Mandibular extension as a trigger of the proprioceptive trigeminocardiac reflex.

The trigeminocardiac reflex (TCR) is a physiological response characterized by a reduction in heart rate and arterial blood pressure following stimulation of any branch of the fifth cranial nerve. This review presents a novel mechanism of TCR induction through proprioceptive activation of the trigeminal nerve via mandibular extension (ME). Accordingly, it is referred to as the "proprioceptive trigeminocardiac reflex" (pTCR). An overview of the existing literature on ME-evoked TCR in humans and animals is presented, with particular emphasis on evidence of cerebral microcirculatory alterations. The magnitude of cardiovascular responses appears to depend on the duration of ME, with repeated applications producing more pronounced and prolonged effects, particularly in hypertensive subjects. In rats, pTCR induction is accompanied by a marked increase in pial arteriolar diameter within the frontal and parietal cortices, apparently independent of neurovascular coupling. Anatomical studies propose a putative neural pathway underlying the pTCR, originating in the mesencephalic trigeminal nucleus and projecting to cardiovascular control centers within the brainstem. Experimental evidence indicates that the TCR may represent a centrally mediated neurogenic reflex resulting in decreased arterial pressure and cerebrovascular vasodilation. A deeper understanding of this reflex may pave the way for developing noninvasive interventions aimed at preventing or delaying the onset of hypertension and stroke, both of which are increasingly prevalent in Western populations.