Browsing by Subject "Luteinizing hormone releasing hormone"
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Item Identification and characterization of cystatin-related epididymal and spermatogenic (CRES) expression in anterior pituitary gonadotropes(Texas Tech University, 2001-08) Sutton-Walsh, Heather GayleMale factor infertility contributes to half of all infertility cases, yet current knowledge remains unable to diagnose all but gross abnormalities in male reproductive physiology. In an effort to identify proteins involved in initiating epididymal sperm maturation, our lab identified the cystatin-related epididymal spermatogenic (CRES) gene based on its preferential expression in the initial epididymal segment. Cres represents a unique subgroup of the cystatin family of cysteine protease inhibitors in that its expression is restricted to reproductive tissues and its sequence predicts specificity distinct from classic cystatins. CRES protein is localized to the caput epididymal lumen and the sperm acrosome. Both compartments contain active proteases responsible for protein processing events that are required for sperm function; however, the regulatory mechanisms controlling these processing events are poorly understood. These observations led to the proposal that CRES protein regulates protein processing in these tissues. We hypothesized that CRES might also regulate proteolysis in the pituitary gland for two reasons: (1) the pituitary gland expresses a number of proteases involved in preprotein processing; and (2) the pituitary gland is functionally connected with the gonad via the hypothalamic-pituitary-gonadal axis. Thus, the goal of these studies was to determine whether CRES is expressed in the pituitary gland and if so, to examine its regulation by hypothalamic and/or gonadal factors. These studies demonstrate that CRES is expressed in the anterior pituitary gland and is co-localized intracellularly with leutinizing hormone (LH) in gonadotrope secretory granules. To examine the regulation of Cres mRNA, we developed a semi-quantitative RT-PCR assay and showed that, unlike steroid hormones, GnRH is the primary physiologic regulator of Cres gene expression. Specifically, GnRH administration causes a rapid decrease in Cres mRNA levels, an effect opposite from its potent stimulation of LHp mRNA expression. In contrast, intracellular CRES and LHP protein levels were regulated similarly by steroid hormones, consistent with their being packaged within the same subset of secretory granules. Taken together, these studies indicate that CRES function is influenced by subtle alterations in the hypothalamic-pituitary-gonadal axis, suggesting it may regulate processing events important at specific times for gonadotrope secretory functions.Item The role of the N-methyl-D-aspartate receptor (NMDAR)--NR2b subunit in female reproductive aging(2008-12) Maffucci, Jacqueline Ann; Gore, Andrea C., 1964-Reproductive senescence in females is a natural part of the aging process. However, the process by which it occurs, and the relative role of each level of the hypothalamic-pituitary-gonadal axis, remains largely unknown. The neural circuitry regulating the hypothalamic axis, including glutamate acting through N-Methyl-D-Aspartate receptors (NMDARs) on GnRH neurons, appears to be key to this process. The NMDAR is tetrameric and composed of an obligatory NR1 subunit together with NR2 subunits. The subunit composition determines the channel kinetics of the receptor and changes through the life span. This dissertation examines the physiological role of the NR2b subunit on LH pulsatile release and LH surge, both important for reproductive function. The expression of NR2b subunits in the anteroventral periventricular (AVPV) nucleus of the hypothalamus was also examined in aging rats. Experiment 1 showed that the NR2b-antagonist, ifenprodil, enhanced pulsatile LH release in estradioltreated females (both age groups). Experiment 2 showed that the LH surge in middle-aged animals was slightly accelerated and that results were dependent upon prior reproductive status of the animals. In Experiment 3, examination of the NR2b-immunoreactive cell population in young, middle-aged, and aged ovariectomized females given vehicle, estradiol, or estradiol with progesterone showed an age-associated decline in NR2b density. However, the immunofluorescent fraction volume of NR1 colocalized with NR2b increased with aging, and that of immunofluorescent fraction volume of NR2b increased with estradiol treatment. This is indicative of the amount of protein expressed in the AVPV. In total, NR2b cell density in the AVPV declines with age, but the amount of NR2b expressed in NR1-positive cells increases, suggesting a larger population of NR2b containing channels. This may translate to age-associated inhibition of GnRH/LH activity, which is relieved with blockade of NR2bcontaining NMDARs. Thus, this dissertation describes a novel way to examine the mechanism by which age-associated changes to neuromodulators of the HPG axis may affect the onset of reproductive senescence.