Validating drg 945
Here, we evaluated if the intra-articular injection of collagenase can be an alternative model to study nociception associated with osteoarthritis.Osteoarthritis was induced by two intra-articular injections of either 250 U or 500 U of collagenase into the left knee joint of adult male Wistar rats.The signal intensity depended on the paw area in contact with the platform and increased with the pressure applied by the paw.Random frames of the videos were analysed: three pairs of frames (one for each hind paw) with the animal walking and three frames with the animal standing still.The contralateral knee was always tested first, in order to avoid an increase in the contralateral score arising from the manipulation of the injected knee.Results for both ipsilateral and contralateral knees were presented.For each hind paw, the number and intensity of pixels above a defined threshold were quantified (Image J 1.37, ) to determine the total paw print intensity (mean pixel intensity × number of pixels), allowing the comparison of the area/pressure applied by each paw.
The expression of transient receptor potential vanilloid 1 (TRPV1) in ipsilateral dorsal root ganglia (DRG) was evaluated.We conclude that the intra-articular injection of 500 U collagenase in the knee of rats can be an alternative model for the study of nociception associated with osteoarthritis, since it induces significant nociceptive alterations associated with relevant osteoarthritis-like joint structural changes. Ideally, it would be desirable that an experimental model could reproduce as closely as possible the different features of a disease.It seems reasonable to state that the development of chronic pain in OA should not be dissociated from the structural articular changes that occur during the onset and progression of OA.Experimental procedures were performed in accordance with the ethical guidelines for the study of experimental pain in conscious animals [ Under brief isoflurane anaesthesia (5% isoflurane for anaesthesia induction, 2% for maintenance), an intra-articular injection was performed with the use of a Hamilton syringe, with a 26 G needle inserted through the patellar ligament into the joint space of the left knee.
Animals received two injections, one on day 0 and another on day 3, with 25 μl of either sterile saline (control group), 250 U or 500 U of type II collagenase from Animals injected with saline, 250 U or 500 U collagenase (72 animals; n = 24/treatment) were randomly divided in groups that were sacrificed at different time-points: one, two, four and six weeks after the first injection (n = 6/group/treatment).The Cat Walk test was always performed prior to the Knee-Bend test, to minimize the effect of manipulation of the affected knee joint on the animals’ gait.Knee diameters were measured to infer joint swelling as an indicator of inflammation resulting from i.a. The diameter of both knees was measured with a manual calliper.The relevance of collagen degradation and of articular instability as features of OA, as observed in the clinical setting, leading to histopathological alterations that highly correlate with those described for human OA , make the i.a.