The dark side of dopamine: Pleasure hormone also responds to pain, UC Berkeley study finds

Johannes De Jong/Courtesy

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Dopamine, a neurotransmitter known for its role in pleasure and reward, may soon lose its reputation as “the pleasure hormone,” according to a new study conducted by UC Berkeley.

Campus scientists recently released a study revealing a new side to dopamine — one that responds to aversive stimuli. This challenges long-held beliefs that dopamine is uniquely involved in reward systems. The molecule helps train the brain to pursue pleasurable stimuli and avoid negative stimuli, but its role is varied — it’s implicated in conditions from addiction to Parkinson’s disease.

“Both in and outside of science, people just assume that it is just involved in pleasure and reward,” campus researcher and first author Johannes de Jong said. “They might not call it the pleasure hormone in science, but they talk about how it’s involved in reward pathways.”

The study, which was conducted by researchers in the campus Lammel Laboratory, used a relatively recent technique called fiber photometry to study neurons. The technique works by tagging certain proteins to fluoresce, or light up, when activated. The researchers threaded fiber optic cables into the brains of lab mice and tracked which neurons lit up in response to various signals.

What they found was that certain neurons released dopamine in response to pain stimuli, including a shock or tail pinch, in addition to responding to pleasure stimuli. These different neurons are located in nearby but anatomically distinct regions of the brain, and activate different circuits.

All dopamine is made in one area of the brain, but where that dopamine goes changes the brain’s reaction. The study found that axons—which carry neurological messages—in the medial nucleus accumbens of the brain released dopamine in response to aversive stimuli, while axons in the lateral nucleus accumbens released dopamine in response to positive stimuli.

“The next step is to figure out what is different about this circuit from other circuits,” de Jong said. “We don’t really understand these circuits, we’ve only recently been able to study these circuits in such detail.”

The study raises as many questions as it answers. Scientists speculate that changes in dopamine pathways can alter pleasure and pain reactions, but how these circuits work and change must be studied further.

According to campus assistant professor of neurobiology and co-author Stephan Lammel, understanding how these dopamine circuits work can provide more insight into addiction, which is known to change the brain’s response to dopamine.

“In addiction, people only look for the next reward, and they will take a lot of risk to get the next shot of drugs of abuse,” Lammel told Berkeley News. “We currently do not know the neurobiological underpinnings of certain high-risk behaviors of individuals with addiction, such as sharing drug paraphernalia despite the proven risk of mortality and morbidity associated with it.”

While there is hope that this new research can help scientists understand and treat addiction and other mental health disorders, the research is still a long way off from clinical applications.

“Our research is very fundamental,” de Jong said. “We built the roadmap that more clinically-oriented scientists can use.”

Contact Madeleine Gregory at [email protected] and follow her on Twitter at @mgregory_dc.

A previous version of this article incorrectly stated that axons in the lateral area of the brain released dopamine in response to positive stimuli. In fact, these axons were found in the lateral nucleus accumbens of the brain.