Visual thalamocortical connections in sheep studied by means of the retrograde transport of Horseradish‐Peroxidase

Abstract

In order to study the visual thalamocortical connections in the sheep, horseradish peroxidase (0.3--0.5 microliter of a 30% solution) has been injected in the gyri marginalis, ectomarginalis medius pars medialis, ectomarginalis medius pars lateralis and ectosylvius caudalis. The results show that: (1) the dorsal lateral geniculate nucleus (LGNd) projects to the former three gyri. Dorsal parts of the LGNd project to caudal areas, whereas its ventral parts project to rostral areas of these gyri; medial parts of the LGNd project to the gyrus ectomarginalis medius pars lateralis, while lateral parts project to the gyrus marginalis; (2) the medial interlaminar nucleus (MIN) or pars geniculata pulvinaris of Rose ('42b) projects to the caudal part of the gyrus marginalis and to the gyrus ectomarginalis medius pars lateralis; (3) the pulvinar proper of Rose (PUL) projects to the caudal part of the gyrus ectosylvius caudalis whereas the rostral part of this gyrus receives input from the medial geniculate body. In relation to Rose's cytoarchitectonic study of the cortex of sheep ('42a) the present study has shown that the LGNd projects to both the area striata (gyrus marginalis + gyrus ectomarginalis medius pars medialis) and area occipitalis (gyrus ectomarginalis medius pars lateralis) of Rose, that the gyrus marginalis and the area occipitals receive a second projection (from the MIN), and that the PUL projects beyond the area occipitalis to the area parietalis of Rose.

Extrastriate connectivity of the mouse dorsal lateral geniculate thalamic nucleus

“…Instead, two studies in cat would establish that the cat (but not primate) LGd provided extensive input to VISp as well as multiple extrastriate visual areas (Glickstein et al, ; Wilson & Cragg, ). Initially, the cat extrastriate LGd projections were thought to be an exception compared to other mammals, but both positive (Benevento & Yoshida, ; Bullier & Kennedy, ; Coleman & Clerici, ; Dräger, ; Fries, ; Garey & Powell, ; Haight et al, ; Hall & Diamond, ; Hernández‐González et al, ; Holländer & Hälbig, ; Hubel, ; Hughes, ; Karamanlidis et al, ; Kennedy & Bullier, ; LeVay & Gilbert, ; Lysakowski et al, ; Niimi & Sprague, ; Raczkowski & Rosenquist, ; Ribak & Peters, ; Sanderson et al, ; Tanaka et al, ; Towns et al, ; Weber et al, ; Winfield et al, ; Wong‐Riley, ; Yukie & Iwai, ) and negative/absent (Benevento & Ebner, ; L. A. Benevento & Standage, ; Caviness & Frost, ; Coleman & Clerici, ; Coleman et al, ; Colwell, ; Diamond et al, ; Dräger, ; Dürsteler et al, ; Garey & Powell, ; Glendenning et al, ; Gould et al, ; Harting et al, ; Hubel & Wiesel, ; Kaas et al, ; Karamanlidis & Giolli, ; Peters & Saldanha, ; Robson & Hall, ) reports of LGd extrastriate projections in multiple species led to debate over the next several decades.…”

The claustrum of the sheep and its connections to the visual cortex

“…The visual area of the ovine cortex was identified based on the available stereotaxic atlases of the species (Richard, 1967; Vanderwolf and Cooley, 2002; Nitzsche et al ., 2015) and relevant literature (Rose, 1942; Clarke and Whitteridge, 1976; Clarke et al ., 1976; Karamanlidis et al ., 1979). The immunocytochemistry of the visual area in the sheep caudal cortex around the lateral sulcus identified largely different GABA‐ergic interneuron populations within the cortical thickness (Figure 4).…”

“…Our data suggest that contralateral connections are absent in the sheep, or perhaps very limited as in the cat (Olson and Graybiel, 1980). We also note that connections (seeding from the claustrum, Figure 5(f)) may reach peristriate areas such as V2, V3, or V4 that we did not map, because their precise location and topography has not been identified in the sheep, although tracing studies showed a quite wide visual territory (Karamanlidis et al ., 1979). The absence of contralateral projections could be of prime importance if confirmed by other studies, to rule out the role of the Cl in stereopsis.…”

“…Later electrophysiological studies pointed out to a much smaller dorso-occipital part of the sheep cortex , whereas thalamo-cortical tracing studies confirmed a wider visual territory (Karamanlidis et al, 1979).…”

“…Rose (1942) found that the striated cortex stretched along most of the lateral and entolateral sulcus. Later electrophysiological studies pointed out to a much smaller dorso‐occipital part of the sheep cortex (Clarke and Whitteridge, 1976; Clarke, et al ., 1976), whereas thalamo‐cortical tracing studies confirmed a wider visual territory (Karamanlidis et al ., 1979).…”