Striated perineal muscles: location of autonomic, sensory and somatic neurons projecting to the male pig bulbospongiosus muscle

The location, number, and size of the neurons innervating the bulbospongiosus muscle (BSM) were studied in male pigs, by means of Fast Blue (FB) retrograde transport. After injection of FB into the left BSM, labeled neurons were found bilaterally in the L2-S4 sympathetic trunk ganglia (STGs), in the caudal mesenteric ganglia (CMGs), in the microganglia of the pelvic plexus (PGs), in a dorsolateral area with respect to the central canal of S1-S3 segments of the spinal cord (SC) and in the S1-S4 ipsilateral and S2-S3 contralateral spinal ganglia (SGs). The mean number of labeled FB cells was 3,122 -1,968 in STGs, 979 - 667 in CMGs, 108 -104 in PGs, 89 -39 in SC and 77 - 23 in SGs. The area of the multipolar neurons was 852 -22 µ2 in the STGs, 878 -23 µ2 in the CMGs and 922 -31 µ2 in the PGs. The multipolar SC neurons had an area of 1,057 -38 µ2, while pseudounipolar SG cells had dimensions of 2,281- 129 µ2. Our research enables us to highlight two peculiarities regarding the innervation of the boar BSM: the very high number of labeled autonomic neurons and the particular localization of the motor somatic nucleus.