An increasingly complex view of intestinal motility, 2020, Rao

[SNT Gatchaman]

An increasingly complex view of intestinal motility
Rao M

Key studies published in 2019 shed new light on how complex motor patterns emerge from the functional organization of circuits in the enteric nervous system and, in turn, how extrinsic afferent neurons and common commensal microorganisms interface with these circuits to modulate intestinal motility.

Link (Paywall, Nature Reviews Gastroenterology and Hepatology)

 

[SNT Gatchaman]

intestinal dysmotility can potentiate infections, cause nutrient malabsorption and manifest with debilitating symptoms, such as diarrhoea and constipation

Research since [1899] has led to the general understanding that enteric neurons located in the gut wall are organized into reflex circuits that detect luminal stretch, both directly and indirectly, to activate ascending and descending relays that modulate the activity of myogenic contractions and drive the directed propulsion of luminal contents.

neurogenic peristalsis has been the most highly studied behavioural output of the enteric nervous system (ENS), yet many fundamental questions remain unanswered.

A series of studies published in 2019 have applied modern neuroscience tools to answering some of these age-old questions and are shifting the understanding of gut motility

One remarkable feature of gut motility is the large variety of motor patterns [...] Yet it is unclear how the waves of synchronized activity observed in large, heterogeneous populations of enteric neurons during propagating neurogenic contractions are modulated to enable switching to and between all of the motor patterns that occur in different digestive states.

These data support the idea that inherent structural differences in ENS composition and connectivity might be the basis for regional differences in colonic motor patterns and behaviours.

Although all the cellular players essential for neurogenic peristalsis are within the gut, in practice, extrinsic innervation also has a role in modulating intestinal motility.

It has long been appreciated that spinal afferent neurons, with cell bodies located in dorsal root ganglia (DRG) adjacent to the spinal cord, extend projections into the gut wall that form extensive networks around myenteric neurons; however, the functional significance of this innervation is largely unknown.

findings suggest that activation of spinal primary afferent neurons influences myenteric neuronal activity and gut motility indirectly, requiring information transfer through parasympathetic pre-ganglionic neurons in the spinal cord. Not only does this study refute the possibility that extrinsic primary afferents have direct efferent inputs onto myenteric neurons, but it also establishes a new mechanistic basis for how stimuli that activate visceral pain, a sensation mediated by these same extrinsic afferents, might also alter colonic motility.

it is important to also consider cells that do not belong to the host, namely the microbiota.

Previous work has shown that gut microbiota influence ENS development by altering serotonin signaling, and that dietary components can interact with specific microbes to alter gastrointestinal transit times in mice. Probiotics are now commonly used to treat a range of health conditions, including functional gastrointestinal disorders.

These new findings highlight the staggering complexity of intercellular interactions that regulate even the most seemingly simple of phenomena in the gut, the directional movement of luminal contents from ingestion to expulsion.