Source Paper
Chronic Morphine Induces Downregulation of Spinal Glutamate Transporters: Implications in Morphine Tolerance and Abnormal Pain Sensitivity
Jianren Mao, Backil Sung, Ru-Rong Ji, Grewo Lim
Journal of Neuroscience • 2002
Source Paper
Jianren Mao, Backil Sung, Ru-Rong Ji, Grewo Lim
Journal of Neuroscience • 2002
Tolerance to the analgesic effects of an opioid occurs after its chronic administration, a pharmacological phenomenon that has been associated with the development of abnormal pain sensitivity such as hyperalgesia. In the present study, we examined the role of spinal glutamate transporters (GTs) in the development of both morphine tolerance and associated thermal hyperalgesia. Chronic morphine administered through either intrathecal boluses or continuous infusion induced a dose-dependent downregulation of GTs (EAAC1 and GLAST) in the rat's superficial spinal cord dorsal horn. This GT downregulation was mediated through opioid receptors because naloxone blocked such GT changes. Morphine-induced GT downregulation reduced the ability to maintain in vivo glutamate homeostasis at the spinal level, because the hyperalgesic response to exogenous glutamate was enhanced, including an increased magnitude and a prolonged time course, in morphine-treated rats with reduced spinal GTs. Moreover, the downregulation of spinal GTs exhibited a temporal correlation with the development of morphine tolerance and thermal hyperalgesia. Consistently, the GT inhibitor l-trans-pyrrolidine-2-4-dicarboxylate (PDC) potentiated, whereas the positive GT regulator riluzole reduced, the development of both morphine tolerance and thermal hyperalgesia. The effects from regulating spinal GT activity by PDC were at least in part mediated through activation of the NMDA receptor (NMDAR), because the noncompetitive NMDAR antagonist MK-801 blocked both morphine tolerance and thermal hyperalgesia that were potentiated by PDC. These results indicate that spinal GTs may contribute to the neural mechanisms of morphine tolerance and associated abnormal pain sensitivity by means of regulating regional glutamate homeostasis.
Objective: Examine the role of spinal glutamate transporters in the development of morphine tolerance and associated thermal hyperalgesia, and evaluate effects of glutamate transporter inhibitor PDC and positive regulator riluzole on these phenomena
This is a Glutamate Transporter Inhibitor (PDC) and Regulator (Riluzole) Effects protocol using rat as the model organism. The procedure involves 8 procedural steps, 6 materials. Extracted from a 2002 paper published in Journal of Neuroscience.
Model and subjects
rat • Not specified • unknown • Not specified • Not specified
Study window
Estimated timing pending
Core workflow
Chronic morphine administration • Assess glutamate transporter downregulation • Verify opioid receptor mediation with naloxone
Primary readouts
Key equipment and reagents
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Administer morphine chronically to rats through either intrathecal boluses or continuous infusion to induce dose-dependent downregulation of glutamate transporters
Note: Two administration routes tested: intrathecal boluses or continuous infusion
“Chronic morphine administered through either intrathecal boluses or continuous infusion induced a dose-dependent downregulation of GTs (EAAC1 and GLAST) in the rat's superficial spinal cord dorsal horn”
Measure downregulation of glutamate transporters EAAC1 and GLAST in the superficial spinal cord dorsal horn following morphine treatment
Note: Downregulation is mediated through opioid receptors
“Chronic morphine administered through either intrathecal boluses or continuous infusion induced a dose-dependent downregulation of GTs (EAAC1 and GLAST) in the rat's superficial spinal cord dorsal horn”
Administer naloxone to verify that glutamate transporter downregulation is mediated through opioid receptors
Note: Naloxone should block glutamate transporter changes
“This GT downregulation was mediated through opioid receptors because naloxone blocked such GT changes”
Evaluate the ability to maintain in vivo glutamate homeostasis at the spinal level by measuring hyperalgesic response to exogenous glutamate in morphine-treated rats with reduced spinal glutamate transporters
Note: Enhanced hyperalgesic response indicates impaired glutamate homeostasis
“the hyperalgesic response to exogenous glutamate was enhanced, including an increased magnitude and a prolonged time course, in morphine-treated rats with reduced spinal GTs”
Measure the temporal correlation between spinal glutamate transporter downregulation and the development of morphine tolerance and thermal hyperalgesia
Note: Temporal correlation should be established between all three phenomena
“the downregulation of spinal GTs exhibited a temporal correlation with the development of morphine tolerance and thermal hyperalgesia”
Administer glutamate transporter inhibitor PDC and measure its effects on the development of morphine tolerance and thermal hyperalgesia
Note: PDC should potentiate both morphine tolerance and thermal hyperalgesia development
“the GT inhibitor l-trans-pyrrolidine-2-4-dicarboxylate (PDC) potentiated, whereas the positive GT regulator riluzole reduced, the development of both morphine tolerance and thermal hyperalgesia”
Administer positive glutamate transporter regulator riluzole and measure its effects on the development of morphine tolerance and thermal hyperalgesia
Note: Riluzole should reduce both morphine tolerance and thermal hyperalgesia development
“the GT inhibitor l-trans-pyrrolidine-2-4-dicarboxylate (PDC) potentiated, whereas the positive GT regulator riluzole reduced, the development of both morphine tolerance and thermal hyperalgesia”
Administer noncompetitive NMDA receptor antagonist MK-801 to determine if PDC effects are mediated through NMDA receptor activation
Note: MK-801 should block both morphine tolerance and thermal hyperalgesia potentiated by PDC
“the noncompetitive NMDAR antagonist MK-801 blocked both morphine tolerance and thermal hyperalgesia that were potentiated by PDC”
This section explains what the experiment is doing, which readouts matter, what the data artifacts usually look like, and how the analysis should flow from raw capture to reported result.
