Autonomic nervous system Cholinergic agonists (CHOLINOMIMETICS) PhD. A.V. Aleksandrova

Functional divisions within the nervous system

Somatic N.S Autonomic N.S What are the differences between the somatic and the autonomic nervous system? Somatic N.S Autonomic N.S Control skeletal muscles Control internal viscera Voluntary Involuntary Somatic nerve is one autonomic nerve is fiber two fibers (Preganglionic & Postganglionic)

Efferent neurons of the autonomic nervous system

Sympathetic ANS The 1st neuron of sympathetic division is located in the thoracolumbar region of the spinal cord (T1-L3) and the 2nd is disposed either in the paravertebral, or in the prevertebral ganglia. Postganglionic non-myelinated nerve fibres arising from neurones in the ganglia, innervate most organs of the body The neurotransmitter released by sympathetic nerve endings is noradrenaline.

Parasympathetic system The 1st neuron of parasympathetic system is located in the brain stem and in the sacral region of the spinal cord. The preganglionic fibres leave the central nervous system in the III, VII, IX and X pairs of cranial nerves and the third and fourth sacral spinal roots. Ganglia are located either in the tissue of effector organ or near it. The nerve endings of the postganglionic parasympathetic fibres release neurotransmitter acetylcholine. All the preganglionic nerve fibres (sympathetic and parasympathetic;) are myelinated and release acetylcholine from the nerve terminals which depolarizes the ganglionic neurones by activating nicotinic receptors.

Parasympathetic Nervous System (craniosacral outflow)

Cholinergic nervous fibres are: 1) preganglionic (sympathetic and parasympathetic); 2) all postganglionic parasympathetic; 3) postganglionic sympathetic which supply sweat glands and vessels of skeletal muscles; 4) somatic nerves; 5) nerves which supply adrenal medulla and carotic sinuses; 6) neurons of CNS Adrenergic nervous fibres are: 1) postganglionic sympathetic, except those which supply sweat glands and vessels of skeletal muscles; 2) neurons of CNS

Cholinergic transmission Main NT is Acetylcholine (Ach). A large number of peripheral ANS fibers which synthesize & release Acetylcholine are called CHOLINERGIC fibers. They include: All pre-ganglionic efferent autonomic fibers. Somatic motor fibers to skeletal muscles. Most parasympathetic post ganglionic fibers. A few sympathetic post ganglionic fibers– to sweat glands. Some parasympathetic post ganglionic fibers utilize nitric oxide or peptides for transmission.

Fate of acetylcholine released by cholinergic fiber ACh is released from the nerve into the synaptic cleft and binds to ACh receptors on the post-synaptic membrane, relaying the signal from the nerve. Ach-esterase, located on the post-synaptic membrane, terminates the signal transmission by hydrolyzing ACh. The liberated choline is reuptaken by the pre-synaptic membrane and used for resynthesis of ACh.

Cholinergic synapse Nerve terminal of cholinergic fibre contains numerous vesicles with neurotransmitter acetylcholine (ACh) that is released from presynaptic membrane. Release of acetylcholine depends on sufficient influx of Ca 2+, which occurs under the influence of action potential.   ATP negative feedback ATP

Cholinergic receptor types Two cholinergic receptor subtypes have been identified by selective agonists: muscarinic (M-cholinoceptors) and nicotinic (N-cholinoceptors). At least 5 subtypes of muscarinic receptors (M1 – M5) have been distinguished. There are 3 main classes of N- cholinoceptors: the muscle, ganglionic, and CNS classes. MUSCARINIC NICOTINIC M1 M5 NM NN M2 M3 M4 Ganglions Carotid sinus Skeletal muscles Adrenal glands CNS Eye Heart Smooth muscles Exocrine glands CNS

Muscarinic receptors High affinity to muscarine M1 – gastric parietal cells, saliva, CNS M2 - cardiac cells, smooth muscle, CNS M3 - bladder, exocrine glands, smooth muscle, eye, CNS M1&M3 – Gq M2 - Gi Amanita muscaria

Nicotinic receptors High affinity to nicotine NM- neuro-muscular junction NN – ganglion, adrenal gland CNS, carotid sinus

Mechanisms of impulse transmission Muscarinic receptors belong to G-protein coupled receptors. Transmission of impulses through M1, M3, M5 cholinoceptors is realized by phospholipase C, inositol triphosphate and diacylglycerol Stimulation of M2 and M4 cholinoceptors results in inhibition of adenylate cyclase and decrease in intracellular cAMP. N- cholinoceptors are ion channel coupled. Their stimulation results in opening of Na+ channels that causes depolarization.

