Anomalous patterns of callosal connections develop in visual cortex of monocularly enucleated hamsters

In this study we analyzed the effect of neonatal monocular enucleation on the pattern of callosal connections in striate cortex of the golden hamster. Callosal connections were revealed in the hemisphere ipsilateral to the remaining eye following multiple injections of either the enzyme horseradish peroxidase or the fluorescent tracer Fluoro-Gold into the contralateral hemisphere. The most salient anomaly induced by the removal of one eye at birth is the appearance of a dense band of callosal connections that runs anteroposteriorly in medial portions of striate cortex. No obvious changes in the laminar distribution of callosal connections were observed. Comparison of our present results with those obtained by Olavarria et al (1987) in monocularly enucleated rats reveals that neonatal enucleation induces remarkably similar anomalies in the callosal patterns of rats and hamsters. This similarity suggests that the role the eyes play in the development of the visual callosal pathway is similar among rodent species. Moreover, the finding of an anomalous callosal band in striate cortex one-eyed hamsters supports the notion that disruption of visual input does not arrest callosal development, but rather leads to the development of entirely new features in the callosal pattern.