1. Introduction to Autonomic Pharmacology Gloanne C. Adolor, RPh, MD, MS, MBA, FPCP

2. Outline Review of ANS (favorite YL5 subjects) Drugs Acting on the ANS –Cholinoceptor-Activating and Cholinesterase-Inhibiting Drugs –Cholinoceptor-Blocking Agents Main Reference: Basic and Clinical Pharmacology by Katzung (11th ed).

4. Autonomic Nervous System (ANS) The ANS consists of motor neurons that: –Innervate smooth and cardiac muscle and glands –Make adjustments to ensure optimal support for body activities –Operate via subconscious control –Have viscera as most of their effectors

5. Functions and origins of the ANS

6. ANS branches cholinergic fibers - acetylcholine adrenergic fibers noradrenaline (norepinepherine NE)

7. ANS Versus Somatic Nervous System (SNS) The ANS differs from the SNS in the following three areas –Effectors –Efferent pathways –Target organ responses

8. Comparison of Somatic and Autonomic Systems

9. Efferent Pathways Heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector Axons of the ANS are a two-neuron chain –The preganglionic (first) neuron has a lightly myelinated axon –The ganglionic (second) neuron extends to an effector organ

10. Effectors The effectors of the SNS are skeletal muscles The effectors of the ANS are cardiac muscle, smooth muscle, and glands

11. Efferent (motor) nerves Two systems –Autonomic nerves (unconscious) Eg cardiac output, respiration, etc –Somatic nerves (voluntary)

12. Interactions of the Autonomic Divisions Most visceral organs are innervated by both sympathetic and parasympathetic fibers This results in dynamic antagonisms that precisely control visceral activity Sympathetic fibers increase heart and respiratory rates, and inhibit digestion and elimination Parasympathetic fibers decrease heart and respiratory rates, and allow for digestion and the discarding of wastes

14. Role of the Parasympathetic Division Concerned with keeping body energy use low Involves the D activities – digestion, defecation, and diuresis Its activity is illustrated in a person who relaxes after a meal –Blood pressure, heart rate, and respiratory rates are low –Gastrointestinal tract activity is high –The skin is warm and the pupils are constricted

15. Role of the Sympathetic Division The sympathetic division is the “fight-or-flight” system Involves E activities – exercise, excitement, emergency, and embarrassment Promotes adjustments during exercise – blood flow to organs is reduced, flow to muscles is increased Its activity is illustrated by a person who is threatened –Heart rate increases, and breathing is rapid and deep –The skin is cold and sweaty, and the pupils dilate

16. Visceral Reflexes Figure 14.7

17. Action of ANS drugs Drugs to block ANS chemical transmission Drugs to mimic ANS action ANS drugs can modify a variety of effector tissues –Cardiac muscle –Blood pressure –Exocrine glands

18. Cholinergic transmission Acetylcholine is at motor neuron and CNS nerve terminals Synthesized from –Acetyl coA (mitochondria) –Choline (dietary) –Catalyzed by choline acetyl transferase (ChAT) Release is dependent on Calcium (Ca 2+ ) Causes muscle contraction

19. Acetylcholine Identified 1921 Present at all NMJ and also CNS Synthesized in the axon terminal Diffuses across synaptic cleft Two receptor subtypes –Nicotinic ACh receptors –Muscarinic ACh receptors

20. Neuromuscular Junction 1999 Sinauer Associates Inc

21. Acetylcholine and NMJ

22. Characteristics of a neurotransmitter Synthesized in (or transported to) presynaptic terminal Stored in vesicles Regulated release Receptor located on postsynaptic membrane Termination of action

23. Neurotransmitter Effects All somatic motor neurons release Acetylcholine (ACh), which has an excitatory effect In the ANS: –Preganglionic fibers release ACh –Postganglionic fibers release norepinephrine or ACh and the effect is either stimulatory or inhibitory –ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector

