Pig has been used recently as an animal model for studying diseases of human urinary tract, however, the sensory innervations of urinary bladder in this species has not been yet described.
Objective: The present study was aimed at neurochemical characterization of sensory neurons of dorsal root ganglia (DRGs) supplying porcine urinary bladder.
Methods: Retrograde tracer Fast Blue (FB) was injected into the right half of the urinary bladder wall of six juvenile female pigs. Three weeks later ipsi- and contralateral DRGs of interest were harvested from all animals and a neurochemical characterization of retrogradely-labeled neurons was performed using routine single-immunofluorescence labeling technique on 10 microm-thick cryostat sections.
Results: 85% of spinal sensory neurons supplying porcine urinary bladder was located in ipsilateral sacral S3-S4 ganglia and in first coccygeal ganglion (Cq1),whereas rest of FB-positive (FB+) nerve cells were found in lumbar L3-L6 DRGs. FB+ neurons belonged mostly to the medium-sized (54%) and small-sized afferent perikarya (45%). Bladder sensory neurons contained substance P (SP), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating peptide (PACAP), galanin (GAL), neuronal nitric oxide synthase (nNOS), somatostatin (SOM) and/or calbindin-28k (CB), and these neurons constituted 45%, 36%, 26%, 6%, 6%, 4% and 3% of all retrogradely traced DRGs perikarya, respectively. Distinct differences in the number of traced cells and their neuropeptide content were observed between the lumbar and sacral/coccygeal division of bladder-projecting DRG neurons. Thus, FB+ neurons expressing CGRP, GAL, nNOS or SOM were more numerous in lumbar DRGs (44%, 9%, 9% and 6%, respectively), than in sacral/coccygeal ganglia (23%, 2%, 1.5% and 0.3%, respectively). On the other hand, more FB+ cells expressed PACAP in sacral (31%) than in lumbar DRGs (23%). However, fractions of SP-IR or CB-IR bladder sensory neurons were similar in lumbar and sacral/coccygeal DRGs.
Conclusions: This novel description of both spatial and neurochemical organization pattern of porcine urinary bladder sensory innervation constitutes a basis for further functional studies aimed at unraveling neurogenic mechanisms of urinary bladder diseases.