This paper summarizes our studies examining whether changes in levels of brain monoamines after chronic exercise are associated with altered behavioral and endocrine responses to stressors other than exercise. The focus is on using animal models relevant for understanding reports by humans that regular physical activity reduces depression and anxiety. We studied the effects of chronic activity wheel running or treadmill exercise training on levels of norepinephrine (NE) measured in brain cell bodies and terminal regions at rest and after behavioral stress. We also measured brain levels of serotonin, i.e., 5-hydroxytryptamine (5-HT), dopamine (DA), and gamma aminobutyric acid (GABA), which function as both antagonists and synergists with NE. In general, we found that chronic activity wheel running increased NE levels in the pons medulla at rest and protected against NE depletion in locus coeruleus cell bodies after footshock: the concomitant reduction in escape-latency was consistent with an antidepressant effect. Wheel running also decreased the density of GABAA receptors in the corpus striatum while increasing open-field locomotion, consistent with an anxiolytic effect, but had no effect on hypothalamic-pituitary-adrenal cortical response to footshock measured by plasma levels of adrenocorticotropic hormone (ACTH), corticosterone, and prolactin. In contrast, treadmill exercise training increased the metabolism of NE in brain ascending terminal areas for NE, increased the secretion of ACTH after footshock and immobilization stress and had no effect on GABAA receptor density or open field locomotion. The validity of animal models for studying depression and anxiety after forced versus voluntary exercise is discussed. Recommendations are offered for improving the methods used in this area of research.
Department of Exercise Science, The University of Georgia, Athens, GA 30602-3654
Received for publication February 1996.
Accepted for publication June 1996.
Thanks go to my colleagues who coauthored the papers discussed herein and to my students, Andrea Dunn, Jaimie Warren, Ho Sang Yoo, Shawn Youngstedt, and Jill White-Welkley, for doing the work.
Address for correspondence: Rod K. Dishman, Ph.D., Department of Exercise Science, Ramsey Student Center, The University of Georgia, 300 River Road, Athens, GA 30602-3654. E-mail: email@example.com.