Long-term unilateral visual cortical lesions and learning of a black-white discrimination by one-eyed rats

Abstract

In a previous study we investigated the effects of callosal transected lesions made 10 weeks earlier (the 10-week-old callosal transected lesions), either at 3 weeks of age or at 13 weeks of age, upon the acquisition of a black-white (BW) discrimination in rats either with one eye removed at birth (OEB) or at 13 weeks of age (OET) following lesions of the contralateral (CT) visual cortex to the remaining eye. The CT visual cortex lesions were performed right before the training of BW discrimination. We found that the 10-week-old callosal transected lesions facilitated the acquisition in OEBs when the callosal lesions were given at 3 weeks of age, and to a lesser extent at 13 weeks of age. We also found that the same type of callosal transected lesions did not do so in OETs, regardless of the age when the callosal lesions were made.Since the CT visual cortex lesions inevitably result in damage of the callosal neurons, and lead to degeneration of the callosal afferents in the ipsilateral (IP) visual cortex, the present study was undertaken to investigate if the CT visual cortex lesions made 10 weeks earlier (the 10-week-old CT visual cortex lesions), made either at 3 weeks of age or 13 weeks of age, would affect the acquisition of BW discrimination in OEBs and OETs, like the 10-week-old callosal transected lesions employed in the previous study mentioned above.We found that in both OEBs and OETs the overall pattern of the facilitation effects of the 10-week-old CT visual cortex lesions on the acquisition of BW discrimination is, in general, the same as that observed in the 10-week-old callosal transected lesions, but the facilitative effect of the 10-week-old CT visual cortex lesions is more prevailing and pronounced. The findings are discussed in relation to the possible involvement of neurotrophic factors, released when the CT visual cortex lesions were made, in synaptic reorganization, and also in relation to the possibility of the increased use of the uncrossed visual pathways.