Intravenous Self-administration In Rats Research Articles

Heroin and cocaine intravenous self-administration in rats: mediation by separate neural systems.

The hypothesis that separate neural systems mediate the reinforcing properties of opiate and psychomotor stimulant drugs was tested in rats trained to lever-press of IV injections of either cocaine or heroin during daily 3-h sessions. Pretreatment with the opiate receptor antagonist drug naltrexone produced dose-dependent increases in heroin self-administration, but had no effect on the rate or pattern of cocaine self-administration. Similarly, pretreatment with low doses of the dopamine antagonist drug alpha-flupenthixol produced dose-dependent increases in cocaine but not heroin self-administration. High doses of alpha-flupenthixol eliminated all responding for cocaine and slightly reduced heroin self-administration. The specificity with which the two antagonist drugs exerted their behavioral effects strongly suggests that independent neural substrates are responsible for the reinforcing actions of heroin and cocaine.

Experimental narcotic dependence models of primary dependence, abstinence and relapse obtained by intravenous self-administration in rat

1. 1. This study evaluated the usefulness of two animal models of morphine dependence, one based on intravenous voluntary self-administration and the other an automated or forced infusion model. 2. 2. The pattern of self-administration observed during primary dependence development in drug-naive rats stabilized after about 14 days with a daily drug intake of 240 mg/kg. 3. 3. On the basis of the self-administration data, a 6-day accelerated model of primary dependence has been produced by passive, automatic administration. In these conditions, animals displayed a similar degree of physical dependence to that observed with self-administration. 4. 4. A triphasic abstinence period is described. The duration, symptoms and propensity to relapse are analysed for each of the three phases: early, intermediate and protracted. 5. 5. The secondary dependence or relapse data obtained in ex-addicted rats allowed to re-administer morphine showed that in comparison with the primary dependence, a higher drug intake was sustained when tested at fixed inter vals between one and six months following morphine removal. 6. 6. Naloxone administered before and in association with morphine during a 7-day period blocked morphine self-administration. This effect was more potent in preventing secondary dependence in ex-addicted animals than the pri mary dependence in drug-naive animals.