The Autonomic Nervous System

1. The Autonomic Nervous System V. GeršlAccording to: - H.P.Rang, M.M.Dale, J.M.Ritter, P.K.Moore: Pharmacology, 5th ed.- R.A.Howland, M.J.Mycek: Lippincott’s Illustrated Reviews: Pharmacology, 3rd ed.

2. Efferent neurons of the autonomic system Brainstem or spinal cord Cell body Preganglionic neuron 1 Ganglionic transmitter Postganglionic neuron 2 Neuroeffector transmitter Effector organ (according to Lippincott´s Pharmacology, 2006)

3. Basic anatomy of the autonomic nervous system • The autonomic nervous system comprises threedivisions: sympathetic, parasympathetic and enteric. • Basic (two-neuron) pattern of the sympathetic and parasympathetic systems consists of preganglionic neurons with cell bodies in the CNS and postganglionic neurons with cell bodies in the autonomic ganglion. • Parasympathetic system is connected to the CNS via: • ― cranial nerve outflow (III, VII, IX, X) • ― sacral outflow. • Parasympathetic ganglia usually lie close to or within the target organ. • Sympathetic outflow leaves the CNS in thoracic and lumbar spinal roots. Sympathetic ganglia form two paravertebral chains, plus some midline ganglia. • The enteric nervous system consists of neurons lying in the intramural plexuses of the gastrointestinal tract. It receives inputs from sympathetic and parasympathetic systems but can act on its own to control the motor and secretory functions of the intestine.

4. Organization of the nervous system Nervous system Central Nervous System Peripheral Nervous System Efferent Division Afferent Division Autonomic System Somatic System Enteric Parasympathetic Sympathetic (according to Lippincott´s Pharmacology, 2006)

5. Summary of the neurotransmitters released and the types of receptors found within the autonomic and somatic nervous system. (according to Lippincott´s Pharmacology, 2006) AUTONOMIC SOMATIC Sympathetic innervation of adrenal medulla Parasympathetic Sympathetic Preganglionic neuron Ganglionic transmitter Acetylcholine Acetylcholine Acetylcholine No ganglia Nicotinic receptor Nicotinic receptor Nicotinic receptor Postganglionic neurons Adrenal medulla Acetylcholine Neuroeffector transmitter Epinephrine release into the blood Acetylcholine Norepinephrine Adrenergic receptor Muscarinic receptor Adrenergic receptor Nicotinic receptor Striated muscle Effector organs

6. Acetylcholine (ACh) and noradrenaline (NA) as transmitters in the peripheral nervous system. Skeletal muscle Somatic efferent system ACh (nic) Blood vessels etc. ACh (nic) NA Sympathetic system ACh (nic) ACh (mus) Sweat glands CENTRAL NERVOUS SYSTEM ACh (nic) Adrenal medulla ACh (mus) Salivary glands etc. ACh (nic) Parasympathetic system (according to Rang HP, Dale MM et al.: Pharmacology, 2003)

7. The efferent autonomic nervous system:divided into the sympathetic and the parasympathetic nervous systems. Sympathetic system: The preganglionic neurons of the sympathetic system come from thoracic and lumbar regions of the spinal cord and synapse in two cord-like chains of ganglia that run in parallel on each side of the spinal cord. Axons of the post- ganglionic neuron extend from these ganglia to the glands and viscera. Note: The adrenal medulla, like the sympathetic ganglia, receives preganglionic fibres from the sympathetic system. Lacking axons, the adrenal medulla, in the response to stimulation by neurotrasmitters, influences other organs by secreting the hormone epinephrine (and lesser amounts of norepinephrine) into the blood.

8. Parasympathetic system: The preganglionic fibres arise from the cranial and sacral areas of the spinal cord and synapse in ganglia near or on the effector organs. In both the sympathetic and parasymphatetic systems, postganglionic fibres extend from the ganglia to effector organs.

