ABSTRACT
Objective To explore the analgesic effect of intra-articular botulinum neurotoxin type A (BoNTA) injection in rats with adjuvant-arthritis pain,to quantify the expression of calcitonin gene-related peptide (CGRP) in the dorsal root ganglia (DRG) associated with arthritis pain,and to investigate the retrograde axonal transport of BoNT-A into the DRG after peripheral injection.Methods Ninety Sprague-Dawley rats were randomly divided into groups A,B,C,D and E,each of 18.A murine model of adjuvant-arthritis pain was established by injecting 50 μL of complete Freund's adjuvant into the left ankle in all the mice except those in group A.The control group A was treated with intra-articular injection of 50 μL of saline solution.Three weeks later,groups A and B were treated with a 20 μL intra-articular saline injection,while groups C,D and E received an intra-articular injection of BoNT-A at 1 U/20 μL,3 U/20 μL or 10 U/20 μL respectively.Pain threshold and muscle strength were graded before and 1,5,15 and 21 days after the modelling,as well as at 1,3,5 and 14 days after the BoNT-A treatments.Protein expression and the CGRP-positive cell number were observed,as well as any BoNT-A-cleaved synaptosomal-associated 25 kDa protein (cl-SNAP-25) in the DRG using Western blotting and immunofluorescence.Results Compared with group A,there was a significant decrease in the average mechanical withdrawal threshold and muscle strength and a significant increase in the protein expression and the CGRP-positive cell number in the other 4 groups.Compared with group B,the mechanical withdrawal threshold had increased significantly more in groups D and E at 5 days after the BoNT-A injection and in group C at 14 days after the treatment.Compared with group B,the protein expression and the number of CGRP-positive cells were significantly lower in groups D and E at 3 days after the BoNT-A injection.The decrease in group C was significant after 14 days.No significant differences were found between groups D and E in any measurement at any time point.There was no significant difference among groups B,C and D in terms of muscle strength.Five days after the BoNT-A injection,significantly decreased muscle strength was observed in group E.In addition,BoNT-A cleaved-SNAP-25 was detected in the DRG.Conclusion BoNT-A can reduce arthritis pain through inhibiting the expression of CGRP in the DRG.Its analgesic effect has a dose response.A peripheral injection of BoNT-A can arrive at the DRG through retrograde axonal transport.