[ Pobierz całość w formacie PDF ]brain chemicals that induce the same actions as drugs, such as heroin ing the reward system. Activation of the receptors in the reward
and morphine. Alcohol activates the core reward system and addi- circuits causes a brief rush of intense euphoria, followed by a
tional structures throughout the brain because it acts where GABA couple of hours of a relaxed, contented state.
and glutamate are used as neurotransmitters. GABA and glutamate Opiates create e"ects like those elicited by the naturally
are widely distributed in the brain, including the cortex, hippocam- occurring opioid peptides. They relieve pain, depress breath-
pus, amygdala and nucleus accumbens. ing, cause nausea and vomiting, and stop diarrhea important
medical uses. In large doses, heroin can make breathing shal-
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NORMAL
Dopamine
Transmitter
recycled
cell
Dopamine
Dopamine
Dopamine
transporter
transporter
Dopamine
Blood carries cocaine
receptor site Receiver
to brain in seconds
cell
Crack
cocaine
inhaled
COCAINE HIGH
into
Dopamine
lungs
HOW CRACK COCAINE AFFECTS
not
recycled
THE BRAIN. Crack cocaine takes
Right Left lung
lung
the same route as nicotine by
Cocaine
entering the bloodstream
blocks
trans- through the lungs. Within sec-
porter
onds, it is carried by the blood
to the brain. The basis for
Heart
increased pleasure occurs at the
gap where the impulses that
represent neural messages are
low or stop altogether the cause of death in thousands of people who have died of a heroin passed from one neuron to
overdose. another. This gap is called a
A standard treatment for opiate addiction involves methadone, a long-acting oral opiate that synapse. Dopamine-containing
helps keep craving, withdrawal and relapse under control. Methadone helps opiate addicts reha- neurons normally relay their
bilitate themselves by preventing withdrawal symptoms that are powerful motivators of drug use. signals by releasing dopamine
A synthetic opiate, known as LAAM, can block the e"ects of heroin for up to 72 hours with min- into many synapses. Dopamine
imal side e"ects when taken orally. In 1993 the Food and Drug Administration approved the use crosses the synapse and fits
of LAAM for treating patients addicted to heroin. Its long duration of action permits dosing just into receptors on the surface of
three times per week, thereby eliminating the need for daily dosing. LAAM will be increasingly the receiving cell. This triggers
available in clinics that already dispense methadone. Naloxone and naltrexone are medications an electrical signal that is
that also block the e"ects of morphine, heroin and other opiates. As antagonists, they are espe- relayed through the receiver.
cially useful as antidotes. Another medication to treat heroin addiction, buprenorphine, causes Then, to end the signal,
weaker opiate e"ects and is less likely to cause overdose problems. dopamine molecules break
Alcohol Although legal, alcohol is highly addictive. Alcohol abuse and alcohol addiction away from the receptors and are
(sometimes referred to as alcoholism or alcohol dependence) are the nation s major drug problem, pumped back into the nerve ter-
with some people being more susceptible to them than others. Nearly 14 million abuse alcohol or minals that released them.
are alcoholic. Fetal alcohol syndrome is the leading preventable cause of mental retardation. It a"ects Cocaine molecules block the
about 0.5 to 3 of every 1,000 babies born in the United States. Chronic liver diseases, including pump or transporter, causing
cirrhosis the main chronic health problem associated with alcohol addiction are responsible more dopamine to accumulate in
for more than 25,000 deaths each year. The annual cost of alcohol abuse and addiction is estimated the synapse. Pleasure circuits
at $185 billion. are stimulated again and again,
Genetic and environmental factors contribute to alcoholism, but no single factor or combi- producing euphoria.
nation of factors enables doctors to predict who will become an alcoholic.
Ethanol, the active ingredient in alcoholic beverages, reduces anxiety, tension and inhibitions.
In low doses it may act as a stimulant, whereas at higher doses, it acts as a depressant. In both
cases, it significantly alters mood and behavior. It can also cause heat loss and dehydration.
The drug, which is easily absorbed into the bloodstream and the brain, a"ects several neuro-
transmitter systems. For example, alcohol s interaction with the GABA receptor can calm anxi-
ety, impair muscle control and delay reaction time. At higher doses, alcohol also decreases the
35
function of NMDA receptors that recognize the neurotrans- tive and anabolic (body building) e"ects. It, too, has been asso-
mitter glutamate. This interaction can cloud thinking and even- ciated with sexual assault. Ketamine is another central nervous
tually lead to a coma. system depressant abused as a date rape drug. Ketamine, or
Researchers are developing treatments, which interfere with Special K, is a rapid-acting general anesthetic. It has sedative-
molecules, such as the opioid peptides, and trigger alcohol s hypnotic, analgesic and hallucinogenic properties. It is marketed
positive reinforcing e"ects. One such drug, naltrexone, recently in the U.S. and a number of foreign countries for use as a gen-
has been approved for treating alcoholism. eral anesthetic in both human and veterinary medical practice.
Marijuana This drug can distort perception, and alter the
Alzheimer s disease
sense of time, space and self. In certain situations, marijuana
can produce intense anxiety. One of the most frightening and devastating of all neurologi-
In radioactive tracing studies, scientists found that tetrahy- cal disorders, is the dementia that occurs in the elderly. The
drocannabinol (THC), the active ingredient in marijuana, binds most common cause of this illness is Alzheimer s disease (AD).
to specific receptors, many of which coordinate movement. This Rare before age 60 but increasingly prevalent in each decade
may explain why people who drive after they smoke marijuana thereafter, AD a"ects an estimated 4 to 5 million Americans.
are impaired. The hippocampus, a structure involved with By the year, 2040, it is predicted to a"ect approximately 14 mil-
memory storage and learning, also contains many THC recep- lion individuals in the U.S.
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