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.