Melatonin elicits protein kinase C-mediated calcium response in immortalized GT1–7 GnRH neurons

Melatonin is suggested to have effects on hypothalamic–pituitary–gonadal (HPG) axis. The pulsatile pattern of GnRH release, which results in the intermittent release of gonadotropic hormones from the pituitary, has a critical importance for reproductive function but the factors responsible from this release pattern are not known. Calcium is a second messenger involved in hormone release. Therefore, investigation of the effects of melatonin on intracellular free calcium levels ([Ca2+]i) would provide critical information on hormone release in immortalized GnRH neurons. The pattern of melatonin-induced intracellular calcium signaling was investigated by fluorescence calcium imaging using the immortalized GnRH-secreting GT1–7 hypothalamic neurons. Melatonin caused a significant increase in [Ca2+]i, which was greatly blocked by luzindole, a melatonin antagonist, or attenuated by pre-treatment with protein kinase C inhibitor. This study suggests that melatonin seems to have a direct effect on GnRH neurons.

► Melatonin increases intracellular calcium levels in GT1–7 cell lines by PKC mediated pathway.
► Melatonin action on intracellular calcium levels is mediated by melatonin receptors in the cell membrane.
► Melatonin causes a different pattern in calcium signaling, which may impair the pulsatile pattern of GnRH release.