Figure 6-2 illustrates the influence of different chemicals on brain function. All brain activity is a result of communication between neurons, which is accomplished by transmitters that are released from a neuron and change the activity of another neuron by stimulating a receptor on that neuron. Stimulation of a receptor by the transmitter requires the transmitter to have the correct chemical “shape,” so that the transmitter fits neatly into the receptor. When the transmitter fits into the receptor, a process known as binding, it stimulates the receptor and thus allows one neuron to influence another neuron.

FIGURE 6-2 Chemical infl uence on brain function.

Some drugs block this activity. A blocker can bind to the receptor but is not similar enough in shape to stimulate the receptor. However, because it is bound to the receptor, the blocker prevents the neurotransmitter from attaching to the receptor and thus influences normal brain activity. Other drugs are similar enough to bind to a receptor and activate it. These activators influence normal brain activity, because they stimulate receptors in the absence of regular transmitters.

All neurotransmitters, except acetylcholine, can be classified in one of three categories: amino acids, chemical compounds that form the building blocks of protein; amines, derived from amino acids—occasionally called neuromodulators; and peptides, a chain of two or more amino acids.

Addiction is a molecular process and physiological and behavioral dependence is produced by neuronal changes. Physical dependence means that the body develops a dependence on the continued presence of a substance and reacts negatively when the drug is removed. This process is known as the withdrawal syndrome. Psychological dependence prompts a persistent desire or even undeniable compulsion to obtain and take a substance to experience satisfaction and pleasure or to avoid discomfort. The body develops resistance to the effects of a substance by requiring progressively larger doses to produce the same desired effect. This drug tolerance develops as the result of chronic drug abuse.

STIMULANTS

Stimulants are drugs that stimulate the central nervous system (CNS), and they can have neurotoxic effects (see Table 6-1). These drugs are used by the individual for weight control, pain control, and for alertness and feelings of calmness. Users risk a high potential for psychological dependence as tolerance develops. Commonly used stimulants are caffeine, found in coffee, tea, cocoa, and cola drinks; nicotine, found in cigarettes, cigars, pipe tobacco, chewing tobacco, and snuff; amphetamines, such as benzedrine, dextroamphetamine (Dexedrine), and dextroamphetamine with amobarbital (Dexamyl); and cocaine, (see Table 6-2 and Table 6-3).

I. Caffeine

A. Found in at least 60 plants, including kola nuts, tea leaves, and cacao and coffee beans. It potentiates the release of cortisol and produces effects similar to the arousal caused by stress. The effect comes by blocking the neurotransmitter adenosine, a calming chemical. In moderate amounts, caffeine appears to stimulate nerve cell activity, temporarily boosting concentration, memory, and alertness. This alertness may occur in the parts of the brain involved in arousal but not in areas managing higher-level reasoning, which seem unaffected. Too much caffeine can result in agitation, restlessness, insomnia, gastrointestinal pain or diarrhea, muscle twitching, psychomotor agitation, and tachycardia.

II. Nicotine

A. A poisonous, colorless, oily fluid with a bitter, burning taste; obtained from tobacco leaves or produced synthetically. Nicotine elevates levels of cortisol, a stress hormone. It is used in veterinary medicine as an external parasiticide and as an agricultural insecticide spray.

B. Chemicals in cigarette smoke are toxic, and with other substances, they cause changes in deoxyribonucleic acid (DNA) that can lead to cancer, heart, and lung disease. Passive smokers, nonsmokers who inhale cigarette smoke, are exposed to the same tar and nicotine as smokers and have the same health-related concerns.

C. Smokeless forms of tobacco, such as chewing tobacco and snuff, include the same chemicals as cigarettes and have the same addictive qualities, but these also lead to an increased risk of leukoplakia (precancer) and throat and mouth cancers. Chewing tobacco can also lead to cancer of the cheek, gums, and tongue. Chewing tobacco is put between the cheek and gum, and when chewed, it releases the nicotine juices that mix with saliva. Smokeless tobacco, or snuff, is ground tobacco that can be chewed but usually is inhaled through the nose.

D. Nicotine, like other drugs, alters neuronal communication, specifically through interaction with acetylcholine receptors, either by increasing or decreasing the release or the amount of neurotransmitter. This neurotransmitter targets release of other reward-system chemicals, like dopamine, and results in feelings of pleasure, followed by feelings of increased mental alertness and acuity. The receptors targeted by nicotine become increasingly less sensitive with chronic use and habituate, a chemical basis of addiction.

E. Chronic smoking causes the brain to produce additional nicotinic receptor sites that increase nicotine craving. This biochemical demand is relieved only by more smoking. Students with attention-deficit/hyperactivity disorder (ADHD), depression, and schizophrenia are more likely to smoke, because it may be a way to self-medicate.

III. Amphetamines

A. This class of stimulants includes methamphetamine and dextroamphetamine. These drugs can be smoked, snorted, taken orally, or injected and can be made in a laboratory or at home. Chemicals similar in pharmacological qualities also are abused, such as amphetamine-like drugs used to treat ADHD (methylphenidate), narcolepsy (methylphenidate and dextroamphetamine), and over-the-counter (OTC) medications for congestion (pseudoephedrine). When taken in therapeutic dosages, these drugs are helpful and do not cause brain damage. When abused, underactivity in the temporal, parietal, and frontal areas has been noted.

