Structure and function of retinal ganglion cells innervating the cat's geniculate wing: an in vitro study

Abstract

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).

Morphological Classification of Ganglion Cells in the Central Retina of Chicks.

“…These 3 morphological types of ganglion cells, α-, β-, and γ-cells corresponded to the physiologically defined groups of Y-, X-, and W-cells, respectively [4,15,38]. So far, RGCs have been divided into 3 major types in most mammals, but it is probable that they could be classified more precisely [25,29,36].…”

Functional Organization of Ganglion Cells in the Salamander Retina

“…Several other anatomical types have coverage factors greater than two (Rodieck 1998;Wässle and Boycott 1991), and even as large as six (Berson 2003;Pu et al 1994). In a recent anatomical classification of rabbit ganglion cells, Rockhill et al (2002) found that their 13 morphological types needed to have an average coverage factor of 3.2 to account for the ganglion cell density that they measured.…”

Molecular Phenotyping of Retinal Ganglion Cells

“…Subsets of mammalian ganglion cell classes project to an array of central targets (Fukuda and Stone, 1974;Farmer and Rodieck, 1982;Leventhal et al, 1985;Rodieck and Watanabe, 1993;Pu et al, 1994;Rodieck, 1998), but a unified description of all classes and distributions in the ganglion cell layer has remained elusive. Several summaries of how neuronal typologies might be abstracted have emerged, some accompanied by debates regarding methods, definitions, and results (Rowe and Stone, 1977;Hughes, 1979;Holden, 1981;Rodieck and Brening, 1982;Famiglietti, 1992;Wingate et al, 1992;Cook, 1998;Masland and Raviola, 2000).…”