Effect of sensory deafferentation on the gabaergic circuitry of the adult cat visual system

The effect of bilateral central retinal lesions on the GAD(67) and GAD(65) messenger RNA levels in the dorsal lateral geniculate nucleus, the perigeniculate nucleus and the visual cortex of the adult cat was investigated by in situ hybridization. Three days post-lesion, a decrease in the number of GAD(67)-expressing cells was apparent in the deafferented dorsal lateral geniculate nucleus. This decrease persisted until 7.5 months post-lesion and was more pronounced with longer survival times. The decrease in GAD(67) mRNA was mirrored by a decrease in glutamate decarboxylase-immunoreactive cells. GAD(65) messenger RNA expression levels were low in the dorsal lateral geniculate nucleus of both control and retinally-lesioned cats. In the perigeniculate nucleus the messenger RNA levels of both glutamate decarboxylase isoforms were clearly decreased over a restricted region. In the lesion-affected visual cortex, no changes at the messenger RNA level were observed for either GAD(67) or GAD(65) although changes in glutamate decarboxylase immunoreactivity have been previously described.(34) Hence, in the dorsal lateral geniculate nucleus, the perigeniculate nucleus and the visual cortex, different intracellular mechanisms seem to lead to decreased GABAergic inhibition in response to sensory deafferentation. (C) 1997 IBRO. Published by Elsevier Science Ltd.