Comparative study of visual inter and intrahemispheric cortico-cortical connections in five native Chilean rodents

Abstract

Previous studies of the visual cortical organization in the rat and other rodent species have raised the possibility that the visual cortical plan in the rat is common to a large number of species within the order. We have tested this idea by comparing the visual plan in the rat to cortical subdivision schemes obtained from five native Chilean rodent species, including members of the Cricetidae family within the Miomorph group, as well as from the Octodontidae family within the Caviomorph group. Cortical subdivision schemes were inferred from the analysis of the patterns of callosal connections revealed following multiple injections of HRP contralaterally, as well as from ipsilateral cortico-cortical connections observed after small injections of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) into striate cortex. As in the rat, callosal connections in the native rodents concentrate at the border between cytoarchitectonic areas 17 and 18a, and along the borders of discrete, sparsely callosal islands of cortex in lateral peristriate cortex. Furthermore, single injections of WGA-HRP into striate cortex produce multiple, separate fields of labeled cells and terminations in the cortex surrounding area 17. Together, our data supports the idea of a common plan of visual cortical organization among rodents by providing evidence that the visual cortex in the native species is subdivided into multiple visual areas in a manner that resembles the rat cortical plan.

Two rules for callosal connectivity in striate cortex of the rat

“…Similar issues arise for the infragranular distribution of callosal neurons that has been described in medial portions of striate cortex in the rat (Olavarria and Van Sluyters, 1983), as well as other rodent species (mouse: Olavarria and Van Sluyters, 1984;hamster: Dursteler et al, 1979;Rhoades et al, 1987; Octodon degus: Bravo et al, 1990). At present it is not known whether callosal linkages in medial striate cortex are organized in a mirror-symmetric fashion with respect to the midline, or in some other way.…”

Area map of mouse visual cortex

“…Mouse extrastriate cortex also differs from that in many nonprimate species (i.e., quoll, hedgehog, guinea pig, rabbit, flying fox, opossum, squirrel, tree shrew, cat) in which V1 is adjoined on the lateral side by a single area, V2 (Kaas et al, 1970(Kaas et al, , 1989Hall et al, 1971;Towns et al, 1977;Payne, 1993;Rosa, 1999;Kahn et al, 2000), and therefore has a "simple" organization . However, mouse extrastriate cortex is similar to that in species with a "simple" organization, in that V1 is adjoined on the medial side by parastriate or splenial visual areas, which in hedgehog, rat, hamster, degu, guinea pig, and cat receive direct V1 input and contain visually responsive neurons (Kalia and Whitteridge, 1973;Choudhury, 1978;Gould and Ebner, 1978;Olavarria and Mendez, 1979;Bravo et al, 1990;Olavarria and Montero, 1990;Spatz et al, 1991;Montero, 1993). Thus, mouse extrastriate cortex is "simple" in the sense that it has a single V2-like area, LM, on the lateral side of V1, but is "complex" in that lateral V1 is adjoined by multiple visual areas.…”

“…Previous single and multitracer experiments in mouse, rat, hamster, degu, guinea pig, and squirrel have labeled similar targets, which were considered either distinct areas Montero, 1989, 1990;Bravo et al, 1990;Spatz et al, 1991;Montero, 1993) or repeating modules within a single area, V2 (Kaas et al, 1989;Malach, 1989;Rumberger et al, 2001). By mapping the connections from a wide range of topographic locations, we found that, unlike stripes in monkey V2, which create map discontinuities within a single global map (Roe and Ts'o, 1995), each of the labeled targets contains a complete map of the entire visual field, and together the maps form a seamless mosaic of extrastriate areas (Fig.…”

Patterns of interhemispheric and striate-peristriate connections in visual cortex of the South American marsupial Marmosa elegans (mouse opossum)

“…In fact, uneven distribution of callosal and striate-peristriate connections are common features of cortical organization among placental mammals (see, e.g., Olavarria and Montero 1984;Sesma et al 1984;Cusick et al 1985;Bravo et al 1990). The radial organization of commissural connections in M.…”