Introduction to Neuropharmacology PDF

# Introduction to Fundamental Neuropharmacology: ## Learning Outcomes: - Define neuropharmacology. - Revisit axonal conduction, neurotransmitters and synaptic transmission using a neuropharmacological approach (3 case stories). - Review different types of neurotransmitters and neurotransmitter rec...

# Introduction to Fundamental Neuropharmacology: ## Learning Outcomes: - Define neuropharmacology. - Revisit axonal conduction, neurotransmitters and synaptic transmission using a neuropharmacological approach (3 case stories). - Review different types of neurotransmitters and neurotransmitter receptors. - Define neurotransmitter pharmacology and discuss the rest of the schedule for this unit. ## Pharmacology and Advancement of Science: - An image shows the progression of pharmacology from 3000 BC to today. ### Timeline: | Year | Field | Development | |---|---|---| | 3000 BC | Therapeutics, tools, and weapons | Magical potions, herbal remedies | | ~1600 AD | Chemistry | Natural products, chemical structure | | ~1800 | Biomedical Sciences | Pathology, physiology, biochemistry, molecular biology | | ~1900 | | Pharmacology, pharmaceutical industry, synthetic drugs, biopharmaceuticals | | ~1970 | | | | ~2000 | | | ## Pharmacological Tools and Their Applications: - Pharmacological tools are used to understand how different organs function. - In neuroscience, pharmacological tools are used to understand how the brain functions. - Pharmacology has many sub-disciplines. - Has been used in armed forces through lethal gases to kill people. ## What is Neuropharmacology? - Neuropharmacology is a term describing the study of drugs that affect the nervous system, whether they affect sensory perception, motor function, seizure activity, mood, higher cognitive function, or other forms of nervous system functioning. - Neuropharmacology is part of the pillars that make up cognitive sciences - neurophysiology, neuroanatomy, neuropharmacology + neuro-techniques. ## Terms: - **Psychopharmacology:** effects of drugs on psychologic parameters such as emotion and cognition. - **Neuropsychopharmacology:** all sorts of drug effects on nervous system. - **Medical neuropharmacology:** effects of medicines and their side-effects. - **In vitro neuropharmacology:** effects of drugs on isolated tissues or neurons - determining concentration (in M) response relationships. - Can use molar (M) as we can measure the number of molecules in a certain amount of fluid. - **In vivo neuropharmacology:** effects of drugs in organisms and animals; determining dose (e.g. mg/kg) response relationships. - Cannot use molar as we can't determine how much of a drug/compound reaches the brain or i.e. muscle. - The term "drug" is used to largely relate to medicines. Other drugs (illicit or not) are referred to as compounds/chemicals/agents. ## Case Story 1: Uses of Picrotoxin - Picrotoxin is a non-competitive antagonist of GABAĄ receptors - it inhibits GABAA receptors. - GABAA receptors are inhibitory channels in the brain. - Has actions against receptors which bind to GABA. - Picrotoxin is derived from fishberry plants – used to poison fish. - Fishberry seeds were commonly used in southeast asia to collect fish. - Picrotoxin breaks down during high temperature treatment. - Seeds are thrown into the pond and fish will consume these seeds and are caught when they are swimming. - Can be used as an antidote for barbiturate toxicity - In the 19th century, picrotoxin was added to beer to make it more intoxicating - now this is banned. ### Case Story 1: Outcomes for the Patient A patient was admitted to the hospital after consuming a poisonous pufferfish. Due to the severity of his illness, and after an extensive literature review, a decision was made to treat the patient with a cholinesterase inhibitor. During the first 24 hours, the patient received 4 doses of intravenous neostigmine 2.5 mg. Immediately after the first dose of neostigmine deep tendon reflexes could be noted along with reversal of the comatose state. Over the next 24 hours, the patient completed a course of 4 doses of neostigmine. During that time a dramatic improvement was observed, which included complete recovery of muscle strength and return to full consciousness. 36 hours after his hospital admission, the patient was extubated and had a complete and uneventful recovery. ## Case Story 2: Food Poisoning A 52-year-old otherwise healthy man presented to the emergency room with nausea and vomiting accompanied by acute dyspnea. Two hours earlier, the patient who was a recreational fisherman reported on consumption of liver and gonads extracted from a fish which he just captured at sea. Several minutes after consumption, he complained of perioral paraesthesias with worsening limb muscle weakness. Shortly after admission to the ER, the patient developed an acute respiratory failure with bradypnea. This was accompanied by bradycardia which quickly deteriorated to cardiac arrest. After a short resuscitation, including tracheal intubation and mechanical ventilation, the