Tachykinin Activation on Enteric Glia: A Novel Mechanism of Enteric Nervous System Dysfunction in Irritable Bowel Syndrome

The Enteric Nervous System (ENS) is the major neural regulator of the gastrointestinal (GI) tract. Enteric circuits involve precise interactions between neurons and glia and abnormal ENS activity is considered a key contributor to gut motility disorders like irritable bowel syndrome (IBS). However, the role of neuron‐glia interactions in functional GI motility disorders is not understood. Tachykinins are important excitatory neurotransmitters in the ENS that contribute to IBS pathophysiology. In the spinal cord, substance P (SP) and neurokinin A (NKA) release by hyperactive neurons drives reactive gliosis. We hypothesize that the activation of enteric glia by tachykinins plays an important role in neuroinflammation during IBS. We tested our hypothesis using immunohistochemistry (IHC) and calcium imaging recordings in tissue from 5–8 week old C57BL/6 male mice. Our results show that both NKA and SP are present in varicosities that surround enteric glia in the myenteric plexus. We found that this population of glial cells primarily express neurokinin‐2 receptors (NK2R) (n=3 animals) which preferentially bind NKA over SP. NK1R labeling in the myenteric plexus was primarily neuronal. However, we could not exclude the possibility of expression on glia. We did not find evidence of NK3R expression in the myenteric plexus. We tested the breadth of responsiveness of myenteric glia to tachykinins such as SP and NKA in whole‐mount preparations loaded with the calcium indicator dye Fluo‐4. Our results show that enteric glia produce robust calcium transients in response to stimulation with NKA but not to SP (n=62 glial cells from 3 animals). To determine if tachykinin receptor activation contributes to neurodegeneration during inflammation, we stimulated enteric glia with either SP or NKA and measured neuronal packing density within myenteric ganglia. Our results show that treatment with NKA significantly reduces neuronal survival (p=0.0416, n=4 animals) while treatment with SP had no effect (p=0.7171, n=3 animals). In conclusion, our results provide strong evidence that the activation of glial NK2Rs by NKA is a novel mechanism of neuroinflammation in the ENS. Support or Funding Information T32NS44928‐11 and RO1DK103723