TORONTO -- New research has pinpointed brain cells responsible for nicotine aversion, which scientists hope will develop ways to help people quit smoking.

Scientists have long known nicotine stimulates both pleasure and disgust responses in different parts of the brain.

But University of Toronto scientists said their newest research strengthens the idea that nicotine is actually hitting the same part of the brain.

Research associate Taryn Grieder and her team found both pleasure and aversion were sensed by a pair of nicotine receptors in the same brain-reward system called the ventral tegmental area (VTA).

The findings, published in the journal Proceedings of the National Academy of Sciences, also suggested that the more people smoke, the more tolerant they become to its aversive effects.

And the more addicted they become, the more their brain signaling will change.


Chemical neurotransmitter dopamine is traditionally associated with pleasure, while neurotransmitter GABA can have an inhibiting effect.

Grieder’s team bred genetically engineered mice to eventually only have either receptors in the VTA, which gave off dopamine, or GABA. The mice were exposed to levels of nicotine comparable to heavy smoking.

The team found that dopamine neurons in the VTA were actually responsible for disgust, not pleasure, and the GABA neurons trigger a reward response in these animals-- which is at odds with traditional thinking.

“The idea that most people have is that the first time they smoke it’s going to be all pleasure but the difference here is that we found that dopamine in nicotine’s case is involved in the more aversive or disgust component,” she said.

In mice that weren’t addicted to nicotine, the dopamine neurons were responsible for aversion. But in mice dependent on nicotine, dopamine neurons triggered both reward and the negative feelings of withdrawal.

And Grieder said the findings could have a big effect on understanding addiction in humans.

“What we think is that certain nicotine receptors in certain people are more stimulated than others. (When smoking for the first time,) some people find it very pleasurable and some people find it really disgusting,” she said.


For Grieder, a neuropsychology professor and staff scientist at the Donnelly Centre for Cellular and Biomolecular Research, her decade-long fight to tackle nicotine addiction is personal.

Six years ago, Grieder lost her father to health issues related to smoking, and out of six members of her family, she’s the only one who doesn’t smoke.

Scientists are still exploring the complex neurological pathways affected by smoking. And she hopes the medical community further explores the idea of nicotine aversion therapy, or causing people to feel disgusted when they’re given nicotine.

She said instead there is currently a bigger push of simply weaning people off nicotine as a means to stop their addiction. But Grieder said “they’re not that effective.”

"If we can selectively stimulate those disgust neurons when someone smokes, then we think they’ll associate feelings of gross with smoking which will make it a lot easier to quit.”