Relative numbers of several types of synaptic connections in the substantia gelatinosa of the cat spinal cord.

The relative numbers of axo-dendritic, axo-axonic, dendro-axonic and dendro-dendritic synapses were determined by classifying and recording all such specialized contacts in sample areas of the substantia gelatinosa. The samples were taken from segments L1-L5 of the cat spinal cord. In the glomerular complexes 97% of all synapses were recorded as axo-dentritic. In substantia gelatinosa deprived of glomerular complexes by dorsal root section, 96.5% were axo-dendritic. The remainders were about equally divided between axo-axonic, dendro-dendritic and dendro-axonic synapses.