SELECTIVE ANTAGONISM OF DOPAMINE D-1 AND D-2 RECEPTORS DOES NOT BLOCK THE DEVELOPMENT OF BEHAVIORAL SENSITIZATION TO COCAINE

The objective of this study was to determine whether the development of behavioral sensitization to cocaine could be prevented by either D-1 or D-2 selective dopamine receptor antagonists. Male Wistar rats were treated daily for 7 days with either cocaine (15 mg/kg, IF) or vehicle in combination with the D-1 dopamine antagonist SCH 23390 (0.3 mg/kg, SC), the D-2 dopamine antagonist sulpiride (100 mg/kg, IF), or vehicle. After the daily injections, the rats were tested for locomotor activity in photocell arenas. Twenty-four hours after the last pre-exposure test session, all rats were given a challenge injection of cocaine (15 mg/kg, IF) and tested for activity. Cocaine treatments produced a greater relative increase in locomotor activity with repeated exposure (i.e. sensitization). Moreover, this increase in cocaine-induced locomotor activity was attenuated by both SCH 23390 and sulpiride. In contrast, neither sulpiride nor SCH 23390 blocked the development of behavioral sensitization to cocaine. That is, rats pretreated with sulpiride or SCH 23390 and cocaine did not differ from rats pre-exposed only to cocaine when given a cocaine challenge injection. These results suggest that behavioral sensitization to cocaine may develop through either D-1 or D-2 dopamine receptor stimulation or possibly through stimulation of some non-dopaminergic receptor.