TYROSINE-HYDROXYLASE MESSENGER-RNA LEVELS IN LOCUS-COERULEUS OF RATS DURING ADAPTATION TO LONG-TERM IMMOBILIZATION STRESS EXPOSURE

The major central norepinephrinergic nucleus, locus ceruleus (LC), is thought to participate in modulation of such brain areas as cerebral c ortex, septum, hippocampus, thalamus, hypothalamus, and cerebellum in animals facing various physiological challenges, including stress. Exp osure of experimental animals to different stressors causes an increas e in LC activity and gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. The aim of this w ork was to investigate the effect of a single and repeated (7 times) o r long-term repeated (42 times) daily immobilization stress (IMMO) on TH mRNA levels in LC of laboratory rats by in situ hybridization metho d.A single IMMO caused significant elevation of LC TH mRNA levels in c omparison to unstressed controls. This was found immediately and at 3 and 6 h after IMMO, and progressively increased up to 24 h after the f irst IMMO terminated. Further exposure to IMMO did not cause additiona l increases in LC TH mRNA levels, which stayed significantly elevated in comparison to unstressed rats. In animals that underwent IMMO for 4 2 times, the LC TH gene expression, 24 h after the last stress exposur e, was significantly lower when compared to that of singly or seven ti mes stressed rats. Thus, our results indicate a possible adaptation of catecholamine-synthesizing system at the level of TH gene expression in LC of rats exposed to long-term repeated IMMO.