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Tolerance develops to spinal morphine analgesia but not morphine-induced convulsions
B C Yoburn1, K Lutfy, V Sierra
1Department of Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions, St. John's University, Queens, NY 11439.
European Journal of Pharmacology
|January 25, 1990
Summary
Spinal morphine provides pain relief but can cause seizures in mice. Tolerance develops to pain relief, not seizures, indicating different spinal mechanisms for these effects.
Area of Science:
- Neuroscience
- Pharmacology
Background:
- The spinal cord plays a crucial role in pain modulation and can be a target for analgesics.
- Opioid receptors in the central nervous system are known to mediate both pain relief and side effects like seizures.
Purpose of the Study:
- To investigate the distinct roles of spinal opioid receptors in mediating analgesia and proconvulsant effects of morphine in mice.
- To examine the development of tolerance to spinal morphine's analgesic and proconvulsant actions.
Main Methods:
- Morphine was administered intrathecally (i.t.) to mice to assess dose-dependent effects.
- Chronic morphine tolerance was induced via subcutaneous (s.c.) pellets.
- Naloxone was used to antagonize opioid receptor activity.
Main Results:
- Intrathecal morphine produced dose-dependent analgesia and hindlimb seizures.
- Chronic morphine treatment led to tolerance to analgesic effects but not proconvulsant actions.
- Naloxone attenuated spinal morphine-induced analgesia but not seizures.
Conclusions:
- Spinal opioid receptors are involved in morphine-induced analgesia.
- Spinal opioid receptors do not appear to mediate morphine-induced seizures.
- Differential mechanisms likely underlie spinal morphine analgesia and seizures.