title: Mechanically evoked cortical potentials: A physiological approach to assessment of anorectal sensory pathways.
abstract: BACKGROUND
  Normal defaecation involves activation of anorectal mechanoreceptors responsive to pressure and stretch. The aim of this study was to develop selective anal and rectal mucosal light-touch stimulation suitable for measurement of cortical evoked potentials (EPs) in order to explore the sensory arm of these pathways.
  
  
  METHODS
  A novel device was manufactured to deliver selective rectal and/or anal light-touch stimulation using a shielded inter-dental brush mounted on a rotating stepper motor (1Hz, 1ms, 15° rotation). Resultant somatosensory EPs recorded with a 32-channel cortical multi-electrode array were compared to those elicited by electrical anorectal stimulation (2mm anal plug electrode [1Hz, 1ms, 10V]).
  
  
  RESULTS
  Eighteen anaesthetized female Wistar rats (body mass 180-250g) were studied. Electrical and mechanical stimulation provoked similar maximal response amplitudes (electrical anorectal 39.0μV[SEM 5.5], mechanical anal 42.2μV[8.1], mechanical rectal 45.8μV[9.0]). Response latency was longer following mechanical stimulation (electrical anorectal 8.8ms[0.5], mechanical anal 16.4ms[1.1], mechanical rectal 18.3ms[2.5]). The extent of activated sensory cortex was smaller for mechanical stimulation. Sensory inferior rectal nerve activity was greater during anal compared to rectal mechanical in a subgroup of 4 rats. Evoked potentials were reproducible over 40min in a subgroup of 9 rats.
  
  
  METHODS
  Cortical EPs are typically recorded in response to non-physiological electrical stimuli. The use of a mechanical stimulus may provide a more localized physiological method of assessment.
  
  
  CONCLUSIONS
  To the authors' knowledge these are the first selective brush-elicited anal and rectal EPs recorded in animals and provide a physiological approach to testing of anorectal afferent pathways.
authors.affiliation: School of Medicine and Medical Science, University College Dublin, Dublin, Ireland; GI Physiology Unit, The Wingate Institute of Neurogastroenterology, Queen Mary University of London, London, United Kingdom; National Centre for Bowel Research and Surgical Innovation (NCRBSI), Queen Mary University of London, London, United Kingdom.
authors.forename: E V
authors.initials: EV
authors.lastname: Carrington
authors.affiliation: School of Medicine and Medical Science, University College Dublin, Dublin, Ireland. Electronic address: judith.evers@ucdconnect.ie.
authors.forename: J
authors.initials: J
authors.lastname: Evers
authors.affiliation: GI Physiology Unit, The Wingate Institute of Neurogastroenterology, Queen Mary University of London, London, United Kingdom; National Centre for Bowel Research and Surgical Innovation (NCRBSI), Queen Mary University of London, London, United Kingdom.
authors.forename: S M
authors.initials: SM
authors.lastname: Scott
authors.affiliation: GI Physiology Unit, The Wingate Institute of Neurogastroenterology, Queen Mary University of London, London, United Kingdom; National Centre for Bowel Research and Surgical Innovation (NCRBSI), Queen Mary University of London, London, United Kingdom.
authors.forename: C H
authors.initials: CH
authors.lastname: Knowles
authors.affiliation: School of Medicine and Medical Science, University College Dublin, Dublin, Ireland; Surgical Professorial Unit, St Vincent's University Hospital, Dublin, Ireland.
authors.forename: P R
authors.initials: PR
authors.lastname: O'Connell
authors.affiliation: School of Medicine and Medical Science, University College Dublin, Dublin, Ireland.
authors.forename: J F X
authors.initials: JF
authors.lastname: Jones
mesh_terms: D001003:Anal Canal / Q000502:physiology*; D000818:Animals; D055615:Electrical Equipment and Supplies; D004867:Equipment Design; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D007413:Intestinal Mucosa / Q000502:physiology; D010812:Physical Stimulation / Q000295:instrumentation / Q000379:methods*; D066330:Printing, Three-Dimensional; D017208:Rats, Wistar; D012007:Rectum / Q000294:innervation / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology*; D014110:Touch / Q000502:physiology; D055698:Touch Perception / Q000502:physiology*
keywords: Anal sensation; Mechanical stimulation; Rectal sensation; Somatosensory cortex; Somatosensory evoked potentials