Modulation of mesolimbic dopaminergic projections by beta-endorphin in the rat

Intracerebroventricular injection of beta-endorphin stimulated the metabolism of dopamine in a dose-dependent, opiate antagonist-reversible manner. Local injections into the nucleus accumbens also caused similar increases, indicating that the actions of this peptide on mesolimbic dopaminergic projections were occurring at opioid receptor sites within the nucleus accumbens. Tolerance experiments suggested that epsilon opioid receptors may be involved in mediating these effects in the n. accumbens, unlike in the striatum.