Effects of mandibular extension on low-frequency components in rat pial arteriolar rhythmic diameter changes

The aim of this study was to in vivo assess the effects of mandibular extension (ME) on rat pial rhythmic diameter changes. ME was induced by U-shaped device placed between the two dental arches. Pial microcirculation was visualized by fluorescence microscopy. The vessel diameter and rhythmic variations in diameter were evaluated with computer-assisted method. Pial arterioles were classified by Strahler method in five orders. Spectral analysis was performed on 30 min recordings under baseline conditions and 30 min tracings after 10 min ME. Under baseline conditions all pial arteriolar orders showed high and low frequency components; the low ones were in the ranges 0.0095-0.021 Hz (endothelial activity), 0.021-0.052 Hz (neurogenic activity), and 0.052-0.145 Hz (myogenic activity), 0.145-0.6 Hz (respiratory activity) and 0.6-2.0 Hz (heart beat). The smallest arterioles showed another low frequency component in the range 0.005-0.0095 Hz. After ME there was a significant increase in the lowest frequency components accompanied by a significant reduction in arteriolar blood pressure and heart rate. In conclusion, 10 min ME induces systemic responses and an increase in cerebral blood flow oscillations triggered by endothelial activity.