Acute systemic blockade of D2 receptors does not accelerate the extinction of cocaine-associated place preference

Facilitation of extinction can be used as a therapeutic tool in treatment of both post-traumatic stress disorder and drug addiction. The present study examined whether the blockade of D2 receptors before each extinction trial would accelerate the extinction of cocaine-induced place preference. Male Wistar rats were initially conditioned and tested for a cocaine-associated place-preference (20 mg/kg). On the following day after the initial test, the animals were submitted to extinction training. This training consisted of daily sessions in which the subjects were alternatively confined during 30 min in the saline and cocaine-associated environment. However, 30 min before each extinction trial the animals received a systemic injection of D2 antagonist sulpiride. While one group was treated with a dose of 50 mg/kg (ip), the other group was treated with a dose of 100 mg/kg. An additional control group received injections of saline during extinction trials. Twenty-four hours after the last extinction trial, the animals were tested again for their preferences to cocaine and saline associated environments. Since one round of extinction trial was not sufficient to produce extinction of cocaine associated place preference, the animals were submitted to a second cycle of extinction trials and test. The systemic administration of the two doses of sulpiride (50 and 100 mg/kg) 30 min before each conditioning did not enhance the extinction of cocaine-associated place preference. This finding suggests that the D2 receptors are not involved in a acute protocol of extinction of cocaine-induced place preference.