Abstract
Two experiments were undertaken to investigate the role of accumbens dopamine (DA) in food-related motor activities. Although presentation of large amounts of food elicits feeding behavior, periodic food presentation (PFP; e.g. a 45-mg pellet every 45 s) induces considerable locomotion, rearing and other motor activities in food-deprived rats. In the first experiment, in vivo microdialysis methods were used to study DA release and metabolism in the nucleus accumbens of behaving rats exposed to periodic food presentation. Four behavioral conditions were used: high rate of PFP (one pellet per 45 s), low rate of PFP (one pellet per 4 min), massed food presentation and food deprivation control. The rats that received a high rate of PFP showed substantial increases in locomotor activity, and also showed significant increases in extracellular DA and DA metabolites. Rats that received massed presentation of food pellets consumed large quantities of food, but showed no significant increases in locomotor activity or DA release. Although the group that received the high rate of PFP showed the highest motor activity and the largest increase in DA release, there was only a modest correlation ( r = 0.34) between motor activity and increased DA release. In the second experiment, the neurotoxic agent 6-hydroxydopamine (6-OHDA) was injected into the nucleus accumbens in order to assess the effects of DA depletion on PFP-induced motor activity. DA depletion significantly reduced PFP-induced motor activity in the first week after surgery, but by the second week DA-depleted rats had recovered normal levels of motor activity. DA levels in the nucleus accumbens of 6-OHDA-treated rats were highly correlated with the initial deficit in PFP-induced activity. These studies demonstrate that PFP increases motor activity through a mechanism that depends upon DA in nucleus accumbens. Accumbens DA could be acting to modulate or facilitate aspects of locomotor function, but the relatively low correlation between DA release and motor activity suggests that accumbens DA release may not directly control the motor output.
Published Version
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