Examine the role of spinal glutamate transporters in the development of morphine tolerance and associated thermal hyperalgesia, and evaluate effects of glutamate transporter inhibitor PDC and positive regulator riluzole on these phenomena
Objective
Examine the role of spinal glutamate transporters in the development of morphine tolerance and associated thermal hyperalgesia, and evaluate effects of glutamate transporter inhibitor PDC and positive regulator riluzole on these phenomena
Subjects
From paperrat • Not specified • unknown • Not specified • Not specified
Cohort notes
From paperNot specified
Chronic morphine administration (Not specified)
Assess glutamate transporter downregulation (Not specified)
Verify opioid receptor mediation with naloxone (Not specified)
Test glutamate homeostasis maintenance (Not specified)
Downregulation of glutamate transporters EAAC1 and GLAST in superficial spinal cord dorsal horn
From paperNot specified
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Morphine tolerance development
From paperNot specified
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Thermal hyperalgesia development
From paperNot specified
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Hyperalgesic response to exogenous glutamate (magnitude and time course)
From paperNot specified
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Downregulation of glutamate transporters EAAC1 and GLAST in superficial spinal cord dorsal horn
From paperRaw artifact
Per-sample or per-animal endpoint measurements collected during the experiment
Processed artifact
Structured table with cleaned measurements ready for comparison
Final reported form
Summary statistics and between-group or across-timepoint comparisons
Morphine tolerance development
From paperRaw artifact
Per-sample or per-animal endpoint measurements collected during the experiment
Processed artifact
Structured table with cleaned measurements ready for comparison
Final reported form
Summary statistics and between-group or across-timepoint comparisons
Thermal hyperalgesia development
From paperRaw artifact
Per-sample or per-animal endpoint measurements collected during the experiment
Processed artifact
Structured table with cleaned measurements ready for comparison
Final reported form
Summary statistics and between-group or across-timepoint comparisons
Hyperalgesic response to exogenous glutamate (magnitude and time course)
From paperRaw artifact
Per-sample or per-animal endpoint measurements collected during the experiment
Processed artifact
Structured table with cleaned measurements ready for comparison
Final reported form
Summary statistics and between-group or across-timepoint comparisons
Acquisition
Collect raw experimental outputs with enough metadata to preserve sample identity, condition, and timing.
Preprocessing / cleaning
Not specified
Scoring or quantification
Quantify the primary readouts for this experiment: Downregulation of glutamate transporters EAAC1 and GLAST in superficial spinal cord dorsal horn; Morphine tolerance development; Thermal hyperalgesia development; Hyperalgesic response to exogenous glutamate (magnitude and time course).
Statistical comparison
Statistical method not yet structured for this page.
Reporting output
Report representative outputs alongside summary comparisons for Downregulation of glutamate transporters EAAC1 and GLAST in superficial spinal cord dorsal horn, Morphine tolerance development, Thermal hyperalgesia development, Hyperalgesic response to exogenous glutamate (magnitude and time course).
Source links and direct wording from the methods section for validation and deeper review.
Citation
Jianren Mao et al. (2002). Chronic Morphine Induces Downregulation of Spinal Glutamate Transporters: Implications in Morphine Tolerance and Abnormal Pain Sensitivity. Journal of Neuroscience
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