• Asunción Romero, Santiago Rojas, David Cabañero, Juan D Gispert, José R Herance, Ana Campillo, and Margarita M Puig.
• Grup de Recerca en Fisiopatologia i Tractament del Dolor, Programa de Neurociències, Department of Anesthesiology, Institut Municipal d'Investigació Mèdica, Hospital del Mar, Universitat Autònoma de Barcelona, Barcelona, Spain.
• Anesthesiology. 2011 Nov 1;115(5):1072-83.

BackgroundNeuroplastic 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.MethodsRats 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-fluorodeoxyglucose (F-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.ResultsSurgery induced minor changes in F-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-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-FDG uptake.ConclusionsSurgery, 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-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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