COLD-EXPOSURE ELEVATES THYROTROPIN-RELEASING-HORMONE GENE-EXPRESSION IN MEDULLARY RAPHE NUCLEI - RELATIONSHIP WITH VAGALLY MEDIATED GASTRIC-EROSIONS

The stimulation of thyrotropin release by cold is associated with an i ncrease in thyrotropin-releasing hormone gene expression in the parave ntricular nucleus of the hypothalamus. Cold exposure also stimulates a utonomic outflow to viscera. There is evidence that caudal raphe nucle i are involved in autonomic regulation through thyrotropin-releasing h ormone projections to the dorsal vagal complex and spinal cord. To det ermine whether cold modulates thyrotropin-releasing hormone gene expre ssion in the caudal raphe nuclei, the effect of cold exposure on thyro tropin-releasing hormone messenger RNA levels in the rat lower brainst em was examined by quantitative Northern blot analysis and thyrotropin -releasing hormone messenger RNA was localized by in situ hybridizatio n. The gastric responses to cold exposure were also assessed in sham o r vagotomized rats with pylorus ligation. Thyrotropin-releasing hormon e messenger RNA signal was detected in the RNA extracted from the medu lla and hypothalamus but not from the amygdala, periaqueductal gray or cerebellum. Cold exposure (4 degrees C) for 1 or 3 h increased thyrot ropin-releasing hormone messenger RNA levels in the medulla by 77 +/- 37 and 142 +/- 39% respectively. In situ hybridization histochemistry showed that the increase in silver grain density occurred exclusively in the raphe pallidus and raphe obscurus. Exposure to cold stress for 2 h stimulated gastric acid secretion and resulted in gastric lesion f ormation in sham but not vagotomized rats. There are established thyro tropin-releasing hormone projections from the raphe pallidus and obscu rus to the dorsal vagal complex. Thyrotropin-releasing hormone is know n to exert an excitatory effect on neurons of the dorsal motor nucleus of the vagus, leading to vagally mediated stimulation of gastric func tion and erosions. The increased thyrotropin-releasing hormone gene ex pression in the raphe pallidus and obscurus induced by cold supports a n important role of endogenous thyrotropin-releasing hormone contained in caudal raphe nuclei-dorsal vagal complex pathways in vagally media ted changes in gastric function induced by cold.