Experimental Study Of Adriamycin Analgesia On Dorsal Root Ganglion

ObjectiveTo investigate the effects of adriamycin(ADM) on the pain behaviours and dorsal root ganglion cells of SNI rats by injecting different concentration of adriamycin to the intervetbral foramina.Observing the effect of different concentration of ADM to the DRG cells according to the changes of pain behaviours and DRG cells in the microscope.Then providing the evidence for using the chemo-ganglionectomy to treat the neuropathic pain in the clinical.MethodAdult male Sprague-Dawley rats weighing 200g on the day of surgery were used in this study.The method of inducing nerve injury using the Decosterd method.After building the spared nerve injury model,all of the SNI rats were randomly assigned to five groups,respectively named control group(n=20),0.25%ADM group(n=20), 0.5%ADM group(n=20),0.75%ADM group(n=20),1.0%ADM group(n=20).After celiac anaesthesia with 10%chloraldurat(0.3ml/100g),the margin of left L4,L5,L6 intervertebral foramina of the rats were exposed under the condition of sterility. Then intervetbral foramina injection with 5μl adriamycin at the concentration of 0.25%,0.5%,0.75%,1.0%into the foamina of the rats correspongding to the groups.The control group rats were injected with NS into the foamina.The rats were then tested the day after surgery or administration and once a week for 4 weeks including the latency of withdrawal to the radiant heat stimulus,acetone test and pin-prick test.After administration respectively dislodge L4 DRG at the day 14 and 28 and L5 DRG at the day 7 of the left side of 3 rats from the five groups.The L4 DRG was stained with HE to observe morphologic change of DRG cells using the light microscope.The L5 DRG was treated by frozen section and observe under the electon microscope.Results1.The pain behavior before administration All the spared nerve injury rats developed qualitative signs indicative of a marked sensory hypersensitivity of the hindpaw ipsilateral to the nerve injury.This was clearly present 24h after the surgery,appeared to reach a peak at about 2 weeks,and continued for as long as the animals were monitored.The animals refrained from weigh bearing on the affected paw and modified their stance accordingly,with eversion of the root.If contact was inadvertently made,either at rest or during locomotion,a prolonged flexion of the hindpaw was generated.Development of a sudden sustained spontaneous withdrawal in the absence of any stimulus of the hindpaw was present intermittently in most animals,the paw being held in a flexed position with paroxysms of smaller flexion.No autotomy or body weight loss was observed,nevertheless during the study and the animals' grooming.2.The pain behavior after administrationCompared to the control group,the other four groups' rat injected with different concentration adriamycin exhibited reversed pain behavior,including increased paw-withdrawal latency to the radiant heat stimulus,decreased paw withdrawal duration to acetone and pin-prick stimulus.In our study,we did not observed obviously motor dysfunction and extremity palsy in the 1.0%ADM group rats.3.Histomophological change of DRG cells3.1 Changes under general light microscopeA small number of dorsal root ganglion cells in control group exhibited degeneration.In 0.25%ADM group,light microscopical study of DRG sections revealed hydropic degeneration and loss of Nissl's body at the second week. Karyopyknosis,cytoplasmic clarifixation and cellular necrosis were observed at the fourth week.In 0.5%ADM group,cellular universal degeneration,crimpy cytoplasmic,fuzziness and loss of Nissl's body were seen 2 weeks after administration,in addition,karyopyknosis and cellular necrosis in a small number of DRG were simultaneously seen.With that,karyopyknosis,karyolysis,satellite phenomenon and swallowing ganglia phenomenon were seen at the fourth week. Despite of cellular universal degeneration,karyopyknosis karyorrhexis and cellular necrosis were seen in a portion of DRG cells 2 weeks after administration in 0.75% and 1%ADM group.At the fourth week,mass cellular necrosis and replacement of hyperplastic neurogliocyte and connective tissue were seen.3.2 Changes under electron microscopeAccording to the diameter of the cell the DRG cells can be divided into big,medium and small cells[17].The big cells can be clearly identified under electron microscope,but it is difficult to distinguish between small and medium cells.In the control group we can see relative complete cell nucleus and well-distributed chromoplasm.In 0.25%ADM group medium or small cells exhibited karyopyknosis, chromatin margination,chondrosome swelling,increased lysosome.In 0.5%ADM group medium or small cells exhibited cell nucleus leaning to one side,nuclear membrane embole,chondrosome swelling,increased lysosome and collagen fibers in intercellular substance.In 0.75%ADM group medium or small cells exhibited generous cellular necrosis,interstitial fibrosis,big cells exhibited irregular shape of cellular nucleus,chondrosome swelling.In 1%ADM group we can not seen normal medium or small cells,but increased fibers in big cells.ConclusionIntervetebral foramina injection with different concentration adriamycin into the dorsal root ganglion corresponding to the nerve injury can reverse the pain behavior of the SNI rats.It also can result in the DRG degeneration.The low concention of adriamycin(0.25%and 0.5%group) mainly damage the small and medium DRG cells responsible for pain and thalposis,the high concention(0.75%,1%)reduces this selectivity.Thus the concention of ADM was used in the clinic can't beyond 0.75%.