Compression and stretch sensitive submucosal neurons of the porcine and human colon

Abstract

The pig is commonly believed to be a relevant model for human gut functions-however, there are only a few comparative studies and none on neural control mechanisms. To address this lack we identified as one central aspect mechanosensitive enteric neurons (MEN) in porcine and human colon. We used neuroimaging techniques to record responses to tensile or compressive forces in submucous neurons. Compression and stretch caused Ca-transients and immediate spike discharge in 5-11% of porcine and 15-24% of human enteric neurons. The majority of these MEN exclusively responded to either stimulus quality but about 9% responded to both. Most of the MEN expressed choline acetyltransferase and substance P; nitric oxide synthase-positive MEN primarily occurred in distal colon. The findings reveal common features of MEN in human and pig colon which we interpret as a result of species-independent evolutionary conservation rather than a specific functional proximity between the two species. The enteric nervous system (ENS), which is integrated into the wall of the gastrointestinal tract (GIT) from the oesophagus to the anal sphincter, enables the GIT to generate reflex activity independent from central influences 1-3. The ENS is organized in two complex neuronal networks called the submucosal plexus (SMP) and the myenteric plexus (MP). In both, the pig and human the SMP consists of two layers interconnected by interganglionic nerve fiber tracts 4,5. The SMP regulates mostly epithelial functions, such as secretion and absorption, as well as blood flow, cell proliferation and immune responses. The distinct parts of the SMP are called inner SMP (ISMP) and outer SMP (OSMP) with the ISMP being located closely to the lamina muscularis mucosae, whereas the OSMP is located on the luminal side of the circular muscle layer 6. In the porcine and human colon mainly neurons in the ISMP predominantly project to the mucosa 7-9 , and hence likely regulate epithelial functions 10. Enteric neurons can be activated by various stimuli, including chemical stimuli as well as mechanical distortion 11-17. During muscle contraction and relaxation enteric neurons are constantly exposed to distorting forces 16,18. Remarkably, even enteric neurons classically defined as interneurons or motoneurons are mechanosensitive, suggesting that mechanosensitive enteric neurons (MEN) are multifunctional 14,15,19. With intracellular recording techniques it has been shown that MEN in the MP respond to distension as well as to mucosal distortion 20-22. An important step forward was the use of imaging techniques, as they allowed to record simultaneously from a larger set of neurons and were also a prerequisite to study enteric neurons in larger animals 14-17,23,24. Using von Frey hair probing and intraganglionic volume injection, compression sensitive MEN have been identified in the MP of the guinea pig gastric corpus, ileum and colon 14,16,23 as well as in mouse ileum and colon 15. Furthermore, von Frey hair probing was used to identify compression sensitive MEN in isol...

Submucosal enteric neurons of the cavine distal colon are sensitive to hypoosmolar stimuli

“…2011; Mazzuoli‐Weber & Schemann, 2015b; Filzmayer et al . 2020). Individual ganglia of the SMP were stained with 20 μ m di‐8‐ANEPPS (1‐(3‐sulfanatopropyl)‐4‐[beta[2‐(di‐n‐octylamino)‐6‐naphthyl]vinyl] pyridinium betaine) by local intraganglionic application through a microinjection glass pipette.…”

“…For the detection of action potentials from enteric neurons an ultrafast neuroimaging technique was used. This technique, allowing the recording of neuronal activity with a high spatial and temporal resolution, was previously described in detail (Michel et al 2011;Mazzuoli-Weber & Schemann, 2015b;Filzmayer et al 2020). Individual ganglia of the SMP were stained with 20 μM di-8-ANEPPS (1-(3-sulfanatopropyl)-4-[beta[2-(di-n-octylamino)-6naphthyl]vinyl] pyridinium betaine) by local intraganglionic application through a microinjection glass pipette.…”

Classification of human enteric neurons

“…Based on the structure and the localizations of ChAT+/SOM+/SP+ endings in the mucosa, we suggest a sensory function. To some extent, the identification of mechanosensitive ChAT+/SP+ neurons (Filzmayer et al 2020 ) supports this assumption.…”

The role of mechanosensitive ion channels in the gastrointestinal tract

“…Unlike extrinsic spinal cord and vagal mechanoreceptors, whether their stimulation is sufficient seems to depend upon the length of the strain, rather than intramural tension (Hibberd et al, 2012). Experimental studies have shown that intestinal neurons have significant mechanosensitive responses to compression, shear stress, stretching, and hypoosmotic solutions (Hibberd et al, 2012;Dong et al, 2015;Kugler et al, 2015;Kugler et al, 2018;Filzmayer et al, 2020).…”