244
Chapter 8
receptors. A modern, milder therapy that stimulates the brain
with electromagnets is described at the end of this chapter.
Another nondrug therapy used for the type of annual depres-
sion known as
seasonal affective depressive disorder
(
SADD
)
is
phototherapy,
which exposes the patient to bright light for
several hours per day during the winter months. Although
light is thought to relieve depression by suppressing melatonin
secretion from the pineal gland, as yet there is little evidence
to support this claim.
Psychoactive Substances, Dependence,
and Tolerance
In the previous sections, we mentioned several drugs used to
combat altered states of consciousness. Psychoactive substances
are also used as “recreational” drugs in a deliberate attempt
to elevate mood and produce unusual states of consciousness
ranging from meditational states to hallucinations. Virtually all
the psychoactive substances exert their actions either directly
or indirectly by altering neurotransmitter-receptor interactions
in the biogenic amine—particularly dopamine—pathways. For
example, the primary effect of cocaine comes from its ability
to block the reuptake of dopamine into the presynaptic axon
terminal. As mentioned in Chapter 6, psychoactive substances
are often chemically similar to neurotransmitters such as dopa-
mine, serotonin (
Figure 8–13
), and norepinephrine, and they
interact with the receptors activated by these transmitters.
Dependence
Substance dependence,
the term now preferred to
addiction
,
has two facets that may occur either together or independently:
(1) a
psychological dependence
that is experienced as a craving
for a substance and an inability to stop using the substance at
will; and (2) a
physical dependence
that requires one to take
the substance to avoid
withdrawal,
which is the spectrum of
unpleasant physiological symptoms that occurs with cessation
of substance use. Substance dependence is diagnosed if three
or more of the characteristics listed in
Table 8–3
occur within
a 12-month period.
Table 8–4
lists the dependence-produc-
ing potential of various drugs.
Several neuronal systems are involved in substance depen-
dence, but most psychoactive substances act on the mesolimbic
dopamine pathway (Figure 8–9). In addition to the actions
of this system mentioned earlier in the context of motivation
and emotion, the mesolimbic dopamine pathway allows a per-
son to experience pleasure in response to pleasurable events or
in response to certain substances. Although the major neu-
Figure 8–13
Molecular similarities between neurotransmitters
(orange) and some substances that elevate
mood. At high doses, these substances can cause
hallucinations.
Figure
8–13
physiological
inquiry
How would you expect dimethyltryptamine
(DMT) to affect sleeping behavior?
Answer can be found at end of chapter.
OPO
3
H
Dimethyltryptamine (DMT)
Dopamine
Amphetamine
Mescaline (peyote)
Dimethoxymethylamphetamine (DOM, STP)
Psilocybin (some mushroom species)
Methamphetamine (speed)
CH
2
CH
2
N
CH
3
CH
3
CH
3
CH
3
CH
3
OH
OH
CH
3
O
CH
2
CH
2
NH
2
CH
2
CH
NH
2
CH
2
CH
NH
2
CH
3
CH
2
CH
N
N
CH
2
CH
2
N
CH
3
CH
3
CH
3
O
CH
3
O
OCH
3
OCH
3
CH
3
OCH
3
Serotonin
(5-hydroxytryptamine)
OH
N
CH
2
CH
2
NH
2
N
CH
3
CH
2
CH
NH
2
CH
3
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