Non-genomic action of vitamin D3 on N-methyl-D-aspartate and kainate receptor-mediated actions in juvenile gonadotrophin-releasing hormone neurons

Abstract

Vitamin D is a versatile signalling molecule that plays a critical role in calcium homeostasis. There are several studies showing the genomic action of vitamin D in the control of reproduction; however, the quick non-genomic action of vitamin D at the hypothalamic level is not well understood. Therefore, to investigate the effect of vitamin D on juvenile gonadotrophin-releasing hormone (GnRH) neurons, excitatory neurotransmitter receptor agonists N-methyl-D-aspartate (NMDA, 30 μM) and kainate (10 μM) were applied in the absence or in the presence of vitamin D3 (VitaD3, 10 nM). The NMDA-mediated responses were decreased by VitaD3 in the absence and in the presence of tetrodotoxin (TTX), a sodium-channel blocker, with the mean relative inward current being 0.56 ± 0.07 and 0.66 ± 0.07 (P < 0.05), respectively. In addition, VitaD3 induced a decrease in the frequency of gamma-aminobutyric acid mediated (GABAergic) spontaneous postsynaptic currents and spontaneous postsynaptic currents induced by NMDA application with a mean relative frequency of 0.595 ± 0.07 and 0.56 ± 0.09, respectively. Further, VitaD3 decreased the kainate-induced inward currents in the absence and in the presence of TTX with a relative inward current of 0.64 ± 0.06 and 0.68 ± 0.06, respectively (P < 0.05). These results suggest that VitaD3 has a non-genomic action and partially inhibits the NMDA and kainate receptor-mediated actions of GnRH neurons, suggesting that VitaD3 may regulate the hypothalamic–pituitary–gonadal (HPG) axis at the time of pubertal development.