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LINKS: ....Your Memory Enhancer ....Neurotech ....Success Tips ....Free....Brain Wisdom Reward Substrate Identified by Chemical Brain StimulationAnother approach to studying brain reward systems is to determine the neurochemical coding of these pathways. This can be accomplished by identifying the neurochemical mechanisms whereby various drugs serve as rewards following either systemic or intracranial administration. Essentially, reinforcing drugs can be used as tools for studying brain reward mechanisms in much the same manner as electrical stimulation. Experimental procedures have been developed where animals can lever press to obtain various drug rewards (see Bozarth, 1987b). Some drugs delivered intravenously can serve as rewards. Most drugs that are self-administered by humans are also self-administered by laboratory animals. The most potent drug rewards include the psychomotor stimulants (e.g., amphetamine, cocaine) and the opiates (heroin, morphine). These drugs are self-administered by laboratory animals that have surgically implanted intravenous catheters. Animals quickly learn to press a lever to intravenously self-administer drugs such as cocaine and heroin. This experimental preparation provides an animal model of human drug-taking behavior and hence a method to study the reinforcing properties of drugs; this reinforcing drug-action forms the basis for drug addiction in humans (see Bozarth, 1987b, 1990). It is important to note that addiction is defined as a behavioral syndrome where a drug seems to exert extreme control over the individual's behavior and is not defined by physiological withdrawal reactions such as those accompanying abstinence from some drugs. Drug use is seen as developing along a continuum, beginning with casual/recreational use where the drug has a modest influence on behavior to the extreme condition (i.e., addiction) where the drug use seems to dominate the individual's behavior (see Bozarth, 1990). Reward from psychomotor stimulants and from opiates appears to involve activation of the same brain reward system as that activated by electrical stimulation. Dopamine is the neurotransmitter most consistently linked with reward from these drugs, and the ventral tegmental dopamine system has been specifically implicated in psychomotor stimulant and opiate rewards. Other drugs that may serve as reinforcers (e.g., alcohol, barbiturates, caffeine, marijuana, nicotine) also activate the ventral tegmental dopamine system, although the data suggesting this activation is critical for their reinforcing effects are not conclusive. Furthermore, abstinence from cocaine or from morphine after repeated administration may decrease dopamine levels in this brain system (Bozarth, 1989; Rossetti, Hmaidan, & Gessa, 1992); this diminished dopamine function may be related to the intense craving associated with withdrawal in drug dependent humans. The subjective experience of craving is probably related to relapse into drug-taking behavior following abstinence and therefore is an important factor in drug addiction. HOME...... Brain Food LINKS: ....Medical Dictionary ....Stress Management ....Allergy Info |