Distribution of sensory neurons of the pudendal nerve in the dorsal root ganglia and their projection to the spinal cord. Horseradish-peroxidase studies in the rat.

The morphology and distribution of the sensory neurons of the pudendal nerve within the spinal ganglia of rats were investigated by use of horseradish peroxidase (HRP). The labelling was visualized in diaminobenzidine (DAB) or tetramethyl-benzidine (TMB)-stained sections. Injection of HRP directly into the pudendal nerve labelled perikarya predominantly in the sixth lumbar DRG (L6). Following injection of HRP into the scrotal skin, however, additional cells were labelled in L5 and S1. Labelling was invariably unilateral. Approximately equal numbers of small (less than 30 micrometers) and large neurones (greater than 40 micrometers) were labelled following subcutaneous injections although injections into the nerve marked twice as many small cells as large cells. This suggests that, in the rat, most of the small-diameter fibers within the pudendal nerve ascend through L6. Although a cluster of neurones was observed in one experiment, the remaining 25 experiments did not reveal any somatotopic arrangement since the labelled perikarya were distributed evenly throughout the ganglion. Similar numbers of retrogradely labelled neurones (somatopetal transport of the tracer) were observed in both DAB- and TMB-stained sections, although TMB allowed the demonstration of anterograde (somatofungal) HRP transport by terminal labelling in the superficial laminae of the lumbar spinal cord, extending into laminae II--IV.