Dopamine is the neurotransmitter of reward active in alcohol, opiate, and cocaine dependence.
Release of dopamine affects the part of the brain that regulates motor behavior. The destruction of the neurons that produce dopamine by substance abuse produces symptoms of Parkinson's disease, such as rigidity and tremor. Blockage of the actions of dopamine in other brain regions accounts for the therapeutic activities of anti-psychotic drugs. This neurotransmitter has been linked to addiction through its role as a pleasure chemical and enhancing learning and appears to be the common neurotransmitter affected by all addictive substances.
Other neurotransmitters involved in the brain reward system are:
Serotonin--Changes in the activity of serotonin producing neurons results in changes in mood, appetite, sleep, and sexual function. Medications to treat depression focus on increasing serotonin levels in the brain.
Enkephalins--These neurotransmitters are normally occurring substances that bind to localized opiate receptors, sites involved in pain perception. They mimic the effects of opiates.
Adapted from Snyder, S.H. Drugs and the Brain, Scientific American Library, New York, 1996.
Terminology
Defining
the terms drug, substance abuse, and chemical dependence is a logical
beginning. Taber's Cyclopedic Medical Dictionary defines a drug as any
substance that when taken into a living organism, may modify one or more
of its functions.6 Drugs are
classified according to their biochemical action, physiologic effect,
or the organ system(s) they affect. According to Inaba, et al., drug abuse
is the continued use of a drug despite negative consequences. Chemical
dependence refers to the interaction between a drug and the individual
when there is a compulsion to take the drug to obtain its effects and/or
to avoid the discomforts of withdrawal.7
Simply stated, if a substance is intentionally taken to alter one's mood
or perception, it can be considered an "abused substance."
Regardless of their legal use status, drugs are classified in specific categories as: cannabinoids; central nervous system (CNS) stimulants (sypathomimetics); CNS depressants (anxiolytics); opiates (opioids); hallucinogens (psychedelics; inhalants; anabolic-androgenic steroids (hormones); prescription drugs; and over-the-counter (OTC) drugs. Categories of drugs with their effects, street names, signs, symptoms, and treatments for the abuse of each are shown in Figure 1.
