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 organizat ion of periaqueductal gray matter neurons labeled with immunocytochemi cal techniques by an anti-glutamate (Glu) polyclonal serum were invest igated 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, calcula ted in semi-thin sections (1-mu m-thick), varied slightly among the su bdivisions of the periaqueductal gray matter. The morphology of Glu-po sitive neurons was similar to that of the multipolar, triangular, and fusiform cells described in previous Golgi studies. Numerous puncta, i nterpreted as dendrites, axons, and axon terminals were also present i n all subdivisions without preferential distribution. At the electron microscopic level, all synaptic contacts made by Glu-positive axon ter minals were of the asymmetric type, but not all presynaptic elements m aking asymmetric synapses were labeled. The vast majority of postsynap tic elements contacted by Glu-positive axon terminals were labeled and unlabeled dendrites. The present results describe for the first time the presence of both Glu-positive neurons and terminals in the feline periaqueductal gray matter and provide further evidence that Glu is th e probable neurotransmitter of numerous excitatory neurons of this str ucture. (C) 1997 Wiley-Liss, Inc.