Luteinizing hormone-releasing hormone (LHRH) biosynthesis and secretion in embryonic LHRH

Evidence indicates that LH-releasing hormone (LHRH) neurons can exhibit neuroendocrine secretory properties before entrance into the central nervous system. In this study, we evaluated LHRH biosynthesis and secretion in embryonic LHRH neurons maintained in nasal explants. Using ELISA and calcium imaging techniques, peptide content and single neuron activities were examined. LHRH neurons maintained for 7-10 days in vitro were found to possess a similar amount of LHRH/cell as the equivalent aged LHRH cells in vivo (postnatal day 1). LHRH peptide was measured in the medium of these relatively young cultures, and 40 mM KCl stimulated a 4-fold increase in LHRH secretion. KCl enhanced medium also resulted in a significant increase in LHRH content per culture (24.5 pg vs. 32.3). A similar effect was observed after muscimol-enhanced media (32.2 pg). Both agents also stimulated a substantial rise in intracellular calcium. Pretreatment of cultures with tetrodotoxin partially blocked the affects of muscimol on both peptide content and calcium activity, but not KCl. Calcium-depleted medium blocked the effects of KCl yet only attenuated the effects of muscimol. Treatment of cultures with cycloheximide blocked the effects of both muscimol and KCl. These results indicate that developing LHRH neurons are capable of synthesizing, secreting, and rapidly replenishing stores of LHRH peptide.