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The lateral geniculate nucleus (LGN) is the thalamic relay center in the visual pathway. Deafferentation induced by different methods is known to result into nerve fibre and nerve cell degeneration. However, information about the minimum time required for such changes to appear is rather scanty. In the present study 20 adult rabbits received monocular enucleation and the non-enucleates served as controls. The operated animals survived from 12h to 3m before they were sacrificed. The lateral geniculate nuclei from the perfusion fixed animals were processed for light and electron microscopic observations. It was found that 24h was the least time required for detectable morphological changes to appear. The light microscopic changes were in the form of swelling of nerve fibres, occurrence of minute holes followed by neuronal death. The spared neurons revealed hypertrophy and gliocytes showed hyperplasia. Electron microscopy revealed loosening of myelin lamellae, intramyelinic oedema, periaxonal vacuolation and electron-dense degeneration of the nerve fibres. With increasing duration these changes also progressed in number, size and morphology followed by neuronal death, glial cell hyperplasia and hypertrophy. Presynaptic axon terminals degenerated earlier than post-synaptic profiles. Conclusions: (i) Minimum time required for microscopic changes to appear was just 24h. (ii) Neurons heavily dependent on retinal inputs degenerated and the least dependent ones hypertrophied. (iii) All progressive degenerative changes could not be rigidly placed in temporal sequence.
Eye enucleation, deafferentation, lateral geniculate nucleus, transneuronal degeneration