DAILY SPONTANEOUS RUNNING ALTERS BEHAVIORAL AND NEUROCHEMICAL INDEXES OF NIGROSTRIATAL FUNCTION

Behavioral and neurochemical indexes of nigrostriatal dopaminergic function were compared between sedentary control rats (n = 12) and daily spontaneous running (DSR) male rats (n = 10). Nine weeks of DSR did not significantly alter body, heart, pituitary, or testes weights. DSR and control animals did differ in performance on a sensorimotor beam walking task, with DSR rats showing significantly shorter times required to cross the beam (60 +/- 17 vs. 119 +/- 14 s; P < 0.02) as well as fewer slips off the beam (3.0 +/- 0.8 vs. 6.2 +/- 1.1; P < 0.05). DSR animals also engaged in significantly greater durations of social investigation than control rats (43 +/- 5 vs. 25 +/- 3 s; P < 0.01) when tested in a social investigation memory-recognition test. Basal dopamine release rates from superfused corpus striatal tissue fragments of DSR rats were about one-half those obtained from control animals (18 +/- 5 vs. 34 +/- 6 pg . mg(-1). min(-1); P < 0.05), whereas responses of these striatal tissue fragments to a depolarizing concentration of potassium were virtually identical (45 +/- 10 vs. 47 +/- 8 pg . mg(-1). min(-1)). These data indicate that a relatively limited intensity of DSR insufficient to alter cardiovascular function can exert substantial effects on behavioral and neurochemical indicators of nigrostriatal dopaminergic activity.