B. Amphetamines have a similar but more powerful effect than cocaine on the neurotransmitters noradrenaline and dopamine by prevention of their reabsorption into neurons. Because these neurotransmitters are not deactivated by reuptake, they build up and exert a prolonged effect on their targets. This effect is seen in the continuous body movements and distractibility exhibited by the user.

IV. Cocaine

A. A natural alkaloid derived from the Erythroxylon coca plant grown in South America. It is used medically as a local anesthetic and appetite suppressant. Cocaine is found in different forms and can be inhaled, smoked, injected, and absorbed intraanally and intravaginally. Crack is a potent form that is smoked to produce a rapid high with intense addictive qualities.

B. The National Institute of Drug Abuse (NIDA) reports that cocaine use leads to repeated microscopic strokes that result in dead spots in the brain’s circuitry (NIDA, 1998).

C. Three important neurotransmitters are disturbed with cocaine use and abuse: norepinephrine, serotonin, and dopamine. Cocaine blocks the reuptake of dopamine from the synapse. This results in dopamine remaining in the synapse for longer periods, where it can stimulate receptors to a greater extent, resulting in an extreme feeling of well-being.

D. Prenatal cocaine exposure has been documented as having subtle effects on motor skills, irritability, attention span, alertness, and intelligence quotient (IQ) level in some children. Prenatal effects are not as dramatic as previously reported, but they are significant when coupled with the environment of the child. Cocaine abuse has a financial impact related to the special education resources needed to support the children through school to succeed in their chosen endeavors.

Table 6-1 Drug Neurotoxic Effects

Table 6-2 Stimulant Effects

Physical and Behavioral Symptoms	Toxic Effects
General: Euphoria, exaggerated sense of well-being Increased energy and alertness Blurred vision Dizziness Talkativeness Restlessness Sleeplessness Anxiety and panic attacks Reduced appetite Insomnia Dilated pupils Increased perspiration when injected Increased blood pressure, heart rate, respiration Elevated body temperature Poor body care	Tremors Cardiac abnormalities, some fatal Seizures, some fatal Deficient immune system; malnutrition; fatal kidney, heart, and lung disorders; brain and liver damage Depression, hallucinations, violent and aggressive behaviors, panic, paranoia, formication (feelings of insects crawling on skin) Learning deficits: attention, concentration, verbal and visual memory, word production, visual motor integration Nicotine and chemicals: increased risk of miscarriages and lower–birth-weight babies, decreased sense of smell and taste; changes in DNA lead to cancer and heart and lung disease; chew and snuff can cause cancer of throat, mouth, cheek, gums, and tongue
Amphetamine: jerky, flailing, writhing movements, extreme nervousness, plus general listed symptoms	Amphetamine: can result in stroke, high fever, sudden heart failure Amphetamine/cocaine psychosis: hallucinations, delusions, paranoia

Physical and Behavioral Symptoms

Toxic Effects

Amphetamine: jerky, flailing, writhing movements, extreme nervousness, plus general listed symptoms

Amphetamine: can result in stroke, high fever, sudden heart failure

Amphetamine/cocaine psychosis: hallucinations, delusions, paranoia

Table 6-3 Stimulant Withdrawal Symptoms

WEB SITE

National Institute on Drug Abuse: Nicotine Addiction http://www.smoking.drugabuse.gov

HALLUCINOGENS

Hallucinogens are drugs that act primarily on the CNS and profoundly alter sensory perception. Individuals see images, hear sounds, and feel sensations that do not exist but seem very real. Rapid and intense emotional swings occur, and changes in feelings and thoughts are exaggerated and magnified. Hallucinogens are usually taken orally. Effects of these drugs vary greatly from person to person and from one episode of drug use to another episode, making “bad trips” unpredictable. Users develop psychological dependence and can develop tolerance. No withdrawal symptoms for hallucinogens have been documented, and effects can last for 12 hours. Currently no accepted medical use for these drugs exists. Commonly abused hallucinogens are lysergic acid diethylamide (LSD), derived from a fungus; psilocybin, derived from mushrooms (found in 90 species); mescaline, derived from the peyote cactus; cannabis, the plant source of marijuana and hashish; and methylenedioxymethamphetamine (MDMA), Ecstasy, and methylenedioxyamphetamine (MDA;see Table 6-4).

Table 6-4 Hallucinogen Effects

Physical and Behavioral Symptoms	Toxic Effects
Increased heart rate and blood pressure	Decreased awareness to touch and pain
Sleep disturbance, sweating, dizziness, tremors	Seizures
Sparse and incoherent speech	Flashbacks leading to unpredictable behaviors, accidents, panic, and suicide
Disturbances in body heat regulation, loss of appetite
Lethargy, fatigue	Behavior similar to schizophrenic psychosis
Inability to feel pleasure
Changes in perception, feelings, and thoughts	Catatonic syndrome: mute, lethargic, disoriented; repetitive, meaningless movements
Decreased motivation, personality change, memory impairment, sense of distance	Kidney and cardiovascular failure
Confusion, suspicion, and loss of control
Depression, anxiety, and paranoia
Violent behavior