9. Functions of the autonomic nervous system 1. Sympathetic:activated in response to stressful situations (trauma, fear, hypoglycemia, cold, or exercise). Increase in heart rate and BP, mobilisation of energy stores of the body, and increase blood flow to skeletal muscles and heart while diverting flow the skin and internal organs. Dilation of the pupils and the bronchioles. "fight or flight" response. Reactions are triggered - by direct sympathetic activationof the effector organs and by stimulation of the adrenal medulla to release ADR (and lesser amounts of NOR). They enter the blood responses in effector organs. The sympathetic system – function as a unit – diffuse distributionof postganglionic fibres.

10. 2. Parasympathetic: Usually acts to oppose or balance the actions of the sympathetic division. The parasympathetic system is not a functional entity as such and never discharges as a complete system(otherwise it would produce massive, undesirable, and unpleasant symptoms). Parasympathetic fibres are activated separately the system functions to affect specific organs (e.g., the stomach or eye). The parasympathetic system - involved in activities as accommodation of near vision, movement of food, and urination and isessential for life. Dominant over thesympathetic system in "rest or digest" situations.

11. The main effects of the autonomic nervous system (according to Rang HP, Dale MM et al.: Pharmacology, 2003)

12. (according to Rang HP, Dale MM et al.: Pharmacology, 2003)

13. Physiology of the autonomic nervous system • The autonomic system controls smooth muscle (visceral and vascular), exocrine (and some endocrine) secretions, rate and force of the heart and certain metabolic processes (e.g. glucose utilisation). • Sympathetic and parasympathetic systems have opposing actions in some situations (e.g. control of heart rate, gastrointestinal smooth muscle) but not in others (e.g. salivary glands, ciliary muscle). • Sympathetic activity increases in stress (fight-or-flight response) whereas parasympathetic activity predominates during satiation and repose. Both systems exert a continuous physiological control of specific organs under normal conditions, when the body is at neither extreme.

14. Role of CNS in autonomic control of viscera: Although the ANS is a motor system, it requires sensory input from peripheral structures to provide information on the state of affairs in the body. 1. Reflex arcs: afferent impulses from the viscera etc. → to integrating centers (in the hypothalamus, medulla oblongata, spinal cord) in the CNS → respond to the stimuli by efferent reflex impulses via ANS. Most of the afferent impulses translated into reflex responses without involving consciousness (e.g., a fall in blood pressure causes pressure-sensitive neurons /baroreceptors/ to send fewer impulses to cardiovascular centers in the brain »»» reflex response of increased symphatetic output to the heart and vasculature, and decreased parasymphatetic output to the heart »»» compensatory rise in blood pressure and tachycardia.

15. 2. Emotions and the autonomic nervous system: Stimuli that evoke feelings of strong emotion (e.g. rage, fear, or pleasure) can modify the activity of ANS. Dual innervation by the autonomic nervous system. Most organs innervated by both divisions of ANS (e.g. the heart has vagal parasympathetic innervation that slows contraction, and symphatetic innervation that speeds contraction). Despite this dual innervation, one system usually predominates in controlling the activity of an organ (e.g., in the heart, the vagus is the predominant system).

16. - Neurotransmitters: 1.Role of transmitters:Communication between nerve cells (and between nerve cells and effector organs) occurs through the release of specific chemical signals from the nerve terminals, called neurotransmitters. Neurotransmitters rapidly diffuse across the gap (synapse) between nerve endings and combine with specific receptors on the postsynaptic (target) cell. 2. Membrane receptors: Neurotransmitters are too hydrophilic to penetrate the membranes. Their signal is mediated by binding to specific receptors on the cell surface. 3. Types of neurotransmitters: Over 50 - each binds to a specific family of receptors. Cholinergic and adrenergic neurotransmitters: the primary chemical signals in ANS; a wide variety of neurotransmitters in the CNS exists.

