Rotational behaviour in AA and ANA rats after repeated administration of morphine and cocaine

The purpose of the present study was to investigate the effects of repeated morphine and cocaine treatments on rotational behaviour in alcohol-preferring AA (Alko Alcohol) and alcohol-avoiding ANA (Alko Non-Alcohol) rats after unilateral 6-hydroxydopamine lesions of the ascending dopamine pathways. We administered saline, morphine (1 or 3 mg/kg) or cocaine (10 mg/kg) once daily for 4 days with an additional challenge 8 days after the repeated drug treatment. Ipsilateral rotations of the animals were monitored after each drug treatment. Both morphine (3 mg/kg but not 1 mg/kg) and cocaine induced more rotational behaviour in AA than in ANA rats over the 4-day drug treatment period. On Day 12, a challenge with 3 mg/kg morphine or cocaine induced significantly more rotations in the AA rats pretreated with morphine or cocaine when compared to saline-treated AA rats exposed to these drugs for the first time. This finding indicates that sensitization to the effects of morphine and cocaine occurs in the AA rats, while no clear sensitization was seen in the ANA rats. Collectively, these results suggest that morphine and cocaine activate the cerebral dopamine pathways to a greater extent in AA than in ANA rats.