Validação de um método para mensurar hiperalgesia primária de tecido profundo em ratos

Abstract

Introduction: Although several instruments with the purpose of evaluating nociception in rats have been developed over time, in short, they focus on the evaluation of nociceptive thresholds in the paws. Thus, painful conditions that go beyond the limits of this region are indirectly assessed, since the test site is distant from the pain site. Given the need for more accurate assessments, a device for measuring primary hyperalgesia in deep tissue was developed, in a partnership between LAPENE and the Department of Electrical Engineering, both at UFS. Thus, the aim of the present study was to validate a method for measuring deep hyperalgesia in rats. Methods: Twenty-four male Wistar rats were divided into 2 groups (arthritis and control). The animals allocated to the arthritis group were submitted to the joint inflammation induction model by injection of a 3% carrageenan and 3% kaolin solution in the left knee. The evaluation of the animals' behavior was divided into five moments: baseline, 24h, 48h, 72h and 96h after the induction of the joint inflammation model. Assessments were carried out by two investigators independently (A and B). The variables measured were the joint withdrawal threshold (instrument for measuring hyperalgesia in deep tissue) and the paw withdrawal threshold (electronic von Frey). Data were analyzed using ANOVA two-way and post Tukey test. Results: According to the data obtained by evaluator A, the mechanical threshold of joint withdrawal of the left limb of the animals belonging to the arthritis group was significantly reduced at 24h, 48h and 72h, when compared to the contralateral paw (p<0.0001, p=0 .0012 and p=0.0483, respectively) and the left paw of the control group (p<0.0001, p<0.0001 and p=0.0188, respectively). At 96h, a statistically significant difference was found only between the left paw in the arthritis group and the left paw in the control group (p=0.0234). For evaluator B, the mechanical threshold of joint withdrawal of the left limb of the animals of the arthritis group also significantly reduced at 24h, 48h and 72h when compared to the contralateral paw (p<0.0001, p=0.0023 and p=0, 0406, respectively) and the left paw of the control group (p<0.0001, p=0.0078 and p=0.0010, respectively). Regarding the time 96h, a statistically significant difference was found only between the left paw of the arthritis group and the left paw of the control group (p=0.0269), there was no difference between the paws of the animals belonging to the arthritis group (p=0 .6779). Regarding the paw withdrawal threshold, evaluator A observed a reduction in the mechanical left paw withdrawal threshold when compared to the contralateral paw (p=0.0063 and p=0.0007) and when compared to the control group (p=0.0134 and p=0.0075) at times 24h and 48h, respectively, while for times 72h and 96h there was no difference. Regarding the evaluations of evaluator B, statistically significant differences were found between the left and right paw of the arthritis group (p=0.0013 and p=0.0029) and between the left paw of the control group (p=0.0087 and p. =0.0411) data interpreted as a reduction in the mechanical threshold of paw withdrawal, at 24h and 48h respectively, while for the times 72h and 96h there was no difference. The inter-rater reliability, that is, the coefficient of agreement between the investigators who used the proposed instrument, was considered good (ICC=0.8). Conclusion: The results of the present study point to the applicability of the instrument for measuring mechanical hyperalgesia in deep tissue to detect nociception in rats when compared with the results of the electronic Von Frey.