title: The subcellular localization of GABA(B) receptor subunits in the rat substantia nigra.
abstract: The inhibitory effects of GABA within the substantia nigra (SN) are mediated in part by metabotropic GABA(B) receptors. To better understand the mechanisms underlying these effects, we have examined the subcellular localization of the GABA(B) receptor subunits, GABA(B1) and GABA(B2), in SN neurons and afferents using pre-embedding immunocytochemistry combined with anterograde or retrograde labelling. In both the SN pars compacta (SNc) and pars reticulata (SNr), GABA(B1) and GABA(B2) showed overlapping, but distinct, patterns of immunolabelling. GABA(B1) was more strongly expressed by putative dopaminergic neurons in the SNc than by SNr projection neurons, whereas GABA(B2) was mainly expressed in the neuropil of both regions. Immunogold labelling for GABA(B1) and GABA(B2) was localized in presynaptic and postsynaptic elements throughout the SN. The majority of labelling was intracellular or was associated with extrasynaptic sites on the plasma membrane. In addition, labelling for both subunits was found on the presynaptic and postsynaptic membranes at symmetric, putative GABAergic synapses, including those formed by anterogradely labelled striatonigral and pallidonigral terminals. Labelling was also observed on the presynaptic membrane and at the edge of the postsynaptic density at asymmetric, putative excitatory synapses. Double immunolabelling, using the vesicular glutamate transporter 2, revealed the glutamatergic nature of many of the immunogold-labelled asymmetric synapses. The widespread distribution of GABA(B) subunits in the SNc and SNr suggests that GABA(B)-mediated effects in these regions are likely to be more complex than previously described, involving presynaptic autoreceptors and heteroreceptors, and postsynaptic receptors on different populations of SN neurons.
authors.affiliation: MRC Anatomical Neuropharmacology Unit, University of Oxford, Oxford OX1 3TH, UK.
authors.forename: Justin
authors.initials: J
authors.lastname: Boyes
authors.forename: J Paul
authors.initials: JP
authors.lastname: Bolam
mesh_terms: D000344:Afferent Pathways / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D017660:Autoreceptors / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D005917:Globus Pallidus / Q000378:metabolism / Q000648:ultrastructure; D018698:Glutamic Acid / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D026901:Membrane Transport Proteins; D008854:Microscopy, Electron; D017072:Neostriatum / Q000378:metabolism / Q000648:ultrastructure; D009433:Neural Inhibition / Q000502:physiology; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018080:Receptors, GABA-B / Q000378:metabolism*; D013378:Substantia Nigra / Q000378:metabolism* / Q000648:ultrastructure; D013570:Synaptic Membranes / Q000378:metabolism / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D017660:Autoreceptors; D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D021122:Protein Subunits; D018080:Receptors, GABA-B; C493475:Slc17a6 protein, rat; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid