Topography of Retinal Efferent Connections in Sciurids; pp. 362–375

Abstract

The sciurid retina projects to the contralateral superior colliculus, pretectal complex, ventral nucleus of the lateral geniculate body and to five distinct zones in the dorsal nucleus of the lateral geniculate. Ipsilateral projections are distributed to the same targets except the superior colliculus. Zones of terminal debris as identified by the Fink-Heimer method do not develop uniformly; instead some structures become argyrophyllic before others do so that an injudicious choice of survival times may produce misleading data.The topography of the retinal mosaic is preserved in all its projections except those to the accessory optic system. In the cases of the superior colliculus, ventral nucleus of the lateral geniculate body and the anterior pretectal nucleus, these retinal projections are in perfect register with other afferent connections which are also retinotopically organized. An enormous proportion of the cells in the dorsal nucleus of the lateral geniculate body are connected with the overlapping portions of the retina; only a very small part of this structure receives input from the much larger nonoverlapping retinal quadrants.

Pattern of retinal projections in the California ground squirrel (Spermophilus beecheyi): Anterograde tracing study using cholera toxin

“…The sublaminar organization of the LGNv in the California ground squirrel is consistent with previous descriptions for sciurids (Abplanalp, 1974;Kicliter and Bruce, 1983;Agarwala et al, 1989) and in tree shrews (Laemle, 1968;Conley and Friederich-Ecsy, 1993). As depicted in Figures 10 -11, the LGNv consists of a complex dorsal zone and a clearly laminated ventral zone.…”

“…As depicted in Figures 10 -11, the LGNv consists of a complex dorsal zone and a clearly laminated ventral zone. This laminated ventral zone has been referred to as the external (or magnocellular) division, which can be further subdivided into an internal and external subzone (Niimi et al, 1963;Abplanalp, 1974). The anterior and ventral portion of the dorsal zone is referred to as the parvocellular or internal zone proper, whereas the most dorsal portion is referred to as the dorsal cap (Abplanalp, 1974;Laemle, 1968;Agarwala et al, 1989).…”

“…This laminated ventral zone has been referred to as the external (or magnocellular) division, which can be further subdivided into an internal and external subzone (Niimi et al, 1963;Abplanalp, 1974). The anterior and ventral portion of the dorsal zone is referred to as the parvocellular or internal zone proper, whereas the most dorsal portion is referred to as the dorsal cap (Abplanalp, 1974;Laemle, 1968;Agarwala et al, 1989). The term intergeniculate leaflet follows from Hickey and Spear (1976) and denotes a nucleus previously described for ground squirrels Smale et al, 1991).…”

“…Early workers using degeneration techniques defined, in keeping with the three layers visible in Nissl-stained preparations of the species initially studied, three corresponding layers alternating among contralateral, ipsilateral, and contralateral eye representation (Tigges, 1970;Abplanalp, 1974). For the gray squirrel, Kaas et al (1972) further delineated separate zones within the outer contralaterally innervated layer 3 complex which, alternated between contralalateral and ipsilateral eye inputs; subsequently, Cusick and Kaas (1982) noted the presence of very small patches of dense ipsilateral input at the medial margin of layer 1.…”

“…There have been several studies on the retinofugal projections in various sciurid species (Tigges, 1970;Abplanalp, 1974;Cusick and Kaas, 1982;Kicliter and Bruce, 1983;Bruce and Kicliter, 1984;Fukuda et al, 1986;Wu and Shen, 1988;Petry et al, 1989;Agarwala et al, 1989). However, there has been no recent work employing more sensitive tracing techniques and no detailed comparisons with primates.…”