Intracellular Ca2+ oscillations in luteinizing hormone-releasing hormone neurons derived from the embryonic olfactory placode of the rhesus monkey

To understand the mechanism of pulsatile luteinizing hormone-releasing horm one (LHRH) release, we examined whether cultured LHRH neurons exhibit spont aneous intracellular Ca2+ ([Ca2+](i)) signaling. The olfactory placode and the ventral migratory pathway of LHRH neurons from rhesus monkey embryos at embryonic ages 35-37 were dissected out and cultured on glass coverslips. Two to five weeks later, cultured cells were labeled with fura-2 and examin ed for [Ca2+](i) signaling by recording changes in [Ca2+](i) every 10 sec f or 30-175 min. Cells were fixed and immunostained for LHRH and neuron-speci fic enolase. In 20 cultures, 572 LHRH-positive cells exhibited [Ca2+](i) os cillations at an interpulse interval (IPI) of 8.2 +/- 0.7 min and a duratio n of 88.8 +/- 2.9 sec. LHRH-negative neurons In culture exhibited only occa sional [Ca2+](i) oscillations. In 17 of 20 cultures with LHRH-positive cell s, [Ca2+](i) oscillations occurred synchronously in 50-100% of the individu al cells, whereas [Ca2+](i) oscillations in cells in the remaining three cu ltures did not synchronize. Strikingly, in 12 of 17 cultures the synchroniz ation of [Ca2+](i) oscillations repeatedly occurred in complete unison at 5 2.8 +/- 3.0 min intervals, which is similar to the period observed for LHRH release, whereas in 5 of 17 cultures the less tight synchronization of [Ca 2+](i) oscillations repeatedly occurred at 23.4 +/- 4.6 min intervals. IPI of [Ca2+](i) oscillations in cells with tight synchronization and less tigh t synchronization did not differ from IPI in cells without synchronization. The results indicate that LHRH neurons derived from the monkey olfactory p lacode possess an endogenous mechanism for synchronization of [Ca2+](i) osc illations. Whether synchronization of [Ca2+](i) oscillations relates to neu rosecretion remains to be investigated.