Effects of Total Absence of Function on the Optic System of Rabbits.

Abstract

Despite numerous experiments on the various morphogenetic factors involved in the development of the central nervous system, the effect of normal physiological stimulation of an end organ on that end organ and on the corresponding brain centers is still little understood. The rôle of function in post-embryonic growth and differentiation of an established functional nerve tract in mammals has received but slight attention. In regard to the visual apparatus, 2 procedures have been used—extirpation of eyes, and sewing of eyelids. The results of extirpation on the visual cortex vary with the animal used, its age, and the experimenter; but the effects on the optic nerve and superior colliculus are uniform. The interpretation of such results from standpoint of lack of function is physiologically unsound as there are complicating factors of traumatic and secondary degeneration, and Von Gudden's degeneration. The results of sewing of eyelids likewise vary with the animal and the experimenter. Whereas Von Gudden noticed no changes in the cerebral cortices of rabbits whose eyes had been enucleated or eyelids sewn at birth, Berger (1900), in artificial ankyloblepharon in cats and dogs found no macroscopic or cytological changes in any part of the optic system except the visual cortex, where he noticed an arrested development both grossly and microscopically. This he attributed to reduced function, though he admitted that all light was not excluded, and suggested that atrophy of the optic nerves and lower reflex centers would probably have also occurred if all light had been excluded. Not much advance has been made since.