BaroreflexPressoreceptorsHeart RateBlood PressureHypertensionSympathetic Nervous SystemPhenylephrineCarotid SinusAutonomic Nervous SystemVagus NerveReflexNitroprussideMild Cognitive ImpairmentSolitary NucleusBradycardiaCognition DisordersValsalva ManeuverDenervationCardiovascular SystemConsciousnessSupine PositionArteriesTrimethaphanReflex, AbnormalVasoconstrictor AgentsHeartCardiovascular Physiological PhenomenaLower Body Negative PressureNeuropsychological TestsVasomotor SystemTilt-Table TestParasympathetic Nervous SystemPostureCarotid ArteriesHypotension, OrthostaticRats, Sprague-Dawley