Journal of Neuroscience, Vol 7, 2214-2231, Copyright © 1987 by Society for Neuroscience
Regional distribution of astrocytes with intense immunoreactivity for glutamate dehydrogenase in rat brain: implications for neuron-glia interactions in glutamate transmission
C Aoki, TA Milner, KF Sheu, JP Blass and VM Pickel
The principally mitochondrial enzyme glutamate dehydrogenase (GDH)
exhibited low-intensity, uniform immunoreactivity in neurons and intense
heterogeneous labeling of glial cells of rat brain. Simultaneous peroxidase
labeling for GDH and immunoautoradiography for glial fibrillary acidic
protein (GFAP) confirmed the astrocytic localization of the enzyme.
Immunoreactivity in astrocytes, but not in neurons, required the presence
of Triton X-100 as a solubilizing agent. Most of the intensely labeled
glial processes were localized to regions previously reported as containing
moderate to high densities of binding sites for the excitatory amino acids,
L-glutamate or L-aspartate, and glutamatergic fibers. These included
several forebrain regions, such as the superficial layers of the rostral
neocortex, dorsal neostriatum, nucleus accumbens, septohippocampal nucleus,
intralaminar thalamic nuclei, and external capsules. However, the central
gray of the midbrain, the nuclei of the reticular formation, brain stem
regions projecting to the cerebellum, and cranial nuclei of the trigeminal
and vagal nerves also exhibited intense glial labeling for GDH, even though
some of these regions are known to receive only weak glutamatergic
projections. A second factor determining the distribution of GDH appeared
to be neuronal activity, as assessed by correspondence with reported high
densities of cytochrome oxidase. We conclude that GDH enriched in glial
populations exists in a subcellular compartment distinct from that of
neurons and may serve as one of the enzymes involved in glutamatergic
transmission. Deficiencies of glial GDH and the consequent cytotoxic
effects of high levels of excitatory amino acids may contribute to a number
of neurodegenerative disorders.