title: Naloxone inhibits not only stress-induced analgesia but also sympathetic activation and baroreceptor-reflex sensitivity.
abstract: Interactions between the sympathetic nervous system and pain are manifold and still have not been sufficiently characterized. Accordingly, several possible neuronal pathways have been described as being involved in mental stress-induced analgesia. We studied the role of the endogenous opioidergic system in stress-induced analgesia in 14 healthy participants in a double-blind cross-over trial. Naloxone or placebo was applied while electrical pain stimulation was started and electrical current increased. After reaching a constant stimulation at 30 mA, a color word interference test (Stroop task) was performed in a stressful and a non-stressful version. Blood pressure, heart rate and baroreflex sensitivity were continuously recorded to assess autonomic activation. Each participant was tested with naloxone and placebo with a randomized and balanced order of trials. The major results are that the opioid-receptor antagonist naloxone prevented (1) stress-induced reduction of tonic current-induced pain, (2) attenuated the simultaneous activation of the sympathetic nervous system, and (3) reduced the counteraction of sympathetic activation by vagal baroreceptor mechanisms. Thus, the opioidergic system not only modulates nociceptive input but also the interplay with vegetative responses. We conclude that acute stress, sympathetic activation and analgesia might be linked via vagal reflexes, which are disturbed when opioid receptors are blocked. This mechanism might underlie increased perception of noxious stimuli in patients with chronic pain or mood disorders.
authors: Department of Neurology, University Medical Center of the Johannes Gutenberg-University Mainz, Langenbeckstrasse 1, D-55101, Mainz, Germany. fechir@uni-mainz.de
authors: M
authors: M
authors: Fechir
authors: M
authors: M
authors: Breimhorst
authors: S
authors: S
authors: Kritzmann
authors: C
authors: C
authors: Geber
authors: T
authors: T
authors: Schlereth
authors: B
authors: B
authors: Baier
authors: F
authors: F
authors: Birklein
mesh_terms: D000328:Adult; D000698:Analgesia / Q000523:psychology*; D017704:Baroreflex / Q000187:drug effects*; D001519:Behavior; D001794:Blood Pressure / Q000187:drug effects; D004311:Double-Blind Method; D004558:Electric Stimulation; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009483:Neuropsychological Tests; D010146:Pain / Q000503:physiopathology* / Q000523:psychology*; D010147:Pain Measurement; D011930:Reaction Time / Q000187:drug effects; D012039:Regional Blood Flow / Q000502:physiology; D013315:Stress, Psychological / Q000523:psychology*; D057190:Stroop Test; D013564:Sympathetic Nervous System / Q000187:drug effects*; D055815:Young Adult
chemical_list: D009292:Narcotic Antagonists; D009270:Naloxone