Transsynaptic response of the lateral geniculate nucleus and the pattern of degeneration of the nerve terminals in the Rhesus monkey after eye enucleation

Abstract

Summary The response of the lateral geniculate neurons to deafferentiation and the anterograde degeneration of the optic terminals have been studied in rhesus monkeys following unilateral and bilateral eye enucleation. The principal features of the transneuronal changes are vacuolation of the perikaryon, chromatolysis, reduction and alterations of mitochondria, nuclear infoldings, proliferation of neurotubules, overall reduction in the cell size, paucity of the dendritic arborization, postsynaptic watery dendrites and profiles with tubulo-vesicular structures. Dark transformation with preservation of filaments was also reported to precede the process of phagocytosis of the filamentous degenerating optic nerve terminals. Other findings related to enucleation were disappearance of axon terminals of other than optic origin, presence of boutons with crowded synaptic vesicles, and glial reaction. ‘Seepage’ of altered substances from the degenerating optic nerve terminals to the postsynaptic site and the multiple mini-traumata induced to the postsynaptic neuron during the phagocytosis of optic nerve terminals engulfed together with fragments of postsynaptic cytoplasm, are considered possible pathogenetic mechanisms of transneuronal degeneration. A chain reaction of transneuronal degeneration may be responsible for the severe reduction of the dendritic arborization.