Journal of Neuroscience, Vol 14, 4338-4358, Copyright © 1994 by Society for Neuroscience
Structure and function of retinal ganglion cells innervating the cat's geniculate wing: an in vitro study
M Pu, DM Berson and T Pan
Department of Neuroscience, Brown University, Providence, Rhode Island 02912.
We have examined in vitro the morphology and visual response properties of
retinal ganglion cells innervating a component of the cat's lateral
geniculate nucleus known as the geniculate wing (or retinorecipient zone of
the pulvinar). Ganglion cells were first labeled in situ by retrograde
transport of fluorescent microspheres from the geniculate wing. Labeled
cells were injected intracellular with Lucifer yellow and biocytin in the
isolated retina and visualized immunohistochemically. With one exception,
stained cells appeared to belong to a single morphological class that
corresponded closely to the epsilon cell of earlier descriptions (Leventhal
et al., 1980; Rodieck and Watanabe, 1986). They had somas comparable in
size to those of beta cells and large, sparse dendritic trees that ramified
in the inner (ON) sublayer of the inner plexiform layer. Dendritic fields
increased in size with eccentricity, but only within the central retina,
and were among the largest so far reported for cat ganglion cells,
exceeding those of alpha cells at most eccentricities. Dendritic profiles
were typically elliptical with long axes pointing toward the area
centralis. Axons were about as thick as those of beta cells and thicker
than those of other varieties of non-alpha, non-beta ganglion cells. We
recorded extracellularly from microsphere-labeled wing-projecting ganglion
cells in a superfused, flattened eyecup preparation. All such cells
exhibited sustained responses to standing contrast and had very large,
concentric receptive fields with ON-centers and OFF-surrounds. Their
response to gratings showed that they have relatively poor spatial
resolution and a moderate amount of nonlinearity of spatial summation.
These cells thus have many physiological response properties in common with
ganglion cells previously termed "on-center tonic W-cells," "on-center
sluggish sustained cells," and "Q-cells." These findings indicate that
ganglion cells innervating the cat's geniculate wing form a structurally
and functionally homogeneous class. Their large dendritic and receptive
fields and low-pass spatial frequency tuning suggest that fine spatial
resolution is not required for the execution of their functional role(s).
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