BEHAVIORAL-EFFECTS IN RATS OF UNILATERAL AND BILATERAL INJECTIONS OF OPIATE RECEPTOR AGONISTS INTO THE GLOBUS PALLIDUS

Unilateral injections of a putative .kappa.-opiate receptor agonist, ethylketocyclazocine, into the globus pallidus of rats caused dose-dependent ipsiversive circling which was inhibited by prior systemic administration of the opiate receptor antagonist naloxone. Neither a putative .delta.-opiate receptor agonist ([D-Ala2,D-Leu5]enkephalin) nor a putative .mu.-opiate receptor agonist (Tyr-D-Ala-Gly-MePhe-Met(0)-ol) [FK 33-824] induced circling behavior after unilateral intrapallidal injection. Bilateral intrapallidal injection of the .delta.-opiate receptor agonist or the .mu.-opiate receptor agonist caused an increase in locomotor activity which in both cases was reduced by systemic administration of naloxone. A specific .delta.-receptor antagonist, (N,N-bisalyl-Tyr-Gly-Gly-.psi.-(CH2S)-Phe-Leu-OH) [ICI 154, 129] had no effect on the increase in locomotor activity caused by the .delta.-opiate receptor agonist. Bilateral intrapallidal injection of the .delta.-opiate receptor agonist had no effect on locomotor activity. Different opiate receptor subtypes within the globus pallidus differentially mediate circling and locomotor behavior.