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Theranostics 2016; 6(6):837-848. doi:10.7150/thno.14837 This issue Cite

Research Paper

MRI/DTI of the Brain Stem Reveals Reversible and Irreversible Disruption of the Baroreflex Neural Circuits: Clinical Implications

Chia-Hao Su^1*, Ching-Yi Tsai^1*, Alice Y.W. Chang², Julie Y.H. Chan¹, Samuel H.H. Chan^1✉

1. Institute for Translational Research in Biomedicine, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan, Republic of China;
2. Institute of Physiology, National Cheng Kung University, Tainan, Taiwan, Republic of China.
*Chia-Hao Su and Ching-Yi Tsai contributed equally to this work.

✉ Corresponding author: Samuel H.H. Chan, Institute for Translational Research in Biomedicine, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung 83301, Taiwan, Republic of China. Tel: +88677317123. Fax: +88677317123. Email: shhchancgmh.org.tw.

Abstract

Baroreflex is the physiological mechanism for the maintenance of blood pressure and heart rate. Impairment of baroreflex is not a disease per se. However, depending on severity, the eventuality of baroreflex dysfunction varies from inconvenience in daily existence to curtailment of mobility to death. Despite universal acceptance, neuronal traffic within the contemporary neural circuits during the execution of baroreflex has never been visualized. By enhancing signal detection and fine-tuning the scanning parameters, we have successfully implemented tractographic analysis of the medulla oblongata in mice that allowed for visualization of connectivity between key brain stem nuclei in the baroreflex circuits. When viewed in conjunction with radiotelemetric analysis of the baroreflex, we found that under pathophysiological conditions when the disrupted connectivity between key nuclei in the baroreflex circuits was reversible, the associated disease condition (e.g. neurogenic hypertension) was amenable to remedial measures. Nevertheless, fatality ensues under pathological conditions (e.g. hepatic encephalopathy) when the connectivity between key substrates in the baroreflex circuits was irreversibly severed. MRI/DTI also prompted partial re-wiring of the contemporary circuit for baroreflex-mediated sympathetic vasomotor tone, and unearthed an explanation for the time lapse between brain death and the inevitable asystole signifying cardiac death that follows.

Keywords: Neuroimaging, Baroreflex-mediated vasomotor tone, Cardiac vagal baroreflex, Neural circuits, Neurogenic hypertension, Hepatic Encephalopathy, Brain death.

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