Abstract

Effects of Accumbens DA Depletions on Lever Pressing

Accumbens DA Depletions do not Block Primary Reinforcement

Effects of Accumbens DA Depletions: Importance of Baseline Rate

On the Relation Between Accumbens DA Release and Operant Response Rate

Conclusions: Involvement of Accumbens DA in Regulating Energy Output

Discussion
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It has been suggested that accumbens dopamine (DA) is involved in the process of enabling organisms to expend energy in various situations, including foraging, maze running, and lever pressing. Although accumbens DA depletions impair stimulant self-administration, the effects of these depletions on various food-reinforced operant schedules are highly variable. Accumbens DA depletions have little or no effect on total response output in rats responding on the simplest schedule of food reinforcement, i.e., the fixed ratio 1. In addition, it has been shown clearly that the effects of accumbens DA depletions do not resemble the effects of extinction or pre-feeding to reduce food motivation. Over the last several years, our laboratory has investigated the effects of accumbens DA depletions on several schedules, including fixed ratio 1, variable interval 30 sec, fixed interval 30 sec, progressive ratio, and fixed ratio 4, 5, 16 and 64. These schedules generate very different rates of responding, ranging from 300-3000 responses per 30 min. Regression analyses of all these studies indicates a significant linear relation between control rates of responding and the degree of suppression of responding produced by accumbens DA depletions. Schedules that generate relatively low response rates, such as fixed ratio 1 or variable interval 30 sec, are little affected by accumbens DA depletions, yet schedules that generate high response rates (e.g., fixed ratio 64) are severely disrupted. Pre-feeding shows different patterns of suppression as a function of response rate. Microanalysis of the temporal characteristics of lever pressing has shown that accumbens DA depletions produce a response slowing, as measured by the interresponse time; extinction and pre-feeding produce a different pattern of effects. These results indicate that accumbens DA depletions do not blunt the reinforcing effects of food, but do suppress responding in a manner directly related to the baseline rate. Accumbens DA appears to be involved in energy expenditure, behavioral activation, or maintenance of high local rates of responding, which are functions that represent an area of overlap between motor and motivational processes.

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Presentation Number SAsalamone0516
Keywords: reinforcement, reward, motivation, motor, activity