Spike broadening in magnocellular neuroendocrine cells of rat hypothalamic slices.

Bursts of action potentials recorded from rat magnocellular neuroendocrine cells (MNCs) are known to be associated with enhanced release of oxytocin or vasopressin from their axon terminals in the neurohypophysis. Intracellular recordings from MNC somata in hypothalamic slices showed that spike broadening was characteristic of such bursts. Transitions from slow to fast firing caused spike broadening in all cells, whether they were silent, slow firing, phasic or fast-continuous. During phasic firing, broadening increased with the intraburst spike frequency. However, the parameters of maximal spike broadening recorded at the soma did not directly coincide with the previously described firing patterns evoking maximal hormone release from neurohypophysial terminals.