Abstract
The effect of varying states of visual deprivation on the development of the optic lobes and cerebral hemispheres has been studied in the chick where the visual pathways are totally crossed over. Unilateral eye extirpation of the new hatched chick resulted in arrested development of the contralateral but not ipsilateral lobe, as measured by weight, protein content and acetylcholinesterase activity. Similar effects but of smaller magnitude were observed in the cerebral hemispheres. Histologic and enzymic evidence revealed the absence of significant degeneration in the optic lobe contralateral to an eye removed 17 days previously. These results were observed in the optic lobes of operated animals maintained either in light of in darkness between 3 and 17 days after hatch. However, in the inpaired cerebral hemispheres, differences could only be detected in birds kept the light. The effects of unilateral eyelid suturing on the development of chick brain regions were also examined. In this group, all asymmetrical differences observed within paired brain regions were totally light dependent and confined to the cerebral hemispheres. The hemisphere contralateral to the sutured eye weighed less and had less acetylcholinesterase activity than its paired hemisphere. The cerebral hemispheres of monocularly treated birds manifested effects of similar magnitude whether the treatment was enucleation or suturing. This suggests that the complete development of the associative centers in avian cerebral hemispheres is dependent on both intact innervation and on the information content of the visual input.
Highlights
The determination of biochemical changes in the central nervous system, which are correlated with differential sensory input, is of primary interest in the study of the molecular basis of cerebral function
We have examined the differential effects of unilateral visual deprivation for comparatively short times on the paired optic lobes and cerebral hemispheres of newly hatched chicks
The anatomical arrangement of the avian brain permits the exploration of asymmetrical changes after unilateral modification of visual input
Summary
The determination of biochemical changes in the central nervous system, which are correlated with differential sensory input, is of primary interest in the study of the molecular basis of cerebral function. The complete decussation of the optic tract in many birds [10] suggests that unilateral manipulation of visual input could be expected to result in ciifferential effects in the two optic lobes of the avian brain. Since one optic lobe can be compared to its contralateral partner, each bird can serve as its own simultaneous internal control. Long-term unilateral histological changes occuring in the adult avian visual system after removal of one eye in the young bird were described many years ago [30]. Autoradiographic studies of the long-term effects of this operation on the optic lobes of adult birds have been described ( 1). Little is known of the early, quantitative biochemical changes in various brain regions after unilateral eye removal in newly hatched birds [26]
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