6/5 DHT تغييرات وابسته به زمان در آستانه درد تونيك موش هاي صحرايي نر پس از تزريق نوروتوكسين

Time-dependent changes in the threshold of tonic pain following injection of the neurotoxin 5,6-dihydroxytryptamine in male rat

Nucleus raphe magnus (NRM) plays an important role in the descending pain modulation system. It contains a hetcrogcnic population of serotonergic and non-serotonergic neurons which densely project to posterior horn of spinal cord. In this research study, the neurotoxin 5,6-dihydroxytryptamine (5/6DHT) was injected into subarachnoidal space of lumbar cord to specifically destroy descending serotonergic pathway and then to evaluate changes in the threshold of tonic pain 5, 14, and 30 days post-lesion. The neurotoxin was intrathecally injected through pre-implanted polyethylene tube. The animals were divided into the groups 5-14 and 30 days (n = 6) and for measurement of the threshold of tonic pain, 50 µl of 10% formalin was injected into the right hindpaw.The results showed that 5 days after the injection of 5,6-DI-IT, a significant increase in pain score occurs at both phases of the formalin test (p<0.05) and the observed hyperalgesic state restored to normal after 14 andlor 30 days. It can be concluded that neurons of NRM are capable of functional adaptation to compensate for deficient serotonergic neuronal system.