Central connections of ventral root afferents as demonstrated by the HRP method

To study the central connections of ventral root afferents, horseradish peroxidase was injected into the lumbosacral spinal cord of the cat and the appropriate dorsal root ganglia were examined from segments with (1) both dorsal and ventral roots intact, (2) both roots sectioned, and (3) only the dorsal root sectioned. The key finding was that a number of labeled cells (up to 133) were observed in the ganglion after dorsal rhizotomy. We interpret these findings to mean that the central processes of the labeled cells projected to the spinal cord through the ventral root. As expected, when both roots were cut, almost no cells were labeled and when both roots were intact, there were large numbers of labeled cells. Of the labeled cells observed in ganglia after dorsal rhizotomy, all were found to be within the ganglion itself. No labeled aberrant dorsal root ganglion cells could be found.