title: Effect of spinal manipulation thrust magnitude on trunk mechanical activation thresholds of lateral thalamic neurons.
abstract: OBJECTIVE
  High-velocity low-amplitude spinal manipulation (HVLA-SM), as performed by doctors who use manual therapy (eg, doctors of chiropractic and osteopathy), results in mechanical hypoalgesia in clinical settings. This hypoalgesic effect has previously been attributed to alterations in peripheral and/or central pain processing. The objective of this study was to determine whether thrust magnitude of a simulated HVLA-SM alters mechanical trunk response thresholds in wide dynamic range (WDR) and/or nociceptive specific (NS) lateral thalamic neurons.
  
  
  METHODS
  Extracellular recordings were carried out in the thalamus of 15 anesthetized Wistar rats. Lateral thalamic neurons having receptive fields, which included the lumbar dorsal-lateral trunk, were characterized as either WDR (n=22) or NS (n=25). Response thresholds to electronic von Frey (rigid tip) mechanical trunk stimuli were determined in 3 directions (dorsal-ventral, 45° caudalward, and 45° cranialward) before and immediately after the dorsal-ventral delivery of a 100-millisecond HVLA-SM at 3 thrust magnitudes (control, 55%, 85% body weight).
  
  
  RESULTS
  There was a significant difference in mechanical threshold between 85% body weight manipulation and control thrust magnitudes in the dorsal-ventral direction in NS neurons (P=.01). No changes were found in WDR neurons at either HVLA-SM thrust magnitude.
  
  
  CONCLUSIONS
  This study is the first to investigate the effect of HVLA-SM thrust magnitude on WDR and NS lateral thalamic mechanical response threshold. Our data suggest that, at the single lateral thalamic neuron level, there may be a minimal spinal manipulative thrust magnitude required to elicit an increase in trunk mechanical response thresholds.
authors.affiliation: Associate Professor, Palmer Center for Chiropractic Research, Davenport, Iowa. Electronic address: william.reed@palmer.edu.
authors.forename: William R
authors.initials: WR
authors.lastname: Reed
authors.affiliation: Professor Emeritus, Palmer Center for Chiropractic Research, Davenport, Iowa.
authors.forename: Joel G
authors.initials: JG
authors.lastname: Pickar
authors.affiliation: Research Associate, Palmer Center for Chiropractic Research, Davenport, Iowa.
authors.forename: Randall S
authors.initials: RS
authors.lastname: Sozio
authors.affiliation: Professor, Director, Palmer Center of Chiropractic Research, Davenport, Iowa.
authors.forename: Cynthia R
authors.initials: CR
authors.lastname: Long
mesh_terms: D000818:Animals; D004566:Electrodes; D020647:Lateral Thalamic Nuclei / Q000502:physiology*; D008297:Male; D020393:Manipulation, Spinal / Q000379:methods*; D009474:Neurons / Q000502:physiology; D009619:Nociceptors / Q000502:physiology; D017208:Rats, Wistar
keywords: Chiropractic; Lumbar Vertebrae; Nociceptive Neurons; Spinal Manipulation; Thalamus