Muscarinic receptors M1 M3

Pharmacological actions gastric parietal cells M-cholinoceptors Pharmacological actions Locations Receptor CNS excitation Gastric acid secretion CNS gastric parietal cells M1 Excitatory Cardiac inhibition (Bradycardia) Heart M2 Inhibitory Secretion of glands Smooth muscle contraction Vasodilatation (via nitric oxide) Exocrine glands Smooth muscles Vascular endothelium M3 Excitatory memory, arousal, attention and M4 & M5

Effects of stimulation N-cholinoceptors Cholinoceptors Localization Effects of stimulation NN Autonomic ganglia (parasympathetic and sympathetic) Increase in parasympathetic and sympathetic reactions Adrenal medulla Increase in adrenaline release, increase in BP NM Skeletal muscle Increase in tone, contraction Carotid sinus Reflex respiratory centre stimulation CNS Stimulation

Peripheral cholinoceptor Nicotinic receptors Central cholinoceptor Muscarinic receptors Peripheral cholinoceptor Nicotinic receptors Central cholinoceptor G protein linked receptors Ion channel linked receptors On all peripheral organs that receive postganglionic parasympathetic fibers Autonomic ganglia (sympathetic & parasympathetic) stimulation ( Nn ) Heart (M2) inhibition exocrine glands (M3) contraction Adrenal medulla (Nn) release of catecholamines (Adrenaline & Noradrenaline) Smooth muscles (GIT, urinary tract, bronchial muscles) (M3) contraction Skeletal muscle (Neuromuscular junction) (Nm) Contraction Excitatory or inhibitory Almost excitatory

Nicotinic actions Skeletal muscles: Low conc. of nicotine  muscle contraction High conc. of nicotine persistent depolarization & relaxation. Ganglia: stimulation of sympathetic& parasympathetic ganglia. Adrenal medulla release of catecholamines (A & NA).

Muscarinic actions Cholinergic actions Organs Contraction of circular muscle of iris (miosis)(M3) Contraction of ciliary muscles for near vision (M3) Decrease in intraocular pressure Eye bradycardia ( heart rate ) (M2) Release of NO (EDRF) Heart endothelium Constriction of bronchial smooth muscles Increase bronchial secretion M3 Lung Increase motility (peristalsis) Increase secretion Relaxation of sphincter M3 GIT Contraction of muscles Relaxation of sphincter M3 - Urination Urinary bladder Increase of all secretions sweat, saliva, lacrimal, bronchial, intestinal secretions M3 Exocrine glands

Cholinomimetics 1. Muscarinic agonists (M-cholinomimetics) Pilocarpine I. Direct acting 1. Muscarinic agonists (M-cholinomimetics) Pilocarpine Oxothermorine Aceclidine 2. Nicotinic agonists Lobeline Dimethylphenylpiperazinum (DMPP) 3. Muscarinic and nicotinic agonists Acethylcholine Carbachol II. Indirect acting (muscarinic and nicotinic agonists – anticholinesterase agents) 1. Reversible Neostigmine (Proserinum) Physostigmine Pyridostigmine Edrophonium Ambenonium chloride (Oxazylum) Galanthamine 2. Irreversible (Organophosphates) Echotiophate Isoflurophate Arminum Drugs used in poisoning with organophosphates 1. Reactivators of acetylcholine esterase Pralidoxime Dipiridoxinum Izonitrozinum Obidoxime 2. M-cholinoblockers Atropine

Pharmacological effects Bradycardia, decrease in blood pressure Raising the tone of smooth muscles of internal organs Stimulation of intestinal motility Reducing sphincter of alimentary canal and bladder Increased secretory activity of the exocrine glands Constriction of the pupil of the eye (miosis) spasm of accommodation Reducing intra ocular pressure Relief of pulses in mionevralnomu skeletal muscle synapse, strengthening their contractility (anticholinergic drugs) Stimulation of the central nervous system (means of penetrating the blood-brain barrier)

