THE GLYCINE TRANSPORTER GLYT2 IS A RELIABLE MARKER FOR GLYCINE-IMMUNOREACTIVE NEURONS

The glycine transporter GLYT2 is present in neurons of the spinal cord , the brain stem and the cerebellum. This localization is similar to t hat of glycine immunoreactivity, suggesting a causal relationship betw een GLYT2 expression and glycine distribution. In this report, we anal yzed if such a relationship does exist by using neuronal cultures deri ved from embryonic spinal cord. GLYT2 was synthesized in a small subpo pulation of neurons where it was targeted both to dendrites and to axo ns, being the axonal content higher than the dendritic one. At early s tages in the development of cultured spinal neurons, the highest GLYT2 levels were found in the axonal growth cones. As the culture matured, immunoreactivity extended to the axonal shaft. Double-immunofluoresce nce experiments indicated a perfect co-localization of GLYT2 and glyci ne immunoreactivity in cultured neurons. Moreover, the concentration o f glycine into neurons expressing GLYT2 was proportional to the concen tration of the transporter. This observation was reproduced in GLYT2-t ransfected COS cells. These evidences indicate that the high content o f glycine observed in some neurons in culture is indeed achieved by th e concentrative task performed by GLYT2, and that GLYT2 can be used as a reliable marker for identification of glycine-enriched neurons. (C) 1997 Elsevier Science B.V.