[Morpho-functional changes in the tegmentum mesencephali of turtles following enucleation]

Morpho-functional changes in the mesencephalic centre of the turtle (Emys orbicularis L.) were studied during optic nerve degeneration. It was observed that synaptic terminals in this centre undergoing the "dark" degeneration are associated with myelinated optic fibres and terminals undergoing the "light" one are associated with unmyelinated fibres. The first low amplitude component of the evoked potential disappears with degeneration of myelinated fibres of large diameter during the "dark" degeneration (4-5 months after enucleation). The first high amplitude component disappears with degeneration of the middle-sized myelinated fibres and the end of the "dark" degeneration (7 months after enucleation). The characteristics of the second high amplitude component which reflects the excitation of both thin myelinated and all unmyelinated fibres, begin to change with degeneration of unmyelinated fibres during "light" degeneration (2.5-3.5 months). This component disappears with degeneration of the thin myelinated fibres (7 months).