Biological Psychology

biological Psychology 00_Higgs_BAB1401B0020_Prelims.indd 3 9/12/2014 4:59:22 PM SAGE Publications Ltd Suzanne Higgs, Alison Cooper, Jonathan Lee and Mike 1 Oliver’s Yard Harris 2015 55 City Road London EC1Y 1SP First published 2015 SAGE Publications Inc. Apart from any fair dealing for the purposes of research or 2455 Teller Road private study, or criticism or review, as permitted under the Thousand Oaks, California 91320 Copyright, Designs and Patents Act, 1988, this publication may be reproduced, stored or transmitted in any form, or by SAGE Publications India Pvt Ltd any means, only with the prior permission in writing of the B 1/I 1 Mohan Cooperative Industrial Area publishers, or in the case of reprographic reproduction, in Mathura Road accordance with the terms of licences issued by the Copyright New Delhi 110 044 Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. SAGE Publications Asia-Pacific Pte Ltd 3 Church Street #10-04 Samsung Hub Singapore 049483 Editor: Michael Carmichael Library of Congress Control Number: 2014933962 Development editor: Christopher Kingston Assistant Editor: Keri Dickens British Library Cataloguing in Publication data Production editor: Imogen Roome Copyeditor: Kate Harrison; Bryan Campbell A catalogue record for this book is available from Indexer: Martin Hargreaves the British Library Marketing manager: Alison Borg Cover design: Wendy Scott Typeset by: C&M Digitals (P) Ltd, Chennai, India Printed in India at Replika Press Pvt Ltd ISBN 978-0-85702-261-5 ISBN 978-0-85702-262-2 (pbk) At SAGE we take sustainability seriously. Most of our products are printed in the UK using FSC papers and boards. When we print overseas we ensure sustainable papers are used as measured by the Egmont grading system. We undertake an annual audit to monitor our sustainability. 00_Higgs_BAB1401B0020_Prelims.indd 4 9/16/2014 9:43:34 AM Chapter 2 Drugs and the Nervous System: Psychopharmacology 03_Higgs_BAB1401B0020_Ch-02.indd 37 9/12/2014 4:59:30 PM 38 BIOLOGICAL PSYCHOLOGY Chapter Breakdown x Introduction to psychopharmacology and the study of psychoactive drugs. x How psychoactive drugs are handled by the body. x The effect of psychoactive drugs on neurotransmission. x Neuroplastic responses to repeated administration of drugs. x The effects of commonly used psychoactive drugs on behaviour and their pharmacological mechanisms of action. ROADMAP The topic of this chapter is psychopharmacology, which is the study of psychoactive drugs and how they affect brain and behaviour. Psychoactive drugs are compounds that are not naturally present in the body but which can nevertheless act on the body to produce changes in mood and/or behaviour. Psychoactive drugs may be found in plants or they may be compounds that have been synthesised in a chemical laboratory. In this chapter we will be exploring the effects of drugs that alter neurotransmission. We will be finding out about the many ways that drugs get from outside to inside the body to affect brain function. We will examine how drugs are eventually removed from the body and how we respond to the effects of repeated drug administration. The specific ways in which drugs alter neurotransmission will be explored and we will look in detail at the effects of commonly used recreational drugs. Why might we be interested in studying the effects of drugs on the brain? One reason is that studying how drugs affect the brain tells us something about how the brain works. We can use drugs as tools to find out about the role of specific transmitters and receptors in psychological processes. For example, if we have a drug that we know alters serotonin neurotransmission then we can examine the effects of this drug on behaviour and infer something about the role of serotonin in the behaviours observed. In this way, we might also learn something about the changes in brain function that underlie psychiatric disorders and this knowledge can help in developing better treatments. If a drug mimics the symptoms of the disorder then this give clues as to changes in neurotransmission that might be giving rise to psychological problems. Recreational drug use is also widespread in many societies and is associated with personal and soci- etal problems. Studying how drugs affect the brain helps us understand and deal with problematic drug use. We will draw on knowledge gained from reading other chapters to help our understanding. We will use our understanding of neurotransmission to think about how drugs alter synaptic communication (Chapter 1). Knowledge of perceptual processes will also be important for understanding some of the effects of drugs (Chapter 5). In 03_Higgs_BAB1401B0020_Ch-02.indd 38 9/12/2014 4:59:30 PM DRUGS AND THE NERVOUS SYSTEM: PSYCHOPHARMACOLOGY 39 addition, there are links to learning and memory