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

The authors used ingracellular recording and iontophoresis of horseradish peroxidase (HRP) to study the morphology of physiologically characterized W-cells in the cat's lateral geniculate nucleus. Morphological study was limited to light microscopy. The data from 20 W-cells of the C-laminae were compared to analogous data. The authors 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 or clusters of appendages near dendritic brand points. X-cell dendrites were also thin and often had clustered appendages. However, 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, whereas the dendrites of every X-cell were always confined to a single lamina. W-cell axons were thinnner than those of X-cells, and X-cells had thinner axons than did Y-cell. All three cell classes commonly had axons that, en route to cerebral cortex innervated the perigeniculate nucleus via collateral branches.