Thalamic inputs to the rabbit visual cortex: identification and organization using horseradish peroxidase (HRP).

Horseradish peroxidase (HRP) has been injected in visual cortical area 1 (V1, striate cortex) of 33 rabbits (16 received a unilateral injection, 17 bilateral injections) in order to identify its thalamic inputs and to determine their retinotopic organization. This study has shown that when HRP is injected into different portions of V1: 1. Labeled cells are consistently seen in the dorsal lateral geniculate nucleus (LGNd) and are always organized into horizontal columns arranged perpendicularly to the long axis of the LGNd; although the columns are always present in the alpha sector of the LGNd, they extend into the beta sector of this nucleus only occasionally. 2. With a series of injection sites that lie on or near the medial edge of V1 and run rostrocaudally, cell columns shift from ventromedial to dorsolateral within the LGNd. With a series of injection sites that are located along the lateral border of V1 and run from rostral to caudal, columns of labeled cells move from ventral to dorsal along the medial edge of the LGNd. 3. In some of the experiments, with injections in either medial or lateral portions of V1, columns of HRP-labeled cells have also been found within the pulvinar.