Electrophysiological responses of neurones in the rat nucleus tractus solitarius to oxytocin-releasing stimuli.

Neurones in the nucleus tractus solitarius (NTS) of the rat are, at least partially, responsible for mediating the excitatory effects of systemic cholecystokinin (CCK) injection and parturition on oxytocin release. Utilising in vivo electrophysiological recordings in urethane-anaesthetised rats we examined the effects of systemic CCK injection and vaginal distension (VD) on NTS neuronal activity. Approximately 25% of neurones were excited by CCK injection and a population of neurones (24%) responded specifically to VD, but only one neurone responded to both oxytocin-releasing stimuli. NTS neurones that projected to the hypothalamus also responded in a specific manner to either CCK or VD. It is known that the excitatory effects of CCK and VD on oxytocin release are mediated by separate peripheral pathways and the results from this study suggest that separation of these two inputs persists at the level of the NTS.