Two types of interneurons in the cat visual thalamus are distinguished by morphology, synaptic connections, and nitric oxide synthase content.
The distribution of the neuronal form of the nitric oxide-synthesizing enzyme, brain nitric oxide synthase (BNOS), was examined in the cat thalamus by using immunocytochemical techniques. BNOS was found in both cells and fibers throughout the visual thalamus. BNOS-stained cells were found consistently in the C laminae of the lateral geniculate nucleus (LGN), the pulvinar nucleus, and the lateral posterior nucleus (LP). In the A laminae of the LGN, variable numbers of BNOS-stained cells also could be detected. BNOS-stained cells were identified as a subset of interneurons because they all stained for glutamic acid decarboxylase (GAD), but not all GAD-stained cells contained BNOS. The average soma area of BNOS-stained cells was slightly greater than the average soma area of GAD-stained cells. BNOS-stained cells display a distinctive dendritic morphology, which is consistent with previous descriptions of class V neurons (Updyke [1979] J. Comp. Neurol. 186:603-619); they have widespread but fairly sparse arbors of thin, somewhat beaded dendrites. BNOS-stained cells participate in a distinct synaptic circuitry. Although many GAD-stained profiles are filled with vesicles and participate in complex synaptic arrangements, known as glomeruli, BNOS-stained dendrites contain small clusters of vesicles and form dendrodendritic contacts in the extraglomerular neuropil. Thus, there appear to be at least two types of gamma-aminobutyric acidergic interneurons in the visual thalamus of the cat. Interneurons that do not contain BNOS (class III morphology) may exert their effects primarily within synaptic glomeruli (Hamos et al. [1985] Nature 317:618-621), whereas interneurons that contain BNOS (class V morphology) contribute primarily to the extraglomerular neuropil.
Bickford
M E
ME
Department of Anatomical Sciences and Neurobiology, University of Louisville, School of Medicine, Louisville, Kentucky 40292, USA. mebick01@ulkyvm.louisville.edu
Carden
W B
WB
Patel
N C
NC
D000818:Animals; D002415:Cats / Q000033:anatomy & histology* / Q000378:metabolism / Q000502:physiology; D005260:Female; D007150:Immunohistochemistry; D007395:Interneurons / Q000201:enzymology / Q000502:physiology*; D009412:Nerve Fibers / Q000201:enzymology; D009419:Nerve Tissue Proteins / Q000032:analysis*; D019001:Nitric Oxide Synthase / Q000032:analysis*; D052248:Nitric Oxide Synthase Type I; D013569:Synapses / Q000502:physiology*; D013788:Thalamus / Q000033:anatomy & histology* / Q000201:enzymology / Q000502:physiology; D014795:Visual Pathways / Q000033:anatomy & histology / Q000502:physiology
D009419:Nerve Tissue Proteins; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I