GABA- and glycine-immunoreactive synapses in spinal cord of frog <Emphasis Type="Italic">Rana temporaria</Emphasis>

Using the method of the double immune label combined with two antibodies, i.e., monoclonal antibodies to gamma-aminobutyric acid (GABA) and polyclonal antibodies to glycine, the distribution of gamma-aminobutyric acid- and glycine-immunoreactive synapses on motoneurons and primary afferent axons was studied in the frog Rana temporaria spinal cord. An analysis of all labeled boutons on the dendrites and soma of motoneurons showed the existence of three categories of immunoreactive synapses as follows: 7% were labeled for GABA, 23% were labeled for glycine, and approximately 70% were immunoreactive to both GABA and glycine. These results confirm the predominant role of glycine in the postsynaptic inhibition of motoneuronal activity. Three similar populations of synaptic boutons were also founded on primary afferent axons, including one GABA-immunoreactive (25%) and one glycine-immunoreactive (5%); the majority of the immunoreactive synapses had the colocalization of two inhibitory transmitters. As a rule, the higher proportion of axo-axonal synapses was organized in synaptic triads. The possible simultaneous roles of glycine as a transmitter of postsynaptic inhibition and as a transmitter that mediates the process of the autoreception of glutamate in the axo-axonal synapses on the primary afferent fibers are discussed.