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The baroreceptor reflex is a key blood pressure regulatory mechanism. This chapter provides an overview of recent advances focusing on novel experimental approaches and mechanisms that determine baroreflex sensitivity. Gene discovery and technological advances now enable molecular mechanisms essential to baroreflex function to be defined. Recent discoveries include: mechanosensitive DEG/ENaC ion channels...
Activation of the peripheral chemoreflex in awake rats produces a complex pattern of cardiovascular, respiratory and behavioral responses. The focus of the present chapter is the different aspects involved in the neurotransmission of sympathoexcitatory component of the chemoreflex, which is responsible for a large increase in arterial pressure. Experiments performed in awake and anesthetized rats...
Afferents from the cardiovascular system including baroreceptors send information via cranial nerves to the nucleus tractus solitarius (NTS) where it is processed for homeostatic reflexes. The basic organization of autonomic pathways for cardiovascular control diverges beyond NTS with the cardiac parasympathetic arc as short as two central neurons. Significant modulation and integration occurs at...
The importance of the nucleus tractus solitarius (nTS) in the regulation of cardiovascular function has been known for a long time. However, the role of different neurotransmitters in this region in mediating cardiovascular functions is just beginning to be delineated. The carotid chemoreceptor afferents terminate predominantly in a midline area around the calamus scriptorius in the commissural subnucleus...
Expression of the immediate early gene, c-fos, has been used to contribute to the understanding of central autonomic pathways which are activated by changes in blood pressure (BP). This approach has been particularly useful in demonstrating multisynaptic pathways involved in cardiovascular regulation, for determining relative strengths of pathways involved and, in combination with other neuroanatomical...
The hypothalamus plays a pivotol role in homeostatic responses and in ensuring optimal physiological responses in different types of behaviour. The adequacy of this regulation is dependent on appropriate cardiovascular changes unique to each behaviour. This chapter surveys the literature describing the different neuronal phenotypes in the hypothalamus and their projections to cardiovascular neurones...
The paraventricular nucleus of the hypothalamus (PVN) is a complex area composed of functionally different subsets of neurons, including magnocellular neuroendocrine, parvocellular neuroendocrine and parvocellular pre-autonomic neurons. Accumulating evidence indicates that PVN pre-autonomic neurons play important roles in cardiovascular control, both under physiological and pathological conditions...
Early studies in our laboratory suggested that in young (3–12 weeks of age) male spontaneously hypertensive rats (SHR), ingestion of a high NaCl diet exacerbates hypertension (Fig. 1), increases peripheral sympathetic nervous system activity and alters the norepinephrine (NE) content of a hypothalamic nucleus known to be involved blood pressure (BP) regulation (Winternitz et al, 1982a, b; Wyss et...
The ventrolateral aspect of the medulla oblongata (RVLM) contains presympathetic (PS) neurons that are highly active and receive strong inhibitory inputs from baroreceptors. These bulbospinal and barosensitive (BSBS) neurons are glutamatergic and express several other phenotypes including adrenergic (C1 cells). BSBS neurons selectively target sympathetic preganglionic neurons (SPGNs) that control...
Serotonin neurons are located in the midline of the brainstem. The axons of these neurons branch profusely throughout the entire neuraxis providing an innervation to neurons that are involved in activities as diverse as the sleep/wake cycle, autonomic control and motor control. Here we review some of the work that has been done in relation to serotonin neurons in the brainstem with particular regard...
The medullary raphe nuclei send both serotonergic and non-serotonergic projections to innervate spinal cord and brain stem targets, including sympathetic and parasympathetic preganglionic neurons in the spinal intermediolateral nucleus and dorsal motor nucleus, respectively. The recent discovery of retrogradely infected neurons within the medullary raphe following Pseudorabies virus injections into...
Sympathetic preganglionic neurons (SPN) in the spinal cord are important for controlling the heart, blood vessels and release of catecholamines from the adrenal medulla. The activity of SPN is predominantly controlled by nerve pathways originating in the brain; but SPN also receive information from interneurons, which lie near them in the spinal cord and relay peripheral sensory or other central nervous...
In response to external and internal signals, the sympathetic nervous system executes complex and highly differentiated commands to multiple target organs including the heart and blood vessels. For example, humans as well as animals, when presented with a threatening stimulus, display a series of physiological responses that may include increased cardiac output, pupillary dilation, constriction of...
Sympathetic ganglia are important components of the neural circuitry for regulation of vascular tone and cardiac dynamics and may contribute to the pathophysiology of hypertension and heart failure. For a long time, these ganglia were viewed as simple relay stations where acetylcholine mediated the transfer of signals from the central nervous system to peripheral effector neurons. However, new information...
The mammalian parasympathetic cardiac ganglia form a complex intrinsic cardiac nervous system composed of parasympathetic postganglionic projection neurons, local interneurons and possibly afferent neurons with central projections. In addition to the preganglionic parasympathetic cholinergic excitatory innervation, the cardiac ganglia are innervated by sympathetic postganglionic fibers and afferent...
It has long been known that arterial baroreflexes participate in regulating peripheral vascular tone, but there has been little evidence to link those reflexes to regulation of the cerebral circulation. In studies reviewed here we show that arterial baroreceptor reflexes modulate cerebrovascular tone through a pathway that connects the cardiovascular nucleus tractus solitarii with parasympathetic...
This chapter focuses on the neurobiology of premotor cardiac vagal neurons that are located in the brainstem. These parasympathetic cardiac neurons play an essential role in the regulation of heart rate, and are responsible for, together with sympathetic activity, cardiovascular homeostasis. Since cardiac vagal neurons are intrinsically silent their activity is determined by the activity and transmitters...
This chapter illustrates briefly the usefulness of viral vectors in studying genes regulating the cardiovascular system in both health and disease. Some advantages of using viral vectors are discussed and recent examples illustrated. A discussion follows on possible refinements for viral vectors as tools for systems physiology. This includes the use of cell-specific promoters, longer term expression...
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