Ultrastructural identification of somata and neural processes immunoreactive to antibodies against glutamic acid decarboxylase (GAD) in the dorsal lateral geniculate nucleus of the cat

Abstract

The cat dorsal lateral geniculate nucleus (LGN) was examined at the light- and electron-microscopic level after immunocytochemistry for GAD (the synthesizing enzyme of the inhibitory neurotransmitter GABA), to identify cells and processes with GAD-like immunoreactivity. GAD-positive perikarya were distributed throughout the A and C laminae, constituting a moderate proportion of cells in the LGN. Labeled cells were characterized by small size, scant cytoplasm, relatively large nuclei with common indentations, small mitochondria, few organelles and few strands of rough endoplasmic reticulum. Unlabeled cells were of large, medium and small size. GAD-positive terminals were identified as F1 and F2 types (Guillery's nomenclature) on the basis of their synaptic relations and ultrastructure. Labeled F2 terminals were postsynaptic to retinal (RLP) boutons and presynaptic to unlabeled dendrites in synaptic glomeruli. Labeled F1 terminals made synapses on unlabeled somata and dendrites, and on labeled dendrites and F2 terminals. Presumably, most labeled F1 terminals originate from GABAergic perigeniculate axons. Retinal (RLP) and cortico-geniculate (RSD) boutons remained unlabeled in the reactive zone. These terminals made synapses with labeled and unlabeled dendrites and with labeled F2 boutons. In conjunction with previous studies on GAD-positive cells in the perigeniculate nucleus, these results provide immunocytochemical and morphological evidence suggesting that the GABAergic intrinsic and extrinsic (perigeniculate) interneurons mediate the different inhibitory phenomena which occur in relay cells of the cat LGN. The ultrastructural features and synaptic relations of GABAergic cells and processes in the cat LGN are similar to those of equivalent neural elements in the LGN of rat and monkey, suggesting general principles of organization and morphology for GABAergic neurons in the thalamus of different mammals.

Two types of interneurons in the cat visual thalamus are distinguished by morphology, synaptic connections, and nitric oxide synthase content

“…Figures 12 and 13 illustrate GAD staining that revealed distinctive clusters of GABAergic terminals participating in complex synaptic arrangements known as glomeruli (see Fitzpatrick et al, 1984;Montero and Singer, 1985). The features of glomerular arrangements are illustrated in Figure 13.…”

Differential gene expression for glutamic acid decarboxylase and type II calcium-calmodulin-dependent protein kinase in basal ganglia, thalamus, and hypothalamus of the monkey

“…Nuclei of the dorsal thalamus contain two fundamental cell populations: relay or projection neurons and GABAergic interneurons (Hendrickson et al, 1983;Penny et al, 1983;Spreafico et al, 1983;Fitzpatrick et al, 1984;Montero and Singer, 1985;Montero, 1986;Jones and Hendry, 1989). There is reason to believe that in the dorsal thalamus, the CAM II kinase-a+x-pressing population of cells represents the thalamocortical and thalamostriatal projection neurons and that the GAD-expressing population represents the local circuit neurons: GABA-immunoreactive neurons in monkey dorsal thalamic nuclei account for approximately 25-3 5% of the total neuronal population and are consistently smaller than the relay neurons (Montero and Zempel, 1986;Hunt et al, 199 1).…”

Circuitry of the Dorsal Lateral Geniculate Nucleus in the Cat and Monkey

“…FI terminals are always presynaptic and usually contain many, very elongated or flattened synaptic vesicles within a dark cytoplasmic matrix; F2 terminals typically dis play clusters of more pleomorphic synaptic vesicles within a light matrix and can be either in a presynaptic or postsynaptic position. Most of the F terminals can be stained immtinohistochemically using antibodies to GABA [Hendrick son et al, 1983;Montero and Singer. 1985;Montero.…”

“…1973b;Conley et al. 1985;Montero and Singer, 1985;Montero and Zempel, 1985;Conley and Wilson. 1992].…”