Basic Science Of Substance Misuse

Question 1

What are the 2 mechanisms of why humans misuse drugs?

Answer 1

Tolerance (basis of physical dependence)
Reward centre (basis of psychological craving)

Question 2

Define tolerance

Answer 2

Reduced responsiveness to a drug caused by previous administration

Question 3

What are the two types of tolerance?

Answer 3

Dispositional tolerance and

Pharmacodynamic tolerance

Question 4

Define dispositional tolerance

Answer 4

Less drug reaches the active site

Question 5

Mechanisms of dispositional tolerance

Answer 5

Less drug absorbed,
Increased rate of metabolism to inactive metabolites,
Decreased rate of metabolism to active metabolites,
More drug excreted

Question 6

Define pharmacodynamic tolerance

Answer 6

Drug has less action at the active site

Question 7

Mechanisms of pharmacodynamic tolerance

Answer 7

Fewer drug receptors,
Less efficient drug receptors,
Compensatory mechanism

Question 8

Why does withdrawal symptoms occur

Answer 8

Drug effect and adaptive response are equal when taking drug
When drug is removed
Balance flips to more of adaptive response
Causing withdrawal symptoms eg if adaptive response was increased sensitivity to transmitter

Thus the withdrawal effect is usually hr reverse of the acute effect

Question 9

What is the reward pathway?

Answer 9

Neurones project from the ventral tegmental area to the nucleus accumbens and prefrontal cortex

When the VTA neurones are stimulated dopamine is released causing a sensation of pleasure/ reward

Question 10

Give examples of how some drugs tap into the reward pathway and increase dopamine levels

Answer 10

Heroin increases firing rate of dopaminergic neurones,
Amphetamine increases dopamine release,
Cocaine inhibits dopamine uptake,