Smoking is associated with multiple health risks. Heart disease and several types of cancer are more likely to occur in individuals who smoke. In trying to understand how to help smokers quit, scientists also want to understand how smokers get started in their addiction.
A new neuroscience research study attempted to pinpoint the specific brain activity that occurs within the first few minutes of exposure to nicotine. The study, published in The Journal of Neuroscience, showed that there was a connection formed between neurons within a single 15-minute exposure to nicotine, causing a long-term excitability between the neurons.
The results show that nicotine behaves similarly to cocaine in the brain, changing mechanisms during the very first contact and creating a long-lasting change in the brain.
Danyan Mao, PhD, is a postdoctoral researcher at the University of Chicago Medical Center and lead author of the study. Mao explains that the change in the brain for smokers is a long-term behavioral change, but that the changes begin at the first exposure to nicotine. The researchers wanted to find out what happened in the brain at first exposure to a cigarette that then led the person to choose to have a second cigarette.
The study’s design was based on the understanding that as neurons are repeatedly activated together, they begin to form a strengthening bond. This leads to the neurons having the ability to excite one another.
Previous research has shown that nicotine can promote plasticity in a region of the brain known as the ventral tegmental area (VTA). Mao monitored the electrical activity of VTA dopamine neurons in slices of brain from adult rats. Each section of the rat’s brain was soaked for 15 minutes in a concentration of nicotine comparable to the exposure experienced in the brain during the smoking of a single cigarette.
After several hours, Mao conducted electrophysiology experiments to test for synaptic plasticity and identify receptors involved. Mao found that the nicotine affected a receptor for the neurotransmitter acetylcholine located on the dopamine neurons. But another surprising result showed that the nicotine affected the D5 dopamine receptor, a component associated with cocaine addiction.
The results of the study show how even one cigarette can introduce changes in the brain that mimic those found in cocaine use. The first time a cigarette is used, neurons begin to make connections, encouraging the pleasurable response associated with smoking. Understanding how nicotine affects the brain, even during the first cigarette smoked, may help scientists develop strategies for helping individuals with smoking cessation.