Axotomy induced changes in neuronal plasticity of sympathetic chain ganglia (SChG) neurons supplying descending colon in the pig

Sympathetic neurons are capable of extensive regeneration following axonal injury. To investigate the response to axotomy of colon-projecting neurons (CPN) localized in the porcine sympathetic chain ganglia (SChG), the retrograde Fast Blue (FB) tracer, axonal transection and double immunohistochemistry methods were applied. The CPN were localized exclusively in the lumbar SChG and displayed a predominantly catecholaminergic [i.e. Tyrosine Hydroxylase (TH)/Dopamine β Hydroxylase (DβH)] and Neuropeptide Y (NPY) positive phenotype under physiological conditions. Axotomy led to a significant decrease in TH/DβH production and a simultaneous increase in the neuropeptides Galanin (GAL) and Somatostatin (SOM), but not NPY or Vasoactive Intestinal Peptide (VIP) expression in retrogradely traced perikarya. Furthermore, the decrease in density of TH-/DβH-, VIP-, Leu5-Enkephalin (LENK)-, Choline Acetyltransferase (ChAT)-immunoreactive (-IR) nerve fibers occurred after axotomy. These data suggest a species-specific response to axonal damage of the CPN localized in porcine SChG. Since the SChG neurons supervise the vasculature of gut both in physiological and pathological conditions, and since pig is a more accurate animal model of human gut than a rodent (Swindle et al., 1992), these data may contribute to the understanding of the pathology of several gut illnesses, like Crohn Disease and Irritable Bowel Syndrome which commonly affect western populations.

Research Highlights
► Colon projecting neurons of sympathetic chain ganglia (SChG) in the pig are located exclusively in the lumbar part of SChG and display catecholaminergic character.
► Enhanced galanin and somatostatin expression is a distinctive feature of porcine SChG neurons projecting to the descending colon in a response to axotomy.
► Pig more accurately models the anatomy and physiology of the human colon than rodents therefore seems to be more useful animal model of human gut what may contribute to the understanding of the pathology of several gut illnesses, which commonly affect western populations.