EFFECTS OF VISION AND DARK-REARING ON SIZE AND DENSITY OF SYNAPSES IN LATERAL GENICULATE NUCLEUS MEASURED BY ELECTRON MICROSCOPY

Axon terminals have been counted and measured in the dorsal part of the lateral geniculate nucleus of the rat. The average diameter of the terminals was about 0.5 μ with a standard deviation of 37% of the mean. The average density of the terminals in the tissue was about 1.2·1012/ml. Two litters of rats were born and reared in darkness. Part of each litter was then exposed to diurnal lighting for 4-5 weeks. Tissue from the LGN of matched pairs of dark- or light-exposed litter-mates was then prepared under identical conditions and measured. The average diameter of the axon terminals was 15% less in the light-exposed rats, but the density of the terminals in the tissue was 34% greater. Tissue taken from the ventro-basal complex of somatic-sensory nuclei in these same rats did not differ significantly between the dark- and light-exposed pairs. Two litters of rats reared under normal diurnal lighting conditions were studied after part of each litter had been kept in darkness for 3 months. The axon terminals in the dark-exposed rats became 11% larger than those in the normally reared litter-mates, but the density in the tissue decreased by 29%. The background to these findings is discussed. © 1969.