17. Transmitters of the autonomic nervous system • The principal transmitters are acetylcholine and noradrenaline. • Preganglionic neurons are cholinergic; ganglionic transmission occurs via N acetylcholine receptors. • Postganglionic parasympathetic neurons are cholinergic, acting on muscarinic receptors in target organs. • Postganglionic sympathetic neurons are mainly noradrenergic, though a few are cholinergic (e.g. glands). • Transmitters other than noradrenaline and acetylcholine (NANC transmitters) are also used extensively in the autonomic nervous system. E.g., nitric oxide and vasoactive intestinal peptide (parasympathetic), ATP and neuropeptide Y (sympathetic). Others (e.g., 5-hydroxytryptamine (5- HT), GABA and dopamine also play a role. • Cotransmission is a general phenomenon.

18. Neuromodulation and presynaptic interactions • As well as functioning directly as neurotransmitters, chemical mediators may regulate: • ― presynaptic transmitter release • ― neuronal excitability. • Both are examples of neuromodulation, and generally involve second messenger regulation of membrane ion channels. • Presynaptic receptors may inhibit or increase transmitter release, the former being more important. • Inhibitory presynaptic autoreceptors occur on noradrenergic and cholinergic neurons, causing each transmitter to inhibit its own release (autoinhibitory feedback). • Many endogenous mediators (e.g., GABA, prostaglandins, opioid and other peptides) as well as the transmitters themselves exert presynaptic control (mainly inhibitory) over autonomic transmitter release.

19. Parasympathetic Sympathetic Rapid response ACh ATP Intermediate response NA NO + Slow response NPY VIP Tissue response The main contransmitters at postganglionic parasympathetic and sympathetic neurons (according to Rang HP, Dale MM et al.: Pharmacology, 2003)

20. ACETYLCHOLINE (ACH): If transmission is mediates by acetylcholine - the neuron is termed cholinergic. ACH mediates the transmission of nerve impulses across autonomic ganglia in both the sympathetic and parasympathetic nervous systems and transmission from the autonomic postganglionic nerves to the effector organs in the parasympathetic system. Transmission at the neuromuscular junction is also cholinergic. ACH also in CNS. NOREPINEPHRINE (NOR) AND EPINEPHRINE (ADR): If norepinephrine (noradrenaline) or epinephrine (adrenalin is the transmitter, the fiber is called adrenergic. NOR mediates the transmission of nerve impulses from autonomic postganglionic nerves to effector organs in the sympathetic system. NOR and ADR also in CNS. A few sympathetic fibers, such as those involved in sweating, are cholinergic.

21. 4. Intracellular response: The binding to receptors proteins within the cell membrane are activated cellular response. second messenger systems "Second messenger" molecules produced in response to transmitter binding to receptor, translate the extracellular signal into a response within the cell. 1. Direct regulation of ionic permeability: Some receptors (e.g., the postsynaptic receptors of nerve or muscle) directly linked to membrane channels - binding of the neurotransmitter rapidly (within a millisecond) and directly affect ion permeability. 2. Regulation involving second messenger molecules: "Second messenger" molecules are part of the cascade of events that translates neurotransmitter binding into a cellular response. The two most widely recognized: the adenyl cyclase system and the calcium/ /polyphosphatidylinositol system.

22. A Receptors coupled to ion channels (according to Lippincott´s Pharmacology, 2006) Neurotransmitter Cl- Cell membrane Extracellular space Cell membrane Cl- Cytosol Changes in membrane potential or ionic concentration within cell

23. B Receptors coupled to adenyl cyclase (according to Lippincott´s Pharmacology, 2006) Hormone or neurotransmitter g b Receptor a Gs protein Inactive adenylyl cyclase Protein phosphorylation

24. C Receptors coupled to diacylglycerol and inositol triphosphate (according to Lippincott´s Pharmacology, 2006) Hormone or neurotransmitter g b Receptor a Gq protein Phospholipase C Diacylglycerol Inositol triphosphate Protein phosphorylation and increased intracellular Ca2+

25. Cholinergic Agonists

26. Summary of cholinergic agonists Cholinergic agonists Direct acting Acetylcholine Bethanechol Carbachol Cevimeline Pilocarpine Indirect acting (reversible) Ambenomium Donepezil Edrophonium Galantamine Neostigmine Physostigmine Pyridostigmine Rivastigmine Tacrine Indirect acting (irreversible) Echothiophate Isoflurophate Reactivation of acetyl-choline esterase (according to Lippincott´s Pharmacology, 2006) Pralidoxime

