Amphetamine, chlorpromazine and clonidine effects on self-stimulation in caudate or hypothalamus of the squirrel monkey

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In 2 separate groups of squirrel monkeys and within 3 animals low rates of intracranial self-stimulation (ICSS) elicited from caudate or lateral hypothalamic brain sites were increased by as much as 200% above control levels by amphetamine (0.5 mg/kg). Thresholds for responding were decreased by 50%. Increasing the drug dose from 2 to 10mg/kg produced response inhibition at both brain sites. The duration of inhibitory action of amphetamine (2.0 mg/kg) on ICSS from the medial forebrain bundle (MFB) area of the lateral hypothalamus was 6 hr. At caudate sites ICSS did not occur until 48 hr had elapsed. A 10 mg/kg dose of amphetamine produced a duration of action of 36 hr in the MFB and 84 hr in the caudate. Chlorpromazine (CPZ) doses of 0.5 and 1.0 mg/kg decreased caudate ICSS significantly more than lateral hypothalamic ICSS. At 1.0 mg/kg the duration of action of CPZ was 6 hr at lateral hypothalamic brain sites and 24 hr at caudate sites. At a 2.0 mg/kg CPZ dose the duration of action was 12 hr in the MFB and 36 hr in the caudate. A dose of 0.10 mg/kg of clonidine blocked high rates of MFB ICSS while within the same animal caudate ICSS was much less affected. Higher doses (0.25 mg/kg) sedated the animal and ICSS was equally inhibited at both sites. These findings, using ICSS as a behavioral measure, suggest that the effects of amphetamine and CPZ involve not only hypothalamic structures but more anterior telencephalic sites as well. The prolonged actions of amphetamine and CPZ on caudate ICSS suggest that drugs acting, in part, on dopamine containing neurons will interfere with certain caudate mediated behavior. Further, since hypothalamic but not caudate ICSS sites are more dose sensitive to drugs that selectively act on NE containing neurons, other amines in addition to NE may play a role in the support of ICSS.