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: Assessment of enhanced hyperalgesic response to exogenous glutamate in morphine-treated rats with reduced spinal glutamate transporters
This is a Exogenous Glutamate Hyperalgesic Response Testing 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 • Test naloxone blockade of transporter changes
Primary readouts
Key equipment and reagents
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Administer morphine chronically to rats through 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”
Measure downregulation of glutamate transporters (EAAC1 and GLAST) in the rat's superficial spinal cord dorsal horn following morphine treatment
Note: Two specific transporter types measured: EAAC1 and GLAST in superficial spinal cord dorsal horn
“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 determine if opioid receptors mediate the morphine-induced glutamate transporter downregulation
Note: Naloxone should block glutamate transporter changes if mediated through opioid receptors
“This GT downregulation was mediated through opioid receptors because naloxone blocked such GT changes”
Administer exogenous glutamate to morphine-treated rats with reduced spinal glutamate transporters and measure hyperalgesic response including magnitude and time course
Note: Measure both increased magnitude and prolonged time course of hyperalgesic response
“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”
Monitor the temporal relationship between glutamate transporter downregulation and the development of morphine tolerance and thermal hyperalgesia
Note: Establish temporal correlation between transporter downregulation and behavioral outcomes
“the downregulation of spinal GTs exhibited a temporal correlation with the development of morphine tolerance and thermal hyperalgesia”
Administer PDC (glutamate transporter inhibitor) to determine its effects on potentiating morphine tolerance and thermal hyperalgesia development
Note: PDC should potentiate both morphine tolerance and thermal hyperalgesia
“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 riluzole (positive glutamate transporter regulator) to determine its effects on reducing morphine tolerance and thermal hyperalgesia development
Note: Riluzole should reduce both morphine tolerance and thermal hyperalgesia
“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 MK-801 (noncompetitive NMDA receptor antagonist) to determine if NMDA receptor activation mediates PDC-potentiated morphine tolerance and thermal hyperalgesia
Note: MK-801 should block both morphine tolerance and thermal hyperalgesia potentiated by PDC if NMDA receptor mediated
“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.
Assessment of enhanced hyperalgesic response to exogenous glutamate in morphine-treated rats with reduced spinal glutamate transporters
Objective
Assessment of enhanced hyperalgesic response to exogenous glutamate in morphine-treated rats with reduced spinal glutamate transporters
Subjects
From paperrat • Not specified • unknown • Not specified • Not specified
Cohort notes
From paperNot specified in provided text
Chronic morphine administration (Not specified)
Assess glutamate transporter downregulation (Not specified)
Test naloxone blockade of transporter changes (Not specified)
Assess hyperalgesic response to exogenous glutamate (Not specified)
Magnitude of hyperalgesic response to exogenous glutamate
From paperNot specified in provided text
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Time course of hyperalgesic response to exogenous glutamate
From paperNot specified in provided text
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Downregulation of spinal glutamate transporters (EAAC1 and GLAST)
From paperNot specified in provided text
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Development of morphine tolerance
From paperNot specified in provided text
Artifact type
Endpoint measurements summarized by group or timepoint
Comparison focus
Compare endpoint magnitude between groups, timepoints, or both
Magnitude of hyperalgesic response to exogenous glutamate
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
Time course of hyperalgesic response to exogenous glutamate
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
Downregulation of spinal glutamate transporters (EAAC1 and GLAST)
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
Development of morphine tolerance
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 in provided text
Scoring or quantification
Quantify the primary readouts for this experiment: Magnitude of hyperalgesic response to exogenous glutamate; Time course of hyperalgesic response to exogenous glutamate; Downregulation of spinal glutamate transporters (EAAC1 and GLAST); Development of morphine tolerance.
Statistical comparison
Statistical method not yet structured for this page.
Reporting output
Report representative outputs alongside summary comparisons for Magnitude of hyperalgesic response to exogenous glutamate, Time course of hyperalgesic response to exogenous glutamate, Downregulation of spinal glutamate transporters (EAAC1 and GLAST), Development of morphine tolerance.
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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