Pain in a Balance: Noxious Events Engage Opposing Processes That Concurrently Modulate Nociceptive Reactivity

• Published in: Behavioral neuroscience 2004-12, Vol.118 (6), p.1418-1426
• Main Authors: Crown, Eric D, Grau, James W, Meagher, Mary W
• Format: Article
• Language: English
• Subjects: Afferent Pathways - drug effects; Analysis of Variance; Anatomical correlates of behavior; Anatomy & physiology; Animal; Animals; Aversive Stimulation; Behavior, Animal; Behavioral psychophysiology; Biological and medical sciences; Brain; Electroshock - adverse effects; Fundamental and applied biological sciences. Psychology; Male; Naltrexone - administration & dosage; Narcotic Antagonists; Neural Inhibition - physiology; Neurology; Nociceptors - physiology; Pain; Pain - physiopathology; Pain - prevention & control; Pain Measurement - methods; Pain Perception; Pain Threshold - physiology; Physical Stimulation - methods; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rats; Rats, Sprague-Dawley; Reaction Time; Reaction Time - drug effects; Reaction Time - physiology; Reflexes; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Spinal Cord - physiopathology; Studies; Vertebrates: nervous system and sense organs; Vocalization, Animal - drug effects; Vocalization, Animal - physiology
• ISSN: 0735-7044; 1939-0084
• DOI: 10.1037/0735-7044.118.6.1418

Studies have shown that noxious cutaneous stimulation engages physiologically different antinociceptive systems to inhibit a spinal reflex, tail withdrawal from radiant heat. Two experiments are reported that examine the relationship between the inhibition of the tail-flick response and brain-mediated responses to nociception. The induction of a spinally mediated antinociception was accompanied by an increase in latency to vocalize to a noxious thermal stimulus, suggesting pain inhibition. Physiological manipulations that eliminated the inhibition of the tail-flick reflex restored vocalization to thermal stimulation and revealed a concurrent sensitization that generally heightened behavioral reactivity. The results suggest that net pain is regulated by 2 opposing processes, a selective inhibition of nociceptive signals within the spinal cord and a general sensitization that heightens stimulus processing.