24. Synaptic vesicles at the NMJ (EM) Heuser and Heuser

25. Presynaptic events Calcium influx releases synaptic vesicles from microtubules Movement of synaptic vesicles to sites of action Interaction of specific proteins Vesicle docking Membrane fusion Calcium dependent exocytosis

26. Synthesis and release of neurotransmitters Synaptic Transmission in: Basic Neurochemistry 6 th Edition

27. Fusion proteins regulate neurotransmitter release Vesicle proteins –Synaptobrevin Presynaptic membrane proteins –Syntaxins –SNAP-25

28. The SNARE hypothesis SNARE (Soluble N’ethylmalemide sensitive fusion Attachment protein REceptor) A. Pestronk www.neuro.wustl.edu/neuromuscular 2003www.neuro.wustl.edu/neuromuscular

31. Many presynaptic proteins regulate neurotransmitter release Synaptic Transmission in: Basic Neurochemistry 6 th Edition

32. Vesicular transport of NT – drug implications Toxins targeting neurotransmitter release –Spider venom (excess ACh release) –Botulinum (blocks ACh release) Tetanus

33. Postsynaptic events Boutons have multiple nerve terminals Simultaneous release Stimulation of contraction via AP Acetylcholine degraded after action –ACETYLCHOLINESTERASE (AChE)

34. RECEPTORS

35. Cholinergic receptors Two classes for acetylcholine Nicotinic and muscarinic –Nicotinic are ion channels Ionotrophic –Muscarinic are G-protein coupled Metabotrophic

36. Nicotinic Receptors Nicotinic receptors are found on: –Motor end plates (somatic targets) –All ganglionic neurons of both sympathetic and parasympathetic divisions –The hormone-producing cells of the adrenal medulla The effect of ACh binding to nicotinic receptors is always stimulatory

37. Muscarinic Receptors Muscarinic receptors occur on all effector cells stimulated by postganglionic cholinergic fibers The effect of ACh binding: –Can be either inhibitory or excitatory –Depends on the receptor type of the target organ

38. Ionotropic AChR Consist of five polypeptide subunits Receptors vary in: – subunit structure – agonist sensitivity – distribution Mediate fast synaptic transmission

39. Nicotinic AChR are sodium channels 1999 Sinauer Associates Inc

40. Metabotropic AChR Five muscarinic AChR subtypes G protein coupled Slower synaptic transmission via intracellular signaling cascade

41. Muscarinic AChR activate G- proteins 1999 Sinauer Associates Inc

42. Many G proteins for many uses G alpha classInitiating signalDownstream signal G alpha s b-Adrenergic amines, glucagon, parathyroid hormone, many others Stimulates adenylate cyclase G alpha i Acetylcholine, a- adrenergic amines, many neurotransmitters Inhibits adenylate cyclase G alpha tPhotons Stimulates cGMP phosphodiesterase G alpha q Acetylcholine, a- adrenergic amines, many neurotransmitters Increases IP3 and intracellular calcium G alpha 13 Thrombin, other agonists Stimulates Na+ and H+ exchange

43. G proteins activate enzymes, most commonly the following: Adenylyl cyclase - converts ATP into cyclic AMP (cAMP) Phospholipase C - cleaves a lipid (inositol phospholipid) into inositol-1,4,5- trisphosphate (IP 3, a hydrophilic sugar) and diacylglycerol (DAG, a lipid in the membrane)

44. Phospholipase C activates 2 signaling pathways

46. The Organization of the Sympathetic Nervous System Martini, Fundamentals of Anatomy and Physiology, 5th Edition, Prentice Hall 2001

47. The Organization of the Sympathetic Nervous System Thoracic Lumbar Martinit, Fundamentals of Anatomy and Physiology, 5th Edition, Prentice Hall 2001

48. Sympathetic Synapses Note location of synapse

49. The Organization of the Sympathetic Nervous System: The Adrenal Medulla

50. The Adrenergic Synapse

51. From: Basic and Clinical Pharmacology 8 th edition, B.G. Katzung; Lange 2001

52. Adrenergic receptors Four receptor subtypes –  1,  2,  1,  2 G protein linked –Bind either norepinephrine or epinephrine

