Photic responses of the lateral geniculate nucleus can be used as a stereotaxic guide for micropipette placement

Neuroanatomical studies of the cat's thalamus require accurate placement of a micropipette for tracer injections. In order to determine interanimal differences, we describe a simple method which compares the location of the different laminae of the dorsal lateral geniculate nucleus (LGNd) with a stereotaxic atlas. The visual electrophysiological response to a flash was recorded from the LGNd with an enamelled stainless-steel electrode. The response steadily increased in amplitude through the optic radiation, lamina A and lamina A1. Further penetration through the LGNd resulted in the reversal of the recorded potential. The reversal point was lesioned and found to lie between lamina A1 and lamina C. Based on the dorsal level of laminae A, A1 and C as determined by the reversal point, these estimates of LGNd location can be compared with a stereotaxic atlas and corrections made to subsequent placement of micropipettes used for injections in other thalamic structures.