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

TL;DR

This study maps the substructure of the dorsal lateral geniculate nucleus in Long-Evans rats using cholera toxin B-subunit tracing, revealing multiple segregated retinal input zones within the nucleus.

Contribution

It provides detailed 3D mapping of retinal input zones in the rat dLGN, showing multiple segregated subdomains instead of a single zone, which is a novel structural insight.

Findings

Retinal terminals are well-segregated by eye of origin.

The dLGN contains three or four spatially separated zones.

These zones may represent distinct functional sublaminae.

Abstract

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.