Effects of delayed monocular enucleation after birth upon black-white discrimination learning in the albino rat

Many investigators have demonstrated that enucleation of one eye in rats and hamsters soon after birth results in an increased number of uncrossed optic nerve terminals in the main visual centers, and that they are physiologically functional. Such changes, however, became less evident as the time of enucleation is delayed after birth. We also have found that rats with one eye removed at birth were able to relearn a black-white discrimination task faster than rats monocularly enucleated at maturity when relearning was conducted after destruction of the visual cortex contralateral to the remaining eye. This faster relearning phenomenon is considered to be a behavioral expression of such morphological and physiological changes. The present study was then undertaken to examine the question of how this faster relearning phenomenon is affected by the delay of enucleation time after birth. Two experiments were conducted. In Experiment 1 the effects of the removal of one eye at 0, 5, 10, 15, 20 days and at three months of age were compared, and in Experiment 2 those at 10, 11, 12, 13, 14 and 15 days of age were compared. Experiment 1 showed that enucleation at 0, 5 and 10 but not at 15, 20 days and at three months of age facilitated relearning, and that the degree of facilitation decreased as age increased. And, although the results were not unequivocal, Experiment 2 did suggest that the removal of one eye at and beyond 13 days of age was no longer able to facilitate relearning.(ABSTRACT TRUNCATED AT 250 WORDS)