Effect of forced-running stress on beta-adrenergic receptors in rat brain regions and liver.

Rats were exposed to forced-running stress for 1 day, 3 days or a long term (approximately 2 weeks), and beta-adrenergic receptor binding was then assayed using [3H]dihydroalprenolol (DHA) in six brain regions and the liver. In the pons + med.obl., hypothalamus and midbrain, a reduction in beta-adrenergic receptor density was first evident on day 1. In contrast, a decrease in beta-adrenergic receptor density in the cerebral cortex and hippocampus was first evident on day 3. Decreased [3H]DHA binding in the pons + med.obl., cerebral cortex and hippocampus subsequently plateaued for the duration of the forced-running stress. In the midbrain and hypothalamus, however, decreased [3H]DHA binding subsequently returned to control levels despite the exposure to the forced-running stress. In the cerebellum and the liver, [3H]DHA binding did not change significantly throughout the stress. These results indicate that the forced-running stress induces both the time- and region-specific changes in beta-adrenergic receptors. Moreover, the rats showed either a behavioral depression or a spontaneous recovery of running activity during the 2 weeks following the end of the long-term stress. Thus, we also examined the relationship of beta-adrenergic receptors to these behavioral differences. [3H]DHA binding for the behavioral depression group was lower in the hippocampus and higher in the liver than for the spontaneous recovery group.