ABSTRACT
Background and Aims: Viscerofugal neurons (VFNs) have cell bodies in the myenteric plexus and axons that project to sympathetic prevertebral ganglia. In animals they activate sympathetic motility reflexes and may modulate glucose metabolism and feeding. We used rapid retrograde tracing from colonic nerves to identify VFNs in human colon for the first time, using ex vivo preparations with multi-layer immunohistochemistry. Methods: Colonic nerves were identified in isolated preparations of human colon and set up for axonal tracing with biotinamide. After fixation, labeled VFN cell bodies were subjected to multiplexed immunohistochemistry for 12 established nerve cell body markers. Results: Biotinamide tracing filled 903 viscerofugal nerve cell bodies (n = 23), most of which (85%) had axons projecting orally before entering colonic nerves. Morphologically, 97% of VFNs were uni-axonal. Of 215 VFNs studied in detail, 89% expressed ChAT, 13% NOS, 13% calbindin, 9% enkephalin, 7% substance P and 0 of 123 VFNs expressed CART. Few VFNs contained calretinin, VIP, 5HT, CGRP, or NPY. VFNs were often surrounded by dense baskets of axonal varicosities, probably reflecting patterns of connectivity; VAChT+ (cholinergic), SP+ and ENK+ varicosities were most abundant around them. Human VFNs were diverse; showing 27 combinations of immunohistochemical markers, 4 morphological types and a wide range of cell body sizes. However, 69% showed chemical coding, axonal projections, soma-dendritic morphology and connectivity similar to enteric excitatory motor neurons. Conclusion: Viscerofugal neurons are present in human colon and show very diverse combinations of features. High proportions express ChAT, consistent with cholinergic synaptic outputs onto postganglionic sympathetic neurons in prevertebral ganglia.
ABSTRACT
Cyclical propagating waves of muscle contraction have been recorded in isolated small intestine or colon, referred to here as motor complexes (MCs). Small intestinal and colonic MCs are neurogenic, occur at similar frequencies, and propagate orally or aborally. Whether they can be coordinated between the different gut regions is unclear. Motor behavior of whole length mouse intestines, from duodenum to terminal rectum, was recorded by intraluminal multisensor catheter. Small intestinal MCs were recorded in 27/30 preparations, and colonic MCs were recorded in all preparations (n = 30) with similar frequencies (0.54 ± 0.03 and 0.58 ± 0.02 counts/min, respectively). MCs propagated across the ileo-colonic junction in 10/30 preparations, forming "full intestine" MCs. The cholinesterase inhibitor physostigmine increased the probability of a full intestine MC but had no significant effect on frequency, speed, or direction. Nitric oxide synthesis blockade by Nω-nitro-l-arginine, after physostigmine, increased MC frequency in small intestine only. Hyoscine-resistant MCs were recorded in the colon but not small intestine (n = 5). All MCs were abolished by hexamethonium (n = 18) or tetrodotoxin (n = 2). The enteric neural mechanism required for motor complexes is present along the full length of both the small and large intestine. In some cases, colonic MCs can be initiated in the distal colon and propagate through the ileo-colonic junction, all the way to duodenum. In conclusion, the ileo-colonic junction provides functional neural continuity for propagating motor activity that originates in the small or large intestine.NEW & NOTEWORTHY Intraluminal manometric recordings revealed motor complexes can propagate antegradely or retrogradely across the ileo-colonic junction, spanning the entire small and large intestines. The fundamental enteric neural mechanism(s) underlying cyclic motor complexes exists throughout the length of the small and large intestine.
