CONCURRENT NIMODIPINE ATTENUATES THE WITHDRAWAL SIGNS AND THE INCREASE OF CEREBRAL DIHYDROPYRIDINE BINDING AFTER CHRONIC MORPHINE TREATMENT IN RATS

The effect of chronic administration of dihydropyridine calcium channel antagonist nimodipine (1 mg/kg/day) given concurrently with morphine on the signs of morphine withdrawal and on the [H-3]nitrendipine binding in the rat brain has been investigated. Chronic morphine administration in increasing daily doses from 20 mg/kg to 70 mg/kg for 24 days and consequent withdrawal for 24 h induced loss of body weight, wet dog shakes, episodes of writhing and yawning behaviour. The density of [H-3]nitrendipine binding was elevated in the cortex and limbic structures but not in the striatum after chronic morphine treatment. Chronic concurrent administration of nimodipine prevented the loss of body weight and reduced the scores of wet dog shakes and writhing, but did not affect yawning behaviour at 24 h after morphine withdrawal. The concurrent nimodipine treatment also prevented the rise in the density of central dihydropyridine binding sites which occurred upon chronic morphine treatment. These results suggest that chronic nimodipine treatment attenuates the development of the withdrawal signs which occur upon the termination of chronic morphine treatment by preventing the up-regulation of the central dihydropyridine-sensitive binding sites.