Tyrosine hydroxylase and norepinephrine transporter mRNA levels increase in locus coeruleus after coitus in rabbits

Abstract

Hypothalamic norepinephrine (NE) plays an important role in the control of sexual behavior and in the secretion of gonadotropin. Our previous study showed that coitus induced simultaneous increases in hypothalamic NE and GnRH releases in female but not in male rabbits. To investigate the activities in noradrenergic neurons during the coitus-induced process of an LH surge, we measured tyrosine hydroxylase (TH, the rate-limiting enzyme in NE synthesis) and NE transporter (NET, a key protein for NE cellular reuptake) mRNA levels in locus coeruleus (LC) noradrenergic 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 sectioned, the LC neurons punched, and TH and NET mRNAs were quantified by ribonuclease protection assay (RPA). Rabbit-specific TH (330 bp) and 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 blood was collected to determine serum LH levels. In female rabbits, serum 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 NET mRNA values were elevated throughout the 4 h of observation. In contrast, 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 an integral part of the coitus-induced NE/GnRH/LH surge process that includes the initiation, sustenance or recovery of the release and/or storage of these neurochemicals.

Neuroendocrine Regulation of GnRH Release in Induced Ovulators

“…Note that due to high levels of GnRH in mated females, different scales were used to plot the patterns of GnRH in mated males and females. after mating (248). Likewise in male ferrets (229), mating with intromission did not significantly increase the percentage of TH-IR neurons colabeled with Fos-IR in any brain stem region.…”

“…The distribution of NE cells in the rabbit is similar to that of the rat (e.g., 100). Yang et al (248) showed that the receipt of mating stimulation increased TH and NET mRNA levels in the LC of female rabbits. Likewise, in estrous ferrets (229), the receipt of an intromission significantly augmented the percentage of TH-IR neurons colabeled with nuclear Fos protein in both the LC (A6) and the rostral A2 cell groups.…”

Oestrogen Upregulates Noradrenaline Release in the Mediobasal Hypothalamus and Tyrosine Hydroxylase Gene Expression in the Brainstem of Ovariectomized Rhesus Macaques

“…Whether this observation in an OVX + E model can be applied to ovarian‐intact primates remains to be resolved. The selection of the locus coeruleus in this study is based on our previous findings in the rabbit that TH mRNA expression is increased in this brainstem noradrenaline area after coitus ( 41). This report does not exclude other brainstem noradrenergic areas, i.e.…”

The “ram effect”: new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions

“…The classical neurotransmitter systems via which socio-sexual stimulation modulates GnRH neurons are only poorly understood. The best documented is the noradrenergic system which is involved in male-stimulated ovulation in rabbits and ferrets (Wersinger and Baum, 1997 ; Yang et al, 1996 , 1997 ). In rabbits for example there is a parallel increase in noradrenalin (NA) and GnRH in the MBH within 10 min of mating (Kaynard et al, 1990 ).…”