Influence of Brainstem's Area A5 on Sympathetic Outflow and Cardiorespiratory Dynamics - PubMed
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Review
Influence of Brainstem's Area A5 on Sympathetic Outflow and Cardiorespiratory Dynamics
Isabel Rocha et al. Biology (Basel). 2024.
Abstract
Area A5 is a noradrenergic cell group in the brain stem characterised by its important role in triggering sympathetic activity, exerting a profound influence on the sympathetic outflow, which is instrumental in the modulation of cardiovascular functions, stress responses and various other physiological processes that are crucial for adaptation and survival mechanisms. Understanding the role of area A5, therefore, not only provides insights into the basic functioning of the sympathetic nervous system but also sheds light on the neuronal basis of a number of autonomic responses. In this review, we look deeper into the specifics of area A5, exploring its anatomical connections, its neurochemical properties and the mechanisms by which it influences sympathetic nervous system activity and cardiorespiratory regulation and, thus, contributes to the overall dynamics of the autonomic function in regulating body homeostasis.
Keywords: area A5; autonomic response; brainstem neurochemistry; cardiovascular regulation; sympathetic nervous system.
Conflict of interest statement
The authors declare no conflicts of interest.
Figures
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This diagram illustrates the two-level organisational structure of the autonomic reflex arc. The first level represents the simpler reflex-oriented pathways that directly modulate target organ activity in response to visceral sensory input. The second, more complex level is the central autonomic network (CAN), which integrates higher neuronal centres. This network controls a wide range of responses in the autonomic and endocrine systems as well as behavioural adaptations. The nucleus tractus solitarius (NTS) serves as a central hub where viscerosensory inputs from visceral organs are viscerotopically and functionally mapped, enabling both immediate reflexes and complex, integrated responses within the CAN.

Schematic representation of the most important afferent and efferent connections of the A5 neurones within the CAN stations and the spinal cord, as well as the most important neurotransmitters involved in those connections. Amyg: amygdala; LC: locus coeruleus; LPB: lateral parabrachial nucleus, PVN: paraventricular nucleus of the hypothalamus; PAG: periaqueductal grey matter; KF: Kolliker-Fuse nucleus; NTS: nucleus of tractus solitarius; RVL/CVL: rostroventrolateral medulla/caudal ventrolateral medulla; Hyppoc: hippocampus; IML: intermediolateral cell column; NE: nor-epinephrine; Glut: Glutamate; GABA: gamma-aminobutyric acid; * refer to the main neurotransmitter of this neuronal pathway; I–IV denote the layers of spinal cord grey matter.
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References
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This work was funded by national funds, Fundação para a Ciência e a Tecnologia, reference number UIDB/00306/2020.
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