Journal of Neuroscience, Vol 4, 1809-1829, Copyright © 1984 by Society for Neuroscience
Glutamic acid decarboxylase-immunoreactive neurons and terminals in the lateral geniculate nucleus of the cat
D Fitzpatrick, GR Penny and DE Schmechel
We have examined the distribution of neurons and terminals that are
immunoreactive for glutamic acid decarboxylase (GAD), the synthesizing
enzyme for the inhibitory neurotransmitter gamma-aminobutyric acid within
the lateral geniculate nucleus of the cat. We estimate that GAD- positive
neurons constitute approximately one-fourth of the neurons in all layers of
the lateral geniculate nucleus and in the medial interlaminar nucleus
(MIN). In addition, almost all of the neurons within the perigeniculate
nucleus are GAD-positive. The mean size of GAD-positive cell bodies is
significantly smaller than the mean size of unlabeled neurons in all
subdivisions of the lateral geniculate nucleus. GAD-positive neurons have
thick primary dendrites which are associated with thin lightly
immunoreactive processes that give rise to clusters of GAD-positive
terminals. Clusters of GAD-positive terminals are prominent in lamina A,
A1, magnocellular C, and MIN but are rare in the parvocellular C laminae.
Within the A laminae, GAD immunoreactivity is found within
vesicle-containing profiles of the synaptic glomerulus lying postsynaptic
to optic axon terminals and presynaptic to unlabeled dendritic profiles.
GAD-positive neurons in the A laminae are distinguished from other small to
medium-sized neurons by their failure to label following injections of HRP
into visual cortex and by their lack of cytoplasmic laminated body. These
results support the idea that GAD-positive neurons constitute a distinct
population of neurons in the lateral geniculate nucleus of the cat; a
population which has a number of features in common with previous
descriptions of presumed local circuit neurons based on Golgi staining.