title: Measurement of strains experienced by viscerofugal nerve cell bodies during mechanosensitive firing using digital image correlation.
abstract: Mechanosensory neurons detect physical events in the local environments of the tissues that they innervate. Studies of mechanosensitivity of neurons or nerve endings in the gut have related their firing to strain, wall tension, or pressure. Digital image correlation (DIC) is a technique from materials engineering that can be adapted to measure the local physical environments of afferent neurons at high resolution. Flat-sheet preparations of guinea pig distal colon were set up with arrays of tissue markers in vitro. Firing of single viscerofugal neurons was identified in extracellular colonic nerve recordings. The locations of viscerofugal nerve cell bodies were inferred by mapping firing responses to focal application of the nicotinic receptor agonist 1,1-dimethyl-4-phenylpiperazinium iodide. Mechanosensory firing was recorded during load-evoked uniaxial or biaxial distensions. Distension caused movement of surface markers which was captured by video imaging. DIC tracked the markers, interpolating the mechanical state of the gut at the location of the viscerofugal nerve cell body. This technique revealed heterogeneous load-evoked strain within preparations. Local strains at viscerofugal nerve cell bodies were usually smaller than global strain measurements and correlated more closely with mechanosensitive firing. Both circumferential and longitudinal strain activated viscerofugal neurons. Simultaneous loading in circumferential and longitudinal axes caused the highest levels of viscerofugal neuron firing. Multiaxial strains, reflecting tissue shearing and changing area, linearly correlated with mechanosensory firing of viscerofugal neurons. Viscerofugal neurons were mechanically sensitive to both local circumferential and local longitudinal gut strain, and appear to lack directionality in their stretch sensitivity.
authors: Bioengineering Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, United Kingdom.
authors: Gwen
authors: G
authors: Palmer
authors: Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, Australia; and.
authors: Timothy J
authors: 0000-0002-3747-140X
authors: TJ
authors: Hibberd
authors: Bioengineering Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, United Kingdom.
authors: Tiina
authors: T
authors: Roose
authors: Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, Australia; and simon.brookes@flinders.edu.au.
authors: Simon J H
authors: SJ
authors: Brookes
authors: School of Computer Science, Engineering and Mathematics, Flinders University, Adelaide, Australia.
authors: Mark
authors: M
authors: Taylor
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D003106:Colon / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D008297:Male; D008465:Mechanoreceptors / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018722:Nicotinic Agonists / Q000494:pharmacology
chemical_list: D018722:Nicotinic Agonists; D004246:Dimethylphenylpiperazinium Iodide
keywords: afferent; biomechanics; digital image correlation; mechanosensory; strain; viscerofugal