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

J Comp Neurol. 1999 Oct 11;413(1):83-100.


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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cats / anatomy & histology*
  • Cats / metabolism
  • Cats / physiology
  • Female
  • Immunohistochemistry
  • Interneurons / enzymology
  • Interneurons / physiology*
  • Nerve Fibers / enzymology
  • Nerve Tissue Proteins / analysis*
  • Nitric Oxide Synthase / analysis*
  • Nitric Oxide Synthase Type I
  • Synapses / physiology*
  • Thalamus / anatomy & histology*
  • Thalamus / enzymology
  • Thalamus / physiology
  • Visual Pathways / anatomy & histology
  • Visual Pathways / physiology


  • Nerve Tissue Proteins
  • Nitric Oxide Synthase
  • Nitric Oxide Synthase Type I