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PSY295 - Chapter 7.docx

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Ryerson University
PSY 402
Jian Guan

Neuropsychology: Chapter 7: The Influence of Drugs and Hormones on Behavior Psychopharmacology: the study of how drugs affect the nervous system and behaviour. Drug: a chemical compound that will bring about a desired change in the body. Psychoactive Drugs: substances that alter mood, thought, or behavior and are used to manage neuropsychological illness. (Can also be a substance of abuse)  To be psychoactive, the drug must reach the nervous system Routes of Administration  Oral  Inhalation  Rectal suppositories  Absorption (patches on skin)  Intravenous (straight to bloodsteam)  Intramuscular (straight into muscle- epi pen)  Intrathecal (into brain) - Drug must be able to withstand obstacles (ex: gastric acid and GI tract walls, blood, extracellular fluid) o Orally taken drugs have the most obstacles to go through to reach the bloodstream o Fewest obstacles faced by drugs directly injected to the brain - Weak acid drugs (alcohol) is easily absorbed through the stomach lining - To pass through the bloodstream a drug must be hydrophilic o Hydrophobic drugs won’t be able to enter the bloodstream o A drug becomes diluted by the 6-L volume of blood - The drug, once past the circulatory system has to go through extracellular fluid o Drug will be modified/destroyed by various metabolic processes in a cell Routes of Drug Removal - Drugs are metabolized by the: kidneys, liver & bile - Drugs are excreted through: urine, feces, breast milk, sweat, and exhaled air - Mercury is not easily eliminated from the body (Minamata disease- mercury poisoning) Blood Brain Barrier - Endothelial cells: help form the brain capillaries, surrounded by astrocyte glial cells o Astrocytes maintain tight junctions between endothelial cells  Substances can pass through endothelial cells in the rest of the body but not in the brain due to the astrocytes o Molecules (oxygen & CO2) are very fat soluble so are able to pass through the capillary wall (in brain) o Glucose, amino acids, and other nutrient can be carried across the capillary wall through active transport systems - Pituitary Gland: o Lacks tight junctions in capillary wall  This absence (at area postrema) can cause toxic substances in the blood to trigger a vomiting response - Pineal Gland: o Lacks tight junctions in capillary wall  Can cause hormones in the blood to affect the day-night cycles that the pineal gland controls Drug Routes and Dosage - Ideal Drug: small, weakly acidic, water/fat soluble, potent in small amounts, not easily degraded Steps in Synaptic Transmission 1. Synthesis: synthesis of the neurotransmitter can take place in cell body, axon, or terminal 2. Storage: in storage granules or vesicles 3. Release: from terminal’s presynaptic membrane 4. Receptor Interaction: act on receptor in the postsynaptic membrane Excess neurotransmitter is: 5. Deactivated or: 6. Reuptake: taken back into presynaptic terminal 7. Reuse or Degradation: excess neurotransmitter is reused or degraded - Agonists: drugs that increase the effectiveness of neurotransmission - Antagonists: Drugs that decrease the effectiveness of neurotransmission Examples of Drug Actions: An Acetylcholine Synpase 1. Black Widow Spider Venom: (agonist) promotes release of acetylcholine; causes paralysis (in other insects) 2. Botulinum toxin: (antagonist) blocks release of acetylcholine 3. Nicotine: (agonist) stimulates cholinergic receptors – at the neuromuscular junction it is called nicotinic receptor; the shape of the nicotine is similar to ACh to fit into its receptor binding sites 4. Curare: (antagonist) at the cholinergic receptors, preventing acetylcholine from acting 5. Physostigmine: inhibits acetylcholinesterases – therefore is an agonist (increasing amount of acetylcholine available) a. Myasthenia gravis (muscular weakness): muscle receptors do not respond to acetylcholine b. Organophosphates: bind irreversibly to acetylcholinesterases & are therefore very toxic Classification of Psychoactive Drugs Class 1: Sedative Hypnotics & Antianxiety Agents - Alcohol: can cause fetal alcohol syndrome (FAS) - Barbiturates: sleeping medication; mainly used for anesthesia before surgery - Benzodiazepines: minor tranquilizers or antianxiety agents; treat stress (ex: Valium) - All sedative-hypnotic drugs work on the GABA (gamma-aminobutyric acid) neurotransmitter receptor o GABA controls the chloride channel (an excitation of the receptor causes