patient returned to sinus rhythm. On examination, shortly after the patient was stabilized, signs of complete paralysis with absence of motor responses and lack of pupil reactions were noted. The patient was noted to be in deep coma with GCS of 3 at this point. Possible poisoning by a paralyzing agent was suspected. The patient was transferred to the intensive care unit and treated by supportive measures. Several hours after his ICU admission, the patient's family approached the medical staff with a fish claimed to be consumed by the patient just two hours prior to his hospital admission. A diagnosis of tetrodotoxin (TTX) poisoning was suggested by typical clinical manifestations and temporal proximity to consumption of TTX-containing fish. The fish remnants were photographed and were immediately analyzed by a marine biologist and by the national center of poisoning. Consequently, the fish was identified as the poisonous Lagocephalus sceleratus. At this point, the patient had a complete muscle paralysis with absent deep tendon reflexes and deep coma. ## Fugu Sashimi: - Made using pufferfish. - Causes a tingling sensation on the tongue due to tetrodoxin interacting with the receptors. ## How Does TTX Work? - Voltage Gated Channels: - TTX blocks sodium channels - A = electrode in a giant squid axon (first recording of action potentials in the world). - E = TTX binds to voltage gated sodium channels + blocks action potentials that are mediated by sodium therefore blocking action potential generation + no neurotransmitter release. - After a wash, there is recovery of the sodium current as TTX is no longer present. - As you increase concentration of TTX, conductance through the channels become inhibited. - IC50 - concentration of a drug or substance needed to block or reduce a biological activity (like an enzyme's function) by 50%. - A measure of how strong or effective the substance is at stopping something. - Lower IC50 values mean the substance is more potent because it takes less of it to do the job. ## TTX Uses: - Induce comas - TTX-like molecules can used for pain treatment. - Local anaesthetics work by blockage of sodium channels. ## Case Story 3: Let's Go Hunting - The curare vine, a liana, is used by the Indians in the Amazon to prepare arrow and dart poisons. - The vine is a rich with alkaloids. - The main alkaloid responsible for the paralysing actions is d-tubocurarine, which is an antagonist at acetylcholine receptor. - Acetylcholine is a major excitatory neurotransmitter in the spinal cord which mediates most of our muscle actions. - These darts cause an inhibition of muscle contraction + allows animals to hunted this way. - Inhibition of the limbs needs much lower concentration than inhibition of the diaphragm – the animal wouldn't be able to move until death. - Inhibition of the brain takes longer so the animal has time to think until death. - A person can be saved by using neostigmine along with poison – recovery + high response. - Response is smaller with the poison. - **In vivo experiment** ## Novichok Poisoning: - A group of nerve agents - Inhibits acetylcholinesterase – prevents degradation of acetylcholine. - This compound is very potent – very little dose will prevent acetylcholine degradation. - Spasm / prevents relaxation of muscles (cardiac and respiratory). - Cause of death asphyxiation or cardiac arrest. - Fast acting - Remain poisonous for a long time period ## Soups vs Sparks: - The leech test was based on the use of eserine (physostigmine), a potent inhibitor of the enzyme acetylcholinesterase. - The technique was based on the discovery by the German pharmacologist Fühner (1918), who showed that when eserine was added to an organ bath in which a leach muscle was suspended, the muscle became extremely sensitive to acetylcholine, and he suggested the preparation as an assay system for eserine. - Wilhelm Feldberg merely reversed the procedure and used the eserinized muscle as a sensitive and simple assay for acetylcholine. - The use of eserine in experiments by adding it to the perfusion fluid, reduced the circulating levels of acetylcholinesterase, increased the amounts of acetylcholine and thus made the accurate measurements possible (Kymograph). ## Neurotransmitter Criteria: 1. A neurotransmitter must be synthesized by and released from neurons. Thus, the presynaptic neuron should contain both the transmitter and the appropriate enzymes needed to synthesize that neurotransmitter. 2. The substance should be released from nerve terminals in a chemically or pharmacologically identifiable form. It should therefore be possible to isolate the transmitter and characterize its structure. 3. A neurotransmitter should reproduce at the postsynaptic cell the specific events (such as changes in membrane properties) that are seen after stimulation of the presynaptic neuron. 4. The effects of a putative neurotransmitter should be blocked by competitive antagonists of the receptor for that transmitter in a dose-dependent manner. In addition, treatments that inhibit synthesis of the transmitter should block the effects of presynaptic stimulation. 