INCREASED OPEN-FIELD LOCOMOTION AND DECREASED STRIATAL GABA(A) BINDING AFTER ACTIVITY WHEEL RUNNING

Open-field behavior has been used to model reductions in anxiety-relat ed behaviors in the rat after chronic physical activity. Plausible mec hanisms for the increased open field locomotion observed after physica l activity have not been studied. Open field locomotion is decreased b y gamma-aminobutyric acid (GABA) and its agonists, and increased by GA BA antagonists, in the ventral striatum. Hence, we tested the hypothes is that increased open field locomotion following chronic physical act ivity would be accompanied by a decrease in the number of GABA(A) rece ptors in the corpus striatum. Young (similar to 55 days) male Sprague- Dawley rats (N = 24) were randomly assigned to three conditions: 24-h access to an activity wheel(AW), running for 1 h without shock 6 days/ week on a motorized treadmill (TM), or sedentary control (C). Open fie ld locomotion (total and center squares traversed), defecation, and ur ination were assessed on each of 3 consecutive days prior to and again after s weeks of physical activity. Open field locomotion (total and center squares) increased after activity wheel running, decreased afte r treadmill training, and did not change for control animals. GABA(A) receptor density indicated by [H-3]bicuculline binding (fmol/mg) was l ower for activity wheel animals compared with treadmill animals and co ntrols. GABA concentration (mu mol/g) was not different between activi ty wheel and treadmill groups but was higher for both groups contraste d with controls. Our findings of decreased GABA(A) density in the corp us striatum concomitant with an increase in open field locomotion are consistent with an anxiolytic effect of chronic activity wheel running .