Related Experiment Videos
Effects of intraplantar morphine in the mouse formalin test
A Baamonde1, M Alvarez-Vega, A Hidalgo
1Departamento de Medicina, Facultad de Medicina, Universidad de Oviedo, Asturias, Spain.
Abstract:
We studied the effects of intraplantar morphine in the formalin test in mice. Intraplantarly administered morphine (30 - 300 microg) induced analgesic effects at lower doses than intraperitoneally administered morphine. Following the administration of [3H]morphine, the % of radioactivity present in brain was the same by either route. In contrast, higher radioactivity values appeared in the injected paw in those mice intraplantarly injected. Since local morphine induces analgesia at doses lower than the intraperitoneally administered drug, especially in the second phase of the test, and the access to brain is undistinguishable, we propose that local morphine enhances central opiate analgesia in the formalin test in mice.
Insights
Local morphine administration in mice produced pain relief at lower doses than systemic administration. This suggests intraplantar morphine enhances central opiate analgesia during the formalin test.
Area of Science:
- Pharmacology
- Neuroscience
- Pain Research
Background:
- The formalin test is a widely used model for evaluating pain and analgesia in rodents.
- Morphine is a potent opioid analgesic, but its efficacy can be influenced by administration route.
Purpose of the Study:
- To investigate the analgesic effects of intraplantar morphine compared to intraperitoneal administration in the formalin test.
- To determine the distribution of morphine in the brain and injected paw following different administration routes.
Main Methods:
- Mice were subjected to the formalin test after receiving varying doses of morphine administered either intraplantarly or intraperitoneally.
- Radioactivity levels of [3H]morphine were measured in the brain and injected paw to assess drug distribution.
Main Results:
- Intraplantar morphine induced significant analgesic effects at lower doses compared to intraperitoneal administration, particularly during the second phase of the formalin test.
- Radioactivity in the brain was similar regardless of administration route, but higher concentrations were found in the injected paw after intraplantar administration.
- These findings suggest a localized effect of intraplantar morphine.
Conclusions:
- Intraplantar morphine administration enhances central opiate analgesia in the formalin test at lower effective doses than systemic administration.
- The localized distribution of morphine in the paw may contribute to its increased efficacy when administered locally.
- This study provides evidence for a potential strategy to improve opioid pain management through targeted local delivery.