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' and the 'non-dependent' rats. The activities of the 5-III deiodinase isoenzyme, which catalyzes the inactivation of T-3 to 3,3'-T-2 was, however, selectively inhibited in the amygdalas of the rats 'behaviorally dependent' on ethanol, but normal in the 'non-dependent' rats. This suggests that increases in intracellular concentrations of T-3 in the amygdala may be specifically related to reward mechanisms and the development of 'behavioral dependence' on ethanol. (C) 1997 Elsevier Science Ireland Ltd.