COEXISTENCE OF CALCITONIN-GENE-RELATED PEPTIDE-LIKE AND SUBSTANCE P-LIKE IMMUNOREACTIVITY IN RETROGRADELY LABELED SUPERIOR SPERMATIC NEURONS IN THE DOG

The coexistence of calcitonin gene-related peptide (CGRP) and substanc e P (SP) was determined in primary afferent neurons of the superior sp ermatic nerve of the dog. Testicular afferent neurons were visualized by retrograde labeling with the fluorescent dye fast blue. CGRP-like i mmunoreactivity (LI) was found in about 80% of testicular L1 and L2 do rsal root ganglion cells, and 81% of CGRP-positive neurons also contai ned SP. Conversely, SP-LI was found in 66% of testicular afferents, an d 96% of SP-positive neurons simultaneously contained CGRP. Both CGRP- and SP-LI were observed in the whole size range of the testicular aff erent neurons. No significant difference in the diameter was detected between CGRP- and SP-positive testicular afferent neurons. In contrast , the diameter of SP-positive cells was significantly smaller than tha t of CGRP-positive cells in the whole population of dorsal root gangli on (DRG) neurons. Compared to skin and muscle afferents, a larger popu lation of the testicular afferents contain these peptides. This is con sider to be one of the characteristic features of visceral afferents. Coexistence of CGRP and SP in testicular afferent neurons suggests a c lose functional relationship between these two neuropeptides in the se nsory nervous system.