Changes in the Subcellular Localization and Functions of GABA-B Receptors in the Globus Pallidus of MPTP-Treated Monkeys
We have analyzed whether the subcellular location of GABA-B receptors and the electrophysiologic effects of local administration of GABA-B receptor ligands in the external and internal segments of the globus pallidus (GPe and GPi, respectively) in monkeys change with the induction of parkinsonism. Rhesus monkeys were rendered parkinsonian by treatment with MPTP. Electron microscopy immunoperoxidase for GABA-B R1 was performed in GPe and GPi. Compared with normal monkeys, the overall density of GABA-B R1-immunoreactive dendrites remained the same, but the density of immunolabeled axons increased significantly in both pallidal segments of MPTP-treated monkeys. Single unit recordings in awake monkeys showed that blockade of GABA-B receptors did not consistently affect the activity of GPe or GPi. However, in all neurons tested, application of a GABA-B agonist inhibited the firing rate. These results suggest that dopamine depletion induces an increased presynaptic expression of GABA-B receptors in both pallidal segments, perhaps facilitating a more prominent role of GABA-B-mediated presynaptic regulation of neurotransmitter release in the pallidum.
KeywordsFiring Rate Normal Monkey Unmyelinated Axon Parkinsonian Monkey Dopaminergic Depletion
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