Increased in vivo tyrosine hydroxylase activity in rat telencephalon produced by self-stimulation of the ventral tegmental area.

Changes in the activity of dopaminergic neurons associated with intracranial self-stimulation of the ventral tegmentum were assessed by measuring the accumulation of 3,4-dihydroxyphenylalanine (DOPA) after inhibition of aromatic amino acid decarboxylase by NSD-1015. When compared to implanted unstimulated controls, DOPA concentrations were elevated significantly in the nucleus accumbens, striatum and olfactory tubercle in the hemisphere ipsilateral to the electrode, after a 30 min session of self-stimulation. The concentration of DOPA in the contralateral nucleus accumbens and striatum did not differ from control levels, although relative to control values it was significantly increased in the contralateral olfactory tubercle. A similar analysis of in vivo tyrosine hydroxylase activity in these brain regions following a 30 min session of lever pressing for food reward on a fixed-ratio (FR-8) schedule failed to reveal any significant changes relative to control subjects. These results are consistent with a role for dopamine in brain-stimulation reward obtained from electrical stimulation of the ventral tegmental area but do not provide evidence for dopaminergic mediation of the rewarding properties of food.