EFFECTS OF SINGLE OR REPEATED IMMOBILIZATION ON RELEASE OF NOREPINEPHRINE AND ITS METABOLITES IN THE CENTRAL NUCLEUS OF THE AMYGDALA IN CONSCIOUS RATS

The release of norepinephrine (NE) and its metabolites in the central nucleus of the amygdala was measured using in vivo microdialysis durin g immobilization (IMMO) stress in conscious rats. Animals underwent 2- hour periods of IMMO either once or daily for 7 days. Extracellular fl uid concentrations of NE, dihydroxyphenylglycol (DHPG), methoxyhydroxy phenylglycol (MHPG), and the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) were measured before, during, and after IMMO. Microdialy sate levels of NE and DHPG attained 2- to 3-fold increments during the 1 h of IMMO and declined thereafter, whereas MHPG and DOPAC levels at tained maximal levels of about twice basal concentrations during the 2 - or 3-h after initiation of IMMO. After the sixth IMMO basal levels o f NE, DHPG, MHPG, and DOPAC were decreased, and NE, DHPG, and DOPAC re sponses during the seventh IMMO failed to attain levels found during t he first IMMO, although the absolute changes during IMMO were similar between animals subjected to IMMO once or seven times. The results ind icate that acute IMMO increases synthesis, release, and metabolism of NE in the central nucleus of the amygdala and that repetition of IMMO decreases basal catecholamine synthesis and noradrenergic turnover in this brain region, without inhibiting acute noradrenergic responses.