27. Sites of actions of cholinergic agonists in the autonomic and somatic nervous system (according to Lippincott´s Pharmacology, 2006) AUTONOMIC SOMATIC Sympathetic innervation of adrenal medulla Parasympathetic Sympathetic Preganglionic neuron Acetylcholine Ganglionic transmitter Acetylcholine Acetylcholine No ganglia Nicotinic receptor Nicotinic receptor Nicotinic receptor Postganglionic neurons Adrenal medulla Neuroeffector transmitter Epinephrine release into the blood Acetylcholine Acetylcholine Norepinephrine Adrenergic receptor Muscarinic receptor Adrenergic receptor Nicotinic receptor Striated muscle Effector organs

28. Cholinergic neuron (ACH is neurotransmitter): -preganglionic fibers terminating in the adrenal medulla, -autonomic ganglia (both parasympathetic and sympathetic !!), -postganglionic fibers of the parasympathetic division, - voluntary muscles of the somatic system (neuromuscular junction), -CNS Neurotransmission at cholinergic neurons: involves six steps. The first four, synthesis, storage, release and binding of ACHto a receptor, are followed by the fifth step -degradation of ACH in the synaptic gap, the sixth step - the recycling of choline.

29. Synthesis and release of acetylcholine from the cholinergic neuron 1 (according to Lippincott´s Pharmacology, 2006) Choline Choline • Synthesis of acetylcholine • Transport of choline is inhibited by hemicholinium. AcCoA Na+ Na+ Acetylcholine 6 2 • Uptake into storage vesicles • Acetylcholine is protected from degradation in the vesicle. • Recycling of choline • Choline is taken up • by the neuron. + Synaptic vesicle Ca2+ Ca2+ 3 • Release of neurotransmitter • Release is blocker by botulinum toxin. • Spider venom causes release of acetylcholine. Presynaptic receptor 5 Acetylcholine • Degradation of acetylcholine • Acetylcholine is rapidly hydrolyzed by acetylcholinesterase in the synaptic cleft Choline 4 • Binding to the receptor • Postsynaptic receptor is activated by binding of the neurotransmitter. Acetate Intracellular response

30. 1.Synthesis of ACH: Choline from extracellular fluid into the cytoplasm of cholinergic neuron (by a carrier system - inhibited by hemicholinium). Choline reacts with acetyl CoA cholinacetyltranferase) »»»acetylcholine. 2. Storage of ACH in vesicles: ACH transported into synaptic vesicles. 3. Release of ACH: When AP arrives at a nerve ending - voltage-sensitive Ca channels in the presynaptic membrane open »» increase in intracellular Ca »»» the fusion of synaptic vesicles with the cell membrane and release of ACH into the synapse (this release is blocked by botulinum toxin). (Black widow spider venom causes all of the cellular ACH stored in synaptic vesicles to spill into the synaptic gap).

31. 4. Binding to receptor: ACH diffuses across the synaptic space and binds to either postsynaptic receptors on the target cell or to presynaptic receptors »»» biological response within the cell, mediated by second messenger molecules. 5. Degradation of ACH: rapidly cleaved into choline and acetate by acetylcholinesterase. 6. Recycling of choline: Choline may be recaptured by transport system into the neuron.

