Neuronal classes and their relation to functional and laminar organization of the lateral geniculate nucleus: A Golgi study of the prosimian primate, Galago crassicaudatus

Abstract

The neuronal organization of the lateral geniculate nucleus of the prosimian primate, Galago crassicaudatus, was studied in Golgi-Kopsch-impregnated material. On the basis of cytoarchitecture, electrophysiology, and connections the nucleus is divisible into three pairs of layers--one magnocellular, one parvocellular, and one koniocellular--each part of a separate retinogeniculate and geniculostriate pathway (Itoh et al., '82; Norton and Casagrande, '82). In Macaca and Saimiri, which have equally distinct geniculate subdivisions, it has been reported that, outside of cell size, no one morphological attribute differentiates magnocellular from parvocellular neurons (Campo-Ortega et al., '68; Wong-Riley, '72; Saini and Garey, '81; Wilson and Hendrickson, '81). Results presented here are not inconsistent with this conclusion. However, when the results are analyzed from the standpoint of the collective traits that distinguish the cell groups that make up the layers, clear morphological differences are evident. Using this approach we find the following differences between presumed projection neurons and interneurons in each pair of layers. The projection neurons of the magnocellular layers, as a group, exhibit large cell bodies with radially arranged dendrites which often extend beyond laminar borders. The magnocellular interneurons are larger than their counterparts in the other layers and, like the magnocellular projection neurons, exhibit radially arranged dendrites. The former, however, also share characteristics in common with other interneurons such as relatively small somata, few proximal dendrites, and complex distal dendritic appendages. In contrast, the projection neurons and interneurons of the parvocellular layers have smaller somata and more restricted dendritic spreads than their counterparts in the magnocellular layers. Dendritic arbors of parvocellular neurons are typically oriented perpendicular to laminar borders and remain confined to their layer of origin. The koniocellular neurons represent a more diverse population but collectively are distinct in that the dendrites of almost all neurons in these layers run parallel to the layers. The fact that presumed interneurons and projection neurons in a single layer share a number of related dendritic features suggests that both groups together are responsible for the structural and, hence, functional architecture of a layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium binding proteins distinguish large and small cells of the ventral posterior and lateral geniculate nuclei of the prosimian galago and the tree shrew (Tupaia belangeri).

“…1 A and B illustrates the main result in the galago. In the parvalbumin section, layers 4 region is largely free of cells. (In the black and white figure it is a gray band.)…”

“…The second possibility is that these are two distinct populations of projection neurons-one calbindin and one parvalbumin. Using the Golgi method, Conley et al (4) identified a second kind of relay cell but the small number of these does not approximate the large number of intermediate tan cells. A third interpretation is simply that cells can take on a pale stain without calbindin.…”

“…The galago provides a good opportunity to illustrate the separation of cell types according to layer. Layers 1 and 2, which are perfectly matched, are dominated by large cells (mean soma area, 402 ,um), whereas layers 4 and 5 (again, one ipsilateral, one contralateral) contain only small pale cells (soma area, 284 pum) (3,4). Finally, cells in the third pair, layers 3 and 6, are intermediate in size.…”

Two types of interneuron in the dorsal lateral geniculate nucleus of the rat: A combined NADPH diaphorase histochemical and GABA immunocytochemical study

“…2A',A, and F). It is appropriate to point out that the processes of Golgi-impregnated interneurons in the dLGN of the cat (Famiglietti and Peters, 1972) and monkey (Leuba and Garey, 1984;Conley et al, 1985) are also preferentially oriented.…”

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

“…Other differences in the size and morphology of interneurons also suggest the possibility that there are at least two types in the cat's and primate's dLGN [Pasik et al. 1973b;Conley et al. 1985;Montero and Singer, 1985;Montero and Zempel, 1985;Conley and Wilson.…”