Brainstem is a region of the brain connecting the cerebrum to the spinal cord. The brainstem is divided into three parts from rostral to caudal; midbrain, pons, and medulla oblongata (6). Critically, the pons and medulla contain the autonomic centres (nuclei) for controlling the principal cardiovascular and respiratory system functions.
The vital respiratory centres in the pons are the parabrachial nuclei and striatum (PBN), kölliker fuse nucleus (KFN), and raphé nuclei (RN), including the nucleus raphé pontis (NRpn) and the rostral portion of the nucleus raphé magnus (NRmg). The medulla contains the caudal portion of the NRmg as well as the nucleus raphé pallidus (NRpa) and nucleus raphé obscurus (NRob) known as the medullary raphe nuclei (MRN). Other crucial medullary respiratory nuclei include the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG), nucleus ambiguus (NA), Bötzinger complex (BC), pre-Bötzinger complex (pBC), solitary tract (ST) and nucleus of the solitary tract (NTS), hypoglossal nucleus (HN), and the rostral/caudal ventral respiratory groups (R/CVRG). The MRN, ST, NTS, NA, rostral/caudal ventrolateral medulla (R/CVLM), and dorsal motor nucleus of the vagus (DMNV) regulate cardiovascular function.
The brainstem cardiorespiratory centres, such as the NTS, MRN, NA, DMNV, pBC and R/CVLM, are highly metabolically active and, in response to hypoxemia, are involved in cardiac drive, respiratory rhythm generation and blood pressure adjustment. Further, the highly metabolic nature of the cardiorespiratory regions may indicate that these nuclei are susceptible to hypoxia. It is possible that chronic fetal hypoxemia and hypoglycemia, hallmarks of FGR, can negatively impact the normal development of these regions and consequently result in cardiorespiratory complications before and after birth.
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