HOUSTON – (Sept. 9, 2009) – Ever wonder why former smokers miss lighting up most when they are in a bar or after a meal with friends?
Researchers at Baylor College of Medicine say nicotine, the addictive component in cigarettes, "tricks" the brain into creating memory associations between environmental cues and smoking behavior. The findings appear in the current issue of the journal Neuron.
"Our brains normally make these associations between things that support our existence and environmental cues so that we conduct behaviors leading to successful lives. The brain sends a reward signal when we act in a way that contributes to our well being," said Dr. John A. Dani, professor of neuroscience at BCM and co-author of the study. "However, nicotine commandeers this subconscious learning process in the brain so we begin to behave as though smoking is a positive action."
Dani said that environmental events linked with smoking can become cues that prompt the smoking urge. Those cues could include alcohol, a meal with friends, or even the drive home from work. To understand why these associations are so strong, Dani and Dr. Jianrong Tang, instructor of neuroscience at BCM and co-author of the report, decided to record brain activity of mice as they were exposed to nicotine, the addictive component of tobacco.
The mice were allowed to roam through an apparatus with two separate compartments. In one compartment, they received nicotine. In the other, they got a benign saline solution. Later, the researchers recorded how long the mice spent in each compartment. They also recorded brain activity within the hippocampus, an area of the brain that creates new memories.
"The brain activity change was just amazing," Dani said. "Compared to injections of saline, nicotine strengthened neuronal connections – sometimes up to 200 percent. This strengthening of connections underlies new memory formation."
Consequently, mice learned to spent more time in the compartment where the nicotine was administered compared to the one where saline was given to them.
"We found that nicotine could strengthen neuronal synaptic connections only when the so called reward centers sent a dopamine signal. That was a critical process in creating the memory associations even with bad behavior like smoking."
Dani said understanding mechanisms that create memory could have implications in future research and treatments for memory disorders, such as Alzheimer's disease, and for dopamine signaling disorders, such as Parkinson's disease.
This study was supported by the National Institute of Neurology Disorders and Stroke and the National Institute of Drug Abuse.
Once the embargo lifts the study can be found at http://www.cell.com/neuron/.
For more information on basic science research at Baylor College of Medicine, please go to www.bcm.edu/fromthelab or www.bcm.edu/news.
Journal
Neuron