Neurones with synchronous bursting discharges in organ cultures of the hypothalamic supraoptic nucleus area.

Explants of the hypothalamic supraoptic nucleus area from newborn rats were cultured. Ultrastructural studies revealed the existence of typical neurosecretory granules in neuronal perikarya as well as in axons. Large nerve cells that were spontaneously active discharged at an average firing rate of 7.2 +/- 4.4 (S.D., n = 98) spikes/sec and 42% of these neurones displayed a phasic firing pattern as shown by the existence of peaks in their autocorrelograms. The firing of 59% of the neurones was synchronous with the activity of other nerve cells. In some neurones, only the onsets of bursts were correlated, whereas in others periods of high correlation alternated with periods of no correlation. The relative proportion of rhythmically or synchronously firing hypothalamic neurones was not altered when a neurohypophysial explant was co-cultured. Field stimulation in the cultures resulted in a short-latency excitation followed by an inhibition which was found to be bicuculline-sensitive. The existence of functional synapses was furthermore demonstrated by intracellular recordings of postsynaptic potentials.