Abstract
In the present study we have extended our previous findings about the effects of 10 minutes of passive mandibular extension in anesthetized Wistar rats. By prolonging the observation time to 3 hours, we showed that 10 minutes mandibular extension caused a significant reduction of the mean arterial blood pressure and heart rate respect to baseline values, which persisted up to 160 minutes after mandibular extension. These effects were accompanied by a characteristic biphasic response of pial arterioles: during mandibular extension, pial arterioles constricted and after mandibular extension dilated for the whole observation period. Interestingly, the administration of the opioid receptor antagonist naloxone abolished the vasoconstriction observed during mandibular extension, while the administration of Nω-Nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, abolished the vasodilation observed after mandibular extension. Either drug did not affect the reduction of mean arterial blood pressure and heart rate induced by mandibular extension. By qRT-PCR, we also showed that neuronal nitric oxide synthase gene expression was significantly increased compared with baseline conditions during and after mandibular extension and endothelial nitric oxide synthase gene expression markedly increased at 2 hours after mandibular extension. Finally, western blotting detected a significant increase in neuronal and endothelial nitric oxide synthase protein expression. In conclusion mandibular extension caused complex effects on pial microcirculation involving opioid receptor activation and nitric oxide release by both neurons and endothelial vascular cells at different times.
Highlights
In a previous study we reported that young normal volunteers subjected to a submaximal passive mandibular extension (ME), obtained by means of a dilator applied for 10 minutes between the upper and lower incisor teeth, showed a prolonged reduction in blood pressure and heart rate
In a previous study on the effects of ME in rats [11], we have demonstrated that animals submitted to 10 minutes ME exhibited a reduction in the mean arterial blood pressure (MABP) and heart rate (HR) following the stimulation of the peripheral branches of the trigeminal nerve
As previously shown [11], the cardiovascular response to ME consisted of an initial gradual reduction of MABP and HR during ME that persisted after ME (80 minutes) without recovering the initial value
Summary
In a previous study we reported that young normal volunteers subjected to a submaximal passive mandibular extension (ME), obtained by means of a dilator applied for 10 minutes between the upper and lower incisor teeth, showed a prolonged reduction in blood pressure (by 12–11 mmHg) and heart rate (by about 13 bpm) These effects appeared after 10 minutes ME and persisted for the successive 80 minutes. It had been suggested that ME could stimulate the terminal nerve branches triggering these responses [1]. This suggestion has been supported by experimental and clinical observations over the last 20 years which have demonstrated that the facial area is an important source of powerful autonomic reflexes that involve different systems including the cardiovascular system. TCR causes changes in systemic blood pressure, heart rate and, in some cases, gastric hypermotility [2,3,4,5,6,7,8]
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