The role of dopamine in reinforcement: changes in reinforcement sensitivity induced by D1-type, D2-type, and nonselective dopamine receptor agonists

Abstract

Dose-dependent changes in sensitivity to reinforcement were found when rats were treated with low, moderate, and high doses of the partial dopamine D1-type receptor agonist SKF38393 and with the nonselective dopamine agonist apomorphine, but did not change when rats were treated with similar doses of the selective dopamine D2-type receptor agonist quinpirole. Estimates of bias did not differ significantly across exposure to SKF38393 or quinpirole, but did change significantly at the high dose of apomorphine. Estimates of goodness of fit (r2) did not change significantly during quinpirole exposure. Poor goodness of fit was obtained for the high doses of SKF38393 and apomorphine. Decrements in absolute rates of responding were observed at the high dose of quinpirole and at the moderate and high doses of SKF38393 and apomorphine. Changes in r2 and absolute responding may be due to increases in stereotyped behavior during SKF38393 and apomorphine exposure that, in contrast to quinpirole, were distant from the response lever. The present data provide evidence that sensitivity to reward is affected more strongly by dopamine D1-like receptors rather than D2-like receptors, consistent with evidence from other studies investigating consummatory dopamine behavior and the tonic/phasic dopamine hypothesis.

Figure 1. Mean estimates of sensitivity to reinforcement (matching), bias, and goodness of fit for quinpirole rats.

Estimates of matching and bias are based on mean relative rates of responding. The log of P1/P2 is plotted on the y axis, and the log of R1/R2 is plotted on the x axis. The dashed line represents hypothetical matching, and the solid line represents the best-fitting linear regression to the obtained data.

Figure 2. Mean estimates of sensitivity to reinforcement (matching), bias, and goodness of fit for SKF38393 rats.

Estimates of matching and bias are based on mean relative rates of responding. The log of P1/P2 is plotted on the y axis, and the log of R1/R2 is plotted on the x axis. The dashed line represents hypothetical matching, and the solid line represents the best-fitting linear regression to the obtained data.

Figure 3. Mean estimates of sensitivity to reinforcement (matching) for the quinpirole and SKF38393 groups in Experiment 1.

Mean matching values are plotted on the y axis, and conditions are plotted on the x axis. Error bars represent the standard error of the mean.

Figure 4. Mean estimates of bias for the quinpirole and SKF38393 groups in Experiment 1.

Mean bias values are plotted on the y axis, and conditions are plotted on the x axis. Error bars represent the standard error of the mean.

Figure 5. Mean estimates of goodness of fit (r²) for the quinpirole and SKF38393 groups in Experiment 1.

Mean r² values are plotted on the y axis, and conditions are plotted on the x axis. Error bars represent the standard error of the mean.

Figure 6. Mean absolute response rates (responses per minute) on P₁ for quinpirole rats as a function of obtained reinforcers per hour (R₁).

Figure 7. Mean absolute response rates (responses per minute) on P₁ for SKF38393 rats as a function of obtained reinforcers per hour (R₁).

Figure 8. Mean estimates of sensitivity to reinforcement (matching), bias, and goodness of fit for apomorphine rats.

Estimates of matching and bias are based on mean relative rates of responding. The log of P1/P2 is plotted on the y axis, and the log of R1/R2 is plotted on the x axis. The dashed line represents hypothetical matching, and the solid line represents the best-fitting linear regression to the obtained data.

Figure 9. Mean estimates of sensitivity to reinforcement (matching) for the apomorphine group in Experiment 2.

Mean bias values are plotted on the y axis, and conditions are plotted on the x axis. Error bars represent the standard error of the mean.

Figure 10. Mean estimates of bias for the apomorphine group in Experiment 2.

Mean bias values are plotted on the y axis, and conditions are plotted on the x axis. Error bars represent the standard error of the mean.

Figure 11. Mean estimates of goodness of fit (r²) for the apomorphine group in Experiment 2.

Mean r² values are plotted on the y axis, and conditions are plotted on the x axis. Error bars represent the standard error of the mean.

Figure 12. Mean absolute response rates (responses per minute) on P₁ for apomorphine rats as a function of obtained reinforcers per hour (R₁).