Sjh Brookes

Dissociation of the ascending excitatory reflex from peristalsis in the guinea-pig small intestine

Localized distension of the intestine evokes an ascending excitatory reflex and a descending inhibitory reflex in the circular muscle layer. The sequential activation of these two reflexes is believed to underlie the motor pattern of peristalsis, which is responsible for the co-ordinated propulsion of intestinal contents. In this study we have shown that the initiation of peristalsis involves mechanisms additional to those mediating the ascending excitatory reflex. A short length of guinea-pig small intestine was mounted in a partitioned organ bath so that the lumen was occluded by the partition, but neuronal continuity was maintained. The anal segment was distended by intraluminal fluid infusion to evoke a peristalsis; in the oral segment, an isotonic transducer was used to record circular muscle contractions due to ascending excitatory reflexes. Stepwise distension of the anal segment with 5 microliters increments at 10 s intervals, or with a large, single-step infusion, elicited both the ascending excitatory reflex and peristalsis, when carried out at 3 min intervals. The threshold volume for the ascending excitatory reflex was smaller than the threshold for peristalsis with either incremental or single-step distensions. The ascending excitatory reflex appeared with a shorter delay than peristalsis. Tetrodotoxin (0.6 microM) or hexamethonium (100 microM) added to the oral compartment abolished the ascending excitatory reflex but not peristalsis. These drugs abolished both the ascending excitatory reflex and peristalsis when added to the anal compartment. When stimuli were delivered at 1 min intervals, peristalsis failed completely after the first trial, but the ascending excitatory reflex persisted, at a slightly reduced amplitude. When the anal segment was distended to just-subthreshold volume, electrical field stimulation (0.25-0.5 ms, 1-5 Hz for 1 s), delivered at 3 min intervals, evoked ascending excitatory responses but not peristalsis. Higher frequency stimulation (10 Hz) consistently evoked both peristalsis and the ascending excitatory responses. When trains of electrical stimulation were repeated at 1 min intervals, peristalsis quickly failed, but the ascending excitatory response persisted, although reduced in amplitude. The initiation of peristalsis can be dissociated from the ascending excitatory reflex by its threshold volume, by the duration of distension or the intensity of electrical stimulation required, and by its susceptibility to fatigue with repeated mechanical or electrical stimuli. This suggests that the ascending excitatory reflex may be part of the mechanism underlying the initiation of peristalsis, but that additional mechanisms must also be involved. Peristalsis should not be regarded as a reflex response but rather as an all-or-nothing motor pattern, triggered by mechanical stimulation, similar to other co-ordinated motor patterns in vertebrates and invertebrates.

Spontaneous release of acetylcholine from autonomic nerves in the bladder

Background and purpose:  Bladder contractility is regulated by intrinsic myogenic mechanisms interacting with autonomic nerves. In this study, we have investigated the physiological role of spontaneous release of acetylcholine in guinea pig and rat bladders.

A teaching module on cellular control of small intestinal motility

*Department of Human Physiology and Centre for Neuroscience, Flinders University, Bedford Park, South Australia Department of Gastroenterology, The St George Hospital, University of New South Wales, Kogarah, New South Wales, Australia Department of Internal Medicine and Gastroenterology, University of Bologna, Italy§Department of Gastroenterology, Hepatology and General Medicine, Royal Adelaide Hospital, South Australia, Australia–Department of Biomedical Science, The University of Sheffield, Sheffield, UK**Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno Nevada, USA Department of Human Biology, Center of Life and Food Sciences, Technical University Munich, Freising-Weihenstephan,Germany Mucosal Biology Research Center, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA§§Department of Physiological and Pharmacological Sciences, University of Pavia, Pavia, Italy

Human enteric neurons: morphological, electrophysiological, and neurochemical identification

Access to tissue, difficulties with dissection, and poor visibility of enteric ganglia have hampered electrophysiological recordings of human enteric neurons. Here, we report a method to combine intracellular recording with simultaneous morphological identification of neurons in the intact myenteric plexus of human colon ex vivo.

Regeneration of nerve fibres across a colonic anastomosis in the guinea-pig

Resection and re‐anastomosis of the bowel interrupts enteric neuronal pathways. The re‐establishment of neuronal connections across a colonic anastomosis was studied using immunohistochemical, retrograde tracing and physiological techniques. In control guinea‐pig proximal colon, retrograde labelling with 1,1′‐didodecyl‐3,3,3,3′‐tetramethylindocarbocyanine perchlorate (DiI) revealed that enteric neurons with anally‐directed projections are more numerous and have longer axons than orally‐projecting neurons. In resected bowel, up to 26 weeks after re‐anastomosis, descending neuronal pathways were substantially interrupted. Immunohistochemical labelling of nerve fibres revealed that some enteric nerve fibres did regenerate across narrow regions of the anastomosis, growing preferentially in the oral to anal direction. However, nerve fibres immunoreactive for neurofilament protein triplet were substantially depleted in myenteric ganglia anal to the anastomosis, even after the longest recovery periods, demonstrating that axonal regrowth was limited. This was confirmed in retrograde tracing studies, as no nerve cell bodies oral to an anastomosis were labelled when DiI was placed on myenteric ganglia just anal to the anastomosis. Physiological studies confirmed that regrowth of nerve fibres across the anastomosis occurred and that it was asymmetric, as electrical stimulation led to aboral conduction across the anastomosis more reliably than oral conduction, as measured by circular muscle contraction. After resection and re‐anastomosis of the colon, the disruption of neuronal pathways in the enteric nervous system was observed, with limited and preferential re‐establishment of aborally‐directed long connections.

Discriminating movements of liquid and gas in the rabbit colon with impedance manometry

High‐resolution impedance manometry is a technique that is well established in esophageal motility studies for relating motor patterns to bolus flow. The use of this technique in the colon has not been established.

ANTI‐HUMAN NEURONAL PROTEIN – A NEW TOOL FOR QUANTIFICATION OF NEURONES IN THE HUMAN ENTERIC NERVOUS SYSTEM

Understanding how the enteric nervous system controls gastrointestinal function requires an account of the different classes of nerve cells present in the gut wall. Accurately quantifying immunohistochemically identified neurones, would make it possible to characterize changes underlying disorders such as slow transit constipation. Until now, quantification of classes of neurones has relied on antisera to Neuron Specific Enolase (NSE) or Protein Gene Product 9.5 (PGP9.5), however, both stain nerve fibres, making accurate counting of cell bodies unreliable. Anti‐Human Neuronal Protein Antibodies (Hu) were originally isolated from patients with paraneoplastic encephalomyelitis and paraneoplastic neuropathies and have been tested here as a marker for all neurons in the human myenteric plexus.