Intestinal inflammation in dogs shifted Substance P receptor (NK1R) expression from neurons to muscle and immune cells, suggesting both benefits and risks of NK1R-targeting drugs for gut inflammation.
NK1R overexpressed on immune/muscle cellsIn inflamed dog intestines, NK1R was overexpressed on muscle cells and immune cells rather than neurons, suggesting both therapeutic potential and motility risks for NK1R antagonist drugs.
What the researchers found
In dogs with spontaneous ileal inflammation (n=8) compared to healthy controls (n=7), the percentage of Substance P-producing neurons was similar in both the myenteric plexus (15–16%) and submucosal plexus (24–26%). However, key differences emerged in receptor distribution: muscle cells and immune cells in inflamed tissue overexpressed NK1R immunoreactivity, while nitrergic (nNOS-positive) neurons expressing NK1R showed a trend toward decrease in inflamed dogs (41% vs 65%, P=0.11).
SP-immunoreactive mucosal nerve fibers also trended toward decreased density in inflamed tissue (P=0.07). These findings suggest that inflammation shifts NK1R from neuronal to non-neuronal tissue compartments, potentially altering how Substance P signaling affects gut function.
Why it matters
NK1R antagonist drugs are already used clinically (aprepitant for chemotherapy-induced nausea), and there's growing interest in targeting Substance P signaling for inflammatory bowel conditions. This study provides a nuanced picture: while NK1R overexpression on immune cells supports the rationale for NK1R antagonists in gut inflammation, the simultaneous role of NK1R in neuronal motility circuits means such drugs could cause motility disorders as a side effect. Understanding this dual role is critical for drug development.
How the study worked
This was a comparative immunohistochemical study of ileal tissue from 7 control dogs and 8 dogs with spontaneous ileal inflammation. Researchers quantified the percentage of Substance P-immunoreactive enteric neurons, SP-positive nerve fiber density, NK1R-expressing neurons (including nitrergic subpopulations), and NK1R expression in non-neuronal cells (muscle and immune cells) across both myenteric and submucosal plexuses.
What this study cannot tell us
This is a small study (7 control, 8 inflamed dogs) with limited statistical power — several important trends (mucosal nerve fiber density, nitrergic NK1R expression) did not reach statistical significance. The study used naturally occurring canine inflammation, which strengthens ecological validity but introduces variability in disease type and severity. The findings are from dogs and may not directly translate to human intestinal inflammation. The functional consequences of NK1R redistribution were not directly tested.
How to read the evidence
This is a small comparative immunohistochemical study in dogs with naturally occurring intestinal inflammation. While the use of spontaneous disease models is a strength, the small sample size limits statistical power and generalizability. No functional or interventional data is presented.
When this study was published
Published in 2017, this study is about 9 years old. The basic findings about Substance P receptor redistribution in intestinal inflammation remain relevant, though the field of NK1R-targeted therapeutics has continued to evolve since publication.
The bigger picture
Substance P is one of the most studied neuropeptides in the gut-brain axis. Its role in inflammatory bowel disease, irritable bowel syndrome, and visceral pain has driven significant pharmaceutical interest in NK1R antagonists. This study adds important context from a spontaneous disease model (rather than artificially induced inflammation), showing that NK1R redistribution during inflammation creates both therapeutic opportunities and pharmacological risks — a common challenge in neuropeptide-targeted drug development.
Questions still open
- Do NK1R antagonists like aprepitant have clinically meaningful anti-inflammatory effects in inflammatory bowel disease?
- Does the shift of NK1R from neurons to immune/muscle cells during inflammation occur similarly in human IBD?
- Could selective targeting of NK1R on immune cells (sparing neuronal NK1R) provide anti-inflammatory benefit without motility side effects?
Common questions
What is Substance P and what does it do in the gut?
Could drugs that block Substance P's receptor help with bowel inflammation?
Read the original research
Substance P and the neurokinin-1 receptor expression in dog ileum with and without inflammation.
Research in veterinary science, 114, 297-307
Citation
Polidoro, Giulia; Giancola, Fiorella; Fracassi, Federico; Pietra, Marco; Bettini, Giuliano; Asti, Martina; Chiocchetti, Roberto. (2017). Substance P and the neurokinin-1 receptor expression in dog ileum with and without inflammation.. Research in veterinary science, 114, 297-307. https://doi.org/10.1016/j.rvsc.2017.06.002