Kisspeptin-Evoked Calcium Signals in Isolated Primary Rat Gonadotropin- Releasing Hormone Neurones

Abstract

Background: Kisspeptin and its cognate receptor GPR54 are the central driving forces in the hypothalamus-pituitary-gonadal axis essential for sexual maturation and reproduction. Kisspeptin/GPR54 signalling stimulates gonadotropin-releasing hormone (GnRH) neurones and induces pulsatile GnRH release. The molecular signalling pathway by which kisspeptin stimulates GnRH neurones is currently under investigation. Methods: Primary GnRH neurones were isolated from young adult rats and loaded with the calcium indicator Fura Red. Cytosolic calcium was measured while the cells were stimulated with kisspeptin. Results: GnRH neurones show a maintained increase of cytosolic calcium upon stimulation with 100 nM kisspeptin-10. The calcium elevation was inhibited 30% by 1 µM tetrodotoxin, a voltage-gated sodium channel blocker, and 76% by 30 µM SKF96365, an inhibitor of receptor-mediated calcium entry. Furthermore, removal of extracellular calcium completely abolished the kisspeptin-induced calcium elevation. Conclusion: Our results suggest that the major part of the kisspeptin-evoked calcium signal is generated by an action potential-independent calcium influx, possibly through channels of the classical transient receptor potential type, with an additional influx through voltage-gated calcium channels activated by sodium action potentials.

Kisspeptin inhibits a slow afterhyperpolarization current via protein kinase C and reduces spike frequency adaptation in GnRH neurons

“…This is analogous to the kainate receptor-mediated inhibition of I sAHP in CA1 pyramidal neurons via activation of PKC (17,35). Our findings are also consistent with the pathway elucidated in both heterologous cell expression systems and in native GnRH neurons in which kisspeptin has been shown to signal via the G q -coupled GPR54 to stimulate PLC, activate PKC, and increase cytosolic calcium oscillations (10,25,26,31,59).…”

Kisspeptin antagonist prevents RF9-induced reproductive changes in female rats

“…In vitro studies also provide evidence that kisspeptins directly affect GnRH neurons (Kroll et al 2011, Ozcan et al 2011. Kisspeptin was demonstrated to increase the intracellular calcium concentration [Ca 2C ] i in isolated GnRH neurons (Kroll et al 2011) as well as in hypothalamic GT1-7 immortalized cell lines (Ozcan et al 2011). Furthermore, GnRH secretion was increased in kisspeptin-activated GT1-7 cells (Jacobi et al 2007, Novaira et al 2009, Tonsfeldt et al 2011.…”

“…Chronic central administration of kisspeptin to immature female rats was shown to induce premature activation of the gonadotropic axis (Navarro et al 2004), and peripheral injection of kisspeptin significantly increased plasma levels of LH (Thompson et al 2004). In vitro studies also provide evidence that kisspeptins directly affect GnRH neurons (Kroll et al 2011, Ozcan et al 2011. Kisspeptin was demonstrated to increase the intracellular calcium concentration [Ca 2C ] i in isolated GnRH neurons (Kroll et al 2011) as well as in hypothalamic GT1-7 immortalized cell lines (Ozcan et al 2011).…”

Kisspeptin Inhibits High-Voltage Activated Ca²⁺ Channels in GnRH Neurons via Multiple Ca²⁺ Influx and Release Pathways

“…Kisspeptin and GPR54 are important for puberty and subsequent fertility; mutations or targeted deletions in the genes encoding kisspeptin or GPR54 cause profound hypogonadotropic hypogonadism, failure to undergo puberty and infertility [9,10,11,12]. Kisspeptin released from presynaptic neurons acts on GnRH neurons directly, and indirectly (transsynaptically), to produce long-lasting (20–30 min) depolarization and increased action potential firing [13,14,15,16,17,18,19,20,21] along with increased cytoplasmic free Ca 2+ concentration ([Ca 2+ ] i ) [17,22,23] required for the increased GnRH secretion. However, the mechanism by which kisspeptin increases [Ca 2+ ] i in GnRH neurons has not been fully elucidated.…”

“…Kisspeptin activation of GPR54 initiates G q/11 -phospholipase C (PLC)-inositol 1,4,5-trisphosphate (IP 3 )/diacylglycerol (DAG) signaling that increases [Ca 2+ ] i in GnRH neurons [17,19,22,23]. Activated PLC hydrolyzes phosphatidylinositol bisphosphate (PIP 2 ) to yield IP 3 and DAG.…”