Dual effect of nicotine injected in the cerebral ventricles on rat gastric motility

Intracerebroventricularly (i.c.v.) administered nicotine 50 and 100 nmol produced dual changes, an early decrease and a succesive increase in gastric motility in urethane-anesthetized rats in which an intragastric balloon had been placed. These dual effects of nicotine were significantly antagonized by simultaneously administered hexamethonium i.c.v. but not by splanchnicectomy or by pretreatment with reserpine. Both atropine pretreatment and vagotomy abolished the stimulating effect of nicotine on gastric motility. Nicotine administered i.c.v. to bilaterally vagotomized rats did not affect gastric motility which was however enhanced by electrical stimulation of the vagus nerve. These observations suggest that central activation of the vagal cholinergic component results in excitation and central activation of the vagal non-adrenergic inhibitory component with i.c.v. administered nicotine results in inhibition of gastric motility. Sympathoadrenal systems and central monoaminergic mechanisms are probably not involved in the inhibitory effect of i.c.v. administered nicotine on gastric motility.