PSYC 2410 Chapter Notes - Chapter 15: Drug Injection, Drug Tolerance, Drug Withdrawal

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19 Apr 2012
Chapter 15
Basic Priniciples of Drug Addiction
Psychoactive drugs act by influencing experience and behavior by acting on the
nervous system
Drug Admin and Absorption
Oral, Injection, Inhalation and Absorption through the Mucous Membranes
Oral- Preferred route of admin, absorbed in the intestine-proceeds into the
bloodstream. Some drugs such as alcohol pass through the stomach wall. These
drugs take effect sooner.
Absorption into the blood stream can be influenced by the amount and type of food
in the stomach. The main advantages are the ease and the safety.
Drug injection- effects are strong fast and predictable, made subcutaneously
intramuscularly or intravenously. Addicts prefer the intravenous route because it
delivers the drug directly to the brain.
After an injection there is little chance to counteract the effects of the drugs. Many
addicts develop scar tissue infections and collapsed veins at the site of injection.
Difficult to regulate the dose and many substances damage the lungs if they are
inhaled chronically.
Absorption through muscous membranes
-Through the mucous membranes of the nose mouth and rectum. Cocaine is
commonly self administered through the nasal membranes.
Penetration of the CNS.
- Once in the bloodstream it is carried in the blood to the blood vessels of the
CNS. The blood-brain barrier helps to prevent blood-borne chemicals to pass
from the blood vessels of the CNS.
Mechanisms of Drug Action
Psychoactive drugs influence the nervous system in many ways. Some drugs act on
the neural membranes throughout the CNS. Others act by binding to particular
receptors- influencing the synthesis, transport, release or deactivation of particular
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Drug Metabolism
The actions of most drugs are terminated by the liver- conversion of active drugs to
non-active forms. This is called drug metabolism. In many cases drug metabolism
eliminates a drugs ability to pass through lipid membranes of cells- no longer
penetrate the blood-brain barrier.
Small amounts of some drugs are passed from the body in urine sweat feces breath
and mothers milk.
Drug Tolerance
-state of decreased sensitivity to a drug that develops as a result of exposure.
Demonstrated in two ways: A given dose of a drug has less effect than it had before
drug exposure OR it takes more of the same drug to produce the same effect.
Drug tolerance is a shift in the dose-response curve.
One drug can produce tolerance to other drugs that act by the same mechanism.-
Cross tolerance.
Tolerance to may develop to some effects of a drug while sensitivity to other effects
of the same drug increases- drug sensitization.
2 categories of changes that underlie drug tolerance: metabolic and functional.
Drug tolerance that reduces the amount of drug getting to sites of action- metabolic
Drug tolerance that results from changes that reduce the reactivity of the sites of
action is called functional tolerance.
Tolerance to psychoactive drugs is functional. E.g exposure to a psychoactive drug
can reduce the number of receptors for it and decrease the efficiency to which is
binds to receptors.
Drug withdrawal effects and physical dependence.
After significant amounts of drug have been in the body or a period of time its
sudden elimination can trigger adverse reactions- withdrawal syndrome.-
opposite to the effects of the drug. Individuals who suffer from withdrawl are said to
be physically dependent on the drug.
Because withdrawl effects are opposite of that to the drug it suggests that the
withdrawal effects may be produced by the same neural changes that produce
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Exposure to a drug produces compensatory changes in the nervous system that
offset the drugs effects and produce tolerance. Then when the drug is not there, the
compensatory neural changes manifest themselves as withdrawal symptoms
because there the drug is not there to offset them.
Addicts- those who use a drug despite its adverse effects on their health and social
The withdrawal effects of drugs are not the motivating factor in the use of drugs.
Contingent Drug tolerance
Tolerance only develops to drug effects that are actually experienced. Two groups
of subjects receive the same series of drug injections and the same tests. But,
one group receives the drug before the test and one receives it after the test.
At the end all the subjects receive the same dose so that the two groups can be
Conditioned drug Tolerance
Refers to the fact that tolerance effects are only expressed when a drug is
administered in the same situation which is had previously admin’d.
e.g rats given injections of alcohol and saline in different rooms. Tolerance was only
seen in the rats that were injected in the environment that had previously been
paired with alcohol.
The situational specificity of drug tolerance led siegel and his colleagues to propose
that addicts may be susceptible to drugs in a new context.
-addicts become tolerant when administering their drug in the same environment.
- siegel found that many more heroin tolerant rats died following a high dose of
heroin in a novel environment
pavlovian conditioning- the incidence- the environment is the conditional stimuli
and the effects of the drug are unconditioned stimuli.
Central assumption of the theory is that conditional stimuli that predict drug
admin come to elicit conditional response opposite to the unconditional
effects of the drug.
As stimuli predict the effects of a drug come to make greater and greater
conditioned responses they increasingly counteract the unconditional effects of the
drug and produce situation ally specific tolerance.
Exteroceptive stimuli- conditional stimuli
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