Clinical Pharmacology Autonomic pharmacology Jane M Johnston Ph.D.

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

ANS branches cholinergic fibres - acetylcholine adrenergic fibres noradrenaline (norepinepherine NE)

Functions and origins of the ANS

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

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

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

The discovery of vagusstoff E.Chudler 2001

Neuromuscular Junction 1999 Sinauer Associates Inc

Acetylcholine and NMJ

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

Synaptic vesicles at the NMJ (EM) Heuser and Heuser

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

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

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

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

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

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

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

Motor neuron innervating skeletal muscle

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

Nicotinic AChR are sodium channels 1999 Sinauer Associates Inc

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

Muscarinic AChR activate G- proteins 1999 Sinauer Associates Inc

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

Mode of cholinergic drug action Cholinomimetics agonist antagonist Cholinesterase inhibitors Clinical applications

Cholinomimetics Katzung, 2001

AChR agonists and antagonists Nicotinic AChR agonists Nicotine Nicotinic AChR antagonists Strychnine Snake toxins Bungarotoxin Muscarinic AChR agonist Muscarine Muscarinic AChR antagonists Atropine

Cholinesterase inhibitors Inhibit breakdown of acetylcholine at the synapse Act by Binding to acetylcholine esterase (steric hinderance or hydrolysis) Actions of acetylcholine persist at synapse Pesticides and nerve gases

Clinical Implications Myasthenia Gravis Glaucoma Cholinergic poisons CNS – Alzheimer’s Disease Schizophrenia

Myasthenia gravis Affects skeletal muscle at NMJ Involves autoimmunity to nicotinic receptors Extreme weakness, difficulty speaking, eating, breathing Cholinesterase inhibitors for therapy

Adrenergic transmission Catecholamines are the neuroTs 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

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

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

Synthesis of norepinephrine (NA)

Synthesis of epinephrine (adrenaline)

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

Sympathetomimetic drugs Can act directly or indirectly Direct binding to receptors Epinepherine, dopamine (CNS and renal) Indirectly Drugs targeting synthesis and release of NE and NA eg DBH inhibitors, reserpine - depletes stores Drugs targeting reuptake at synapse eg cocaine, Tricyclic antidepressants

Importance of sympathetomimetic drugs Cardiovascular system Regulation of smooth muscle affects heart and blood pressure beta blockers Respiratory tract Smooth muscle relaxation – bronchodilation Isoproterenol, albuterol (asthma) Metabolic effects Liver effects, insulin secretion CNS Nervousness, emotional well-being, psychosis etc