AN ULTRASTRUCTURAL-STUDY OF THE GLYCINE TRANSPORTER GLYT2 AND ITS ASSOCIATION WITH GLYCINE IN THE SUPERFICIAL LAMINAE OF THE RAT SPINAL DORSAL HORN

The glycine transporter GLYT2 is present in axonal boutons throughout the spinal cord, and its laminar distribution matches that of glycine- enriched axons, which are presumed to be glycinergic. In order to dete rmine whether boutons which possess GLYT2 are glycine-enriched, we hav e carried out pre-embedding immunocytochemistry with antibody raised a gainst GLYT2, and combined this with post-embedding detection of glyci ne, in the rat. GLYT2 immunoreactivity was present in boutons which fo rmed symmetrical axodendritic, axosomatic or axoaxonic synapses, and w as often seen in peripheral axons of type II synaptic glomeruli. One h undred and fifty GLYT2-immunoreactive boutons were analysed quantitati vely, and in 142 (94.6%) of these the density of gold particles repres enting glycine-like immunoreactivity exceeded the background level (ov er presumed glutamatergic boutons) by at least a factor of two. Within immunoreactive boutons, the GLYT2 reaction product was associated wit h the plasma membrane, but often appeared as discrete clumps and was g enerally excluded from the region of the active sites of synapses. The se results confirm that GLYT2 is associated with glycine-enriched axon al boutons in the superficial dorsal horn. They also suggest that GLYT 2 is unevenly distributed on the plasma membrane of these boutons, and raise the possibility that it may be excluded from synaptic clefts. ( C) 1997 IBRO.