Autonomic nervous system epinephrine

Adrenal medulla. Derived from neural crest tissue, the adrenal medulla forms the inner portion of the adrenal gland. It is the site of production of the catecholamines, epinephrine and norepinephrine, which serve as a circulating counterpart to the sympathetic neurotransmitter, norepinephrine, released directly from sympathetic neurons to the tissues. As such, the adrenal medulla and its hormonal products play an important role in the activity of the sympathetic nervous system. This is fully discussed in Chapter 9, which deals with the autonomic nervous system. 

Adrenaline (epinephrine)-producing (adrenergic) and acetylcholine secreting (cholinergic) neurones of the autonomic nervous system have direct and complimentary effects on the tone of blood vessels. 

The physiological effects of the catecholamines are mediated by a large number of different receptors that are of particular interest in pharmacology. Norepinephrine acts in the autonomic nervous system and certain areas of the brain. Epinephrine is also used as a transmitter by some neurons. 

Ang II also interacts with the autonomic nervous system. It stimulates autonomic ganglia, increases the release of epinephrine and norepinephrine from the adrenal medulla, and—what is most important—facilitates sympathetic transmission by an action at adrenergic nerve terminals. The latter effect involves both increased release and reduced reuptake of norepinephrine. Ang II also has a less important direct positive inotropic action on the heart. 

Dopamine, norepinephrine, and epinephrine (adrenalin) are biologically active amines that are collectively termed catecholamines. Dopamine and norepinephrine function as neurotransmitters in the brain and the autonomic nervous system. Norepinephrine and epinephrine are also synthesized in the adrenal medulla. 

The release of epinephrine and norepinephrine from the adrenal medulla is controlled by the sympathetic division of the autonomic nervous system. As discussed in Chapter 18, sympathetic cholinergic preganglionic neurons directly innervate this gland. An increase in sympathetic activity causes increased firing in these neurons, which in turn stimulates the release of epinephrine and norepinephrine from the adrenal medulla. 

FIGURE 14.5 The autonomic nervous system innervates smooth muscle, cardiac muscles, and gland. ACh = acetylcholine N = nicotinic cholinergic receptors M = muscarinic cholinergic receptors S = sympathetic chain P = parasympathetic chain E = epinephrine D = dopamine NE = norepinephrine Sup. = superior Inf. = inferior. 

The brain and the immune system are accepted as the two major body s adaptive systems (Elenkov et al., 2000). The brain can modulate immune functions and the immune system also sends messages to the brain. The communication between these two systems is done mainly by the hypothalamic-pituitary-adrenal axis and the autonomic nervous system (ANS). The sympathetic nervous system (SNS), which is part of the ANS, innervates the lymphoid organs (Elenkov et al., 2000) (Flierl et al., 2007). Catecholamines, like dopamine, serotonin, epinephrine and norepinephrine, are the end products of the SNS. 

Adrenergic transmission is well known to be involved in the regulation of homeostatic control through its functions in the autonomic nervous system. Additionally, adrenergic projections in the brain have been identified with important roles in neurocognition. Adrenoreceptors are seven transmembrane G-protein-coupled receptors that mediate the physiological responses of epinephrine and norepinephrine. The first classification of these receptors resolved a (alpha)-adrenoreceptors (aARs) from P (beta)-adrenoreceptors (PARs) (Ahlquist, 1948). Since then, additional subtypes and variants have been described. 

Autonomic nervous system (A, middle). In analogy to autonomic ganglia, NAChR are found also on epinephrine-releasing cells of the adrenal medulla, which are innervated by spinal first neurons. At all these synapses, the receptor is located postsynaptically in the somatodendritic region of the gangliocyte. 

Keywords Acetylcholine Autonomic nervous system Cyclosporine Epinephrine General anesthetics Immunostimu-lating agents Immunosuppressive agents Mycophenolate mofetil Opioid drugs Sedative-hypnotic agents... 

Figure 6-1. Schematic diagram comparing some features of the parasympathetic and sympathetic divisions of the autonomic nervous system with the somatic motor system. Parasympathetic ganglia are not shown as discrete structures because most of them are diffusely distributed in the walls of the organs innervated. ACh, acetylcholine Epi, epinephrine NE, norepinephrine, D, dopamine N, nicotinic M, muscarinic a, p, alpha and beta adrenoceptors D, dopamine, receptors. (Reproduced, with permission, from Katzung BG [editor] Basic Clinical Pharmacology, 8th ed. McGraw-Hill, 2001.)...

An example of a molecular disease is the panic state, which results from the flooding of the brain with epinephrine (adrenaline), a hormone carried in the blood. It is also a neurotransmitter released into neuronal synapses of activated neurons of the autonomic nervous system. Both epinephrine and norepinephrine are responsible for the emotions anger and fear. 

Epinephrine is released from the adrenal medulla by activation of the sympathetic nerves of the autonomic nervous system. Norepinephrine is released from the adrenal medulla. About 20% of the total catecholamine released from the adrenal is norepinephrine. Most norepinephrine released by sympathetic nerves is taken back up into presyn-aptic neurons. A small amount diffuses into the blood and circulates throughout the body. When the sympathetic nervous system is highly activated, the amount of norepinephrine entering the circulation increases. 

The enzyme MAOA is located in synapses of NE, 5-HT, and DA neurons, which are located in the locus ceruleus, placenta, intestine, and autonomic nervous system. MAOA breaks down 5-HT, NE and DA, rendering them inactive. Inhibition of MAOA activity helps alleviate depression because it slows the breakdown of epinephrine and NE. 

---