EFFECTS OF HALOTHANE, KETAMINE AND NITROUS-OXIDE ON DYNORPHIN MESSENGER-RNA EXPRESSION IN DORSAL HORN NEURONS AFTER PERIPHERAL TISSUE-INJURY

Peripheral tissue injury is known to induce changes in gene expression in spinal neurons and result in a prolonged alteration of neuronal ex citability. The purpose of this study was to examine the effect of hal othane on the dynorphin mRNA expression in spinal dorsal horn neurons after peripheral tissue injury by formalin injection and compare the e ffect to that of ketamine and nitrous oxide. Male Sprague-Dawley rats were anesthetized with 1.3% halothane, ketamine, or 67% nitrous oxide. Fifteen minutes after induction of anesthesia, rats received an intra plantar injection of 150 mu l 5% formalin into the unilateral hindpaw. General anesthesia was maintained for 8 h, and the expression of prep rodynorphin (PPD) and preproenkephalin (PPE) mRNAs in the spinal cord (L4-5) was examined by in situ hybridization. The degree of edema of t he inflamed foot was not different among the three anesthesia groups a nd the control (no anesthesia) group. The number of neurons expressing PPD mRNA dramatically increased in the superficial dorsal horn ipsila teral to the formalin injection in the control group compared to the c ontralateral side. The number of neurons labeled for PPD mRNA in the h alothane group was significantly less than the control group. However, the number of PPD mRNA-expressing neurons in both the ketamine and ni trous oxide groups was significantly less than the halothane group. Th e expression of PPE mRNA was not influenced by these anesthetics. Thes e data indicate that the suppressive effect of halothane anesthesia on the induction of PPD mRNA in dorsal horn neurons was smaller than tho se of ketamine and nitrous oxide, suggesting an important supplemental way to control the alteration of gene expression in spinal neurons fo r clinical settings. (C) 1998 Published by Elsevier Science B.V. All r ights reserved.