MONOAMINES IN THE DORSOMEDIAL HYPOTHALAMUS OF RATS FOLLOWING EXPOSURETO DIFFERENT TESTS OF ANXIETY

1. Adult male Sprague-Dawley rats were subjected to the fear-potentiat ed startle, elevated plus-maze and social interaction tests and the le vels of norepinephrine, dopamine and serotonin in the dorsomedial hypo thalamus were determined by high-performance liquid chromatography. 2. Only rats subjected to the full fear potentiated startle test and not the other tests of anxiety or components (foot shocks or acoustic sta rtle) of fear-potentiated startle showed significant increases in nore pinephrine and dopamine levels after 24 hours. 3. A time course experi ment specific for the norepinephrine changes in the dorsomedial hypoth alamus of fear-potentiated startle rats revealed a significant increas e in tissue content as compared to controls at both the 12 and 24 hour post-test time points. 4. Tyrosine hydroxylase activity in the dorsom edial hypothalamus of the fear-potentiated startle rats did not show a significant change from controls. 5. An in vitro release study found a significant decrease in potassium-stimulated release of norepinephri ne in the dorsomedial hypothalamus as compared to controls at 24 hours posttest. 6. These results suggest that animals exposed to fear-poten tiated startle and not other tests of ''anxiety'' have a change in tis sue catecholamine levels and that the norepinephrine change may be the result of a decrease in release and not an increase in synthesis.