Chapter 18 – drug abuse
Common features of addiction
Addiction – latin word addicere ‘to sentence’ in term of involuntary
servitude, being obliged to fulfill the demands of his or her drug
A little history
Long ago, people discovered that the natural plants contains the
medicinal characteristics, can reduce pain, prevent infections and also
They also discovered the ‘recreational drug’ = this gives the
pleasurable effects when eaten, drunk or smoked.
Table 18.1 addictive drugs
Drug Sites of action
Ethyl alcohol NMDA receptor (indirect
antagonist), GABA receptor
Barbiturates GABA receptor (indirect agonist)
Benzodiazepines (tranquilizers) GABA receptor (indirect agonist)
Cannabis (marijuana) CB1 cannabinoid receptor
Nicotine Nicotinic Ach receptor (agonist)
Opiates (heroin, morphine, etc.) miu and sigma opiate receptor
Phencyclidine (PCP) and ketamine NMDA receptor (indirect
Cocaine Blocks reuptake of dopamine (and
serotonin and norepinephrine)
Amphetamine and Causes release of dopamine (by
methamphetamine running dopamine transporters in
Positive reinforcement – this refers to the effect the certain stimuli
have on the behavior that preceded them. Additive drugs have reinforcing effects.
Role in drug abuse – the most potent reinforcement occurs when
drugs produce sudden changes in the activity of the reinforcement
mechanism; slow changes are much less reinforcing.
Neural mechanisms – addictive drug (amphetamine, cocaine,
opiates, nicotine, alcohol, PCP and cannabis) trigger the release of
dopamine in the nucleus accumbens, different drugs release the
dopamine in different ways. Furthermore, the fact that the reinforcing
properties of addictive drugs involve the same brain mechanisms as
natural reinforcers indicated that these drugs ‘hijack’ brain
mechanisms that normally help us adapt to our environment.
It appears that addiction appears that the process of addiction begins
in the mesolimbic dopaminergic system and then produces long-term
changes in other brain regions that receive input from these neurons:
• Ventral tegmental area changes, this is resulted from insertion
of additional AMPA receptors into the postsynaptic of the DA
• This leads to the increased activation in a variety of regions that
receive dopaminergic input from the VTA: ventral striatum, NAC
and the dorsal striaum, caudate nucles and putamen.
• Synaptic changes that are responsible for the compulsive
behaviors that characterize addiction occur only after continued
use of an addictive drug.
• The alterations that occur in the NAC and later in dorsal striatum
include changes in dopamine receptors on the medium spiny
neurons, further, increases are seen in dopamine D1 receptors,
which cause excitation and faciliate behavior, and decreases are
seen in dopamine D2 receptors, causes the inhibition and
Firstly, the potential addict experiences the pleasurable effects of the
drug, reinforcing the behaviors that cause the drug to be delivered to
the brain. Then, these behaviors become habitual, and the impulse to
perform them becomes difficult to resist.
The early reinforcing effects that take place in the ventral striatum
encourage drug-taking behavior, but the changes that make the
behaviors become habitual involve the dorsal striatum.
One of the important feature of the dorsal striatum – automatic
behavior, impaired for people with the parkinson’s disease. Negative reinforcement – the removal or reduction of an aversive
stimulus that is contingent on a particular response, with an attendant
increase in the frequency of that response. This often in the situation,
where an individual is unhappy with his/her social status, a drug that
reduces these feelings can reinforce drug-taking behavior by means of
Craving – the urge of taking the drug to which one has become
Commonly abused drug
1. Opiates – derived from a sticky resin produced by the opium poppy, it
has been eaten and smoked for centuries. Addiction to this drug has
several high personal and social costs.
1) Herion – type of opiates, has been criminal.
2). Tolerance, a person must take increasing amounts of the drug to
achieve a ‘high’, since the drug is very expensive, and so the people
spending a lot money on it, and become poor and then become a
criminal for buying the drug.
3). Taking this drug by using unsanitary needle, and thus has a high
chance of getting AIDS virus.
4). If the addict is a pregnant woman, her infant will also become
dependent on the drug.
5). The uncertainty about the strength of a given bat