Apomorphine and 7-OH DPAT reduce ethanol intake of P and HAD rats

Adult male rats of the alcohol-preferring (P) line (N = 10) and high alcohol drinking (HAD) line (N = 12) were used to study the effects of IP administration of 0.125-0.50 mg/kg 7-OH DPAT (a putative D agonist) and 0.25-1.0 mg/kg apomorphine (a dopamine agonist with 50-fold higher affinities for the D1 and D2 receptors than for the D3 receptor) on the concurrent intakes of 10% (v/v) ethanol and 0.0125% (g/v) saccharin during a daily 4-h scheduled access period. Control intakes by the P rats for the 4-h period were 17.9 +/- 0.5 and 7.2 +/- 0.4 ml for the ethanol and saccharin solutions, respectively. For the HAD line, ethanol consumption was 18.7 +/- 0.2 ml and saccharin intake was 8.7 +/- 1.6 ml for the 4-h period. In terms of grams ethanol/kg body wt, the 4-h intakes were 2.2 +/- 0.2 for the P line and 3.0 +/- 0.3 for the HAD rats. Both P and HAD rats consumed approximately 40% of their total ethanol intake in the first 15 min of access while consuming only about 15% of their total saccharin intake during this 15-min period. The putative D3 agonist 7-OH DPAT produced a decrease in ethanol intake in the first h to 45-55% of control levels for the P rat (p < 0.01) and to 25-70% of control values in the HAD line (p < 0.001). Apomorphine caused a dose-dependent decrease in ethanol intake in the first hour to 15-70% of control values in the P rat (p < 0.001) and to 25-60% of control levels in the HAD line (p < 0.001). Saccharin and 4-h food intakes for both lines were not altered by either 7-OH DPAT or apomorphine. Overall, these results suggest that D2 and D3 dopamine receptors may play a role in mediating alcohol drinking behavior of the selectively bred HAD and P lines of rats.