Opioids are the most powerful analgesics currently used for the treatment of pain, but repeated administration induces tolerance which significantly decreases the analgesic effect of opioids. The general goal of this project is to elucidate the contribution of different types of opioid receptors to the mechanisms of opioid tolerance. The nucleus raphe magnus (NRM) in the medulla is critically implicated in opioid analgesia through its direct projections to the spinal dorsal horn, the first relay for pain transmission. Our previous studies have shown how agonists of the mu-opioid receptor act in the NRM to produce analgesia. Recently we have demonstrated the neural mechanism by which kappa-opioid receptor agonists in the NRM oppose the mu-receptor-mediated analgesia. The hypothesis for the current project is that opioid tolerance results from a functional reduction of the mu-receptor mediated actions and an up-regulation of other endogenous anti-mu systems such as the kappa-receptor system and the GABA transmission system, a major target of inhibitory actions of analgesic opioids. Using the NRM as a model system, the proposed studies are designed to determine the functional changes both in the synaptic properties of NRM neurons and in the actions mediated by mu- and kappa-receptors in opioid-tolerant rats versus opioid-naive rats. Both intracellular/whole-cell patch clamp recording in NRM slices in vitro and NRM microinjection in freely-moving rats in vivo will be used to characterize the cellular mechanisms of the adaptive changes and their behavioral significance in animals. This research will significantly expand our knowledge of the neural mechanisms for opioid tolerance and contribute to our efforts to improve the treatment for chronic pain and other chronic opioid-related problems.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA014524-05
Application #
6878951
Study Section
Integrative, Functional and Cognitive Neuroscience 8 (IFCN)
Program Officer
Thomas, David A
Project Start
2001-05-01
Project End
2007-04-30
Budget Start
2005-05-01
Budget End
2007-04-30
Support Year
5
Fiscal Year
2005
Total Cost
$262,500
Indirect Cost
Name
University of Texas MD Anderson Cancer Center
Department
Anesthesiology
Type
Other Domestic Higher Education
DUNS #
800772139
City
Houston
State
TX
Country
United States
Zip Code
77030
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Zhu, Wei; Bie, Bihua; Pan, Zhizhong Z (2007) Involvement of non-NMDA glutamate receptors in central amygdala in synaptic actions of ethanol and ethanol-induced reward behavior. J Neurosci 27:289-98
Ma, Junyi; Zhang, Yong; Kalyuzhny, Alex E et al. (2006) Emergence of functional delta-opioid receptors induced by long-term treatment with morphine. Mol Pharmacol 69:1137-45
Ma, Junyi; Pan, Zhizhong Z (2006) Contribution of brainstem GABA(A) synaptic transmission to morphine analgesic tolerance. Pain 122:163-73
Bie, Bihua; Peng, Yi; Zhang, Yong et al. (2005) cAMP-mediated mechanisms for pain sensitization during opioid withdrawal. J Neurosci 25:3824-32
Zhu, W; Pan, Z Z (2005) Mu-opioid-mediated inhibition of glutamate synaptic transmission in rat central amygdala neurons. Neuroscience 133:97-103
Bie, Bihua; Pan, Zhizhong Z (2005) Increased glutamate synaptic transmission in the nucleus raphe magnus neurons from morphine-tolerant rats. Mol Pain 1:7
Zhu, W; Pan, Z Z (2004) Synaptic properties and postsynaptic opioid effects in rat central amygdala neurons. Neuroscience 127:871-9
Pan, Zhizhong Z (2003) Opioid tolerance in adult and neonatal rats. Methods Mol Med 84:223-32
Bie, B; Fields, H L; Williams, J T et al. (2003) Roles of alpha1- and alpha2-adrenoceptors in the nucleus raphe magnus in opioid analgesia and opioid abstinence-induced hyperalgesia. J Neurosci 23:7950-7