The effect of monocular deprivation on synaptic terminals in the visual cortex of rabbits. A quantitative electron microscopic study

Abstract

The effect of prolonged (7 month) monocular deprivation (right eye sutured) on the density of synapses (N A) and the number of synaptic vesicles (N ves) in the visual cortex of rabbits is studied. The results can be summarized as follows: (1) No changes (N A and N ves) are observed in the non-deprived hemisphere (visual areas I and II, motor cortex) as compared to control animals. (2) N A has not changed, as compared to control animals, in the binocular field of the deprived visual cortex. (3) A significant rise in N A, as compared to control animals, is observed in the monocular field of area I and in the motor cortex of the deprived cortex. This rise is similar to that found after recovery from prolonged dark rearing. (4) The increase in N A is mainly restricted to the laminae I–III, indicating that, most likely, we are not dealing with an increase in specific visual afferents. (5) The deprived visual cortex shows a significant decrease (16%) in N ves. This decrease is less pronounced than after dark rearing (40%). This probably points to the fact that eye suturing does not fully prevent light penetration. The results are discussed in the light of recent discussions on the plasticity of synapses and the effect of retinal input on the development of the visual system.