Morphological and physiological properties of geniculate W-cells of the cat: a comparison with X- and Y-cells

Abstract

Intracellular recording and iontophoresis of horseradish peroxidase (HRP) was used to study the morphology of physiologically characterized W-cells in the cat''s lateral geniculate nucleus. Morphological study was limited to light microscopy. Data from 20 W-cells of the C-laminae were comapred to analogous data previously published for geniculate X- and Y-cells of the A- and C-laminae. W-cell somata were comparable in size to X-cell somata, and both classes had smaller somata than did Y-cells. W-cell dendrites were thin and usually varicose or beaded; some had complex, stalked appendages of clusters of appendages near dendritic branch points. X-cell dendrites were also thin and often had clustered appendages. Y-cell dendrites were thick and generally appendage free. W-cell dendritic arbors were slightly more extensive than those of X- and Y-cells. While Y-cell arbors exhibited approximately spherical symmetry, those of W-cells were elongated parallel to the geniculate laminar borders and those of X-cells were elongated perpendicular to these borders. Some dendrites of every W- and Y-cell crossed laminar borders; the dendrites of every X-cell were always confined to a single lamina. W-cell axons were thinner than those of X-cells, and X-cells had thinner axons than did Y-cells. All 3 cell classes commonly had axons that, en route to cerebral cortex, innervated the perigeniculate nucleus via collateral branches. Occasionally, intrageniculate axon collaterals (i.e., within the main geniculate laminae) were seen for W-, X- and Y-cells. The striking morphological differences among geniculate W-, X- and Y-cells suggest corresponding differences in neuronal processing and synaptic integration. Functional differences among the W-, X- and Y-cell pathways are probably not limited to and solely determined by retinal processing but are further elaborated by these geniculate neurons. How the different morphological features of geniculate W-, X- and Y-cells might relate to their different physiological properties and functional roles is speculated upon.