EFFECT OF MORPHINE ON ROTATIONAL BEHAVIOR OF UNILATERALLY BRAIN-LESIONED MICE AND RATS - MORPHINE-WITHDRAWAL AND DEVELOPMENT OF TOLERANCE

1. The effect of acute morphine administration on the rotational behav ior of unilaterally brain lesioned mice and on the amphetamine induced rotational behavior of unilaterally brain-lesioned rats was studied. 2. The effect of repeated morphine administration on the rotational be havior of mice and rats was also investigated. 3. Acute administration of 40 mg/kg of morphine induced strong ipsilateral rotation in unilat erally brain lesioned mice. 4. One day after withdrawal, mice given mo rphine repeatedly for 5 days and treated acutely with 40 mg/kg of morp hine rotated significantly less ipsilaterally than mice that had recei ved the same dose of morphine for the first time. 5. Rats given 2 mg/k g of morphine 1 hr before administration of 5 mg/kg of amphetamine ten ded to rotate slightly more in the ipsilateral direction than the simi larly lesioned control rats that received amphetamine alone. 6. After 1 day of withdrawal from 5 days of repeated morphine administration, r ats given morphine before amphetamine tended to rotate less ipsilatera lly than those given morphine before amphetamine for the first time. 7 . Thus, repeated administration of morphine appears to induce toleranc e to the effect of morphine on circling behavior in unilaterally brain lesioned mice and rats. (C) 1997 Elsevier Science Inc.