L>THE BRAIN FROM TOP TO BOTTOM
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You are watching: Cocaine blocks the reuptake of ________.
Pleasure-Seeking Behaviour Pleasure and Drugs Avoiding Pain
Nearly 15% of all men and 30% of all women admit to a craving for chocolate. Over 300 substances have been identified in chocolate. Some of these, including caffeine and theobromine (another, less powerful stimulant) could actually cause dependency effects. But the amounts of these substances in chocolate are too small to really have any effect. The same goes for phenylethylamine, a substance related to a family of stimulants called amphetamines. For example, chocolate contains less phenylethylamine than goat cheese. Anandamide, a neurotransmitter produced naturally by the brain, has also been isolated in chocolate. The neural receptors for anandamide are the same ones to which THC, the main active ingredient in cannabis, binds. The anandamide in chocolate might therefore contribute to the feeling of well-being reported by “chocoholics” (though you would have to eat well over 30 kilos of chocolate to experience effects comparable to one dose of cannabis!). Be that as it may, many scientists agree that dependency on chocolate could simply be due to its taste, which causes a sensation of intense pleasure that people want to repeat.
HOW DRUGS AFFECT NEUROTRANSMITTERS
Dopamine appeared very early in the course of evolution and is involved in many functions that are essential for survival of the organism, such as motricity, attentiveness, motivation, learning, and memorization. But most of all, dopamine is a key element in identifying natural rewards for the organism. These natural stimuli such as food and water cause individuals to engage in approach behaviours. Dopamine is also involved in unconscious memorization of signs associated with these rewards. It has now been established that all substances that trigger dependencies in human beings increase the release of a neuromediator, dopamine, in a specific area of the brain: the nucleus accumbens.
But not all drugs increase dopamine levels in the brain in the same way.
Some substances imitate natural neuromediators and take their place on their receptors. Morphine, for example, binds to the receptors for endorphin (a natural “morphine” produced by the brain), while nicotine binds to the receptors for acetylcholine. Other substances increase the secretion of natural neuromediators. Cocaine, for example, mainly increases the amount of dopamine in the synapses, while ecstasy mainly increases the amount of serotonin. Still other substances block a natural neuromediator. Alcohol, for example, blocks the NMDA receptors.
Click on the names of each of the following drugs to read about how they work and what effects they have.
Alcohol —– Opiates (heroin, morphine, etc.) —– Cocaïne —– Nicotine
Caffeine —– Amphetamines —– Cannabis —– Ecstasy —– Benzodiazepines
Cocaine acts by blocking the reuptake of certain neurotransmitters such as dopamine, norepinephrine, and serotonin. By binding to the transporters that normally remove the excess of these neurotransmitters from the synaptic gap, cocaine prevents them from being reabsorbed by the neurons that released them and thus increases their concentration in the synapses (see animation). As a result, the natural effect of dopamine on the post-synaptic neurons is amplified. The group of neurons thus modified produces much more dependency (from dopamine), feelings of confidence (from serotonin), and energy (from norepinephrine) typically experienced by people who take cocaine. In addition, because the norepinephrine neurons in the locus coeruleus project their axons into all the main structures of the forebrain, the powerful overall effect of cocaine can be readily understood. In chronic cocaine consumers, the brain comes to rely on this exogenous drug to maintain the high degree of pleasure associated with the artificially elevated levels of some neurotransmitters in its reward circuits. The postsynaptic membrane can even adapt so much to these high dopamine levels that it actually manufactures new receptors. The resulting increased sensitivity produces depression and cravings if cocaine consumption ceases and dopamine levels return to normal. Dependency on cocaine is thus closely related to its effect on the neurons of the reward circuit.
General links about cocaine:
For a description of the effects of cocaine and the risks of dependency associated with it, click on the following links: