© copyright 2011, pearson education, inc. all rights reserved. chapter 3 how drugs work in the body...

© Copyright 2011, Pearson Education, Inc. All rights reserved.

Chapter 3

How Drugs Work in the Body and on the Mind


How Drugs Enter the Body • There are four basic ways to administer drugs

into the body:

– oral administration

– injection

– inhalation

– absorption through the skin or membranes.

• Each of these imposes constraints on which kinds of drugs will be effectively delivered into the bloodstream.

Oral

Routes of Administration

• easy—no skill required• non-invasive (does not penetrate skin barrier)• may interact with food• may cause nausea• must be readily absorbable (not suitable for all drugs)• generally inefficient• precise dosing can be difficult

Injection


• Intravenous (i.v.)o fast-acting, dosing precise, efficient, short-lived

• Intramuscular (i.m.)o slower-acting, longer lived than i.v., small volume

• Subcutaneous (s.c.)o slow acting, longer lived than i.v., small volumes

Inhalation *(into lungs... not the same as trans-mucousal!)


• Non-invasive (does not penetrate skin)• very fast• recreational use often introduces toxins• therapeutic use limited to respiratory

system, anesthetics

Absorption


• trans-dermal o very slow, long lasting

• trans-mucosal (e.g. intranasal, intra-oral) antihistamines, drugs of abuse


This figure was taken from Dr. Lori Knackstedt’s lecture: Psychopharmacology and Neural Communication


iClicker Question

What is the best route of drug administration?

A. IntravenousB. OralC. Inhalation (into lungs, not intranasal)D. It depends on the drug, and the

intended effect

What happens to drugsonce in the body?

1. Metabolized by liver enyzmesmetabolites excreted in urine (also sweat, breathand feces to lesser extent)

2. Excreted as administered3. Metabolized by target to active form

e.g. l-DOPAdopamine, heroinemorphine4. Metabolized by target to inactive form, excreted

in urine


How Drugs Exit the Body

• Most drugs are eliminated from the body through urinary excretion.

• Drugs are broken down for elimination by the action of enzymes in the liver (and in the brain).

• An index of how long this process takes is the elimination half-life: how long it takes for the current amount of drug to lose ½ of it’s pharmacokinetic activity


Factors Determining the Behavioral Impact of Drugs • The factors that can make the physiological effect of

a drug vary include the time elapsed since its administration, drug interactions when it is administered with other drugs at about the same time, and the personal characteristics of the individual consuming the drug.

– Examples: weight, gender, and ethnic background (predisposition to certain biological traits)


Figure 3.1


Introducing theNervous System

• Understanding the organization of the nervous system helps us to understand where and how psychoactive drugs are working in our bodies.


Figure 3.2


Introducing theNervous System

• The nervous system consists of the peripheral nervous system and the central nervous system, with the latter divided into the brain and the spinal cord.

• Autonomic nerves control our cardiac and smooth muscles to respond either to stress (sympathetic activation) or to demands for nurturance and renewal (parasympathetic activation).


Figure 3.3


Understanding the Brain

• Hindbrain -medulla, pons, cerebellum

• Midbrain -tegmentum, tectum

• Forebrain -Diencephalon hypothalamus, thalamus -Telencephalon limbic system, basal ganglia, cerebral cortex

Within the brain are three major divisions: the hindbrain, midbrain, and forebrain.

Figure 3.4 in textbook


Understanding the Biochemistry of

Psychoactive Drugs

• Understanding the functioning of neurons and their interaction through synaptic communication helps us to understand how psychoactive drugs work in our bodies.


iClicker Question

Structures commonly thought to regulate motivational and emotional behaviors are located in which major brain region?

A. The forebrainB. The midbrainC. The hindbrainD. The spinal cord


Figure 3.5

/ Axon terminal

How do neurons communicate?

1. The dendrites and cell body of a neuron receive information from other neurons in the form of chemical signals (neurotransmitters).

2. These chemical signals cause changes in the receiving neuron from its “resting state” (an electrochemical equilibrium of about -70 mv)

• these changes can cause the equilibrium to change to a more positive voltage (depolarization) or more negative voltage(hyperpolarization)

3. If the receiving neuron is depolarized to its threshold (about -65 mv), an “action potential” will occur down the length of its axon, causing it to release neurotransmitters from the axon terminal

• **Note: once threshold is reached, an action potential will always occur – it is an “all-or-nothing” response.


How do neurons communicate?


This figure illustrates an action potential.

You DO NOT need to memorize the specific order of ion channel opening / closing in an action potential for this course.


Figure 3.7

**OR by a cascade of “second messengers” that indirectly effect other activities / functions of the cell.

Neurotransmitters are packaged into vesicles primarily near the cell body, not at the axon terminal, as illustrated in the book.

Change in voltage caused by action potential results in vesicle docking / transmitter release

Flow of information through neurons


Understanding the Biochemistry of Psychoactive Drugs

• In general, psychoactive drugs work by altering neurotransmitter release, receptor binding, or reuptake at the synapse.

• Agonists enhance neurotransmitter action

• Antagonists reduce neurotransmitter action

– NOTE: antagonists do bind to the receptor, but do not exert the an effect like the neurotransmitter would.


Figure 3.6

The “Big Seven”

AcetylcholineDopamineNorepinephrineSerotoninGamma aminobutyric acid (GABA)GlutamateOpiates

Catecholamines Monoamines

Receptor Subtypes

• Each Neurotransmitter has multiple types of receptors it can bind to. Each receptor causes a slightly different effect on the neuron.

– Example:

• D1 dopamine receptors = excitatory*

• D2 dopamine receptors = inhibitory*

* these channels cause their effects INDIRECTLY through 2nd messenger cascades



Table 3.1


Physiological Aspects of Drug-Taking Behavior

• Three important issues need to be understood in looking at the physiological effect of drugs: – the extent to which drugs pass from the

bloodstream to the brain

– the extent to which tolerance effects occur

– the extent to which a drug influences activity in the nucleus accumbens in the forebrain

• This area is highly involved with reward and motivation, so it is also technically involved in “psychological” factors.


Psychological Factors in Drug-Taking Behavior

• Although the physiological actions of psychoactive drugs are becoming increasingly well understood, great variability in the effect of these drugs remains, largely because of psychological factors.


Figure 3.8


Psychological Factors in Drug-Taking Behavior

• The most prominent psychological factor is the influence of personal expectations on the part of the individual consuming the drug.

• The impact of expectations on one’s reaction to a drug, a phenomenon called the placebo effect, is an important consideration in drug evaluation and research.


iClicker Question

In clinical studies on drugs, one group is often given a sugar pill instead of the drug. Patients in this control group often report some improvement in symptoms, similar to the group actually receiving the drug. This is due to ____________.

A. the sugar effectB. the placebo effectC. investigator biasD. reporting error

© copyright 2011, pearson education, inc. all rights reserved. chapter 3 how drugs work in the body...

Documents

pearson education

mind copyright

drugs work

kinds of drugs

excretedin urine copyright

intended effect copyright

neural communication

behavioral impact of