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Role of μ-opioid receptors in formalin-induced pain behavior in mice
- Source :
-
Experimental Neurology . Dec2003, Vol. 184 Issue 2, p839. 7p. - Publication Year :
- 2003
-
Abstract
- Intraplantar formalin injection is widely used as an experimental model of tonic pain. We investigated the role of endogenous μ-opioid receptor mechanisms in formalin-induced nocifensive behavior in mice. The flinching response induced by formalin (2%, 20 μl) was studied in mice with normal (wild type, n = 8) and absent (homozygous μ-opioid receptor knockout, n = 8) μ-opioid receptor levels. The flinch responses were counted every 5 min for 60 min post-formalin injection. Lumbar spinal cord (L4, 5) was harvested 2 h post-formalin injection to examine c-Fos expression using immunohistochemistry. The effects of naloxone (5 mg/kg, sc) administered 30 min before the intraplantar formalin injection on the flinching response of wild-type mice (n = 7) were also recorded. The second-phase formalin response (10–60 min after formalin) was higher in homozygous μ-opioid receptor knockout mice compared to the wild-type mice (P < 0.01). Naloxone administration in wild-type mice before formalin injection resulted in pain behavior similar to that observed in homozygous μ-opioid receptor knockout mice (P > 0.05). The c-Fos expression induced by formalin injection in the knockout mice was not different from that observed in wild-type mice. Our results suggest that the endogenous μ-opioid system is activated by intraplantar formalin injection and exerts a tonic inhibitory effect on the pain behavior. These results suggest an important modulatory role of endogenous μ-opioid receptor mechanisms in tonic pain states. [Copyright &y& Elsevier]
- Subjects :
- *OPIOID receptors
*MICE behavior
*FORMALDEHYDE
*NALOXONE
Subjects
Details
- Language :
- English
- ISSN :
- 00144886
- Volume :
- 184
- Issue :
- 2
- Database :
- Academic Search Index
- Journal :
- Experimental Neurology
- Publication Type :
- Academic Journal
- Accession number :
- 12173024
- Full Text :
- https://doi.org/10.1016/S0014-4886(03)00346-7