Role of globus pallidus GABA and opiate receptors in apomorphine circling in nigro-striatal lesioned rats

Summary The effect of lesioning the ipsilateral globus pallidus (GP) on apomorphine-induced circling in nigrostriatal lesioned rats was investigated. A GP electrolesion almost abolished circling. Drugs that affect GABA and opiate receptors were injected in GP through a cannula. Circling was antagonized by the GABA antagonists picrotoxin and bicuculline, the GABA agonist muscimol and by baclofen. Opiate receptor agonists including morohine, levorphanol, [d-Ala², d-Leu⁵]-enkephalin and -endorphin had no effect on circling in GP. Ethylketazocine caused a pronounced, naloxone-reversible slowing of apomorphine circling. Apomorphine-induced circling behaviour may be modulated by GP GABA receptors and kappa-type opiate receptors.