Substance Use Disorders 399P SNP SNthereby creates excess serotonin in the synapse (analogous to the effect of cocaine
on dopamine in a synapse; see Figure 9.6). This excess serotonin can have a calm-
ing, relaxing effect. However, high levels of serotonin in the synapse not only affect
the receiving neuron, but also cause the sending neuron to produce less serotonin
in the future. This effect persists even after the person has stopped using the drug.
Moreover, in animals, even short-term use of MDMA can produce enduring damage
to the terminal buttons of serotonin-releasing neurons, which in turn contributes to
disrupted learning, memory, sleep, and appetite (NIDA, 2007e; Parrott, 2002). As
a stimulant, then, MDMA not only affects the dopamine
reward system, but also the serotonin system.
Finally, some stimulants operate on very specific re-ceptors. For example, nicotine acts on a specific type of
acetylcholine receptor called the nicotinic receptor. Such re-
ceptors are located on the cell bodies of dopamine-releasing
neurons. Activation of these receptors leads to increased
release of dopamine in the nucleus accumbens, as well as
removing the inhibiting effect of other neurotransmitters
(Picciotto, 1998; Tomkins & Sellers, 2001). The dopamine
reward system is activated within 10 seconds of inhaling
tobacco, which activates nicotinic receptors. Nicotine may
activate brain areas in a pattern that parallels the brain ar-
eas affected by cocaine (Pich et al., 1997). Table 9.6 lists
the neurological factors that contribute to the abuse of and
dependence on stimulants.
Psychological Factors: From Learning to Coping
Various psychological factors contribute to stimulant abuse and dependence, and to
substance abuse and dependence in general. One type of psychological factor is ob-
servational learning: Through observing others, people develop expectations about
when to use drugs and what the experience of using a given substance should be
like. These expectations in turn act as feedback that affects how the brain actually
responds to a drug (Nitschke et al., 2006; Wager et al., 2004). Another psychologi-
cal factor is operant conditioning: When the consequences (effects) of drug use are
rewarding, the person is likely to use drugs again and again. Repeated drug use, in
turn, can produce classical conditioning, whereby stimuli associated with drug use,
such as the vial containing crack, elicit a craving (a strong urge or desire) for the
drug (Epstein et al., 2009). Such factors affect each other and can become feedback
loops that create a spiral of substance abuse and dependence.
Let’s examine these psychological factors in more detail, fi rst considering obser-vational learning and then moving on to operant and classical conditioning—which
are involved in the progression from use to abuse and dependence and in the main-
tenance of abuse and dependence once they develop.
Observational Learning
People may develop substance abuse or dependence, in part, through observing use
or abuse of drugs by models—family members, peers, celebrities, or mentors. Not
everyone who observes substance use or abuse will follow suit, but simply observing
how other people use substances as a coping strategy can provide a model for that par-
ticular way to cope (Winfree & Bernat, 1998). For example, suppose a girl witnesses
her respected older brother having an argument with their father. The brother and
sister leave the house after the fi ght, and the brother proceeds to smoke crack while
complaining about the father. Through observation, the younger sister learns that one
way to cope with stress is through substance use. Similarly, studies have found that if a
person’s peers use or abuse substances, that person is likely to do the same (Dishion &
Medici Skaggs, 2000; Fergusson, Swain-Campbell, & Horwood, 2002).
However, the relation between observing another person and then subsequentlyimitating his or her behavior is only a correlation—and, as we saw in Chapter 2,
- Stimulants bind to dopamine transporters, leading to increased dopamine
in the synapse. - Substance activates the dopamine reward system, specifi cally the nucleus
accumbens and ventral tegmental area.* - Associations between drug-related stimuli and drug use can activate the
limbic system (and the dopamine reward system).* - GABA, glutamate, and serotonin are involved in the shift from recreational
drug use to abuse and dependence.
This factor is not unique to stimulant abuse and dependence.
Table 9.6 • Neurological Factors That Contribute to the
Abuse of and Dependence on Stimulants