Influence of Ocular Dominance Columns and Patchy Callosal Connections on Binocularity in Lateral Striate Cortex: Long Evans vs. Albino Rats

• Published in: Journal of comparative neurology (1911) Vol. 528; no. 4; pp. 650 - 663
• Main Authors: Andelin, Adrian K., Doyle, Zane, Laing, Robyn J., Turecek, Josef, Lin, Baihan, Olavarria, Jaime F.
• Format: Journal Article
• Language: English
• Published: 18.10.2019
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.24786

In albino rats, it has been reported that lateral striate cortex (V1) is highly binocular, and that input from the ipsilateral eye to this region comes through the callosum. In contrast, in Long Evans rats this region is nearly exclusively dominated by the contralateral eye even though it is richly innervated by the callosum ( Laing et al., 2015 ). We hypothesized that the inability of callosal connections to relay ipsilateral eye input to lateral V1 in Long Evans rats is a consequence of the existence of ocular dominance columns (ODCs), and of callosal patches in register with ipsilateral ODCs in the binocular region of V1 ( Laing et al., 2015 ). We therefore predicted that in albino rats input from both eyes intermix in the binocular region, without segregating into ODCs, and that callosal connections are not patchy. Confirming our predictions, we found that inputs from both eyes, studied with the transneuronal tracer WGA-HRP, are intermixed in the binocular zone of albinos, without segregating into ODCs. Similarly, we found that callosal connections in albino rats are not patchy, but instead are distributed homogeneously throughout the callosal region in V1. We propose that these changes allow the transcallosal passage of ipsilateral eye input to lateral striate cortex, increasing its binocularity. Thus, the binocular region in V1 of albino rats includes lateral striate cortex, being therefore about 25% larger in area than the binocular region in Long Evans rats. Our findings provide insight on the role of callosal connections in generating binocular cells. In Long Evans rats, input from both eyes segregate in the binocular region of V1 forming ocular dominance columns (ODCs, left), and callosal connections form patches in register with ipsi ODCs. In these rats lateral V1 is strongly dominated by the contralateral eye. In contrast, in albino rats we found that input from both eyed intermix in the binocular region (right), and that callosal connections are not patchy. We propose that these differences allow the transcallosal passage of ipsilateral eye input to lateral V1 of albino rats, increasing its binocularity.