Baroreflex functionality in the eye of diffusion tensor imaging

Abstract

By applying diffusion tensor imaging (DTI) as a physiological tool to evaluate changes in functional connectivity between key brainstem nuclei in the baroreflex neural circuits of mice and rats, recent work has revealed several hitherto unidentified phenomena regarding baroreflex functionality. (1) The presence of robust functional connectivity between nucleus tractus solitarii (NTS) and nucleus ambiguus (NA) or rostral ventrolateral medulla (RVLM) offers a holistic view on the moment‐to‐moment modus operandi of the cardiac vagal baroreflex or baroreflex‐mediated sympathetic vasomotor tone. (2) Under pathophysiological conditions (e.g. neurogenic hypertension), the disruption of functional connectivity between key nuclei in the baroreflex circuits is reversible. However, fatality ensues on progression from pathophysiological to pathological conditions (e.g. hepatic encephalopathy) when the functional connectivity between NTS and NA or RVLM is irreversibly severed. (3) The absence of functional connectivity between the NTS and caudal ventrolateral medulla (CVLM) necessitates partial rewiring of the classical neural circuit that includes CVLM as an inhibitory intermediate between the NTS and RVLM. (4) Sustained functional connectivity between the NTS and NA is responsible for the vital period between brain death and the inevitable cardiac death. (5) Reduced functional connectivity between the NTS and RVLM or NA points to inherent anomalous baroreflex functionality in floxed and Cre‐Lox mice. (6) Disrupted NTS‐NA functional connectivity in Flk‐1 (VEGFR2) deficient mice offers an explanation for the hypertensive side‐effect of anti‐vascular endothelial growth factor therapy (anti‐VEGF) therapy. These newly identified baroreflex functionalities revealed by DTI bear clinical and therapeutic implications.

Causal contribution of malignancy to anomalous baroreflex functionality in patients with cancer: An overlooked aspect of cardio-oncology

“…Based on results from topographic analysis of the baroreflex neural circuits using diffusion tensor imaging, we proposed recently (Tsai et al, 2019) that the basal baroreflex-mediated sympathetic vasomotor tone is sustained by tonic inhibitory output from the nucleus tractus solitarii (NTS) where the baroreceptor afferents terminate to the rostral ventrolateral medulla (RVLM), which in turn lessens the tonic excitatory action of these premotor sympathetic neurons on vasomotor tone. Likewise, the basal cardiac vagal baroreflex activity is sustained by a tonic excitatory output from the NTS to the nucleus ambiguus (NA), which in turn exerts a tonic inhibitory action on the heart via the vagus nerve.…”

“…On-line digitized BP signals (Notocord, Croissy-Sur-Seine, France) were first analyzed by an arterial blood pressure analyzer (APR31a, Notocord) to obtain systolic BP (SBP), mean BP (MAP), HR, and pulse interval (PI). SBP signals were subsequently subjected to spectral analysis (SPA10a, Notocord) to detect the power density of the low-frequency (0.04-0.15 Hz) component in the SBP spectrum, an index for spontaneous baroreflex-mediated sympathetic vasomotor tone (Li et al, 2001; Tsai et al, 2019). To evaluate the cardiac vagal baroreflex, we used a baroreflex sequence analyzer (BRS10a, Notocord) to determined baroreflex sensitivity (BRS) based on detection of spontaneous sequences of consecutive increases or decreases in SBP and the associated changes in HR (Tsai et al, 2019).…”

Microglia-mediated inflammatory destruction of neuro-cardiovascular dysfunction after stroke

“…In addition, NTS also regulates blood pressure by activating the CVLM and RVLM. Simultaneously, the CVLM also projects onto the inhibitory projective fibers to RVLM (Tsai et al, 2019 ) to restrain vasoconstriction and cardiovascular excitation. Stressful conditions in the brain can reduce activity in the medial prefrontal cortex, leading to the overactivation of the amygdala.…”