THYROID-HORMONE METABOLISM IN THE RAT-BRAIN IN AN ANIMAL-MODEL OF BEHAVIORAL DEPENDENCE ON ETHANOL

Thyroid hormone metabolism was investigated in the frontal cortex and amygdala in groups of rats either 'behaviorally dependent' on ethanol or chronically exposed to ethanol, but not 'dependent'. The activities of the 5'II deiodinase isoenzyme, which catalyzes the deiodination of thyroxine (T-4) to the active metabolite triiodothyronine (T-3), was elevated in the frontal cortex in both the 'behaviorally dependent' an d the 'non-dependent' rats. The activities of the 5-III deiodinase iso enzyme, which catalyzes the inactivation of T-3 to 3,3'-T-2 was, howev er, selectively inhibited in the amygdalas of the rats 'behaviorally d ependent' on ethanol, but normal in the 'non-dependent' rats. This sug gests that increases in intracellular concentrations of T-3 in the amy gdala may be specifically related to reward mechanisms and the develop ment of 'behavioral dependence' on ethanol. (C) 1997 Elsevier Science Ireland Ltd.