5. There should be active mechanisms to terminate the action of the neurotransmitter. Among such mechanisms are uptake of the transmitter by the presynaptic neurons or glial cells through specific transporter molecules and enzymatic inactivation of the chemical messenger. - **Neurotransmitters** are substances which are synthesised by neurones either in cell surfaces or locally in the presynaptic zones. - **Needs to be detectable** - **Should be able to isolate them + replicate them synthetically in the lab.** - **Should be able to apply to preparation + produce an action potential** - **Having specific antagonists for specific types of receptors proves the action of these molecules + provides proof.** ## Peripheral vs Central Excitatory Transmission: - **Neuromuscular junction:** - Multi-vesicular release - Acetylcholine (Ach) - Ach breakdown (cholinesterase) - **Central synapse** - Single release zones - Glutamate (Glu) - Glu re-uptake (transporters) - **Cholinesterase in the synaptic cleft which terminates that action.** - **Glutamate is a very important neurotransmitter in the brain – most synapses mediate glutamate.** - **Glu uptake terminates the action via recycling.** - **TTX blocks action potentials** ## Neurotransmitter Receptor Types: - **Ionotropic** - **Metabotropic** - **G-protein coupled** ## Classical Neurotransmitters and their Receptors: | Transmitter | Chemical | Receptor Name, Mechanism, Ion permeability* | Synaptic Action | Distribution of Receptors in the CNS | Localization of Neurons Synthesizing the Transmitter in the CNS | Localization of Neurons in the PNS | |---|---|---|---|---|---|---| | Glutamate | Amino acid | AMPA: ionotropic, Na*; NMDA: ionotropic, Ca2+; MG1uR1-5: metabotropic | Fast, excitation; Fast, excitation; Slow, excitation or inhibition; metabolic effects | "Everywhere" | "Everywhere" | Spinal ganglion cells | | GABA | Amino acid | GABA ionotropic, Cl- ; GABA, metabotropic, K+, Ca2+ | Fast, inhibition; Slow, inhibition | "Everywhere" | "Everywhere" | Gut, ganglia | | Glycine | Amino acid | Ionotropic, Cl- | Fast, inhibition | Cerebral cortex, spinal cord (and other places) | Brain stem, spinal cord, cerebellum | Motoneurons, preganglionic autonomic neurons, basal nucleus, septal nuclei, nuclei in the reticular formation of the brain stem (and other places).| | Acetylcholine | Quaternary amine | Nicotinic: ionotropic, Na+; Muscarinic: metabotropic, K+, Ca2+ | Fast, excitation: Slow, excitation or inhibition | Cerebral cortex, hippocampus, thalamus (and other places) | | Parasympathetic ganglia | | Norepinephrine | Amine | α (α1, α2), metabotropic; β β1, β2), metabotropic | Slow; Slow | "Everywhere" | Locus coeruleus and diffuse cell groups in the reticular formation | Sympathetic ganglia | | Dopamine | Amine | D1 (D1, D5), metabotropic, increase cyclic AMP; D2 (D2, D3, D4), metabotropic, decrease cyclic AMP | Slow; Slow | "Everywhere" (especially basal ganglia and prefrontal cortex) | Mesenchephalon (Substantia nigra and ventral tegmental area) | | | Serotonin (5-HT) | Amine | 5-HT1: metabotropic, K+; 5-HT2: metabotropic; 5-HT3: ionotropic, Na* | Slow, inhibition; Slow, excitation; Fast, excitation | "Everywhere" | Raphe nuclei (brain stem) | | | * There are more receptor subtypes than shown here. | | * The table is not complete regarding distribution of neurons and receptors. | ## Neurotransmitter and Other Signaling Molecules: A neurotransmitter is a chemical substance released from nerves upon electrical stimulation, that binds to a receptor or “receptive substance”. ### Classical: - **Acetylcholine (Ach)** - **Amino acids:** - **Glutamate** - **GABA** - **Glycine** - **Monoamines** - **Noradrenaline** - **Adrenaline** - **Serotonin (5-HT)** - **Dopamine** ### Non-classical: - **Neuromodulators (neuropeptides, opiates, gasses)** - **Neurotrophic factors (BDNF, NGF)** - **Non-classical are much slower – work in mins** - **Growth factors are even slower – can take days** ## Fundamental Neuropharmacology is Neurotransmitter Pharmacology: What are you going to learn during the rest of the fundamental neuropharmacology component? - During fundamental neuropharmacology you will study neurotransmitter pharmacology, i.e. how different ligands, compounds and drugs interact with neurotransmitter receptors and how they induce or inhibit effects in nervous systems, tissues and cells. - These effects may be neuronal or cellular, behavioural or cognitive, medicinal or illicit, wanted or unwanted, and you will learn to measure, quantify and interpret such effects. ## Neurotransmitters + Their Function: - **Adrenaline:** Fight or flight neurotransmitter - **Noradrenaline:** Concentration neurotransmitter - **Dopamine:** Pleasure neurotransmitter - **Serotonin:** Mood neurotransmitter - **GABA:** Calming neurotransmitter - **Acetylcholine:** Learning neurotransmitter - **Glutamate:** Memory neurotransmitter - **Endorphins:** Euphoria neurotransmitter - **Endorphins are not neurotransmitters but provide signals for pleasure.**