Two types of GABA-containing axon terminals in cerebellar glomeruli of cat: an immunogold-EM study

Immunogold demonstration of GABA was used in ultrathin sections of cerebellar cortex of cat to identify GABA(+) profiles in cerebellar glomeruli. In addition to small, GABA-containing axonal varicosities found at the periphery of all glomeruli, a few complex glomeruli were found to contain a second type of GABA(+) terminal, with a mossy ending appearance. GABA(+) type "I" axon terminals, which were identified as the axonal arborization of local Golgi cells, contained ovoid, small synaptic vesicles. GABA(+) type "II" terminals, however, exhibited large, spheroid synaptic vesicles. Experimental evidence is provided that type "II" GABA(+) mossy like terminals are the endings of nucleocortical fibers.