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 observed 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 aggression has been studied in this work. Mice were rendered dependent by a daily injection of morphine (2.5 mg/kg) for 14 days. Three different experiments were carried out with the objective to evaluate the antiaggressive effect of the dopamine antagonists on: first, spontaneous morphine withdrawal; second, naloxone-induced withdrawal; and third, naloxone-induced withdrawal after previous administration of the neuroleptics. Thirty minutes after injection 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 different behavioral categories. Morphine withdrawal produced an increase in aggressive behavior and a decrease in social and nonsocial behaviors. The three neuroleptics counteracted this aggression, but when SCH 23390 (selective D1 antagonist) and haloperidol (mixed D1/D2 antagonist) were administered in naloxone-induced withdrawal, the effect was greater in comparison to the spontaneous withdrawal. However, no changes were observed after raclopride administration (selective D2 antagonist). In conclusion, the alterations in the dopaminergic system produced by opiate withdrawal depend on the type of withdrawal produced, and this produces a change in the antiaggressive potency of the dopamine antagonists.