The effects of monocular deprivation on different neuronal classes in the lateral geniculate nucleus of the cat.

Retrograde axonal transport of horseradish peroxidase (HRP) was used to identify two populations of cells in the lateral geniculate nucleus (LGN) of the cat. HRP was injected into area 17 and 18 separately in the same animals, and the neuronal somata giving rise to thalamo-cortical axons, identified by the presence of granular HRP reaction product within them, were measured. The mean size of LGN neurones labelled by injections in area 17 ("17-relay" cells) was less than of neurones filled from area 18 ("18-rely" cells). Similar separate injections into area 17 and 18 of monocularly deprived kittens also showed that in non-deprived LGN laminae 17-relay cells were, on average, smaller than 18-relay cells. In deprived laminae, 17-relay cells were some 20% smaller than in non-deprived laminae, but deprived 18-relay cells were 50-60% smaller than normal, being on average, actually smaller than deprived 17-relay cells. We conclude that the population of large LGN neurones projecting to area 18 is more severely affected by monocular deprivation than the smaller neurones projecting to area 17, and discuss the relationship of the morphological results to physiologically defined X and Y cells in the LGN.