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Y. Sauve, H. Karten, A. Brzozowska-Prechtl, F. P. Gaillard; Primary Retinal Projections in the Nile Rat (Arvicanthis Niloticus), a Diurnal Cone Rich Murid. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1874.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the distribution of the retinal efferents in the cone-rich diurnal rodent, Arvicanthis niloticus. This rodent has 35-40% cones, compared to the 1-3% reported in Mus musculus and the common Norwegian rat.
Cholera toxin (subunit b) was injected in one eye of two Nile rats (3 mo of age; weight 64 and 73g) under anesthesia. Five days after injection, the two brains were cut in the coronal and sagittal planes, respectively (30 µm thick cryosections). The sections were processed with anti-CTb antibody and DAB and counterstained with Giemsa or Cresyl violet. Sections were scanned and analyzed with the Aperio system. Nomenclature is based on Paxinos and Watson (1986).
Efferent projections from the Nile rat retina travel to the brain through three major tracts: the retino-hypothalamic tract, the accessory optic tract and the main optic tract. Contralateral projections are always dominant. Ipsilateral projections arise from the dorsalmost fibers at chiasma level. Retinal projections distribute to six major targets: (1) the supra-chiasmatic nucleus (SCN), bilaterally, with a small contingent to the peri-supraoptic field; (2) the contralateral accessory optic nuclei (particularly the medial terminal nucleus, MTN), ; (3) the ventral geniculate complex (GLv) including the intergeniculate leaflet (IGL), bilaterally; (4) the dorsal nucleus of the lateral geniculate (GLd), bilaterally. The contralateral geniculate projection displays some lamination pattern; (5) the pretectum, bilaterally. Prominent projections fill the olivary pretectal nucleus (OPT) and occupy the dorsal shell of the anterior pretectal nucleus (APTd); (6) the superior colliculus (SC), mostly contralateral but with clear patches on the ipsilateral side. Lamination seems to be present. Additional, but more scattered retinal projections consistently found in usual laboratory rodents (rats and mice), have also been identified. The superior colliculus appears disproportionately enlarged, compared to that of a C57BL/6 mouse and a pigmented Norwegian rat. The dorsal nucleus of the lateral geniculate appears only slightly more highly differentiated than in these nocturnal species.
Efferent projections from the Nile rat retina are quite similar to those found in all other rodents examined so far. Ongoing studies are examining whether some of these projections share subtle topographic differences with those of mice and rats in relation with the animals’ diurnal lifestyle.
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