32. Events and sites of drug action at a nicotinic cholinergic synapse AcCoA Choline Vesamicol CAT (according to Rang HP, Dale MM et al.: Pharmacology, 2003) Presynaptic nicotinic ACh receptor ACh CoA ACh carrier - - Empty vesicle ACh + Choline carrier - Exocytosis - Presynaptic toxins e.g. botulinum Hemicholinium ACh leak Choline + Acetate ACh AChE Presynaptic toxins, e.g. botulinum - - + Depolarising blocking agents, e.g. suxamethonium Anticholinesterase e.g. neostigmine Na+ Postsynaptic nicotinic ACh receptor K+

33. CHOLINERGIC RECEPTORS(CHOLINOCEPTORS): • Two families, muscarinic and nicotinic receptors. • Muscarinic receptors: In addition to ACH, also recognize • muscarine (an alkaloid in mushrooms). Only a weak affinityfor nicotine. • Located:- autonomic effector organs (i.e., heart, smoothmuscle, • exocrine glands) and in some parts of CNS. • Muscarinic receptors - at least five different subtypes: • M1, M2, M3, M4 and M5. All subtypes found on neurons. • M1 receptors also found on gastricparietal cells, • M2 receptors on cardiac cells and smooth muscle, • M3 receptors onexocrine glands and smooth muscle. • Pirenzepine = anticholinergic drug, selectively inhibits M1»»» • treatment of gastric and duodenal ulcers). • Prototype of non-subtype-specific drug: atropine.

34. Muscarinic acetylcholine receptor subtypes (according to Rang HP, Dale MM et al.: Pharmacology, 2003)

35. 2. Nicotinic receptors: In addition to binding ACH, also recognize nicotine (but only a weak affinity for muscarine). Nicotine initially stimulates and then blocks receptor. Located: CNS, adrenal medulla, autonomic ganglia, neuromuscular junction. The nicotinic receptors of autonomic ganglia (NN)differ from those of the neuromuscular junction(NM).

36. Nicotinic acetylcholine receptor subtypes (according to Rang HP, Dale MM et al.: Pharmacology, 2003)

37. Acetylcholine receptors • Main subdivision:nicotinic (nAChR) andmuscarinic (mAChR). • N receptors- directly coupled to cation channels and mediate fast excitatory synaptic transmission at the neuromuscular junction, autonomic ganglia and in the CNS. Muscle and neuronal N receptors differ in their molecular structure and pharmacology. • Both M and N receptors occur presynaptically and postsynaptically and function to regulate transmitter release. • M receptors - G-protein-coupled receptors, causing: • ― activation of phospholipase C ( formation of IP3 and DAG) • ― inhibition of adenylate cyclase • ― activation of K channels or inhibition of Ca channels. • M receptors - mediate ACH effects at postganglionic parasympathetic synapses (heart, smooth muscle, glands etc.), and contribute to ganglionic excitation. They occur in many parts of the CNS. • AllM receptors are activated by ACH and blocked by atropine. There are alsosubtype-selective agonists and antagonists.

38. Summary of cholinergic agonists Cholinergic agonists Direct acting Acetylcholine Bethanechol Carbachol Cevimeline Pilocarpine Indirect acting (reversible) Ambenomium Donepezil Edrophonium Galantamine Neostigmine Physostigmine Pyridostigmine Rivastigmine Tacrine Indirect acting (irreversible) Echothiophate Isoflurophate Reactivation of acetyl-choline esterase (according to Lippincott´s Pharmacology, 2006) Pralidoxime

39. Sites of actions of cholinergic agonists in the autonomic and somatic nervous system (according to Lippincott´s Pharmacology, 2006) AUTONOMIC SOMATIC Sympathetic innervation of adrenal medulla Parasympathetic Sympathetic Preganglionic neuron Acetylcholine Ganglionic transmitter Acetylcholine Acetylcholine No ganglia Nicotinic receptor Nicotinic receptor Nicotinic receptor Postganglionic neurons Adrenal medulla Neuroeffector transmitter Epinephrine release into the blood Acetylcholine Acetylcholine Norepinephrine Adrenergic receptor Muscarinic receptor Adrenergic receptor Nicotinic receptor Striated muscle Effector organs

40. Comparison of the structures of some cholinergic agonists (according to Lippincott´s Pharmacology, 2006)

41. DIRECT - ACTING CHOLINERGIC AGONISTS • - ACH • - synthetic esters of choline (e.g., carbachol and bethanechol) • - naturally occurring alkaloids (pilocarpine, muscarine, arecoline). • Other than ACH mimic effects of ACH by binding directly to • cholinoceptors. All have longer duration of action than ACH. • Some preferentially bind to muscarinic receptors. • A. ACETYLCHOLINE • Therapeutically of little importance (both because of its multiplicity • of actions and its rapid inactivation by acetylcholinesterase). • Both muscarinic and nicotinic activity.

