Scientists identify dopamine-rich brain pathways that fuel cocaine-seeking behavior

Researchers at the University of Pittsburgh have recently uncovered insights into how specific brain pathways influence cocaine addiction. The study, published in Neuropharmacology, found that dopamine signaling from the ventral tegmental area (a brain region associated with reward) to the basolateral amygdala (a region critical for associative learning) plays an important role in how individuals learn to associate environmental cues with cocaine’s effects.

The new study aimed to examine the brain mechanisms that make certain environmental cues trigger drug-seeking behaviors in individuals with addiction. Drug addiction extends beyond a substance’s immediate effects, as repeated use creates strong associations between drug use and specific environmental cues.

For example, someone recovering from addiction may feel a strong craving simply by seeing a place they used to visit for drug use. By investigating how the brain learns these associations, researchers hope to find ways to reduce the chances of relapse, potentially leading to more effective therapies.

Previous studies have shown that the amygdala, a brain region associated with memory and emotional responses, is involved in learning associations between cues and the effects of addictive drugs like cocaine. Dopamine, a chemical messenger often linked to feelings of reward and pleasure, plays a major role in this learning process.

The ventral tegmental area, a dopamine-rich brain region, sends dopamine to the basolateral amygdala, supporting learning and memory tied to these cues. However, it was unclear how directly this dopamine pathway influences the initial development of drug-related habits, so the team focused on examining this connection.

“Dopamine has long been studied in the context of reward and mediating the positive feelings elicited by drugs of abuse. However, these effects of dopamine have largely been attributed to its actions in striatal regions of the brain, even though there are also robust dopamine projections to other brain regions like the amygdala,” said study author Mary Torregrossa, an associate professor of psychiatry at the University of Pittsburgh.

“We do know that the amygdala is important for learning associations about environmental stimuli predictive of reward (such as with Pavlov’s dogs where a bell predicts food), but whether or not dopamine projections to the amygdala were required for the rewarding or learning components related to cocaine seeking were not known. Therefore, we performed experiments to determine what would happen if we turned off dopamine projections to the amygdala when rats learned to press a lever to obtain cocaine infusions, when they formed stimulus-cocaine associations, and when they learned to associate a location with the rewarding effects of cocaine.”

The researchers conducted the study on adult male and female Sprague Dawley rats, a common model in neuroscience research due to their similarity to human brain function. The study used a technique called chemogenetics, which enables researchers to control specific brain pathways with drugs. In this case, they modified dopamine neurons in the ventral tegmental area that connect to the basolateral amygdala, allowing them to either excite or inhibit these pathways during various tests.

The researchers performed several experiments to observe how dopamine pathways influenced cocaine self-administration. In the main experiment, rats were trained to press a lever to receive an infusion of cocaine. Some of the rats had their dopamine signaling from the ventral tegmental area to the basolateral amygdala inhibited during this learning period, while others had this pathway excited. To measure whether the rats had developed an association between drug cues and cocaine, researchers observed how often the rats pressed the lever when only a light or sound cue was presented.

Additionally, the researchers tested the rats’ preferences for a place associated with cocaine to assess whether inhibiting the dopamine pathway affected their overall desire for the drug, as opposed to the cue-based craving. In these tests, rats that received cocaine in one part of a two-chamber apparatus were observed to see whether they preferred the cocaine-paired side even without the drug present.

The researchers found that inhibiting dopamine signals from the ventral tegmental area to the basolateral amygdala during the initial cocaine self-administration period reduced the rats’ acquisition of cocaine-seeking habits. This inhibition also diminished the power of cocaine-related cues to trigger drug-seeking behaviors later on. In other words, these rats were less responsive to cues once they had learned to associate the cues with cocaine access.

“The main takeaway from our findings is that dopamine projections to the amygdala are necessary to develop robust cocaine-taking actions,” Torregrossa told PsyPost. “In our model, rats can press a lever to receive cocaine infusions in daily sessions, which normally leads to consistent high levels of lever pressing to obtain cocaine. However, without dopamine signaling to the amygdala, rats never lever pressed very much for cocaine and showed weak learning about a cocaine-associated stimulus.”

Interestingly, the effect of dopamine inhibition was specific to cue-based responses, rather than the drug itself. When presented with cocaine without any accompanying cues, the rats’ behavior remained the same as the control group. This distinction suggests that dopamine projections to the basolateral amygdala are essential for developing drug-cue associations but do not affect the primary reward of cocaine.

“The effects on cocaine taking seem to be related more to learning processes than to altering the rewarding properties of cocaine, as rats were able to learn to associate a location with the effects of cocaine even when dopamine signaling to the amygdala was disrupted,” Torregrossa said.

On the flip side, stimulating the dopamine pathway between the ventral tegmental area and basolateral amygdala during cocaine self-administration enhanced the rats’ responses to drug cues, reinforcing cocaine-seeking behaviors. This increased sensitivity to cues following stimulation indicates that strengthening this dopamine pathway could make the environment’s signals more potent in driving drug-seeking behavior.

“One of the most surprising findings was that dopamine signaling in the amygdala was particularly important for acquiring a robust lever response for cocaine and a cocaine-associated stimulus. But if rats acquired cocaine-seeking normally, and had the dopamine projection silenced later in a test of cocaine stimulus seeking, the rats’ behavior was unaffected,” Torregrossa added. “In other words, once the rats had learned this association, dopamine in the amygdala was no longer needed, which we were not expecting.”

However, like all research, there are limitations to consider. Since the research used rats, direct application to humans requires caution. Although rat models often predict human behaviors accurately in similar brain mechanisms, human experiences with addiction involve a much more complex interaction of social, environmental, and psychological factors.

Future research could further investigate the precise role of this dopamine pathway in addiction. Studies might explore whether similar pathways impact other addictive substances and how varying individual traits may influence sensitivity to environmental cues.

These pathways could be promising targets for therapies designed to reduce cue-based triggers in people recovering from substance use disorders. Since traditional therapies often struggle with relapse caused by environmental triggers, identifying specific pathways involved in this learning process may enable new treatments that target these neural circuits without affecting the overall reward system.

“The long-term goal is to understand the circuits that drive maladaptive drug-using behaviors so that those circuits might be targeted as a treatment for substance use disorders,” Torregrossa said.

The study, “The ventral tegmental area dopamine to basolateral amygdala projection supports acquisition of cocaine self-administration,” was authored by Dana M. Smith and Mary M. Torregrossa.