Observations on the lateral geniculate nucleus of the monkey (Macaca fasicularis) after eye removal: a light and electron microscopic study. II. Axonal and dendritic degeneration.

Morphological parameters of the axons and dendrites in the lateral geniculate nucleus have been studied in the normal monkey and after varying periods of enucleation, at the light and electron microscopic levels. Gross aspects of the alterations evident at the ultrastructural level can be correlated with changes visible in the light microscope. Signs of axonal fragmentation were never observed following enucleation; retinal afferent fibres seem to gradually thin out and disappear, taking on an osmiophilic appearance in the electron microscope during this process. Changes in the surface structure of axons are considered to be due to an altered reaction of myelin in the degenerating nucleus. Myelin is not removed to any great extent. The dendritic responses to enucleation (including those of synaptic profiles containing flat vesicles) are believed to result from an unspecific compensatory reaction to increased hydration and are not considered to be primarily degenerative. Since pale terminal degeneration seems to be of the same nature it is concluded that such early signs of presumed terminal death are unreliable. Dark degeneration of dendrites was not observed in the lateral geniculate nucleus of the enucleated monkey.