Neurohypophysial peptides as retrograde transmitters in the supraoptic nucleus of the rat

A possible role for vasopressin and oxytocin in the physiology of the supra optic nucleus was investigated using nystatin-perforated patch recording in acute brain slices from the rat containing the supraoptic nucleus. We obse rved that exogenously applied oxytocin reduced glutamate-mediated synaptic transmission by acting at a presynaptic oxytocin receptor. Endogenous oxyto cin, released either by afferent excitation (tetanus) or by postsynaptic de polarization of the recorded magnocellular neurone caused a similar reducti on of excitatory input and this could be blocked with an oxytocin antagonis t. Thus endogenous oxytocin, released From magnocellular dendrites, acts as a retrograde transmitter to reduce afferent excitation. We discuss the pos sible significance of these results in terms of the physiological role of o xytocin in the intact animal and suggest possible avenues for further exper imentation.