The glycinergic inhibitory synapse

Glycine is one of the most important inhibitory neurotransmitters in the sp inal cord and the brainstem, and glycinergic synapses have a well-establish ed role in the regulation of locomotor behavior. Research over the last 15 years has yielded new insights on glycine neurotransmission. Glycinergic sy napses are now known not to be restricted to the spinal cord and the brains tem. Presynaptic machinery for glycine release and uptake, the structure an d function of postsynaptic receptors and the factors (both pre- and postsyn aptic) which control the strength of glycinergic inhibition have been exten sively studied. It is now established that glycinergic synapses can be exci tatory in the immature brain and that some inhibitory synapses can coreleas e gamma -aminobutyric acid (GABA) and glycine. Moreover, the presence of gl ycine transporters on glial cells and the capacity of these cells to releas e glycine suggest that glycine may also act as a neuromodulator. Extensive molecular studies have revealed the presence of distinct subtypes of postsy naptic glycine receptors with different functional properties. Mechanisms o f glycine receptors aggregation at postsynaptic sites during development ar e better understood and functional implications of variation in receptor nu mber between postsynaptic sites are partly elucidated. Mutations of glycine receptor subunits have been shown to underly some human locomotor disorder s, including the startle disease. Clearly, recent work on glycine receptor channels and the synapses at which they mediate inhibitory signalling in bo th young and adult animals necessitates an update of our vision of glyciner gic inhibitory transmission.