title: Two types of interneuron in the dorsal lateral geniculate nucleus of the rat: a combined NADPH diaphorase histochemical and GABA immunocytochemical study.
abstract: The rationale for this study was to provide a comprehensive light microscopical description of the morphology of diaphorase-reactive neurons and neuropil elements in the dorsal lateral geniculate nucleus (dLGN) of the rat. An additional objective was to quantitatively assess whether a subpopulation of the diaphorase-reactive neurons, previously shown to be GABA-immunoreactive, constitute a distinct type of local-circuit neuron in the rat dLGN. Diaphorase activity was localised in a population of predominantly bipolar fusiform neurons. These cells were weak to moderately stained and possessed the morphological features of intrinsic inhibitory neurons, previously called class B neurons in the rat dLGN. Quantitative estimates indicated that the diaphorase-reactive neurons constituted approximately 10% of the total neuron composition of the dLGN. The majority (about 83%) of the diaphorase-reactive cells were located in the lateral half of the nucleus. In addition, a dense plexus of diaphorase-reactive varicose fibres was found throughout the dLGN lying between the oriented fibre bundles coursing dorsoventrally through the LGN. Diaphorase-reactive punctae were found to be closely associated with the somata and proximal dendritic segments of nonreactive neurons and also with the stained proximal dendritic segments of diaphorase-reactive dLGN neurons. The source of the diaphorase-reactive fibres in the dLGN was unknown. Evidence suggests, however, that they are of extrinsic origin. The GABA-immunoreactive nature of the diaphorase neurons in the dLGN was demonstrated by colocalising GABA immunoreactivity within the somata of diaphorase-reactive cells. The majority (> 90%) of diaphorase-reactive dLGN neurons were GABA-immunopositive. Also present was a distinct population of GABA-immunopositive neurons that were not diaphorase-reactive. In this study, cells that were solely GABA-immunopositive have been called class B1 neurons, while cells that were both diaphorase-reactive and GABA-immunoreactive have been called class B2 neurons. Size-frequency distributions of somatic profile areas established that the two populations of GABA-immunoreactive neuron were significantly different. Class B1 neurons constituted 57%, with class B2 cells representing 43% of all GABA-immunostained neurons in the rat dLGN. The characteristic morphological features, neurochemical identity and frequency of the diaphorase-reactive neurons in the rat dLGN indicate that they represent a subpopulation of inhibitory interneurons with the ability to affect intrinsic dLGN operations and thalamocortical interactions using the neuromodulator nitric oxide.
authors.affiliation: University Department of Pharmacology, Oxford, United Kingdom.
authors.forename: P L
authors.initials: PL
authors.lastname: Gabbott
authors.forename: S J
authors.initials: SJ
authors.lastname: Bacon
mesh_terms: D000818:Animals; D005829:Geniculate Bodies / Q000737:chemistry* / Q000201:enzymology; D006651:Histocytochemistry; D007124:Immunoenzyme Techniques; D007395:Interneurons / Q000737:chemistry* / Q000201:enzymology; D009252:NADPH Dehydrogenase / Q000032:analysis*; D009457:Neuroglia / Q000737:chemistry / Q000201:enzymology / Q000648:ultrastructure; D009474:Neurons / Q000737:chemistry / Q000201:enzymology / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D005680:gamma-Aminobutyric Acid / Q000032:analysis*
chemical_list: D005680:gamma-Aminobutyric Acid; D009252:NADPH Dehydrogenase