When a smoker lights up, nicotine in the cigarette turns on reward pathways in the brain, providing a sense of pleasure. Researchers know how nicotine triggers the dopamine-responsive reward pathway, and now scientists at the University of Pennsylvania have found how nicotine stimulates the opioid pathway.
The team reports in the June 16 issue of Neuron that after conditioning, environmental cues were enough to trigger gene activity in the opioid pathway. When mice were given repeated nicotine injections in a cage distinct from their home cage, then placed in the injection cage but not given nicotine, the opioid pathway was activated. When given a choice, the mice preferred the injection cage.
Significantly, both the nicotine-and environment-induced opioid responses were blocked by pretreatment with an opioid inhibitor. After this treatment, the mice lost interest in the injection cage.
“We can block the molecular mechanisms and block the behavior,” says lead author Julie Blendy, an assistant professor of pharmacology. That suggests opioid inhibitors might help people stop smoking by breaking the link between environmental triggers and reward sensations.