COLOCALIZATION OF GABA, GLYCINE, AND THEIR RECEPTORS AT SYNAPSES IN THE RAT SPINAL-CORD

To determine whether GABA and glycine can act as cotransmitters at syn apses in the rat spinal cord, we have compared the ultrastructural dis tribution of GABA(A)-receptor beta(3) subunit with that of the glycine receptor-associated protein gephyrin and combined this with postembed ding detection of GABA and glycine. We also used a dual-immunofluoresc ence method to confirm that gephyrin was associated with the glycine-r eceptor alpha(1) subunit throughout the cord. GABA(A) beta(3)-subunit immunoreactivity was restricted primarily to synapses, and at a majori ty of these synapses the presynaptic axon was GABA-immunoreactive. Man y synapses showed both GABA(A) beta(3) and gephyrin immunoreactivity, and at most of these synapses GABA and glycine were enriched in the pr esynaptic axon. These results strongly support the idea that cotransmi ssion by GABA and glycine occurs in the spinal cord.