INDUCTION OF ADRENAL TYROSINE-HYDROXYLASE MESSENGER-RNA BY SINGLE IMMOBILIZATION STRESS OCCURS EVEN AFTER SPLANCHNIC TRANSECTION AND IN THEPRESENCE OF CHOLINERGIC ANTAGONISTS

Immobilization (IMO) stress elevates plasma catecholamines and increas es tyrosine hydroxylase (TH) gene expression in rat adrenals. This stu dy examined the mechanism(s) of IMO-induced changes in adrenal TH mRNA levels. Innervation of the adrenal medulla is predominantly cholinerg ic and splanchnicotomy as well as nicotinic receptor antagonists preve nt the cold-induced rise in TH mRNA levels. In this study, the IMO-ind uced rise in plasma catecholamines, but not TH mRNA levels, was reduce d by the antagonist chlorisondamine. Muscarinic antagonist atropine al so did not prevent the IMO stress-elicited rise in TH mRNA. Furthermor e, denervation of the adrenals by unilateral splanchnicotomy did not b lock the IMO-induced rise in TH mRNA but completely prevented the indu ction of neuropeptide Y mRNA. These results suggest that (1) the large increase in adrenal TH gene expression elicited by a single IMO stres s is not regulated via cholinergic receptors or splanchnic innervation , and (2) there is a dissociation between regulatory mechanisms of cat echolamine secretion and elevation of TH gene expression in the adrena l medulla of rats during IMO stress.