Journal
ANESTHESIOLOGY
Volume 115, Issue 5, Pages 1072-1083Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1097/ALN.0b013e31823425f2
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Funding
- Fondo de Investigacion Sanitaria, Instituto de Salud Carlos III (Madrid, Spain) [PI060669, PS09/01270]
- Marato de Televisio de Catalunya TV3 (Barcelona, Spain) [071110]
- Endowed Chair in Pain Management Universitat Autonoma de Barcelona, Parc de Salut Mar-Menarini, Barcelona, Spain
- Spanish Ministry of Education (Madrid, Spain) [AP2006-4718]
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Background: Neuroplastic changes involved in latent pain sensitization after surgery are poorly defined. We assessed temporal changes in glucose brain metabolism in a postoperative rat model using positron emission tomography. We also investigated brain metabolism after naloxone administration. Methods: Rats were given remifentanil anesthetic and underwent a plantar incision, with 1 mg/kg of (-)-naloxone subcutaneously administered on postoperative days 20 and 21. Using the von Frey test, mechanical thresholds were measured pre- and postoperatively at different time points in awake animals during F-18-fluorodeoxyglucose (F-18-FDG) uptake. Brain images were also obtained the day before mechanical testing, using a positron emission tomography R4 scanner (Concorde Microsystems, Siemens, Knoxville, TN). Differences in brain activity were assessed utilizing a statistical parametric mapping. Results: Surgery induced minor changes in F-18-FDG uptake in the cerebellum, hippocampus, and posterior cortex, which extended to the thalamus, hypothalamus, and brainstem on days 6 and 7. Changes were still present on day 21. Maximal postoperative hypersensitivity was observed on day 2. The administration of (-)-naloxone on day 21 induced significant hypersensitivity, greatly enhancing the effect on F-18-FDG uptake. In sham-operated rats, naloxone induced changes limited to the striatum and the cerebellum. Nonnociceptive stimulation with von Frey filaments had no effect on F-18-FDG uptake. Conclusions: Surgery, remifentanil, and their combination induced long-lasting and significant metabolic changes in the pain brain matrix, with a positive correlation with hypersensitivity after naloxone. Changes in brain F-18-FDG precipitated by naloxone suggest that surgery under remifentanil anesthetic induces the greatest neuroplastic brain adaptations in opioid-related pathways involved in nociceptive processing and long-lasting pain sensitization.
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