Locomotor activation induced by infusion of endorphins into the ventral tegmental area: evidence for opiate-dopamine interactions

beta-Endorphin in nanomole quantities produced a stimulation of locomotor activity when infused into the region of the dopamine cell bodies of the ventral tegmental area (VTA) in rats. alpha-, gamma-, and des-Tyr-gamma-endorphin produced similar effects, but the D-alanine analogues of alpha and gamma-endorphin produced a larger and longer-lasting activation, presumably reflecting their resistance to degradation. This locomotor activation was reversible by pretreatment with naloxone and by destruction of the terminal projections of the mesocorticolimbic dopamine system originating in the VTA. These results demonstrate that locally infused endorphin can interact with the opioid receptors in the VTA, and they suggest a means by which endorphins activate limbic excitability.