| Chronic musculoskeletal pain is a major clinical problem and sterile saline is used to produce short-lasting acute noninflammation and hyperalgesia in animal models. Two unilateral injections of pH 4.0 saline into the gastrocnemius muscle result in a bilateral decrease in mechanical withdrawal threshold after the second injection. Loxoprofen were administered at one of two different time points: (1) just after the second intramuscular injection of pH 4.0 saline on Day 5, and (2) 1 week after the second injection. Mechanical withdrawal thresholds were measured with von Frey filaments before, 4 h , and 24 h after injection 1 and before, 4 h, 24 h, and 1 week after injection 2. In the study, we injected the rats with pH 4.0 preservative-free sterile saline in gastrocnemius muscle and hyperalgesia to mechanical (measured as decreased withdrawal threshold) stimuli of both paws assessed before , varying times after injection and at every two days after application of Loxoprofen within 4 weeks.Neuropeptide-expressing small diameter sensory neurones are thought to be vital in generating inflammatory hyperalgesic responses. Within the dorsal root ganglion (DRG), the numbers of CGRP-immunoreactive (CGRP-IR) DRG neurones have been shown to increase in a number of acute adjuvant-induced inflammatory pain models.This study shows that Loxoprofen reduces muscle hyperalgesia in noninflammatory models of muscle pain. The aim of this study was to look specifically at changes in numbers of CGRP-IR DRG neurones in a chronic model of noninflammatory muscle pain following complete injection into the rat gastrocnemius muscle. |
