THE periaqueductal gray (PAG) and rostral ventrome-dial medulla (RVM) are important brain stem pain modulating regions. Recent evidence suggests that κ opioids antagonize the effects of μ opioids in the RVM. However, the anatomical relationship between μ and κ opioid receptors in PAG and RVM is not well characterized. This study examined relationships between μ and κ opioid receptor immunoreactivity (IR) and mRNA in PAG and RVM. Brain slices were processed for either immunocytochemistry or in situ hybridization. We found considerable anatomical overlap of μ and κ opioid IR and mRNA in the RVM and PAG. These results provide an anatomical basis for recent behavioral and electrophysiological findings in RVM, and suggest modulatory interactions between μ and κ opioids in PAG.
1Mental Health Research Institute, The University of Michigan, 205 Zina Pitcher Place, Ann Arbor, MI 48109-0720
2Departments of Neurology, Physiology and the Keck Center for Integrative Neuroscience, The University of California, San Francisco, CA 94143, USA.
3Corresponding Author: Howard B. Gutstein
ACKNOWLEDGEMENTS: This work was supported by NIH grants DA 00223 (to H.B.G.), DA 022675, DA 08920 (to H.A. and S.J.W.), and NS 21445 (to H.L.F.). The authors thank Sharon Burke for outstanding technical assistance.
Received 19 February 1998; accepted 8 March 1998