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Initial and phenamine-stimulated frequencies of self-stimulation of the lateral hypothalamus were not significantly different in rats reared in communities and in conditions of social isolation. Unilateral lesioning of the ventral tegmental area and the medial prefrontal cortex in early ontogenesis increased phenamine sensitivity only in isolated rats. The dopamine receptor agonist apomorphine, at a dose of 0.05 mg/kg, which affects presynaptic receptors, inhibited the self-stimulation response in intact group-reared animals and in rats reared in isolation, by 21-23%. Stimulation of the ventral tegmental area did not change, while stimulation of the medial prefrontal cortex doubled the sensitivity of rats to apomorphine in animals reared in isolation (at doses of 0.05 and 0.5 mg/kg). Conditions of partial sensory and complete species isolation resulted in the development of a state of presynaptic receptor hypersensitivity of dopamine receptors in mesocorticolimbic brain systems in rats.