Cocain can exhert a variety of effects on the brain. The most intense acute effects result from increased levels of natural substances which circulate in the blood, called catecholamines.

Recently, scientists have investigated the euphoria-inducing effect of cocaine by means of brain images using the PET (Positron Emission Tomography) scanner, a sophisticated apparatus which permits the visualization of brain function, using mapping with certain types of radioactive substances (markers). The resulting paper was published in the scientific journal Nature [1].

They discovered that cocaine occupies naturally- existing receptors in neural cells, called dopamine transport sites. Dopamine is a substance synthesized by certain neurons in several areas of the brain, which is associated to the systems which control motivation, emotion, etc. These sites capture free dopamine which has been released in synaptic terminais and take the molecules back to the releasing neurons, after their effect. Since cocaine blocks these reuptake sites, dopamine stays in large amounts near the brain neurons where it exherts its stimulating effect for a longer time. Click here to see the PET images comparing the brain of a non-addicted patient to those of two cocaine-addicted pacients.

Dopamine, as well as other substances which may increase in the brain, cause a constriction of the brain vessels, which often lead to small lesions such as acute hemorrhages, and a hypoxia (lack of oxygen) and resulting cell death, or strokes. The same effect can happen in the heart, causing a heart infarction or attack (sudden death). Pregnant women using cocaine may strongly affect their placenta and fetuses, who are often born with low weight, or with irreversible lesions of the brain, causing mental and physical defficiencies. In many countries, the so-called  "cocaine babies" are a serious public health problem, which has been made tremendously worst by the wide dissemination of "crack".

In red, dopamine transport sites are mapped by the PET scanner. Only the sites which have not been occupied by cocaine are shown.

Why cocaine is addictive?

Another scientific study carried out with the help of PET, made by scientists from the Johns Hopkins University and the National Institute on Drug Abuse (NIDA) in the USA, has shown compelling evidences that cocaine addiction is directile related to the increase of the number of receptors to opioid substances (such as morphin and heroin) in the brain of addicted persons. These receptors exist naturally, because our brain synthesizes substances called endorphins, which seem to be neurotransmitters, too. The higher the intensity of addiction, the larger is the number of these receptors [2].

When the cocaine addicts observed in this study were kept away from the drug for a month, in many of them the number of receptors returned to a normal level; but in some of them this number continued to be high. This might be an indication that there is a correlation of this individual difference to the susceptibility of relapsing in drug use after withdrawal.

See also: Graphical animations showing the effects of cocaine on the brain

References

1. Nature, April 24, 1997

2. Nature Medicine, vol. 2, no. 11, November 1996.

The Authors

Silvia Helena Cardoso and Renato M.E. Sabbatini hold doctor degrees in Neurosciences by the University of São Paulo, Brazil, and are researchers at the Center for Biomedical Informatics of the State University of Campinas. They publish the on-line magazine of scientific dissemination, Brain & Mind.