Inhibitory neurotransmission in rat spinal cord: co-localization of glycine- and GABAA-receptors at GABAergic synaptic contacts demonstrated by triple immunofluorescence staining.
Synaptic inhibition in rat spinal cord is mediated by the amino acids gamma-aminobutyric acid (GABA) and glycine. Most spinal cord neurons respond to both neurotransmitters, suggesting co-expression of GABAA- and strychnine-sensitive glycine-receptors in individual cells. While the distribution of glycine-receptors has been extensively characterized, much less is known about the cellular localization of GABAA-receptors in spinal cord neurons. In the present study, the distribution of GABAA-receptors was analyzed immunohistochemically with a subunit-specific antiserum recognizing the alpha 1-subunit. Their co-localization with glycine-receptors and their apposition to GABAergic axon terminals were assessed by confocal laser microscopy in sections processed for double- and triple-immunofluorescence staining, using a monoclonal antibody against the 93 kDa glycine-receptor-associated protein, gephyrin, and an antiserum to glutamic acid decarboxylase. Staining for the GABAA-receptor alpha 1-subunit decorated the soma and dendrites of numerous neurons in laminae III-VIII and X of the spinal cord, revealing their morphology in clear detail. By contrast, laminae II and IX contained little immunoreactivity for these GABAA-receptors. Double-immunofluorescence staining showed that most GABAA-receptor-positive cells in layers III-VIII and X also exhibited a prominent glycine-receptor immunoreactivity. Both types of receptors had very similar distribution patterns in the cell membrane and were frequently co-localized in sites apposed to GABAergic axon terminals. These results indicate that GABAA- and glycine-receptors may co-exist within single postsynaptic densities, suggesting a possible synergism in the action of GABA and glycine in spinal cord neurons.
Institute of Pharmacology, University of Zurich, Switzerland.
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S
Bohlhalter
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Mohler
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JM
Fritschy
D000818:Animals; D002352:Carrier Proteins / Q000032:analysis; D005455:Fluorescent Antibody Technique; D007834:Lasers; D008297:Male; D008565:Membrane Proteins / Q000032:analysis; D008853:Microscopy / Q000379:methods; D008970:Molecular Weight; D017729:Presynaptic Terminals / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000032:analysis*; D018009:Receptors, Glycine / Q000032:analysis*; D013116:Spinal Cord / Q000737:chemistry / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D002352:Carrier Proteins; D008565:Membrane Proteins; D011963:Receptors, GABA-A; D018009:Receptors, Glycine; C073441:gephyrin; D005680:gamma-Aminobutyric Acid