Junctional Transmission in Smooth Muscle and the Autonomic Nervous System

Overview of the Anatomy, Physiology, and Pharmacology of the Autonomic Nervous System

Comprised of the sympathetic nervous system, parasympathetic nervous system, and enteric nervous system, the autonomic nervous system (ANS) provides the neural control of all parts of the body except for skeletal muscles. The ANS has the major responsibility to ensure that the physiological integrity of cells, tissues, and organs throughout the entire body is maintained (homeostasis) in the face of perturbations exerted by both the external and internal environments. Many commonly prescribed drugs, over-the-counter drugs, toxins, and toxicants function by altering transmission within the ANS. Autonomic dysfunction is a signature of many neurological diseases or disorders. Despite the physiological relevance of the ANS, most neuroscience textbooks offer very limited coverage of this portion of the nervous system. This review article provides both historical and current information about the anatomy, physiology, and pharmacology of the sympathetic and parasympathetic divisions of the ANS. The ultimate aim is for this article to be a valuable resource for those interested in learning the basics of these two components of the ANS and to appreciate its importance in both health and disease. Other resources should be consulted for a thorough understanding of the third division of the ANS, the enteric nervous system. © 2016 American Physiological Society. Compr Physiol 6:1239-1278, 2016.

Time course of the development of pre- and postjunctional supersensitivity in the rabbit ear artery after decentralization

Changes in the sensitivity of the rabbit ear artery to exogenous norepinephrine and potassium and to sympathetic nerve electrical stimulation were examined in vitro following decentralization which was performed by removing the unilateral preganglionic nerve proximal to the superior cervical ganglion. The contralateral side was left intact as a control. The postjunctional supersensitivity to exogenous norepinephrine and potassium had fully developed one week after the decentralization and was sustained for at least 8 weeks; the arteries decentralized for 1-8 weeks were about 2.1- and 1.3-fold supersensitive to norepinephrine and potassium, respectively, as compared with the contralateral control arteries. The frequency-response curve of the electrically stimulated decentralized artery shifted gradually to the left of the control within weeks after decentralization. Since the response to electrical stimulation was attributed to endogenous norepinephrine released from the sympathetic nerve terminals within the adventitial-medial junction, the leftward shift of the frequency-response curve in the decentralized artery probably reflects a gradual increase in the released norepinephrine per pulse by electrical stimulation, i.e., the prejunctional supersensitivity to electrical stimulation. It is concluded that the prejunctional sympathetic supersensitivity to electrical stimulation develops slower than the postjunctional nonspecific supersensitivity in the rabbit ear artery. The change in the sensitivity of the denervated postganglionic neuron, including the superior cervical ganglion is also discussed with regard to the "law of denervation supersensitivity".