Or by prior treatment with the sympathetic neurotoxic agent, 6-hydroxydopamine. Is reduced but not prevented by superior cervical ganglionectomy Phenylethanolamine N-methyltransferase and can, therefore, synthesize epinephrine this synthesis 16 Cervical sympathetic stimulation increases their levels. Both have beenĭemonstrated in iris neurons 15 and in the aqueous humor. 14 Increasing this frequency facilitates norepinephrine release. Rather, release is partially a function of theįrequency of action potentials. Release of norepinephrine may not occur withĮach action potential. Stored in granular vesicles located in varicosities in the terminals Tyrosine hydroxylase, dopa decarboxylase and dopamine-beta-hydroxylase. Norepinephrine is synthesized from tyrosine by the sequential actions of TRANSMITTER SYNTHESIS, RELEASE, AND INACTIVATION In the blood flow to the choroid of the rabbit, 13 suggesting that this structure, too, has a sympathetic nervous system 11, 12 Electrical stimulation of the superior cervical ganglion causes a 58% to 70% reduction Not all, investigators have shown catecholamine-containingįibers in the retinal blood vessels of human eyes. 9, 10 This innervation is much more extensive in arterioles than venules andįalls off rapidly with increasing distance from the optic nerve head. Innervation from the superior cervical ganglion. 8 In chickens and rabbits, the retinal blood vessels have a sympathetic 7 A limited number of adrenergic fibers have been found in the iris sphincter 6 Their numbers are much reduced in the rat iris after superior cervical In the iris dilator muscle and ciliary processes. Of the trabecular meshwork and corneal limbus of mammals, includingĬatecholamine-containing nerve fibers are found in their greatest concentrations 3 Catecholamine-containing nerve endings have been demonstrated in the areas Rabbit corneal epithelium transport by a cAMP related mechanism. Is based on experiments demonstrating that exogenous catecholamines stimulate Known but they may mediate epithelial chloride transport this theory The physiologic role of these corneal fibers is not 2 In the fetus, these are subepithelial in the adult, they are found only Have also been demonstrated in human cornea. The axon terminals release the transmitter, norepinephrine 1 resulting in dilation of the pupil, blanching of the conjunctiva, and Smooth muscle fibers in the iris dilator muscle, conjunctival blood Postganglionic axons innervate multiple tissues including the The superior cervical ganglion, a sympathetic nervous system structure. The eye is innervated by catecholamine-containing axons originating from SYSTEMIC SIDE EFFECTS FROM TOPICAL PHENYLEPHRINE Alpha-Adrenergic Drugs Chapter 29ĬATECHOLAMINE-CONTAINING NEURONS OF THE EYE
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