Download LESSON 5.6 WORKBOOK What are the long-term effects of drug

S
LESSON 5.6 WORKBOOK
What are the long-term effects of drug
abuse and addiction?
DEFINITIONS OF TERMS
Tolerance – decreased
response to a drug as a
direct result of repeated drug
exposure.
Dependence – state of drug use
in which user requires drug to
maintain normal bodily function.
Withdrawal symptoms — the
condition brought on by the
elimination from the body of a
drug on which the person has
become physically dependent.
For a complete list of defined
terms, see the Glossary.
Wo r k b o o k
Lesson 5.6
Now that we’re familiar with the reasons why people start
taking drugs, and the factors that can influence the likelihood of someone becoming addicted, let’s turn our attention to the long-term effects of drug abuse and addiction.
How does long-term drug abuse affect our brains?
Just as we turn down the volume on a radio that is too loud, our brains adjust to the overwhelming surges
in dopamine caused by drugs of abuse by producing less dopamine and/or reducing the numbers of dopamine receptors that receive the signals. As a result, dopamine’s impact on the reward circuit can become
abnormally low, and the ability to experience any pleasure is reduced. This is why abusers eventually
feel flat, lifeless, and depressed, and why they are unable to enjoy things that previously brought them
pleasure. Now, they need to take drugs just to try and bring their dopamine function back up to normal.
And, they must take larger amounts of the drug than they first did to create the same dopamine high – an
effect known as tolerance.
We know that the same sort of mechanisms involved in the development of tolerance can eventually lead
to profound changes in neurons and brain circuits that can severely affect the brain’s long-term health. The
early stages of addiction are characterized by tolerance and dependence. After a drug binge, an addict
needs more of a substance to get the same effect on mood. This increase in tolerance then provokes an
escalation of drug use that develops into dependence – needing a drug to function normally. Once dependent, if an addict abstains they face withdrawal symptoms – painful emotional, and at times, physical
reactions that result from stopping drug use (Figure 23). Both tolerance and dependence occur because
frequent drug use can, ironically, suppress parts of the brain’s reward circuit.
How do our brains adjust to the overwhelming surges of dopamine in the case of drug
addiction?
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
What causes tolerance?
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
What is dependence?
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
167
LESSON READING
A. B. DEFINITIONS OF TERMS
Transcription factors —
proteins that bind to DNA and
influence the expression of
particular genes.
For a complete list of defined
terms, see the Glossary.
Figure 23: Model of tolerance and withdrawal. (A) Theoretical
model suggesting that the nervous system adapts to the disturbing presence of a drug, so tolerance develops, but if the
drug is suddenly stopped, the adaptive mechanisms continue
to function, causing disturbed homeostasis characterized by
withdrawal symptoms. (B) Application of model to morphine
addiction. Morphine acutely inhibits cAMP, but the effect
becomes less as tolerance develops and neural adaptation
occurs. If morphine is suddenly withdrawn, a larger than
normal amount of cAMP is produced, resulting in withdrawal
effects and suggesting that the adaptive mechanism is still
operating. With time, cells once again adapt, this time to the
absence of the drug.
At the heart of this cruel suppression lie molecules known as transcription factors, proteins that regulate
the expression, or activity of genes and thus the overall behavior of neurons. When drugs of abuse are
consumed, specific transcription factors are switched on. After these transcription factors are switched on,
they bind to a specific set of genes, triggering the production of the proteins those genes encode.
What causes relapse?
Chronic exposure to cocaine and other
drugs of abuse is known to induce the dendrites of nucleus accumbens neurons to
sprout more dendritic spines (Figure 24).
Increasing the number of dendritic spines,
bolsters the cell’s connections to other neurons. In rodents, this sprouting can conFigure 24: Chronic exposure to drugs of abuse
tinue for months after drug use stops. It’s
results in neurons changinf their structures, including
suggested that specific transcription facincreased dendritic spines, which increases the contors may be responsible for these added
nections between neurons
spines. It is speculated that the extra connections can amplify the signal in the nucleus accumbens for years and that the heightened signaling might
cause the brain to overact to drug-related cues. These dendritic changes may, in the end, be the key to
adaptation that accounts for how hard addiction is to break. These changes in dendritic spines and thus
connections between neurons may also underlie relapse.
Wo r k b o o k
Lesson 5.6
What are withdrawal symptoms?
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
What are transcription factors?
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
How do neurons in the nucleus accumbens
change in response to chronic exposure to
drugs?
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
168
LESSON READING
Additionally, learning may also be involved in relapse. Conditioning is one example of this type of learning
and memory, in which environmental cues become associated with the drug experience and can trigger uncontrollable cravings if the individual is later exposed to these cues, even without the drug being
available. This learned “reflex” is extremely robust and can emerge even after many years of abstinence,
leading to relapse.
Drugs of abuse change our brains
In summary, researchers have discovered that long term drug abuse changes our brains. Drug abuse
activates transcription factors, which in turn stimulate the production of different proteins that ultimately
increase the number of dendritic spines, thus increasing the number of synapses and altering our synaptic
connections. This response lasts long after drug use stops. The synaptic connections created are stable
additions to our neural circuits, and may underlie relapse.
How might these changes in NAc neurons
explain relapse?
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
___________________________________
__________________________________
__________________________________
__________________________________
__________________________________
Put the following in order: Protein, DNA,
RNA.
__________________________________
_________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
__________________________________
Wo r k b o o k
Lesson 5.6
169
STUDENT RESPONSES
How does drug abuse and addiction change our neurons and thus our brains?
____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
Remember to identify your
sources
____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
Wo r k b o o k
Lesson 5.6
170