Activity-Wheel Stress: Effects on Brain Monoamines and the Pituitary-Gonadal Axis

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Abstract
Recent clinical research on husbands of barren couples suggests that a stress-induced ergotropic status of the organism is associated with impaired fertility. The ''activity-wheel'' paradigm, which may be considered an animal model of active behavioral coping under stress conditions is suitable for the study of possible physiological mediators of the stress response. The study was designed to study the possible role of dopaminergic and serotonergic systems in pituitary gonadal function following activity stress. Three groups of rats were caged individually. One 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 a 24-h 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 9 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 testes 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. A dopaminergic and serotonergic involvement in pituitary-gonadal function under activity-stress conditions is suggested.

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