Search

Abstract Gut motility undergoes a switch from myogenic to neurogenic control in late embryonic development. Here, we report on the electrical events that underlie this transition in the enteric nervous system, using the GCaMP6f reporter in neural crest cell derivatives. We found that spontaneous calcium activity is tetrodotoxin (TTX) resistant at stage E11.5, but not at E18.5. Motility at E18.5 was characterized by periodic, alternating high‐ and low‐frequency contractions of the circular smooth muscle; this frequency modulation was inhibited by TTX. Calcium imaging at the neurogenic‐motility stages E18.5–P3 showed that CaV1.2‐positive neurons exhibited spontaneous calcium activity, which was inhibited by nicardipine and 2‐aminoethoxydiphenyl borate (2‐APB). Our protocol locally prevented muscle tone relaxation, arguing for a direct effect of nicardipine on enteric neurons, rather than indirectly by its relaxing effect on muscle. We demonstrated that the ENS was mechanosensitive from early stages on (E14.5) and that this behaviour was TTX and 2‐APB resistant. We extended our results on L‐type channel‐dependent spontaneous activity and TTX‐resistant mechanosensitivity to the adult colon. Our results shed light on the critical transition from myogenic to neurogenic motility in the developing gut, as well as on the intriguing pathways mediating electro‐mechanical sensitivity in the enteric nervous system. Highlights What is the central question of this study? What are the first neural electric events underlying the transition from myogenic to neurogenic motility in the developing gut, what channels do they depend on, and does the enteric nervous system already exhibit mechanosensitivity? What is the main finding and its importance? ENS calcium activity is sensitive to tetrodotoxin at stage E18.5 but not E11.5. Spontaneous electric activity at fetal and adult stages is crucially dependent on L‐type calcium channels and IP3R receptors, and the enteric nervous system exhibits a tetrodotoxin‐resistant mechanosensitive response. Abstract figure legend Tetrodotoxin‐resistant Ca2+ rise induced by mechanical stimulation in the E18.5 mouse duodenum.

Gut motility undergoes a switch from myogenic to neurogenic control in late embryonic development. Here, we report on the electrical events that underlie this transition in the enteric nervous system, using the GCaMP6f reporter in neural crest cell derivatives. We found that spontaneous calcium activity is tetrodotoxin (TTX) resistant at stage E11.5, but not at E18.5. Motility at E18.5 was characterized by periodic, alternating high‐ and low‐frequency contractions of the circular smooth muscle; this frequency modulation was inhibited by TTX. Calcium imaging at the neurogenic‐motility stages E18.5–P3 showed that CaV1.2‐positive neurons exhibited spontaneous calcium activity, which was inhibited by nicardipine and 2‐aminoethoxydiphenyl borate (2‐APB). Our protocol locally prevented muscle tone relaxation, arguing for a direct effect of nicardipine on enteric neurons, rather than indirectly by its relaxing effect on muscle. We demonstrated that the ENS was mechanosensitive from early stages on (E14.5) and that this behaviour was TTX and 2‐APB resistant. We extended our results on L‐type channel‐dependent spontaneous activity and TTX‐resistant mechanosensitivity to the adult colon. Our results shed light on the critical transition from myogenic to neurogenic motility in the developing gut, as well as on the intriguing pathways mediating electro‐mechanical sensitivity in the enteric nervous system. Highlights: What is the central question of this study?What are the first neural electric events underlying the transition from myogenic to neurogenic motility in the developing gut, what channels do they depend on, and does the enteric nervous system already exhibit mechanosensitivity?What is the main finding and its importance?ENS calcium activity is sensitive to tetrodotoxin at stage E18.5 but not E11.5. Spontaneous electric activity at fetal and adult stages is crucially dependent on L‐type calcium channels and IP3R receptors, and the enteric nervous system exhibits a tetrodotoxin‐resistant mechanosensitive response. Abstract figure legend Tetrodotoxin‐resistant Ca2+ rise induced by mechanical stimulation in the E18.5 mouse duodenum. [ABSTRACT FROM AUTHOR]

Peristalsis enables transport of the food bolus in the gut. Here, I show by dynamic ex vivo intra-cellular calcium imaging on living embryonic gut explants that the most primitive form of peristalsis that occurs in the embryo is the result of inter-cellular, gap-junction-dependent calcium waves that propagate in the circular smooth muscle layer. I show that the embryonic gut is an intrinsically mechanosensitive organ, as the slightest externally applied mechanical stimulus triggers contractile waves. This dynamic response is an embryonic precursor of the 'law of the intestine' (peristaltic reflex). I show how characteristic features of early peristalsis such as counter-propagating wave annihilation, mechanosensitivity and nucleation after wounding all result from known properties of calcium waves. I finally demonstrate that inter-cellular mechanical tension does not play a role in the propagation mechanism of gut contractile waves, unlike what has been recently shown for the embryonic heartbeat. Calcium waves are a ubiquitous dynamic signalling mechanism in biology: here I show that they are the foundation of digestive movements in the developing embryo. This article is part of the Theo Murphy meeting issue on 'Mechanics of development'. [ABSTRACT FROM AUTHOR]

To investigate relationships between changes in the 3-dimensional structure of the myenteric plexus and the time at which functional movement of intestine begins in mammalian embryos, whole mounts of embryonic rat intestine were examined under confocal laser scanning microscopy on spacer-equipped glass slides after immunostaining with antiprotein gene product 9.5 antibody. At embryonic day 12.5, very few nerve cells were scattered throughout the small intestine, but no immunostained structures were apparent on the anal side of the large intestine. At embryonic day 13.5, immunostained fibers appeared on the oral side of the large intestine. Nerve cells and associated fiber bundles formed neuronal networks with large meshes in both intestines. Marked increases in number of nerve fibers and decreases in mesh size were seen in the small intestine between embryonic days 13.5 and 15.5. Similar changes were found in the large intestine between embryonic days 13.5 and 16.5. After embryonic day 16.5, nerve cells were arranged parallel to circular muscle fibers, and networks formed by cell fibers elongated until the neonatal period in both intestines. Meconium passed through the large intestine from embryonic day 17.5. Thin fiber bundles extended from the ganglion to the inner side of the myenteric layer, parallel (and occasionally extending) to the circular muscle fibers. Formation of nerve fiber networks and arrangement of nerve cells parallel to circular muscle fibers probably relate to movement coordination for inner circular muscle fibers in the intestinal wall, and development of this neural network may be important for acquiring intestinal movements before birth. [ABSTRACT FROM AUTHOR]