It's Not a Choice: Cocaine Addiction Is a Biological Reprogramming

Researchers investigated how cocaine alters specific brain circuits linked to memory and reward. They discovered that the drug activates a gene called FosB in neurons of the ventral hippocampus that connect to the nucleus accumbens. This activation increases the production of a protein called calreticulin, which modifies the functioning of these nerve cells. As a consequence, the brain circuit begins to favor the search for the drug. The study shows that cocaine addiction involves profound biological changes in the brain, and not just behavioral decisions.

Cocaine addiction is now considered one of the major public health challenges. Unlike what many people imagine, it doesn't happen simply because someone "chooses to use drugs."

Research shows that repeated cocaine use causes profound changes in brain function. These changes alter the systems responsible for motivation, pleasure, and decision-making, causing the person to develop a strong urge to seek the drug even when it brings negative consequences.

Between 2015 and 2020, for example, cocaine overdose deaths tripled in some countries, demonstrating the seriousness of the problem. Despite this, there are still no officially approved medications to specifically treat cocaine addiction.

To create effective treatments, scientists need to understand exactly how the drug modifies the brain. Addiction involves alterations in neural networks responsible for the reward system, which is the brain mechanism that makes us repeat pleasurable behaviors, such as eating or socializing.

When cocaine interferes with this system, it artificially reinforces the sensation of reward, causing the brain to prioritize the search for the drug. This process also involves changes in how neurons communicate with each other and how certain genes are activated within nerve cells.

An important brain region in this process is the ventral hippocampus, an area linked to emotional memory. This part of the brain helps associate external experiences, such as places or situations, with internal states, such as pleasure or desire. For example, a person may associate a particular environment or group of friends with drug use.

Thus, when they encounter these situations again, a strong desire to use cocaine may arise. This mechanism helps explain why relapses are common even after periods of abstinence.

Researchers also investigated the connection between the ventral hippocampus and another brain area called the nucleus accumbens, which participates directly in the reward system. Neurons in the hippocampus send signals to this region and help regulate behaviors motivated by the pursuit of rewards.

Previous studies had already shown that this brain connection plays an important role in the craving for and seeking of cocaine. However, it was still unclear how the drug alters the functioning of the nerve cells that are part of this circuit.

To study this, scientists conducted experiments on laboratory animals. They repeatedly administered cocaine or allowed the animals to learn to self-administer the drug by pressing a lever. Then, the researchers directly examined the electrical activity of specific neurons in the hippocampus that connect to the nucleus accumbens. This analysis allowed them to observe how easily these neurons fire electrical signals, indicating the level of activity and sensitivity of these cells.

In addition, the scientists genetically manipulated some cells to remove a specific gene called FosB. This gene is known to respond rapidly to drug exposure and control the activation of other genes within nerve cells.

By eliminating this gene only in the cells participating in the studied circuit, the researchers were able to observe how the animals' behavior changed. They also used laboratory techniques to identify which genes were being activated in these cells after cocaine exposure.

The results showed that cocaine increases the activity of a specific form of protein produced by the FosB gene. This protein, in turn, activates another gene responsible for the production of a protein called calreticulin. This protein regulates the storage of calcium within nerve cells, an essential element for the functioning of neurons.

When the amount of calreticulin increased, the neurons in the ventral hippocampus became less excitable, that is, they began to respond differently to stimuli.

This alteration in the functioning of nerve cells had direct consequences on drug-related behavior. Animals exhibiting these changes showed a greater tendency to seek cocaine and respond to stimuli associated with it. When scientists prevented the action of the FosB gene or reduced the production of calreticulin, this behavior decreased.

These results suggest that cocaine causes a kind of "biological reprogramming" in the brain, altering genes and neural circuits in a lasting way, which helps explain why addiction is so difficult to overcome.

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Transcriptional regulation of ventral hippocampus-nucleus accumbens circuit excitability drives cocaine seeking

Andrew L. Eagle, Chiho Sugimoto, Marie A. Doyle, Daniela Anderson, Seyedeh Leila Mousavi, Megan M. Dykstra, Hayley M. Kuhn, Brooklynn R. Murray, Ryan M. Bastle, Sarah Simmons, Jin He, Ian Maze, Michelle S. Mazei-Robison, and Alfred J. Robison

Science Advances. 4 Mar 2026. Vol 12, Issue 10

DOI:10.1126/sciadv.adv1236

Abstract:

Ventral hippocampus (vHPC) CA1 pyramidal neurons send glutamatergic projections to nucleus accumbens (NAc), and this vHPC-NAc circuit mediates cocaine seeking and reward, but it is unclear whether vHPC-NAc neuron properties are modulated by cocaine exposure to drive subsequent behavior. The immediate early gene transcription factor FosB/ΔFosB is induced throughout the brain by cocaine and is critical for cocaine seeking, but its function in vHPC-NAc neurons is not understood. We now show that circuit-specific knockout of FosB/ΔFosB in vHPC-NAc neurons impaired cocaine reward expression and forced abstinence–induced seeking. We also found that vHPC-NAc excitability was decreased by experimenter-administered repeated cocaine and cocaine self-administration, and this cocaine-induced excitability decrease was mediated by ΔFosB expression. To uncover the mechanism of this change in circuit function, we used circuit-specific translating ribosome affinity purification to assess cocaine-induced, FosB/ΔFosB-dependent changes in gene expression in vHPC-NAc. We found that cocaine causes a FosB/ΔFosB-dependent increase in the expression of calreticulin, an endoplasmic reticulum–resident calcium-buffering protein. Calreticulin expression mediated vHPC-NAc excitability and was necessary for cocaine reward. These findings uncover a noncanonical mechanism by which cocaine increases calreticulin in vHPC leading to decreased vHPC-NAc excitability and drives cocaine seeking and reward.