Retinotopic organization within the thalamic reticular nucleus demonstrated by a double label autoradiographic technique.

A 'visual receptive zone' of the thalamic reticular nucleus can be defined in rabbits by the transneuronal transport of [3H]proline from the retina through the lateral geniculate nucleus to the reticular nucleus. Small injections of [3H]proline into the striate cortex of rabbits produce localized patches of label within this visual receptive zone, smaller than the zone itself. The sum of these small patches corresponds approximately to the total extent of the visual receptive zone, suggesting that there is a retinotopic map within the corticoreticular pathway. This map has been studied by double injections, using [3H]proline and [35S]methionine to label two different parts of the striate cortex. After axoplasmic transport of the isotopes, the reticular distribution of these two labels can be demonstrated by a double emulsion technique. This allows a distinction to be made between the radiation emitted by each isotope and demonstrates that within the reticular nucleus there is an accurate retinotopic map. In accuracy and in the orientation of the major visual field axes, this map corresponds closely to the map established in the dorsal lateral geniculate nucleus. However, the reticular map shows an elongation in the dorsoventral axis, which corresponds to the orientation of dendritic arbors within the nucleus.