AN IMMUNOCYTOCHEMICAL STUDY OF GLYCINE RECEPTOR AND GABA IN LAMINAE-I-III OF RAT SPINAL DORSAL HORN

In order to provide information about the function of glycine in the s uperficial three laminae of the rat dorsal horn and the possible coexi stence of glycine and GABA at synapses in this region, we have carried out a combined study involving preembedding immunocytochemistry with a monoclonal antibody to the glycine receptor and postembedding immuno cytochemistry with antiserum to fixed GABA. Glycine receptor-like immu noreactivity was present at axodendritic and axosomatic synapses in al l three laminae, and at dendrodendritic synapses in lamina II. Althoug h axons that formed axoaxonic synapses were often presynaptic at immun oreactive axodendritic synapses (and thus probably contained glycine), the axoaxonic synapses themselves did not show glycine receptor-like immunoreactivity. Many of the profiles that were presynaptic at glycin e receptor-immunoreactive synapses showed GABA-like immunoreactivity. These results suggest that glycine acts as a postsynaptic inhibitory t ransmitter at various types of synapses in laminae I-III, and that it may coexist with GABA at many synapses in this region. However, it app ears that while glycine and GABA may both be released at axoaxonic syn apses, either glycine does not act as a transmitter at these synapses, or else it acts at an atypical receptor that was not recognized by th e antibody used in this study.