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GABA B receptors in the centromedian/parafascicular thalamic nuclear complex: An ultrastructural analysis of GABA B R1 and GABA B R2 in the monkey thalamus
Author(s) -
Villalba Rosa M.,
Raju Dinesh V.,
Hall Randy A.,
Smith Yoland
Publication year - 2006
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.20950
Subject(s) - axon , biology , postsynaptic potential , immunogold labelling , thalamus , glutamate receptor , synaptic vesicle , neuroscience , axon terminal , gabaa receptor , receptor , microbiology and biotechnology , biochemistry , ultrastructure , anatomy , vesicle , membrane
Strong γ‐aminobutyric acid type B (GABA B ) receptor binding has been shown throughout the thalamus, but the distribution of the two GABA B receptor subunits, GABA B receptor subunit 1 (GABA B R1) and GABA B receptor subunit 2 (GABA B R2), remains poorly characterized. In primates, the caudal intralaminar nuclei, centromedian and parafascicular (CM/PF), are an integral part of basal ganglia circuits and a main source of inputs to the striatum. In this study, we analyzed the subcellular and subsynaptic distribution of GABA B receptor subunits by using light and electron microscopic immunocytochemical techniques. Quantitative immunoperoxidase and immunogold analysis showed that both subunits display a similar pattern of distribution in CM/PF, being expressed largely at extrasynaptic and perisynaptic sites in neuronal cell bodies, dendrites, and axon‐like processes and less abundantly in axon terminals. Postsynaptic GABA B R1 labeling was found mostly on the plasma membrane (70–80%), whereas GABA B R2 was more evenly distributed between the plasma membrane and intracellular compartments of CM/PF neurons. A few axon terminals forming symmetric and asymmetric synapses were also labeled for GABA B R1 and GABA B R2, but the bulk of presynaptic labeling was expressed in small axon‐like processes. About 20% of presynaptic vesicle‐containing dendrites of local circuit neurons displayed GABA B R1/R2 immunoreactivity. Vesicular glutamate transporters (vGluT1)‐containing terminals forming asymmetric synapses expressed GABA B R1 and/or displayed postsynaptic GABA B R1 at the edges of their asymmetric specialization. Overall, these findings provide evidence for multiple sites where GABA B receptors could modulate GABAergic and glutamatergic transmission in the primate CM/PF complex. J. Comp. Neurol. 496:269–287, 2006. © 2006 Wiley‐Liss, Inc.