processes and their role in the propensity of some psychoactive drugs to engender dependence (Chapter 4). The first step in understanding the effects of psychoactive drugs is to consider how the body handles them. How do drugs get to their sites of action and why don’t they just build up in the body if we keep taking them? Pharmacokinetics is the term given to studying how drugs are handled by the body and how they are eliminated. HOW DRUGS ARE HANDLED BY THE BODY: PHARMACOKINETICS When we take a drug it is only able to have its effects if it is absorbed into the bloodstream and distributed throughout the body to reach its site of action. After a while, the effects of the drug disappear because it is transformed (metabolised) into a compound that can be eliminated from the body. Pharmacokinetics is the study of these processes of absorption, distribution, metabolism and elimination. We will look at each process in turn and what is involved at each step, consider- ing the implications for understanding the effects of drugs and the design of effective treatments. Absorption Drugs can enter the bloodstream in many different ways, referred to as routes of administration. Routes of administration are important to consider because some drugs can only be taken via a particular route and this may affect compliance with the taking of therapeutic drugs. People would generally rather swallow a tablet than have to inject a drug. Some routes of administration such as smoking can also be harmful. The amount of drug that gets delivered to the site of action also varies on the route of administration. For some routes of administration the drug has to cross biological membranes such as the lining of the intestine or mucous membranes in the mouth. Biological membranes are primarily made of fat (lipids) and so drugs need to be lipid soluble to cross them. The extent to which a drug is able to reach its sites of action is referred to as bioavailability. Routes of administration The most common form of drug administration is to swallow a tablet or a capsule contain- ing a liquid form of the drug (Figure 2.1). This is known as oral administration. Once swal- lowed, the tablet or capsule dissolves in the stomach and passes from the stomach to the intestines where it can travel across the intest- inal membranes and enter the bloodstream. Not all drugs can be administered this way though because some are destroyed by acids Figure 2.1 Oral administration of drugs is often preferred in the stomach and others induce vomiting, to other routes of administration because it is most meaning the drug is unable to reach the small convenient and usually the safest and least expensive intestines for absorption. If a drug does not ¤Djomas/Shutterstock.com 03_Higgs_BAB1401B0020_Ch-02.indd 39 9/12/2014 4:59:31 PM 40 BIOLOGICAL PSYCHOLOGY get into the bloodstream it is said to have low bioavailability. Another issue is that once the drug enters the bloodstream from the intestines it is car- ried directly to the liver via the hepatic portal vein. In the liver, the drug may undergo sub- stantial metabolism, which is a process known as the first pass effect. Some drugs may be almost completely inactivated in this way and so may never reach their sites of action. However, an advantage of oral administration is that it is relatively safe and an overdose can be dealt with by pumping the stomach to Figure 2.2 Some drugs can be inhaled but specialised remove the drug before too much of it enters equipment may be needed and inhalation should be the system. However, absorption after oral monitored to ensure the right amount of drug is delivered administration can be unpredictable because ¤ Ljupco Smokovski/Shutterstock.com it is affected by factors such as how much food is in the stomach. This is why some drugs are directed to be taken on an empty stomach. An alternative to oral administration for drugs that cause stomach upset is to use a suppository that is inserted in the rectum. The rectal route may be used if a person is unable to take a drug orally, for example if they are unconscious; but absorption from rectal membranes can be incomplete and unpredictable and the suppository may cause irritation. Drugs can also be absorbed via other membranes in the body including mucous membranes in the mouth and nose. Drug tabs can be placed under the tongue to dis- solve, which is known as sublingual administration, or they may be absorbed via the cheek membrane, which is known as buccal administration. An example would be nicot- Figure 2.3 When a drug is administered intravenously, is goes directly into the bloodstream and tends to take ine replacement therapies formulated as sub- effect more quickly than when given by any other route of lingual tabs or chewing gums.

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