Dorsal lateral geniculate substructure in the Long-Evans rat: A cholera toxin B-subunit study

This study describes the substructure of the dorsal lateral geniculate nucleus of the thalamus of the pigmented rat (Rattus norvegicus) based on the eye-of-origin of its retinal ganglion cell inputs. We made monocular intra-ocular injections of the B-subunit of cholera toxin (CTB), a sensitive anterograde tracer, in three adult male Long-Evans rats. In four additional subjects, we injected fluorophor-conjugated CTB in both eyes, using a different fluorophor in each eye. Brains of these subjects were fixed and sectioned, and the labeled retinal ganglion cell termini were imaged with wide-field sub-micron resolution slide scanners. Retinal termination zones were traced to reconstruct a three dimensional model of the ipsilateral and contralateral retinal termination zones in the dLGN on both sides of the brain. The dLGN volume was 1.58 \pm0.094 mm^{3}, comprising 70 \pm 3% the volume of the entire retinorecipient LGN. We find the retinal terminals to be well-segregated by eye of origin. We consistently found three or four spatially separated ipsilateral-recipient zones within each dLGN, rather than the single compact zone expected. It remains to be determined whether these subdomains represent distinct functional sublaminae.