influx of Cl) o An influx of Cl causes increase in negative concentration inside the cell membrane = hyperpolarizing the membrane o Hyperpolarizing makes an action potential less likely to occur; therefore, GABA has an inhibitory effect by decreasing the neurons rate of firing - A sedative-hypnotic acts like GABA – and the effects are enhanced by anti-anxiety drugs. o Small doses of antianxiety and sedative-hypnotic drugs together can cause coma/death - Dissociative anesthetics: (group of sedative-hypnotics) produce altered states of consciousness o Example: GHB (date rape drug) Class 2: Antipsychotic Agents - Psychosis: neuropsychological conditions that are characterized by hallucinations or delusions - Drugs that treat psychosis are called: major tranquilizers & neuroleptics o Major tranquilizers:  Causes immediate reduction in motor activity  Can produce symptoms of Parkinson’s and dyskinesia (involuntary movement) - Antipsychotics block a dopamine receptor (D Re2eptor) o Dopamine Hypothesis of Schizophrenia: schizophrenia is caused by excessive dopamine activity  Proof: amphetamine (a dopamine agonist) causes schizophrenia like symptoms) Class 3: Antidepressants - Major depression: a mood disorder characterized by prolonged feelings of worthlessness, guilt, disruption of normal eating habits, sleep disturbance, slow behavior, frequent thoughts of suicide - Three drugs with antidepressant effects: o Monoamine oxidase inhibitors (MAO inhibitors)  MAO is an enzyme that breaks down serotonin in the axon terminal – the MAO inhibitor allows for more serotonin release with each action potential o Tricyclic antidepressants  Blocks the transporter that takes serotonin back into the axon terminal o Second-generation antidepressants (atypical antidepressants) (selective serotonin reuptake inhibitors [SSRI’s])  When the transporter is blocked (to be taken back into the axon terminal), the SSRI’s keeps it in the postsynaptic cleft - Antidepressants- improve chemical transmission in serotonin, noradrenaline, histamine, acetylcholine (and dopamine) synapses. - Obsessive Compulsive Disorder (OCD): obsessive thoughts and compulsive behavior; associated with guilt and anxiety Class 4: Mood Stabilizers - Bipolar disorder: (once referred to as manic-depressive illness) disorder of the mood where a person undergoes period of depression and normal periods and intense excitation o Treated with mood stabilizers: include salt lithium & valproate (used to treat epilepsy); lithium increases synaptic release of serotonin ; valproate stimulates GABA activity Class 5: Narcotic Analgesics - Narcotic analgesics: have sleep inducing (narcotic) and pain relieving (analgesic) properties - Derived from opium- codeine and morphine - Heroin: an opiate drug; more fat soluble than morphine = penetrates blood-brain barrier faster than morphine - Methadone: treats addiction; used as a substitute for heroin or other abused opioid drugs - Opium antagonists- nalorphine & naloxone – block the action of opioid overdose Class 6: Psychomotor Stimulants - Behaviour stimulants o Cocaine:  Derived from Peruvian coca shrub  Purified cocaine (snorting or injection) = crack  Crack is chemically altered ti vaporize at low temperatures  Amphetamine: a synthesized compound discovered when the trying to synthesize the neurotransmitter epinephrine  Amphetamine and cocaine: dopamine agonists: block dopamine transport back into synaptic cleft  Freud – suggested cocaine be used a local anesthetic (ex: novocaine) o Amphetamine:  First used to treat asthma (Benzedrine- sold as inhaler) - General Stimulants o Caffeine: inhibits cyclic adenosine monophosphate (cyclic AMP)  Increase in cyclic AMP increases glucose production- making more energy available; higher rates of cellular activity Class 7: Psychedelics and Hallucinogens - Psychedelic drugs: alter sensory perception and cognitive processes and produce hallucinations - 4 groups: 1. Acetylcholine psychedelics: block or facilitate transmission at Ach synapses in brian (act on muscarine receptor; atropine- a muscarinic blocker that crosses blood-brain barrier 2. Norepinephrine psychedelics: includes mescaline (obtained from the flowering head of the peyote cactus) ; causes intoxication with delusions of color and sound a. Legal for Native Americans for religious practices 3. Tetrahydrocannabinol (THC): active ingredient in marijuana; obtained from hemp plant. a. Cannabis acts on CB1 and CB2 receptors for the neurotransmitter anadamide (plays a role in forgettin
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