42. 1. Actions: Muscarinic: a. Decrease in heart rate and cardiac output: The action of ACH mimics the effects of vagal stimulation. ACH i.v. »»» brief decrease in cardiac rate and stroke volume – a reduction in the rate of firing at the SA node. b. Decrease in blood pressure: Vasodilatation and the lowering of BP. Cholinergic receptors on the blood vessels cause vasodilation. In the absence of administered drugs, these receptors have no known function (ACH never released into the vasculature in any significant quantities).

43. c. Other actions: - stimulates the gut to increase motility, contraction of GIT smooth muscle, dilatation of sphincter -bronchoconstriction -increased secretions in GIT and in the bronchioles - stimulates secretions from salivary glands -increases motility of smooth muscle in the genitourinary tract. -eye: stimulation of ciliary muscle contraction for near vision and constriction of the pupillae sphincter muscle »»» miosis.

44. Nicotinic: - CNS - adrenal medulla (release of ADR) - autonomic ganglia (transmission from pre- to postganglionic sites in parasympathetic and sympathetic ganglia) - neuromuscular junction (contraction of striated muscle) 2.Therapeutic uses: Practically no therapeutic uses. dms 0.1 g

45. SYNTHETIC ESTERS: A. BETHANECHOL(be THAN e kole) carbamic ester, not rapidly hydrolyzed by AChE, little or no nicotinic actions, strong muscarinic activity. May be used orally. Major actions - smooth musculature of the bladder and GIT, duration of action of about 1 hour. Increased intestinal motility and tone, stimulates the detrusor muscles of the bladder »»» expulsion of urine. Therapeutic applications: Urological treatment (stimulation of the atonic bladder). Atony of GIT. Adverse effects: Action of generalized cholinergic stimulation, including sweating, salivation, flushing, decreased blood pressure, nausea, abdominal pain, diarrhea, and bronchospasm.

46. B. CARBACHOL(KAR bakole) both muscarinic (higher) and nicotinic actions, is not readily hydrolyzed. Biotransformed by other esterases at a much slower rate - longer activity. Actions: Profound effects on both the cardiovascular system and the GIT. It can cause release of ADR from the adrenal medulla by its nicotinic action. Therapeutic uses: Rarely used; except in the eye - miotic agent. Adverse effect: Similar to bethanechol. C. METHACHOLINE especially M (and lower N) effects, longer duration, profound effects on the cardiovascular system, rarely used.

47. Comparison of the structures of some cholinergic agonists (according to Lippincott´s Pharmacology, 2006)

48. NATURALLY OCCURING ALKALOIDS • A. PILOCARPINE(pye loe KAR peen) • Less potent than ACH. Unaffected by AChE. Mainly muscarinic activity. • Actions:Topically to cornea a rapid miosis andcontraction of the ciliary muscle. • Therapeutic use:in glaucoma (extremely effective in opening Schlemm’s canal »»» immediate drop in intraocular pressure - a result of the escape of aqueous humor). • Drug of choice in the acute lowering of intraocular pressure of both • narrow-angle and open-angle glaucoma. Action lasts a few hours. • Adverse effects:Enters CNS  CNS disturbances. • It stimulates sweat secretion.

49. B. MUSCARINE - only M effects Occurrence in mushrooms - possible intoxication - profound M symptom. Therapy: atropine C. OXOTREMORINE Synthetic tertiary amine, strong stimulation of M receptors (higher activity in CNS in comparison with other M agonist). Used experimentally. D. ARECOLINE Areca catechu (betel) - both M and N effect, stimulatory effects on CNS.

50. Muscarinic agonists (according to Rang HP, Dale MM et al.: Pharmacology, 2003)