Cold exposure increases TRH gene expression in hypothalamic and raphe nuclei and results in a vagal activation of gastric function. We investigated the role of medullary TRH receptors in cold (4-6 C, 90 min)-induced stimulation of gastric motor function in fasted conscious rats using intracisternal injections of TRH receptor (TRHr) antisense oligodeoxynucleotides (100 microg twice, -48 and -24 h). The gastric emptying of a methyl-cellulose solution was assessed by the phenol red method. TRH (0.1 microg) or the somatostatin subtype 5-preferring analog, BIM-23052 (1 microg), injected intracisternally increased basal gastric emptying by 34% and 47%, respectively. TRHr antisense, which had no effect on basal emptying, blocked TRH action but did not influence that of BIM-23052. Cold exposure increased gastric emptying by 64%, and the response was inhibited by vagotomy, atropine (0.1 mg/kg, i.p.), and TRHr antisense (intracisternally). Saline or mismatched oligodeoxynucleotides, injected intracisternally under similar conditions, did not alter the enhanced gastric emptying induced by cold or intracisternal injection of TRH or BIM-23052. These results indicate that TRH receptor activation in the brain stem mediates acute cold-induced vagal cholinergic stimulation of gastric transit, and that medullary TRH may play a role in the autonomic visceral responses to acute cold.