Intracranial self-stimulation in rats as a function of various stimulus parameters

The effects of different subcutaneous doses of cocaine (0.63, 1.25, 2.50, 5.00 and 10.0 mg/kg) on self-stimulation in rats were studied. Monopolar nichrome electrodes were implanted in the medial forebrain bundle at the level of the lateral hypothalamus. Six different stimulus parameter combinations (SPC's), inducing different predictable response rates were used. Cocaine showed a dose-related response stimulation, the highest at 10 mg/kg (49.7%); the response depression was very low at all doses and ranged from 3.20–8.23%.In the described experimental conditions apomorphine, amphetamine and cocaine have some properties in common but there are also important differences. With the three compounds response stimulation is related to the total control response rates at the different SPC's and is the highest at the two SPCs inducing the lowest control response rate. The differences in response stimulation associated with low intensity and low frequency SPC's could be related to a different mechanism of action.The response depression, the highest with apomorphine and the lowest with cocaine seems to be related to the stereotype inducing property of the compounds.The obtained effects of the three compounds are discussed in terms of their possible different influence on the dopaminergic system.