COMPARISON BETWEEN THE EFFECTS OF DOPAMIN E AGONISTS ON HYPOTHALAMIC SELF-STIMULATION OF RATS WITH MESOLIMBIC LESIONS BRED UNDER CONDITIONSOF SOCIAL-ISOLATION

In rats bred in groups or under conditions of social isolation, amphet amine administration did not change significantly the basic rate of hy pothalamic self-stimulation. The unilateral lesions of ventral tegment al area and medial prefrontal cortex in the early ontogeny (on the 17t h day after birth) increased the sensitivity to amphetamine only in is olated rats. Apomorphine, the dopamine receptor agonist, in the dose w hich mainly affected the presynaptic receptors (0.05 mg/kg) inhibited self-stimulation by 21-23% both in grouped and socially isolated rats. Destruction of the ventral tegmental area did not change, but that of the medial prefrontal cortex doubled the sensitivity of isolated rats to apomorphine. It is suggested that the hypersensitivity of presynap tic dopamine receptors in the mesocorticolimbic system develops as a r esult of partial sensory and full intraspecies isolation in rats.