The broad, long-term objective is to elucidate the mechanism(s) of the pubertal increase in gonadotropin- releasing hormone (GnRH) secretion required for sexual maturation and fertility.
The specific aim i s to test the hypothesis that pubertal changes in calcium (Ca2+) and calcium-activated potassium (K(Ca)) channel activity in GnRH neurons underlie the pubertal increase in GnRH secretion. The project will be the first to investigate pubertal changes in Ca2+ and K(Ca) channel activity in GnRH neurons in brain slices and to correlate the changes with GnRH secretion. The knowledge obtained may aid in developing new leads for contraception, as well as treatments for infertility and the pubertal disorders polycystic ovary syndrome, hypogonadism, precocious puberty, and delayed puberty, which possibly result from an abnormal increase in GnRH secretion. These public health goals are relevant to the mission of the Reproductive Sciences Branch of the National Institute for Child Health and Human Development. The project's rationale is that since neuroendocrine secretion depends on increased cytoplasmic free Ca2+ ([Ca2+]j), the mechanism(s) of the pubertal increase in GnRH secretion likely involves a pubertal increase in [Ca2+]j. This may be due to Ca2+ entry through voltage-dependent Ca2+ channels or Ca2+ release from intracellular stores in response to activation of neurotransmitter and/or hormone receptors on GnRH neurons by presynaptic neurons that convey information about age, growth, availability of metabolic fuels such as glucose and fats, circadian rhythm, and other factors. Ca2+ and K(Ca) currents of green fluorescent protein (GFP)-labeled GnRH neurons will be recorded using the perforated-patch technique, characterized by subtype with pharmacological antagonists, and compared in brain slices of gonadectomized and testosterone-clamped, as well as of gonadal-intact, male prepubertal, pubertal, and adult GnRH-GFP transgenic mice. GnRH in slice superfusates will be measured using radioimmunoassay. The relative contributions of the Ca2+ channel subtypes to increased [Ca2+]j will be assessed by comparing K(Ca) channel activity and GnRH secretion in the absence and presence of Ca2+ channel subtype antagonists. The contribution of Ca2+ mobilization to increased [Ca2+]j will be determined by measuring K(Ca) channel activity in response to kisspeptin activation of G protein-coupled receptor 54. There may be pubertal changes in the activity of one or more of the Ca2+ and K(Ca) channel subtypes, e.g., an increase in the activity of L-type Ca2+ channels, which are important for secretion in other endocrine cells, or increases in the activity of N-, P/Q-, and/or R-type Ca2+ channels, which are important for secretion in other neurons. It is also expected that kisspeptin-induced Ca2+ mobilization will increase at puberty and that these changes will account for the pubertal increase in GnRH secretion.
|Zhang, Xiao-Bing; Spergel, Daniel J (2012) Kisspeptin inhibits high-voltage activated Ca2+ channels in GnRH neurons via multiple Ca2+ influx and release pathways. Neuroendocrinology 96:68-80|
|Israel, Davelene D; Sheffer-Babila, Sharone; de Luca, Carl et al. (2012) Effects of leptin and melanocortin signaling interactions on pubertal development and reproduction. Endocrinology 153:2408-19|
|Spergel, Daniel J (2007) Calcium and small-conductance calcium-activated potassium channels in gonadotropin-releasing hormone neurons before, during, and after puberty. Endocrinology 148:2383-90|