Maintained activity, excitation and inhibition of lateral geniculate neurons after monocular deafferentation in the adult cat.

Monocular deafferentation of the lateral geniculate nucleus (LGN) was accomplished by photocoagulation of the retinal vessels and the optic disc of one eye. Single cells with normal excitatory innervation from the intact eye (N-cells) and deafferented (D-) cells were recorded extracellularly with glass micropipettes from layers A and A1 of the LGN 10 days and 10 weeks after visual deafferentation. The maintained activity of D-cells was severely reduced after 10 days but had recovered significantly after 10 weeks. Different interspike interval distributions indicated a change in the main input source for the reactivated cells after 10 weeks. Stimulation of the intact retina with diffuse, high-intensity light flashes revealed missing or very small responses in the acutely deafferented cells. A still weak influence of the non-dominant eye on the deafferented cells after 10 days developed after 10 weeks into a biphasic response with an initial inhibitory period followed by a post-inhibitory exciation. Electrical stimulation of the optic chiasm revealed an increased inhibition during chronic deafferentation. Excitation following this inhibitory period was rare after 10 days but occurred frequently after 10 weeks. An enhanced excitability following stimulation of the visual cortex and the mesencephalic reticular formation was also observed after 10 weeks of deafferentation. An increased efficiency of all remaining inputs to the visually deafferented cells is concluded from the augmented inhibition and non-retinal excitation.