Contraversive circling induced by ventral tegmental microinjections of moderate doses of morphine and [D-Pen2, D-Pen5]enkephalin.

Unilateral ventral tegmental area (VTA) injections of morphine and [D-Pen2,D-Pen5]enkephalin (DPDPE), caused contraversive circling at doses of 1.2, 12, and 24 nmol. Similar doses of the selective kappa-agonist U-50,488H were ineffective. These data suggest a common mechanism for the circling, locomotion and facilitation of brain stimulation reward caused by VTA morphine, and distinguish this mechanism for that of feeding which is caused by both morphine and kappa-actions in this region.