Effects of SCH 23390, raclopride, and haloperidol on morphine withdrawal-induced aggression in male mice

Dopamine seems to play a very important role in aggressive behavior observe d in morphine withdrawal. The effect of SCH 23390 (0.5 mg/kg), raclopride ( 0.3 mg/kg), and haloperidol (0.1 mg/kg) on morphine withdrawal-induced aggr ession has been studied in this work. Mice were rendered dependent by a dai ly injection of morphine (2.5 mg/kg) for 14 days. Three different experimen ts were carried out with the objective to evaluate the antiaggressive effec t of the dopamine antagonists on: first, spontaneous morphine withdrawal; s econd, naloxone-induced withdrawal; and third, naloxone-induced withdrawal after previous administration of the neuroleptics. Thirty minutes after inj ection of the dopamine antagonists, experimental animals were confronted in a neutral area with anosmic, group-housed conspecifics (standard opponents ), and aggression was evaluated by estimation of times allocated to 11 diff erent behavioral categories. Morphine withdrawal produced an increase in ag gressive behavior and a decrease in social and nonsocial behaviors. The thr ee neuroleptics counteracted this aggression, but when SCH 23390 (selective D-1 antagonist) and haloperidol (mixed D-1/D-2 antagonist) were administer ed in naloxone-induced withdrawal, the effect was greater in comparison to the spontaneous withdrawal. However, no changes were observed after raclopr ide administration (selective D-2 antagonist). In conclusion, the alteratio ns in the dopaminergic system produced by opiate withdrawal depend on the t ype of withdrawal produced, and this produces a change in the antiaggressiv e potency of the dopamine antagonists. (C) 1999 Elsevier Science Inc.