Substance P as a neuronal factor in the enteric nervous system of the porcine descending colon in physiological conditions and during selected pathogenic processes.

The present investigation pertains to changes in substance P-like immunoreactive (SP-LI) nerve structures of the enteric nervous system (ENS) in the porcine descending colon, caused by chemically-induced inflammation and nerve injury (axotomy). The distribution pattern of SP-LI structures was studied using the double immunofluorescence technique in the myenteric (MP), outer submucous (OSP) and inner submucous (ISP) plexuses, as well as in the circular muscle and mucosal layers. Under physiological conditions, SP-LI neurons have been shown to constitute 4.13 ± 0.24%, 3.36 ± 0.26%, and 7.92 ± 0.16% in the MP, OSP, and ISP, respectively. Changes in SP-immunoreactivity depended on the pathological factor studied. The numbers of the SP-LI perikarya amounted to 7.89 ± 0.34, 5.56 ± 0.30, and 19.96 ± 0.57 in chemically-induced colitis, and 4.28 ± 0.13%, 7.18 ± 20%, and 11.62 ± 0.48% after axotomy in MP, OSP, and ISP, respectively. The both studied processes generally resulted in an increase in the number of SP-LI nerve fibers in the circular muscle and mucosal layers. The obtained results suggest that SP-LI nerve structures of the ENS may participate in various pathological processes in the porcine descending colon and exact functions of SP probably depend on the type of the pathological factor.