Behavioural effects in rats of unilateral and bilateral injections of opiate receptor agonists into the globus pallidus

Abstract

Unilateral injections of a putative k- 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 δ-opiate receptor agonist ([ d-Ala 2, d-Leu 5]enkephalin) nor a putative μ-opiate receptor agonist (Tyr- d-Ala-Gly-MePhe-Met(0)-ol) induced circling behaviour after unilateral intrapallidal injection. Bilateral intrapallidal injection of the δ-opiate receptor agonist or the μ-opiate receptor agonist caused an increase in locomotor activity which in both cases was reduced by systemic administration of naloxone. A specific δ-receptor antagonist, ( N, N-bisalyl-Tyr-Gly-Gly-ψ-(CH 2S)-Phe-Leu-OH) had no effect on the increase in locomotor activity caused by the δ-opiate receptor agonist. Bilateral intrapallidal injection of the k- opiate receptor agonist had no effect on locomotor activity. It is suggested that different opiate receptor subtypes within the globus pallidus differentially mediate circling and locomotor behaviour.