| Using GTI-7 cells, a model for gonadotropin-releasing hormone (GnRH) neurons, the hypothesis that the melatonin-mediated regulation of GnRH transcription is mediated through membrane melatonin receptor activation, and transcriptional changes at the level of the gene was analyzed. We have demonstrated that specific activation of membrane MT2 melatonin receptors resulted in downregulation of GnRH mRNA, and that GT1-7 nuclear proteins specifically bind to the −1736/−1728 region of the GnRH-neuron specific enhancer.; The hypothesis that GnRH neurons may contain intrinsic circadian oscillators is based on the observation of intrinsic rhythms within GnRH neurons. Using the GT1-7 cell line the expression of mclock, mbmal1, mtimeless, mperiod1/2, and mcryptochrome1/2 was demonstrated. CLOCK, BMAL1, and PERIOD1 proteins are also expressed and BMAL1 expression appears to be circadian. mBmal1, mPer1 and mCry1 gene expression also changes over 24 h. These studies support a direct role for melatonin and circadian rhythms in GnRH neuronal function. |
