Gastric motility in conscious rats given oxytocin and an oxytocin antagonist centrally.

Previous experiments have shown that gastric motility is inhibited by microinjection of oxytocin (OT) into the dorsal motor nucleus of the vagus (DMN) in anesthetized rats, and that the inhibition of gastric motility after electrical stimulation of the hypothalamic paraventricular nucleus (PVN) is blocked by microinjection of an OT receptor antagonist directly into the DMN. As an extension of these observations, the present series of studies demonstrate that gastric motility in unanesthetized, freely moving rats was reduced both by intracerebroventricular (i.c.v.) administration of OT and by electrical stimulation of the PVN, and that both of these inhibitory effects were blocked by i.c.v. administration of an OT antagonist. Moreover, an OT antagonist administered i.c.v. alone caused an increase in baseline gastric motility. However, pretreatment with the same OT antagonist i.c.v. did not block the inhibitory effects of systemic LiCl or cholecystokinin on gastric motility in conscious rats. These results suggest that oxytocinergic neurons exert a tonic inhibitory effect on gastric motility in rats, but that the inhibitory effects of LiCl and cholecystokinin on gastric motility are not primarily mediated by parvocellular OT-containing neurons projecting from the PVN to the DMN.