Use of a novel thermal operant behavioral assay for characterization of orofacial pain sensitivity.
Orofacial pain has been well-characterized clinically, but evaluation of orofacial pain in animals has not kept pace. The objective of this study was to describe behavioral responses to facial thermal stimulation and inflammation with/without an analgesic using a novel operant paradigm. Animals were trained to voluntarily place their face against a stimulus thermode (37.7-57.2 degrees C) providing access to positive reinforcement. These contingencies present a conflict between positive reward and tolerance for nociceptive stimulation. Inflammation was induced and morphine was provided as an analgesic in a subset of animals. Six outcome measures were determined: reward intake, reward licking contacts, stimulus facial contacts, facial contact duration, ratio of reward/stimulus contacts, and ratio of facial contact duration/event. Animals displayed aversive behaviors to the higher temperatures, denoted by a significant decrease in reward intake, total facial contact duration, and reward licking events. The number of facial contacts increased with increasing temperature, replacing long drinking bouts with more frequent short drinks, as reflected by a low ratio of facial contact duration/event. The number of reward licking/facial contact events was significantly decreased as the thermal stimulus intensity increased, providing another pain index derived from this operant method. These outcomes were significantly affected in the direction of increased nociception following inflammation, and these indices of hyperalgesia were reversed with morphine administration. These data reflect an orofacial pain behavior profile that was based on an animal's responses in an operant escape paradigm. This technique allows evaluation of nociceptive processing and modulation throughout the neuraxis.
Department of Orthodontics, College of Dentistry, University of Florida, 1600 SW Archer Road, P.O. Box 100444, Gainesville, FL 32610-0444, USA Department of Oral Surgery, College of Dentistry, University of Florida, Gainesville, FL, USA Department of Neuroscience, College of Medicine, University of Florida, Gainesville, FL, USA Evelyn F. and William L. McKnight Brain Institute, University of Florida, Gainesville, FL, USA.
John K
JK
Neubert
Charles G
CG
Widmer
Wendi
W
Malphurs
Heather L
HL
Rossi
Charles J
CJ
Vierck
Robert M
RM
Caudle
D000701:Analgesics, Opioid / Q000008:administration & dosage; D000818:Animals; D001522:Behavior, Animal; D044723:Chondrus; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology*; D004924:Escape Reaction / Q000187:drug effects / Q000502:physiology; D005145:Face / Q000294:innervation; D005157:Facial Pain / Q000139:chemically induced / Q000188:drug therapy / Q000503:physiopathology*; D006358:Hot Temperature; D008297:Male; D009020:Morphine / Q000008:administration & dosage; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D014276:Trigeminal Nerve / Q000503:physiopathology
D000701:Analgesics, Opioid; D009020:Morphine