Cocaine, a crystalline drug derived from the leaves of the coca plant, is a commonly abused central nervous system stimulant. It exerts its effects on the brain by interfering with the flow of neurotransmitters, or chemical messengers, such as dopamine, serotonin and norepinephrine. The resultant disruption of normal brain chemistry causes psychological and physiologic effects that can lead to repeated use of the drug and, eventually, to dependence and addiction.
Definitions
The terminology surrounding illicit drug use is frequently misstated. Substance abuse is simply the use of a substance in a manner different from its intended use, usually with undesirable consequences. Dependence, or habituation, is a predictable physiologic adaptation to repeated use of a substance that leads to tolerance--the need for escalating doses to achieve the same effects--and to withdrawal when the substance is unavailable. Addiction is the preoccupation with continued use that typically leads to behaviors designed to acquire more of the abused substance, accompanied by a deterioration in social function. Dependence is not necessarily associated with addiction.
Neurotransmitters
Impulses, or messages, are transmitted through the brain and body via a network of cells, called neurons, which collectively form the nervous system. One neuron transfers an impulse to adjacent neurons by releasing chemicals into the microscopic space, or synapse, that separates the neurons. These chemicals, called neurotransmitters, stimulate receptors that propagate the impulse along the network. In most cases, once the impulse has passed, the neurotransmitters are reabsorbed into the neurons, where they can be reused when the next impulse comes along. As neurotransmitter levels within a given synapse wax and wane, the number and sensitivity of receptors also change to maintain a normal flow of impulses.
Dopamine
The brain uses several neurotransmitters to perform its tasks. Some neurotransmitters are inherently stimulating, while others are inhibitory or calming. Because the brain's interconnections are so complex, one impulse can lead to the release of both stimulatory and inhibitory neurotransmitters from different neurons, and one neurotransmitter can fulfill different roles in different parts of the brain. Dopamine is a neurotransmitter with a multitude of functions, but overall it is similar to epinephrine, or adrenalin, as its effects tend to be stimulatory. Dopamine exerts its effects on processes that involve pleasure, pain, learning, memory, alertness, mood, emotional responses and movement.
Cocaine Addiction
Cocaine evokes central nervous system stimulation through two mechanisms. First, it augments the release of dopamine from neurons that normally use this neurotransmitter to relay impulses. More importantly, cocaine inhibits the reabsorption of dopamine that has been released into the synapse. The resulting increase in dopamine within the synapse leads to heightened and prolonged stimulation of pleasure centers in the brain, which sets the stage for repeated use. The brain compensates for the dopamine surfeit by decreasing the number and sensitivity of dopamine receptors, thus prompting physiologic dependence, evidenced by a need for increased cocaine doses to achieve a similar "high." Addiction ensues when the user's behaviors change to ensure continued acquisition of the drug.
Treatment
Treatment for addiction disorders is complicated, and cocaine addiction is no exception. Attention to the multiple needs of the addicted individual is necessary, in addition to management of the medical problems associated with addiction to a specific substance. Detoxification, usually in a medical setting, is often required to deal with immediate withdrawal symptoms. Medications to mitigate neurotransmitter abnormalities can help, as can drugs that alleviate the mood disturbances associated with withdrawal. A vaccine to reduce the likelihood of relapse is under investigation.
