Gastrointestinal mechanosensors: analysis of multiple stimuli may require complex sensors.

摘要

Visceral afferents are believed to monitor many internal parameters in the gut, to elicit local axonal reflex responses - via intrinsic or extrinsic primary afferent collaterals - and/or to convey information towards the central nervous system to maintain a coordinated motility programme and to keep up with energy balance and fluid homeostasis. One particular subclass of receptors, i.e. those involved in mechanosensitive pathways, will transmit at different time points information on the physical properties of the gut, such as tension, pressure and stretch, to the brain. Apart from the branching varicose mucosal free endings, which have been described as mainly mechano- and chemo-sensitive but for which recent evidence is available to assign an additional nociceptive role, at least to some of them, two additional sensory structures have been identified, namely (i) varicose branching nerve processes running within the outer muscle layers and referred to as intramuscular arrays (IMAs) and (ii) flattened branching nerve endings creating leafy extensions within myenteric ganglia and referred to as intraganglionic laminar endings (IGLEs; for review). Polymorphic hybrid receptor-like structures, exhibiting multiple collaterals that terminate both as IMAs and as IGLEs, have occasionally been described as well. A method combining dextran labelling of IMAs and IGLEs with electron microscopy, presented byPowley et al. in this issue of Neurogastroenterology and Motility, offers further perspectives to study the relationship between vagal afferents and their target cells and, more in particular, the hypothesized role of intramuscular interstitial cells of Cajal (ICC-IM) in mechanoreceptive pathways.