Main clinical usage 1. Glaucoma (Pilocarpine, Physostigmine, Armine) 2. Infants (Neostigmine) 3. Postoperative atony of the intestines and bladder (Neostigmine) 4. Paralysis, paresis, neuritis, polyneuritis (Neostigmine) 5. Dusturbances of skeletal muscle contractile function after cranial trauma, polio and stroke (Galanthamine hydrobromide) 6. Belladonna poisoning (Neostigmine, Physostigmine, Galanthamine) 7. Overdose nondepolarizing muscle relaxants (Neostigmine) 8. Xerostomia (Pilocarpine) 9. Respiratory depression (Cititon, Lobeline)

Side effects of cholinomimetics 1. Bradycardia 2. Bronchospasm 3. Intestinal cramps, colic, diarrhea 4. Hypersalivation 5. Blurred vision

Contraindications 1. Bradycardia, A-V block 2. Asthma 3. Gastric ulcer and 12 duodenal ulcer 4. Epilepsy (Neostigmine) 5.Pregnancy (Neostigmine)

Direct acting cholinergic agonists ACETYLCHOLINE

Direct acting cholinergic agonists ACETYLCHOLINE Decrease in heart rate and cardiac output 2. Decrease in blood pressure

Direct acting cholinergic agonists ACETYLCHOLINE 3. Other actions 4. Clinical use very rare: eye drops to obtain miosis Muscarinic and nicotinic agonist not used clinically because Ach is not selective (N, M) Has short duration of action. Why? Due to rapid metabolism by acetycholinesterase

Direct acting cholinergic agonists Stimulation of atonic bladder Nonobstructive urinary retention Neurogenic atony Megacolon Ophthalmology

Direct acting cholinergic agonists PILOCARPINE Tertiary nitrogen Good adsorbtion Penetrate BBB

Direct acting cholinergic agonists PILOCARPINE Natural alkaloids Tertiary amine lipophilic Pharmacokinetics It is well absorbed Good distribution Cross BBB (has central effects). Long duration of action Direct muscarinic agonist (mainly on eye & secretion). Jaborandi (Pilocarpus pennatifolius)

Direct acting cholinergic agonists PILOCARPINE

Pilocarpine Uses: Xerostomia (dry mouth). Drug of choice in emergency glaucoma applied as eye drops. Adverse effects: Profuse sweating Salivation Bronchoconstriction Diarrhea CNS effects

Aceclidinum a synthetic preparation; administered SC, IM, or topically (eye drops); not toxic; does not penetrate CNS; M-cholinomimetic; used for the treatment of atonia of the intestine and urinary bladder, as well as for glaucoma.

Atropine Mushroom poisoning Miosis Hyper salivation Excessive sweating, lacrimation Cold, wet skin Bradycardia Polyuria Diarrhea Convulsions Atropine

N-CHOLINOMIMETICS They stimulate N-cholinoreceptors in zona carotis and initiate a reflexive increase in the activity of the respiratory and vasomotor centers resulting in the short stimulation of breathing and elevation of BP. They also stimulate N-cholinoreceptors in the adrenal medulla, increase the secretion of epinephrine, which causes vasoconstriction and the elevation of BP

NICOTINE It is a tobacco alkaloid with a dose-dependent action on N-cholinoreceptors. Effects of nicotine are manifested in tobacco smoking. Nicotine causes dependence that leads to abuse of tobacco and results in the development of cardiovascular and lungs pathology.

Physiological effects of nicotine at CNS NN receptors • ↑Emesis (vomiting) due to actions on chemoreceptor trigger zone of medulla oblongata • Dependence (i.e. makes it hard to quit smoking) • Respiratory depression (only at very high doses) due to actions on medulla oblongata - also contribution from blockade of diaphragm and intercostal muscles • Tremors + convulsion (only at very high doses)

Physiological effects of nicotine at peripheral NN receptors Many Effects of Nicotine Involve Ganglia • ↑GI motility (nausea, diarrhea, vomiting) – Stimulation of parasympathetic ganglia • ↑Heart rate, ↑blood pressure – Stimulation of sympathetic ganglia innervating heart and blood vessels – Release of EPI from adrenal medulla – Stimulation of chemoreceptors → reflex ↑heart rate, vasoconstriction

Lobeline is an alkaloid; is administered IV and acts during 3-5 min; stimulates N-cholinoreceptors; is used for emergency help in the respiratory arrest, asphyxia, asphyxia of newborns; is used to treat tobacco abuse in the form of combined tablets is not used for collapse due to its ability to provoke transitory a decrease in BP resulting from the stimulation of n.vagus center.

