Effects of occlusal interference on blood pressure were examined in 47 unanaethetized rats. The occlusal interference was produced by insertion of unilateral bite-raising splints (1, 2 or 3 mm in vertical dimension). The splints were set on the upper teeth for 20 days. The systolic blood pressure was measured from the caudal artery by the tail-cuff method before, during and after insertion of the splints. The blood pressure of the 1 mm unilateral bite-raising group did not change significantly between before and during insertion of the splints. In the 2 and 3 mm bite-raising groups, the blood pressure during insertion of the splints increased significantly as compared with that before insertion of the splints; after removal of the splints, the increased blood pressure returned to the pre-insertion level. Reproducibility in the increase of blood pressure was observed when the insertion of the splints was applied repetitively. Unilateral bite-raising also produced a statistically significant reduction of body weight during insertion of the splints. However, when the effect of fasting on the blood pressure was examined, the blood pressure did not change significantly, whereas the body weight decreased remarkably during fasting. This indicates that the increase of blood pressure depends primarily on unilateral bite-raising. The results of the present study suggest that activation of the autonomic nervous system is involved in the increase of blood pressure induced by insertion of unilateral bite-raising splints, and that occlusal interference activates the autonomic nervous system as a stressor.
To determine whether the sympathetic nervous system is involved in the increase of blood pressure induced by occlusal interference, the effects of adrenergic antagonists on blood pressure were examined in 22 male Wistar rats. Systolic blood pressure was measured by using the tail-cuff method. Prazosin (0.5 mg/kg, i.p.) and propranolol (1 mg/kg, i.p.) were used as α-and β-adrenergic antagonists, respectively. When a 3 mm unilateral bite-raising splint was applied for 20 days, the blood pressure during insertion of the splints increased significantly compared with that before insertion of the splints. However, the heart rate was not statistically significant between before and during insertion of the splints. The increased blood pressure, 143.1±6.6 mmHg, decreased significantly to 108.8±9.6 mmHg 1 h after the administration of prazosin. There was no statistically significant difference of heart rate between before and after administration of prazosin, although the heart rate increased from 333.6+29.2 to 377.6±22.1 bpm. Propranolol significantly reduced the blood pressure from 141.8±8.3 to 134.5±7.6 mmHg. The heart rate decreased from 323.6±15.8 to 294.8±34.0 bpm after administration; however, no statistically significant difference was observed. These results provide evidence that the increase of blood pressure induced by occlusal interference is mediated by activation of the sympathetic nervous system.
In intact anaesthetized rats, large myelinated afferent stimulation (LMAS) produced a decrease of discharge frequency in response of spinal cord dorsal horn neurons to noxious heating. In spinalized rats, in which the cervical cord (C2-C3 segments) was transected completely, LMAS failed to reduce the neuronal discharges in response to noxious heating. This result suggests that inhibition of nociceptive responses of dorsal horn neurons produced by LMAS is mediated via descending spinal pathways from supraspinal structures.