Nondependent Rats Research Articles

Effect of apomorphine and nigrostriatal lesions on aggression and striatal dopamine turnover during morphine withdrawal: evidence for dopaminergic supersensitivity in protracted abstinence.

Reliable aggression was seen in rats which were grouped 30 days after undergoing continuous withdrawal from morphine. This withdrawal aggression, associated with long-lasting effects of morphine dependence, was blocked by morphine or lesions of the nigrostriatal bundle, but not by lesions of the median forebrain bundle. When the nigrostriatal lesioned rats were treated with a small dose of apomorphine, the aggression was reinstated. Apomorphine reduced the turnover of dopamine in the 30-day withdrawn rats at doses which were ineffective in similarly housed non-dependent rats. These results suggest that animals undergoing protracted morphine abstinence show aggression due to a latent dopaminergic supersensitivity, similar to that previously reported during acute narcotic withdrawal.

Imparting reinforcing property to the taste of morphine through morphine injections

The present experiment tested the hypothesis that the taste of morphine would become a secondary reinforcer for rats made physically dependent on morphine by large, rapid intravenous injections. Rats made dependent by such injections and then withdrawn licked a dilute morphine solution more during a 30-sec licking period than did nondependent rats. A second experiment indicated that rats made physically dependent on morphine by 8 days of rapid injections licked a morphine solution more during withdrawal than did rats made dependent by 8 days of slow infusions. The results supported the preliminary hypothesis.

Limbic system and opioid addiction in the rat

Statistical comparisons of means in groups of morphine-dependent (or post-dependent) rats with and without bilteral lesions in the cingulum, the dorsomedial thalamic nucleus, the anterior temporal lobe (amygdaloid complex and ventral hippocampus), or the septum, and in nondependent rats with and without such lesions, revealed no significant lesion effects on specific signs of the 24-hr primary morphine-abstinence syndrome in this species: decreased water intake; increased “no-choice” drinking of a 5-μg/ml aqueous solution of a potent opioid (etonitazene); increased “wet dog” shake frequency; fall in colonic temperature. Lesions in the cingulum attenuated one sign of the secondary (protracted) morphine-abstinence syndrome (increased 24-hr water consumption). None of the lesions altered the suppressive effects on the primary morphine-abstinence syndrome of “no-choice” etonitazene-drinking or of intraperitoneal injection of morphine. None of the lesions prevented “relapse” of postdependent rats, as measured by comparisons of mean volumes of etonitazene (5-μg/ml) and water consumed in “choice” trials 9–72 days after permanent withdrawal of morphine.