title: Differential Suppression of Spontaneous and Noxious-evoked Somatosensory Cortical Activity by Isoflurane in the Neonatal Rat.
abstract: BACKGROUND
  The effect of neonatal anesthesia and pain on the developing brain is of considerable clinical importance, but few studies have evaluated noxious surgical input to the infant brain under anesthesia. Herein, the authors tested the effect of increasing isoflurane concentration on spontaneous and evoked nociceptive activity in the somatosensory cortex of rats at different postnatal ages.
  
  
  METHODS
  Intracortical extracellular field potentials evoked by hind paw C-fiber electrical stimulation were recorded in the rat somatosensory cortex at postnatal day (P) 7, P14, P21, and P30 during isoflurane anesthesia (n = 7 per group). The amplitudes of evoked potentials and the energies of evoked oscillations (1 to 100 Hz over 3 s) were measured after equilibration at 1.5% isoflurane and during step increases in inspired isoflurane. Responses during and after plantar hind paw incision were compared at P7 and P30 (n = 6 per group).
  
  
  RESULTS
  At P7, cortical activity was silent at 1.5% isoflurane but noxious-evoked potentials decreased only gradually in amplitude and energy with step increases in isoflurane. The resistance of noxious-evoked potentials to isoflurane at P7 was significantly enhanced after surgical hind paw incision (69 ± 16% vs. 6 ± 1% in nonincised animals at maximum inspired isoflurane). This resistance was age dependent; at P14 to P30, noxious-evoked responses decreased sharply with increasing isoflurane (step 3 [4%] P7: 50 ± 9%, P30: 4 ± 1% of baseline). Hind paw incision at P30 sensitized noxious-evoked potentials, but this was suppressed by higher isoflurane concentrations.
  
  
  CONCLUSIONS
  Despite suppression of spontaneous activity, cortical-evoked potentials are more resistant to isoflurane in young rats and are further sensitized by surgical injury.
authors.affiliation: From the Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom (P.-s.C., M.F.); Pain Research (Respiratory Critical Care and Anaesthesia), UCL Institute of Child Health, London, United Kingdom (S.M.W.); and Department of Anaesthesia and Pain Medicine, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom (S.M.W.).
authors.forename: Pi-shan
authors.initials: PS
authors.lastname: Chang
authors.forename: Suellen M
authors.initials: SM
authors.lastname: Walker
authors.forename: Maria
authors.initials: M
authors.lastname: Fitzgerald
mesh_terms: D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D004558:Electric Stimulation; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D036421:Nerve Fibers, Unmyelinated; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000187:drug effects*
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane