title: Activation of mu-opioid receptors in thalamic nucleus submedius depresses bee venom-evoked spinal c-Fos expression and flinching behavior.
abstract: Previous studies have indicated that mu-opioid receptors in the thalamic nucleus submedius (Sm) are involved in descending antinociception in behavioral tests. The present study examined the effect of mu-opioid receptor activation in the Sm upon bee venom-evoked c-Fos expression in the spinal dorsal horn associated with flinching behavior, and determined whether the ATP-sensitive potassium channel (K-ATP channel) was involved in this effect in a rat model. A dilute bee venom solution, subcutaneously injected unilaterally into a rat hind paw pad, induced significant c-Fos expression in the lumbar spinal dorsal horn, which is associated with paw flinching behavior. This effect was depressed by microinjection of the mu-opioid receptor agonist [d-Ala2, N-MePhe4, Gly-ol5]-enkephalin (DAMGO) into the Sm, which was antagonized by pre-treatment with mu-receptor antagonist beta-funaltrexamine at the same Sm site. Further studies found that glibenclamide, a K-ATP channel inhibitor, also blocked DAMGO-induced inhibition. These results provide functional anatomic support for the involvement of Sm and mu-opioid receptors in the modulation of persistent inflammatory nociception, and suggest that these effects were produced by opening K-ATP channel and inhibiting neuronal activity. Together with previous studies, the inhibition of the neuronal activity induced by mu-opioid receptor activation may activate descending antinociceptive pathways through a GABAergic disinhibitory mechanism and depress the nociceptive information transmission at the level of the spinal cord.
authors.affiliation: Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University, School of Medicine, Yanta Road W. 76#, Xi'an, Shaanxi 710061, PR China.
authors.forename: J
authors.initials: J
authors.lastname: Feng
authors.forename: F Q
authors.initials: FQ
authors.lastname: Huo
authors.forename: N
authors.initials: N
authors.lastname: Jia
authors.forename: C L
authors.initials: CL
authors.lastname: Qu
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: Y Q
authors.initials: YQ
authors.lastname: Li
authors.forename: J-S
authors.initials: JS
authors.lastname: Tang