Related Experiment Video
Updated: Aug 2, 2026
Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Strain-dependent effects of morphine injected into the periaqueductal gray area of mice
R L Nunes-de-Souza1, F G Graeff, B Siegfried
1Laboratório de Psicobiologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Brasil.
Abstract:
1. Microinjection of morphine (0.31, 1.25 and 5.0 micrograms) into the periaqueductal grey area (PAG) of C57BL/6 (C57) and DBA/2 (DBA) mice increased the pain threshold in the tail-flick test. The highest dose also caused a behavioral reaction in both strains characterized by periods of immobility alternating with explosive motor behavior. 2. In the DBA strain, the analgesic effect was demonstrated with all doses of morphine, while in the C57 strain only the highest dose induced analgesia. 3. DBA mice presented a decrease in activity with the lowest dose of morphine, whereas in the C57 strain, this effect was obtained only with the highest dose of morphine. 4. These data corroborate at the PAG level the results of other studies which have shown that central and peripheral injections of morphine produce analgesia and alter motor activity in C57 and DBA strains. They also confirm that these two strains of mice present genotype-dependent differences in sensitivity to opioids as determined after injections of morphine into the PAG.
Insights
Morphine microinjections into the periaqueductal gray area (PAG) of mice demonstrated genotype-dependent differences in pain relief and motor activity. DBA mice were more sensitive to morphine
Area of Science:
- Neuroscience
- Pharmacology
- Genetics
Background:
- Opioid analgesics like morphine are widely used for pain management.
- Understanding the genetic basis of opioid response is crucial for personalized medicine.
- The periaqueductal gray area (PAG) is a key brain region involved in pain modulation.
Purpose of the Study:
- To investigate the effects of morphine microinjections into the PAG on pain perception and motor activity in different mouse strains.
- To determine if C57BL/6 (C57) and DBA/2 (DBA) mice exhibit genotype-dependent differences in their response to PAG-administered morphine.
Main Methods:
- Morphine was microinjected into the PAG of C57 and DBA mice at varying doses (0.31, 1.25, and 5.0 micrograms).
- Pain threshold was assessed using the tail-flick test.
- Motor activity and behavioral responses were observed.
Main Results:
- Morphine administration into the PAG increased the pain threshold in both mouse strains.
- DBA mice showed analgesic effects with all morphine doses, while C57 mice required the highest dose.
- Motor activity was affected differently across doses and strains, with DBA mice showing decreased activity at lower doses compared to C57 mice.
Conclusions:
- The study confirms genotype-dependent differences in opioid sensitivity between C57 and DBA mice at the PAG level.
- These findings highlight the importance of genetic background in modulating the central effects of morphine on pain and behavior.