Cytitonum the name of a cytizine solution; administered IV, acts 3-5 min; stimulates N-cholinoreceptors; reflexly stimulates respiration and increases BP; used for emergency help in respiratory arrest and collapse; an ingredient of combined tablets against tobacco abuse.

Indirect acting cholinergic agonists Reversible Irreversible Edrophonium Neostigmine Physostigmine Rivastigmine Galantamine Echothiophate Organophosphates Arminum

Mechanism of action Mechanism of action: Anticholinesterases prevent hydrolysis of Ach by antagonizing cholinesterase thus increase Ach concentrations and actions at the cholinergic receptors (both nicotinic and muscarinic).

Pharmacological effects of anticholinesterases Muscarinic actions Nicotinic actions CNS actions: Excitation, convulsion, respiratory failure, coma only for lipid soluble anticholinesterases physostigmine & phosphate ester except Ecothiophate.

Reversible Reversible anticholinesterase Tertiary ammonium compound Physostigmine Reversible anticholinesterase Tertiary ammonium compound Non polar (lipid soluble) Good lipid solubility Good oral absorption Has muscarinic & nicotinic actions cross BBB (has CNS effects) Calabar Bean

Reversible Physostigmine Indications 1. Atony of intestine 2. Atony of bladder 3. Glaucoma 4. Overdose of ATROPINE, ANTIPSYCOTICS, ANTIDEPRESSANTS Side effects Convulsions Bradycardia Paralysis of skeletal muscle

Reversible Quatenary nitrogen Poor adsorbtion Not penetrate BBB Neostigmine Quatenary nitrogen Poor adsorbtion Not penetrate BBB Reversible anticholinesteras Has muscarinic & nicotinic actions (prominent on GIT & urinary tract).

Reversible Neostigmine Indications Side effects Paralyzes Salivation Myastenia gravis Antidote of neuro-muscular blocker TUBOCURARINE Salivation Flushing Decreased BP Abdominal pain Diarrhea Bronchospasm

Contraindications Neostigmine Bronchial asthma Intestinal inflammation, obstruction Bladder obstruction Peritonitis

Galantamine an alkaloid from Galanthus Woronowi; administered SC, IM; penetrates into CNS; has a reversible anticholinesterase action; used for the treatment of paralysis, neuritis, early stages of Alzheimer’s disease and other neurological diseases; is not used in glaucoma due to its irritative action.

Reversible Quatenary nitrogen Poor adsorbtion Not penetrate BBB Edrophonium Quatenary nitrogen Poor adsorbtion Not penetrate BBB Fast elimination Duration 10-20 min

Reversible Edrophonium Diagnosis of myasthenia gravis Antidote of neuro-muscular blocker

Reversible Tertiary nitrogen Good adsorbtion Penetrate BBB Rivastigmine Tertiary nitrogen Good adsorbtion Penetrate BBB

Reversible Rivastigmine Alzheimer disease

Irreversible -Used for glaucoma. Mechanism Echothiophate Mechanism -Irreversible anticholinesterase -Binds to cholinesterase by strong covalent bond. -Have very long duration of action -Aging make bond extremely stable -Used for glaucoma.

Toxicology Organophosphates

SLUDGEM Toxicology Salivation Lacrimation Urination Defecation Gastrointestinal motility Emesis Miosis SLUDGEM Death is caused by breath insufficiency, bronchospasm and lungs edema

Toxicology Reactivation of acetylcholinesterase PRALIDOXIME Not enter BBB M-cholinoblocker ATROPINE Antimuscarinic only Anticonvulsant DIAZEPAM

Pralidoxime (PAM) cholinesterase reactivator Acts by regeneration of cholinesterase enzyme. reactivates recently inhibited enzymes before aging. Uses I.V.  over 15-30 min for organophosphate intoxication.

Summary for cholinomimetics & their uses Eye : treatment of glaucoma Pilocarpine (direct muscarinic agonist) Physostigmine -Ecothiophate (indirect cholinomimetics) Urinary retention and paralytic ileus Bethanechol (direct) Neostigmine (indirect) Myasthenia gravis (only indirect cholinomimetics) Pyridostigmine, Neostigmine, Ambenonium Xerostomia Pilocarpine –Cevimeline (Sjogren’s syndrome) Alzheimer’s disease: Rivastigmine, Donepezil