Fig. 3.
Synergistic effect of 1 or 2 minimum alveolar concentration (MAC) of isoflurane and nitrous oxide on formalin-induced neurokinin 1 receptor (NK1r) internalization. Scattergram presents the percent of NK1r (+) neurons showing internalization after unilateral intraplantar formalin in the ipsilateral and contralateral lumbar (L4–L6) dorsal horn of each animal as a function of receiving pretreatment with a combination of isoflurane at 1 or 2 MAC with N2O (66%). As indicated, either combination significantly reduced NK1r internalization in the ipsilateral dorsal horn compared with saline-treated animals (P < 0.05). The inhibition of NK1r internalization produced by isoflurane (2 MAC) and nitrous oxide (66%) was not reversed by intraperitoneal naloxone (1 mg/kg). Contralateral NK1r internalization in naloxone-treated rats was not evaluated. #Represents a significant difference between ipsilateral and contralateral spinal dorsal horn. *Represents a significant difference between control and treated animal, P < 0.05. ISO (1) = 1 MAC isoflurane; ISO (2) = 2 MAC isoflurane; N2O = nitrous oxide; NLX = naloxone.