Glycine high affinity uptake and strychnine binding associated with glycine receptors in the frog central nervous system

Accumulation of [³H]glycine into synaptosomal fractions occurs by high affinity systems in cerebral cortex, optic tectum, brain stem and spinal cord of the frog. Specific [³H]strychnine binding which appears associated with postsynaptic glycine receptors is also demonstrable in these regions. By contrast, only very low levels of strychnine binding and high affinity glycine uptake occur in higher centers of the rat central nervous system. The relative potencies of small neutral amino acids in competing for [³H]strychnine binding are similar in frog brain and spinal cord. No evidence for a high affinity accumulation of [³H]taurine by synaptosomal fractions of frog spinal cord can be demonstrated. These observations favor glycine rather than taurine as an inhibitory transmitter in frog spinal cord. Moreover, these findings suggest that glycine may have a synaptic role in higher brain centers in the frog.