Synchronous development of spontaneous and evoked calcium-dependent properties in hypothalamic neurons.

The development of various related parameters was compared in hypothalamic neurons grown in primary culture. We measured: (i) low- and high-voltage-activated calcium currents; (ii) spontaneous and N-methyl-D-aspartate (NMDA)-induced fluctuations of intracellular calcium concentration; (iii) basal and NMDA- or potassium-evoked somatostatin release. Spontaneous calcium fluctuations appeared after 5 days in culture and increased progressively in amplitude and frequency over the next 8 days studied. Basal release of somatostatin was not detectable in 3 day-old cultures and reached a plateau at day 5. Responses evoked by exogenous stimulations (voltage-activated calcium currents, agonist-induced intracellular calcium rise and somatostatin release) appeared early in culture, increased in amplitude during 7-10 days and then stabilized. We conclude that, in hypothalamic neurons, the main neuronal functions develop in synchrony over a limited period of time.