Activity-wheel stress: effects on brain monoamines and the pituitary-gonadal axis

The study was designed to study the possible role of dopaminergic and serotonergic systems in pituitary gonadal function following activity stress. 3 groups of rats were caged individually. 1 group of rats (AW) was fed for 1 h each day and had free access to a running wheel. The 2nd group (FC) had no access to a running wheel and received exactly the same amount of food as animals of the AW group. The 3rd group (UC) had 24-hour access to food. AW rats showed a gradual increase in running activity which accompanied a gradual decrease in food consumption. AW rats were sacrificed, together with their matched FC counterpart and a UC control rat, on the day that their food consumption fell below 4 g/day. The brains were dissected into nine specific areas and subjected to analysis for dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) using high-performance liquid chromatography with electrochemical detection. Trunk blood was analyzed for serum levels of testosterone (T), luteinizing hormone (LH) and corticosterone (C), and weights of tests and epididymides were recorded. Both activity stress and restricted food intake resulted in a fall in serum levels of T and LH. Elevated levels were found for DOPAC in the hippocampus, hypothalamus, brainstem, and midbrain of activity-stressed rats. Levels of 5-HT and 5-HIAA were lower in the hypothalamus of these animals. Data analysis suggests a dopaminergic and serotonergic involvement in pituitary-gonadal function under activity-stress conditions.