The effect of eye enucleation on the number of fibres in the supraoptic decussation of posthatch chicks (Gallus gallus).

In this study of the young chick we examine the effects of unilateral or bilateral eye enucleation on the number of axons in the supraoptic decussation, a major interhemispheric tract subserving visual function. On posthatch day 25, chicks underwent removal of either one or both eyes. After a survival period of 32 days, electron microscopic examination of the supraoptic decussation revealed a substantial loss of fibres. In the bilaterally enucleated group, a significant decrease in the number of axons occurred in both the dorsal and ventral aspects of the supraoptic decussation. The effect of unilateral enucleation was not as severe. The results indicate that enucleation of the precocial and functioning visual system of the chick leads to a transneuronal loss of axons. The degree of loss may reflect the amount of fibres in the crossed visual projection within the supraoptic decussation.