  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.
