Electrical recordings of magnocellular supraoptic and paraventricular neurons displaying both oxytocin- and vasopressin-related activity.

In suckled rats, some magnocellular neurons displayed both vasopressin-related phasic activity and oxytocin-related milk ejection bursts. Characteristics of basal activity and interspike intervals resembled those of vasopressin neurons. Bursts were coincident with those of oxytocin neurons and were facilitated by centrally injected oxytocin, but had lower maximum instantaneous frequency and often no after-inhibition. These data provide evidence of magnocellular neurones of mixed electrophysiological phenotype and complement reports of peptide coexistence.