GENEVA, Switzerland — As of 2019, there are almost 25 million cocaine users worldwide. According to researchers, only one in five cocaine users wind up becoming addicted to the drug. The drug triggers a massive increase in serotonin, say scientists, in addition to the dopamine rush common to all drugs that, in some, can be extremely addictive. In a recent study, however, researchers have discovered that in some people serotonin actually winds up acting as a “natural brake” on that rush of excitement in the brain’s reward system that’s elicited by dopamine.
So, while serotonin levels rise from cocaine consumption, scientists believe it actually could be the reason more people don’t become addicts. The study suggests that addiction occurs when an imbalance is created between these two neuroregulators, and dopamine ends up overtaking serotonin.
“Dopamine triggers a phenomenon of synaptic plasticity, through the strengthening of connections between synapses in the cortex and those in the dorsal striatum. This intense stimulation of the reward system then triggers compulsion. Serotonin has the opposite effect by inhibiting the reinforcement induced by dopamine to keep the reward system under control,” explains lead researcher Christian Lüscher, a neuroscientist at the University of Geneva, in a statement.
To demonstrate, scientists first taught a large group of mice to self-administer cocaine voluntarily. They then added a constraint: each time the mice self-administered cocaine, the rodents received a slightly unpleasant stimulus, such as an electric shock or an air jet burst. Two groups then emerged: 80% of the mice stopped their consumption, while 20% continued, despite the unpleasantness.
“This compulsive behavior is precisely what defines addiction, which affects 20% of individuals, in mice as well as in humans,” notes Dr. Vincent Pascoli, a scientific collaborator on the study.
The experiment was repeated with mice in which cocaine was no longer linked to the serotonin transporter so that only dopamine increased when the substance was taken. Three out of five of the animals then developed an addiction.
“If serotonin is administered to the latter group, the rate of addiction falls to 20%. Cocaine, therefore, has a kind of natural brake that is effective four times out of five,” adds Dr. Lüscher.
Statistics show an average of 5.5 million Americans having used cocaine in 2017, the most recent year for which records are available. Those between the games of 18 and 25 used cocaine more than any other age group in that year.
The results were published in the journal Science.
South West News Service writer Joe Morgan contributed to this report.