Abstract
Previously, in normotensive rats, it has been observed that a repetitive sub-maximal mouth opening (mandibular extension, ME) obtained by placing a home-made U-shaped dilator between the superior and inferior dental arches of the rat caused modulation of pial arteriolar tone. The present study was aimed to characterize pial microcirculation in two different cortical brain regions and to assess the hemodynamic effects of a single or double ME on pial arteriolar rhythmic diameter changes in rats rendered hypertensive by dexamethasone administrations. Cranial windows were prepared on parietal and frontal region. Pial arterioles were classified by Strahler method in five orders by in vivo fluorescence microscopy technique associated with a computerized system that permits off-line measurements of arteriolar diameter changes. Two 10 min ME at 10 min interval were applied; then the animals were monitored for further 240 min. Dexamethasone-treated rats exhibited a marked arterial rarefaction and asymmetry of bifurcation in the pial microvascular networks more evident in the frontal region. Starting from ME1, in both cortical areas, the arterioles dilated, and the vasodilation became significant compared to baseline after ME2 for the entire observation period. The spectral analysis carried out on order 2 arteriolar diameter change tracings, showed that double ME increased the spectral density of the frequency components related to endothelial, neuronal and myogenic activities in both the cortical regions studied. In conclusion, double ME has a generalized effect in the cortical areas by restoring the physiological vasomotion of the pial arterioles that was severely impaired by the experimentally hypertension.
Highlights
It has been shown that the mandibular extension (ME), consisting in a submaximal mouth opening for 10 min, placing a home-made U-shaped dilator between the superior and inferior dental arches of normotensive rats, caused cardiovascular effects and a pial arteriolar dilation due to the peripheral activation of the trigeminal nerve
Pial arterioles of hypertensive rats were organized in five orders as observed in normotensive rats (Lapi et al, 2008); in the frontal region only three orders of vessels were detected in hypertensive rats, compared to four orders of vessels recognized in normotensive animals (Table 1 and Figure 2)
We described that repeated MEs in normotensive rats markedly prolonged the long-lasting dilation of pial arterioles produced by single ME, promoting a change in the regulation of their diameters (Lapi et al, 2017)
Summary
It has been shown that the mandibular extension (ME), consisting in a submaximal mouth opening for 10 min, placing a home-made U-shaped dilator between the superior and inferior dental arches of normotensive rats, caused cardiovascular effects and a pial arteriolar dilation due to the peripheral activation of the trigeminal nerve. These effects can be included in the so called. A second ME applied 10 min after the first one prolonged (almost up to 4 h) the effects of the single ME on both blood pressure, heart rate and arteriolar tone (Lapi et al, 2017)
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