Glutamate-positive neurons and terminals in the cat periaqueductal gray matter (PAG): a light and electron microscopic immunocytochemical study

The morphology, distribution, proportion, size, and synaptic organization of periaqueductal gray matter neurons labeled with immunocytochemical techniques by an anti-glutamate (Glu) polyclonal serum were investigated in six adult cats (PAG-GLU 1-6). At the light microscopic level, numerous Glu-positive neurons were found throughout each subdivision of the periaqueductal gray matter. Their proportion and size, calculated in semi-thin sections (1-pm-thick), varied slightly among the subdivisions of the periaqueductal gray matter. The morphology of Glu-positive neurons was similar to that of the multipolar, triangular, and fusiform cells described in previous Golgi studies. Numerous puncta, interpreted as dendrites, axons, and axon terminals were also present in all subdivisions without preferential distribution. At the electron microscopic level, all synaptic contacts made by Glu-positive oxon terminals were of the asymmetric type, but not all presynaptic elements making asymmetric synap...