Avaliação das alterações comportamentais e nociceptivas em um modelo experimental de carcinogênese oral em ratos

Abstract

The main experimental model for the study of oral squamous cell carcinoma (OSCC) is based on the dilution of the 4-nitroquinoline oxide (4-NQO) in the drinking water of the animals, causing lesions specially in the tongue, however there is a lack of studies focused on the changes that occur along the trigeminal pathway that contribute to the development of pain in oral cancer. This work investigated the nociceptive and morphological changes involved in the progression of carcinogenesis by 4-NQO in a modified model. For this, 40 wistar rats (100-150g) were used, divided into a control group (C; n = 8) and groups that received 4-NQO (n = 8 each) for 8,12,16 or 20 weeks, (T8, T12, T16 and T20, respectively). Aiming at greater safety in the vivarium environment and guaranteeing the receipt of the drug equally among the animals, the administration of this substance was performed by topical drip (2x / day) of the 4-NQO suspension (0.6 mg / day) in propylene glycol. Mechanical hyperalgesia, assessment of facial expressions and open field test were performed to analyze anxiety and depression. After euthanasia, the animals' tongues were removed for macro and microscopic analysis. The trigeminal ganglion and region of the subnucleus caudalis of the trigeminal spinal tract were also removed for analysis by immunofluorescence for c-FOS. During the development of the experimental model, it was observed through histopathological analyzes that the T20 group presented 50% of the samples with tongue SCC, thus being the best time to obtain cancerous lesions. In the other groups, potentially malignant lesions were observed, ranging from hyperkeratosis to carcinomas in situ, with progressive epithelial changes throughout the experimental protocol. It is also worth mentioning that this model did not cause sample losses or losses in weight gains over time. In the analysis of mechanical hyperalgesia, changes in nociceptive thresholds could be observed throughout the experimental protocol, in which, in its first 2 weeks, there was a significant reduction (p<0.001), followed by interspersed periods of threshold return to baseline levels with subsequent significant reduction in the nociceptive threshold from the 12th week until the end of the experimental protocol (p<0.01). An increase in scores for facial expressions was observed only at T20 (p<0.05) and a significant increase in grooming and horizontal activity at 8 weeks. In trigeminal ganglion, there was a significant reduction in c-FOS immunoexpression at T12 when compared to T8 (p<0.05), as well as an increase in this expression at T20 compared to groups C (p<0.05) and T12 (p<0.001). In the analysis of the caudal subnucleus region, a significant increase in this immunoexpression was observed in groups T16 and T20, when compared to C (p<0.05). Thus, we concluded that the modification of the model was able to induce potentially malignant lesions and OSCC in the tongue. The development process of these lesions is accompanied by behavioral and nociceptive threshold changes, with increased expression of c-FOS at the peripheral and central levels, in longer times of exposure to the carcinogen.