Changes in Lateral Geniculate Neurones of Rats as a Result of Continuous Exposure to Light

Abstract

THE results of several investigators demonstrate that environmental manipulations can affect the structure of the brain. Environmental conditions studied most often have been deprivation and enrichment. In the visual system different forms of light deprivation have been found to induce a decrease in spine density^1–3, dendritic branching^4,5 and in cell areas⁶. A number of studies have described changes resulting from enriched environmental conditions, including an increase in cortical weight and depth^7,8, ratio of glial cells to neurones⁹, spine density¹⁰, and dendritic branching¹¹. The effects of excess light stimulation in the visual system have also been studied. Continuous exposure to light has been found to cause irreversible damage to photoreceptors^12,13 and an increase in spine density in the visual cortex of albino rats¹⁴. Under these conditions, investigators have reported a decrease or absence of evoked potentials in adult albino rats¹⁵. Black-white discrimination and two pattern discrimination tests did not indicate any difference between these animals and control rats¹⁶. We have been able to show significant quantitative morphological changes in the dendritic field of neurones in the dorsal lateral geniculate of rats reared under continuous illumination from birth to 35 d.