Cocaine Use Results in New Brain Growth That Increases Drug-Seeking Behaviors

A recent study provides evidence of the changes in the brain that follow cocaine use. The study shows that cocaine can trigger rapid growth of new brain cells in mice that impact learning and memory related to drug-seeking behaviors. The study was conducted by researchers at the Ernest Gallo Clinic and ResearchCenter at the University of California at San Francisco. The findings were published in a recent issue of the journal Nature Neuroscience. The researchers conducted their trial using laboratory mice to examine the effects of cocaine on the brain’s structures and how the use of cocaine impacted environmental choices. Using a microscope to look at the nerve cells in the brains of the mice, principal investigator Linda Wilbrecht, Ph.D. and colleagues could detect fast-growing new cells. Two hours after the mice were introduced to cocaine the scientists were able to detect increased density in the dendritic spines in the frontal cortex. Dendritic spines are central players in the processes that allow messages to be passed from one nerve cell on to another, storing neuronal information. By contrast, when mice were given saline solution there was no increase in dendritic spine density observed. The researchers also noted a relationship identified between dendritic spine density and drug-associated learning — the mice with the highest number of new spines were more likely to seek out the environment in which they received the cocaine when compared with the other mice. Previous studies have shown decreased activity in the frontal cortex connected with mundane tasks, but with increased activity related to drug behaviors in those who have used for a long time. The new study gives clues to the process in which the brains of drug users become more attuned to drug associations. Wilbrecht described the frontal cortex as the “steering wheel” of the brain, responsible for many of the major functions including decision-making and high reasoning. The changes in the brain related to cocaine use may explain the deterioration of decision-making skills in drug users. One of the more puzzling behaviors of drug addicts is the focus on obtaining drugs at the expense of any other responsibility or interest. The findings may help explain that tendency. For the study, the mice were divided into two groups, with one group receiving cocaine injections and the second group receiving saline injections. The brain cells of the mice were measured using a 2-photon laser-scanning microscope. The researchers were surprised to note that brain changes were observable in the mice after only one dose of cocaine. In a separate trial, the brains of the mice in each group were observed both before and two hours following a cocaine or saline dose. New dendritic spines were evident in the cocaine group two hours after the first dose of the drug. The following morning, the mice in the cocaine group had increased their dendritic spines to four times more connections with the nerve cells when compared with the saline group. A third experiment compared the reactions of mice given cocaine in one chamber and saline in a separate chamber. While the procedure to administer the substance was the same in the two chambers, there were visual and textural differences. The mice with the greatest change in dendritic spines also showed the greatest preference in going to the chamber in which cocaine was administered. The finding suggests that the changes in dendritic spines may represent associations with which chamber contained access to cocaine.

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