53. Adrenergic Receptors The two types of adrenergic receptors are alpha and beta Each type has two or three subclasses (  1,  2,  1,  2,  3 ) Effects of NE binding to: –  receptors is generally stimulatory –  receptors is generally inhibitory A notable exception – NE binding to  receptors of the heart is stimulatory

54. Adrenergic Receptors It will be important to understand how alpha and beta receptors and the subtypes are distinguished: Originally by relative potency Now by cloning From: Basic and Clinical Pharmacology 8 th edition, B.G. Katzung; Lange 2001

55. Pharmacologic Demonstration of Adrenoreceptor Types The existence of alpha and beta receptors was originally proposed by Ahlquist in 1948 Latter Lands et al 1967, suggested the beta1 beta2 distinction

56. Adrenergic Receptors

58. Adrenergic transmission Catecholamines are the neurotransmitters Complex synthesis Secretion at nerve terminals and adrenal glands Adrenal glands –Two adrenal glands –Consist of cortex (outer) medulla (inner) medulla secretes: –Epinephrine (adrenaline) –Norepinephrine

59. NE and E are released at nerve terminals and secreted by the adrenal medulla

60. Norepinephrine and epinephrine Catecholamines Synthesized from dopamine Present in CNS and sympathetic nerves Widely distributed, general behavioral arousal eg raise blood pressure etc Stress increases release of norepinephrine

61. Epinephrine targets a G-protein coupled receptor

62. Beta-adrenergic receptor pathway 1 On binding of ligand, the receptor activates a G protein.

63. Dual Innervation Most of viscera receive nerve fibers from both parasympathetic and sympathetic divisions Both divisions do not normally innervate an organ equally

64. Dual Innervation Antagonistic effects –oppose each other –exerted through dual innervation of same effector heart rate decreases (parasympathetic) heart rate increases (sympathetic) –exerted because each division innervates different cells pupillary dilator muscle (sympathetic) dilates pupil constrictor pupillae (parasympathetic) constricts pupil

65. Dual Innervation Cooperative effects seen when 2 divisions act on different effectors to produce a unified effect –parasympathetics increase salivary serous cell secretion –sympathetics increase salivary mucous cell secretion ANS cooperation is best seen in control of the external genitalia –Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris –Sympathetic fibers cause ejaculation of semen in males and reflex peristalsis in females

66. Dual Innervation of the Iris

67. Without Dual Innervation Some effectors receive only sympathetic –adrenal medulla, arrector pili muscles, sweat glands and many blood vessels Sympathetic tone –a baseline firing frequency –vasomotor tone provides partial constriction increase in firing frequency = vasoconstriction decrease in firing frequency = vasodilation can shift blood flow from one organ to another as needed –sympathetic stimulation increases blood to skeletal and cardiac muscles -- reduced blood to skin

68. Sympathetic and Vasomotor Tone Sympathetic division prioritizes blood vessels to skeletal muscles and heart in times of emergency. Blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise.

69. Regulation of ANS Autonomic reflexes control most of activity of visceral organs, glands, and blood vessels. Autonomic reflex activity influenced by hypothalamus and higher brain centers, but it is the hypothalamus that has overall control of the ANS. Sympathetic and parasympathetic divisions influence activities of enteric (gut) nervous system through autonomic reflexes.

70. Levels of ANS Control The hypothalamus is the main integration center of ANS activity Subconscious cerebral input via limbic lobe connections influences hypothalamic function Other controls come from the cerebral cortex, the reticular formation, and the spinal cord

71. Hypothalamic Control Centers of the hypothalamus control: –Heart activity and blood pressure –Body temperature, water balance, and endocrine activity –Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex) –Reactions to fear and the “fight-or-flight” system

72. Levels of ANS Control Figure 14.9