Localization of high affinity [3H]glycine transport sites in the cerebellar cortex

A study was made of 3H]glycine uptake sites in a preparation greatly enriched in large pieces of the cerebellar glomeruli (glomerulus particles) and in morphologically well preserved slices of rat cerebellum. Electron microscopic autoradiography revealed that of the neurones in the cerebellar cortex only Golgi cells transported 3H]glycine at the low concentration used. Glial cells also took up 3H]glycine but to a lesser extent than the Golgi neurons. It was also confirmed that under comparable conditions Golgi cells transport 3H]GABA. Kinetic studies utilizing the Golgi axon terminal-containing glomerulus particles showed that glycine is a weak non-competitive inhibitor of 3H]GABA uptake (Ki over 600 microM vs the Kt of about 20 microM) and that GABA is an even weaker inhibitor of 3H]glycine uptake. These observations indicated that glycine and GABA do not share the same carrier. Quantitative electron microscopic autoradiography showed that the uptake of the two amino acids, in terms of the unit area of labelled Golgi axon terminals, was not additive. In contrast, their uptake in terms of unit protein was strictly additive. These observations, the first relating to unit volume and the latter to the total volume of Golgi terminals, are consistent with the view that there are two biochemically separate populations of Golgi neurons, one transporting glycine the other GABA. Saturable 3H]strychnine binding was detected in the preparations of glomerulus particles, but in comparison with those from the spinal cord the affinity was lower and 3H]strychnine was not displaced by glycine. Available information on glycine receptors, however, suggest that this should not exclude the possibility of strychnine resistant glycine receptors in the rat cerebellum.