SEGMENTAL DISTRIBUTION OF AFFERENT NEURONS INNERVATING THE CANINE TESTIS

To clarify the afferent innervation of the canine scrotal contents, re trograde labeling of neurons in the dorsal root ganglia (DRG) has been carried out using two methods: (1) horseradish peroxidase (HRP) injec tion into the surface of the testis and epididymis; and (2) exposure o f the superior spermatic nerve to a fluorescent dye (Fast blue; FB). I njections of HRP resulted in labeling of DRG cells located predominant ly from T10 to L4 (87%) and, to a lesser extent, at S1-S3 (13%), Trans ection of the vas deferens previous to testicular injections eliminate d labeling in the S1-S3 DRG, but not at thoracolumbar levels. These fi ndings indicated that primary afferent fibers of the testis and epidid ymis project mainly to the DRG at higher than L4 through the superior spermatic nerve, but an additional population of the fibers also proje cts the sacral level through the inferior spermatic nerve. Exposure of the superior spermatic nerve to FB resulted in a; similar distributio n of labeled cells as compared with testicular injections of HRP after vasectomy. Labeled cells (8.1%) were also observed in the contralater al T13-L3 DRG, In both FB and HRP groups, the major part of the labele d cells was located in L1 and L2. The sizes of HRP- and FB-labeled cel ls were smaller than those of unlabeled cells in the L1 and 1,2 DRG. T he cumulative frequency distribution histogram for the diameter of HRP - and FB-labeled cells could be fitted by a normal distribution.