27.01 Electrophysiological Characterisation Of Human Visceral Afferent Nerves: First In Man

Posted on December 22, 2014

K. S. Ng1,2, N. A. Montes-Adrian2, D. A. Mahns3,M. A. Gladman1,2 1Academic Colorectal Unit, Sydney Medical School – Concord Hospital Campus, University of Sydney, NSW, Australia. 2Enteric Neuroscience & Gastrointestinal Research Group, ANZAC Research Institute, University of Sydney, Australia 3Department of Integrative Physiology, School of Medicine, University of Western Sydney, NSW, Australia

Introduction:  During the last decade, abnormal afferent activity gained recognition as being important in the development of functional gastrointestinal disorders. Since it is not possible to directly measure visceral afferent activity ‘in vivo’ in humans, in this study we aimed to make direct electrophysiological recordings (in vitro) from extrinsic afferents supplying the human colon and rectum. 

Methods:  SSections of normal rectum and colon were procured from anterior resection and right hemicolectomy specimens, respectively. Sections were pinned flat and mesenteric nerves dissected. Extracellular visceral afferent nerve activity was recorded. Neuronal responses to chemical (capsaicin and ‘inflammatory solution’ [IS]1) and mechanical (Von Frey probing) stimulation were recorded and quantified by determining peak firing rates [range] in onesecond intervals. 

Results: 21 nerves were studied from six rectums. Of these, spontaneous afferent activity was recorded in 18 nerves. Peak discharge rates increased significantly following capsaicin (7 [4-25] spikes/sec vs. 3 [2-6], P=0.001) and IS (5 [3-18] spikes/sec vs. 4 [3-12], P=0.003) application. Punctate mechanosensitive ‘hot-spots’ were identified in 11 nerves (threshold 2.0g [1.4–4.0g]). In six of these, the threshold decreased following IS (1.0g [0.4–1.4g]). By comparison, no ‘hot spots’ were identified and spontaneous activity in only one of 18 nerves studied from five
colons. 

Conclusion:  This is the first study to record from extrinsic rectal afferent nerves and to confirm their chemoand mechanosensitivity. Colonic afferents appear less responsive to mechanical stimulation, suggesting differences in electrophysiological characteristics. This technique offers the opportunity to measure electrophysiological properties of extrinsic nerves in disease states. 

References:  

  1. 10μM each of histamine, serotonin, bradykinin, and prostaglandin E2, as in Feng B, Gebhart GF. Characterization of silent afferents in the pelvic and splanchnic innervations of the mouse colorectum. Am J Physiol Gastrointest Liver Physiol. 2011; 300(1): G170-80.