In the female New Zealand White rabbit, coitus induces a massive release of hypothalamic gonadotropin-releasing hormone (GnRH) that triggers the surge of luteinizing hormone (LH), and therefore ovulation. The coital signals, relayed by peripheral nerves through the spinal cord, do not synapse directly on GnRH neurons. Instead, these signals are transduced by interneurons whose secretions stimulate GnRH release. The nature of, and interactions between these interneurons are not fully understood. Furthermore, increases of LH and androgens in males have been suggested, but whether coital activities induce neuroendocrine responses in the male hypothalamus similar to those in the female are unknown. Our hypothesis is that coitus provokes changes in norepinephrine (NE) and/or neuropeptide Y (NPY) gene expression, secretion and synaptic transmission that result in a dramatic release of hypothalamic GnRH in both male and female rabbits.
Specific aim 1 is to find out if coitus activates GnRH/NPY/NE secretions in male and Ovariectomized, estradiol-17beta-treated female rabbits; uninterrupted hypothalamic perfusion (i.e., microdialysis and push-pull perfusion) and venous blood samples will be collected remotely from tethered, freely moving rabbits at 2.5- to 10-min intervals 5 h before and 4 h after mating with a partner of the opposite sex. Concentrations of GnRH, NPY and NE in perfusate and LH and gonadal steroids in blood will be measured by specific radioimmunoassays (RlA) and high-performance liquid chromatography (HPLC, for NE).
Aim 2 is to see if hypothalamic releases of NE and/or NPY mediate coitally-induced GnRH changes; prazosin, an alpha- adrenergic antagonist, and anti-NPY serum will be used to block the stimulatory action of NE and NPY, respectively, during initiation of the coitally-induced GnRH surge.
Aim 3 is to examine if blockade of presynaptic NE transporter protein at hypothalamic nerve terminals can (a) initially enhance GnRH secretion by increasing local NE and (b) subsequently reduce hypothalamic NE, and therefore GnRH, release by down- regulation of tyrosine hydroxylase (TH) gene expression; acute, intrahypothalamic treatment with desipramine (DMI), a specific blocker for NE transporter, will be given to animals, some of which will be pre- treated systemically with DMI or saline (twice-daily for 14 days). Effects of acute and chronic DMI treatment will be assessed, respectively, by measuring NE/GnRH release in the hypothalamus (by HPLC and RIA) and TH and NPY mRNA content in cell bodies located in locus coeruleus and lateral tegmentum of the brainstem (by RNase protection assay) in either male or steroid-treated females.
Aim 4 is to assess (a) if and when brainstem changes in TH and NPY messenger RNAs occur after coitus and (b) if prolonged intrahypothalamic DMI infusion suppresses TH and NPY mRNA expression in brainstem NE neurons; altered gene expression in brainstem neurons will be measured at times parallel to changes in NE and NPY secretions. Specific rabbit TH probe has been cloned and human NPY probe has been validated for use in the rabbit in our laboratory. These findings will be the first to address the role of neurotransporter molecules in reproduction. The outcome of the studies should increase understanding of neural factors that influence normal endocrine processes and those associated with malfunctioning neural circuitry in sexually-related disorders in men and women.
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