Behavioral and electrophysiological effects of pallidal GABAB receptor activation and blockade on haloperidol-induced akinesia in rats

The globus pallidus plays an important role in movement regulation. Morphological studies have revealed GABAB receptor expression in the globus pallidus. To investigate the behavioral and electrophysiological effects of pallidal GABAB receptors on haloperidol-induced akinesia, microinjection and extracellular recordings were performed in the present study. Unilateral microinjection of GABAB receptor agonist, baclofen, into globus pallidus produced ipsilateral dystonic posturing in haloperidol-induced akinesia rats. However, microinjection of GABAB receptor antagonist, CGP55845, induced contralateral dystonic posturing, suggesting the tonic activity of pallidal GABAergic neurotransmission. Micro-pressure ejection of baclofen into globus pallidus decreased the spontaneous firing of pallidal neurons. Furthermore, local administration of CGP55845 alone induced a weak but consistent increase in the frequency of pallidal firing. The presence of CGP55845 prevented baclofen-induced effects completely. From the present in vivo findings it may be concluded that pallidal GABAB receptors may contribute to the therapy of parkinsonian akinesia by modulating the activity of globus pallidus.