET mRNA levels in females was similar to that in serum LH levels . Both TH and NET mRNAs increased significantly by 15 min (73% and 85% respectively) and were elevated for 2 h (87% and 111% respectively). TH mRNA levels returned to basal levels by 4 h after coitus, whereas N ET mRNA values were elevated throughout the 4 h of observation. In con trast, LH, TH and NET mRNA levels did not change after coitus in males . The enhanced gene expression of both TH and NET in the LC in females , in accord with our previous demonstration of increased hypothalamic NE release, suggests that regulation of NE synthesis and reuptake is a n integral part of the coitus-induced NE/GnRH/LH surge process that in cludes the initiation, sustenance or recovery of the release and/or st orage of these neurochemicals.