Adrenergic fibers

The answers are 318-d, 319-c, 320-a. (Hardman, pp 120-1220 Norepinephrine is synthesized from dopamine by dopamine-p-oxidase, which hydnoxylates the p-carbon This enzyme is localized in the amine storage granules. Norepinephrine is found in adrenergic fibers, the adrenal medulla, and in neurons in the locus ceruleus and lateral ventral tegmental fields of the CNS. 

I 8. Adrenergic fibers 3 I 9. Adrenal medulla 320. Caudate nucleus... 

The adrenergic pathways that use epinephrine as a neurotransmitter, which have been explored only recently. One of these systems is also tegmental and is mixed with noradrenergic cells. The other is thalamic-hypothalamic, involved with the vagus nerve. Some adrenergic fibers are also found in the fourth ventricle and the spinal cord. 

It has been known for many years that autonomic effector tissues (eg, gut, airways, bladder) contain nerve fibers that do not show the histochemical characteristics of either cholinergic or adrenergic fibers. Both motor and sensory NANC fibers are present. Although peptides are the most common transmitter substances found in these nerve endings, other substances, eg, nitric oxide synthase and purines, are also present in many nerve terminals (Table 6-1). Capsaicin, a neurotoxin derived from chili peppers, can cause the release of transmitter (especially substance P) from such neurons and, if given in high doses, destruction of the neuron. 

The enteric system in the gut wall (Figure 6-2) is the most extensively studied system containing nonadrenergic, noncholinergic neurons in addition to cholinergic and adrenergic fibers. In the small intestine, for example, these neurons contain one or more of the following nitric oxide synthase,... 

Previous studies have shown that accommodation mediated via ciliary smooth muscle activity also receives sympathetic innervation. Sympathetic nerves reach the ciliary muscle through the uveal blood vessels in close association with arteries and terminal arterioles. The distribution of the adrenergic fibers in the ciliary muscle appears to vary across species. In primates sympathetic nerve terminals, mainly 3 receptors, can generally be found in the anterior portion of the ciliary muscle. The accommodative amplitude significantly decreased in human subjects after instillation of phenylephrine (an a agonist) or hydroxyamphetamine (an a and (3 agonist). Such observations provide evidence that both sympathetic and parasympathetic divisions of the autonomic nervous system can affect accommodation but not equally. Furthermore, the nature of sympathetic innervation can be summarized as follows ... 

It has been proposed that adrenergic fibers terminate at inhibitory B receptors on smooth muscle fibers, and at inhibitory a receptors on parasympathetic cholinergic (excitatory) ganglion cells of Auerbach s plexus. 

The thyroid gland consists of two lobes connected by an isthmus and is positioned on the ventral surface of the trachea just below the larynx. It receives adrenergic fibers from the cervical ganglion and cholinergic fibers from the vagus and is profusely vascularized by the superior and inferior thyroid arteries. Histologically, thyroid tissue is composed of numerous follicles lined by a single layer of epithelial cells around a lumen filled with proteinaceous material called colloid. 

This interest in the nature of chemical transmission in the central nervous system continues to bear fruit. For example, studies on nerve terminals of postganglionic adrenergic fibers (6) and on the adrenal medulla had, over a period of many years, provided a fairly clear picture of the biosynthesis, release, reuptake, and destruction of the adrenergic transmitter norepinephrine. Other studies had shown that in patients with classical Parkinson s disease parts of the brain—the substantia nigra and corpus striatum—contained less dopamine than did normal brains (7). Dopamine is one of the intermediates in the biosynthesis of norepinephrine from phenylalanine. 

The neurotransmitter of all preganglionic autonomic fibers, all postganglionic parasympathetic fibers, and a few postganglionic sympathetic fibers is acetylcholine (ACh). Adrenergic fibers comprise the majority of the postganglionic sympathetic fibers here, the transmitter is norepinephrine (NE, noradrenaline). The terms cholinergic and adrenergic are used to describe neurons that release ACh or NE, respectively. 

E. Nonadrenergic, Noncholinergic (NANC) Transmission Some nerve fibers in autonomic effector tissues do not show the histochemical characteristics of either cholinergic or adrenergic fibers. Some of these are motor fibers that cause the release of ATP and possibly other purines related to it. Purine-evoked responses have been identified in the bronchi, gastrointestinal tract, and urinary tract. Other motor fibers are peptidergic, ie, they release peptides as the primary transmitters (see list above under Cotransmitters). 

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