Abstract
The patterns of 892 synapses with participating GABA elements were examined in the rat anterior cingulate cortex, using a preembedding immunohistochemical method. Somas and dendrites of pleomorphic GABA neurons received both GABA and unstained terminals at a ratio of 2 to 5, forming axo-somatic and axo-dendritic synapses. Some GABA terminals displayed axo-axonic contacts with either GABA or unstained terminals at an almost equal ratio. Occasionally, two GABA elements forming a synapse in turn showed further contacts with common or separate postsynaptic elements to constitute large synaptic complexes. Triadic arrangement of GABA terminals was noted adjacent to a nonGABA terminal forming an axo-dendritic synapse. The other GABA terminals formed synapses with nonGABA pyramidal cells on their apical dendrites, somas and axon initial segments. The majority of these GABA terminals, including small round vesicles, displayed symmetric contacts. A quarter of the examined synapses were found to be composed of contacts between two GABA elements. The high incidence of synapses between two GABA elements suggested the presence of a particular local network of GABA system in a restricted cortical area.
