Asymmetric behavior induced by enkephalinergic agents in the basal ganglia

The caudate-putamen (CDp) and the globus pallidus (GP) are sites rich in both leucine (LEU) and methionine-enkephalin (MET-ENK) and in ENK receptors. Since chemical and electrolytic lesions of the CDp and GP result in a reduction in ENKs and their receptors and in motor asymmetry, there may be a role for CDp and GP ENKs in rotational behavior and bodily asymmetry. To test this possibility, various doses of D-ALA-2-LEU-ENK, D-ALA-2-MET-ENK, naloxone and naltrexone were injected into the CDp and GP through chronically implanted cannulae. The injections of MET and LEU-ENK caused dose-dependent ipsiversive rotations while injections of naloxone and naltrexone caused contraversive rotations. All of the drug injections also caused bodily asymmetries which were in the same direction as the circling. Intraperitoneal injections of naloxone dose-dependently blocked the rotational behavior induced by the most effective dose of the ENKs used. ENK injections into sites adjacent to the CDp and GP (i.e., cortex, nucleus accumbens and the region bordering the bed nucleus of the stria terminalis and the bed nucleus of anterior commissure) failed to produce any significant circling. These results clearly suggest that CDp and GP ENKs cause ipsiversive rotational behavior and bodily asymmetry and must be considered as one element of the control exerted by the basal ganglia over the motor system.