NIDA BRAIN SLIDE SHOW (continued) PSY273 - QCC
Brain
regions mediating the development of morphine dependence
The
development of dependence to morphine also involves specific areas of
the brain, separate from the reward pathway.
In this case, point to the thalamus and the brainstem (green
dots). The parts of the
reward pathway involved in heroin (morphine) addiction are shown for
comparison. Many of the
withdrawal symptoms from heroin or morphine are generated when the
opiate receptors in the thalamus and brainstem are deprived of
morphine.
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Addiction
vs dependence
Different
parts of the brain are responsible for the addiction and dependence to
heroin and opiates. Review
the areas in the brain
underlying the addiction to morphine (reward pathway) and those
underlying the dependence to morphine (thalamus and brainstem).
Thus, it is possible to be dependent on morphine, without being
addicted to morphine. (Although,
if one is addicted, they are most likely dependent as well.)
This is especially true for people being treated chronically
with morphine for pain, for example associated with terminal cancer.
They may be dependent--if the drug is stopped, they suffer a
withdrawal syndrome. But,
they are not compulsive users of the morphine, and they are not
addicted. Finally, people
treated with morphine in the hospital for pain control after surgery
are unlikely to become addicted;
although they may feel some of the euphoria, the analgesic and
sedating effects predominate. There
is no compulsive use and the prescribed use is short-lived.
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Summary;
addictive drugs activate the reward system via increasing
dopamine neurotransmission
In
this last slide, the reward pathway is shown along with several drugs
that have addictive potential. Just
as heroin (morphine) and cocaine activate the reward pathway in the
VTA and nucleus accumbens, other drugs such as nicotine and alcohol
activate this pathway as well, although sometimes indirectly (point to
the globus pallidus, an area activated by alcohol that connects to the
reward pathway). While each drug has a different mechanism of action,
each drug increases the activity of the reward pathway by increasing
dopamine transmission. Because
of the way our brains are designed, and because these drugs activate
this particular brain pathway for reward, they have the ability to be
abused. Thus,
addiction is truly a disease of the brain.
As scientists learn more about this disease, they may help to
find an effective treatment strategy for the recovering addict.
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