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 hormone (LHRH) release, we examined whether cultured LHRH neurons exhibit spontaneous 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 examined for [Ca2+]i signaling by recording changes in [Ca2+]i every 10 sec for 30–175 min. Cells were fixed and immunostained for LHRH and neuron-specific enolase. In 20 cultures, 572 LHRH-positive cells exhibited [Ca2+]i oscillations at an interpulse interval (IPI) of 8.2 ± 0.7 min and a duration of 88.8 ± 2.9 sec. LHRH-negative neurons in culture exhibited only occasional [Ca2+]i oscillations. In 17 of 20 cultures with LHRH-positive cells, [Ca2+]i oscillations occurred synchronously in 50–100% of the individual cells, whereas [Ca2+]i oscillations in cells in the remaining three cultures did not synchronize. Strikingly, in 12 of 17 cultures the synchronization of [Ca2+]i oscillations repeatedly occurred in complete unison at 52.8 ± 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 [Ca2+]i oscillations repeatedly occurred at 23.4 ± 4.6 min intervals. IPI of [Ca2+]i oscillations in cells with tight synchronization and less tight synchronization did not differ from IPI in cells without synchronization. The results indicate that LHRH neurons derived from the monkey olfactory placode possess an endogenous mechanism for synchronization of [Ca2+]i oscillations. Whether synchronization of [Ca2+]ioscillations relates to neurosecretion remains to be investigated.