Caracterização de um novo método de avaliação da atividade muscular mastigatória em um modelo de bruxismo em ratos: avaliação da nocicepção e das diferenças entre os sexos

Abstract

Bruxism is the habit of squeezing and grinding the teeth. The incidence of this pathology has increased progressively in the population, prevailing in females in the proportion of 5:1, possibly due to the susceptibility to emotional or anatomical factors, but not affecting males. The aim of this study was to evaluate a new method of electromyography (EMG) of the masticatory muscular activity, associated nociception and differences between sexes in a model of bruxism in rats. Experimental bruxism was induced by emotional stress through the communication box for fourteen days (D1 to D14). The masticatory muscle activity (MMA) was evaluated every 2 days before and after induction of stress using a mobile device for EMG made by ower one, which was positioned in the region of the masseter and temporal muscles. Nociception was evaluated by the mechanical hyperalgesia test in these muscles. Stages of the estrous cycle, anxiety behavior, body weight, adrenal gland weight, and expression of c-Fos in trigeminal ganglion (TG) and dopamine D2 (D2R) receptors were also evaluated in the striatum. The results showed that there was no differences between the basal register made with the mobile device and the subcutaneous implanted electrodes, validating the new method. There was a significant (p <0.001) increase in MMA in D7 and D10 for females and in males that occurred in D3 and D7. In D10 and D14, in male there was a decrease in the frequencies, which only occurred in D14 for females. Comparison between males and females showed a significant difference (p <0.001) in D7 and 14. Ovariectomized females (OF) were significantly different (p <0.001) from normal females from D7 to 14. In relation to nociceptive threshold, there were differences between males and females. We observed that females reached the peak of nociception more early than males, occurring in D4 (females) whereas in males the peak appears in D14 (m.temporal) and from D11 (m.masseter ). OF, after D11 began to show an increase in nociception, similar to males that also increased their nociceptive behavior in the same period. There was a positive correlation between MMA and nociception for the females, but not for the males. The phases of the estrous cycle had a correlation with MMA. Both males and females showed anxiety behavior. The results also showed that the male and female stressed animals presented accumulation of cytoplasmic vacuoles in the adrenal gland cortex, with no differences between the sexes. There was a greater expression of c-Fos in TG of male and female stressed rats. Ovariectomy inhibited this increased expression in stressed females. In the stressed rats there was an increase in D2R expression in the striatum which was inhibited by ovariectomy. The data suggest that the mobile device used for EMG recording worked in a similar way to the implanted electrode, evidencing an increased MMA in stressed animals. There were differences between males and females with regard to bruxism and nociception. Ovariectomy modified these responses. Nociception seems to be associated with bruxism in females, but it does not depend on the estrous cycle, whereas bruxism seems to be related to female hormones depending on the estrous cycle. D2R appears to be associated with emotional stress / bruxism in females, which may be influenced by gonadal hormones.