For many smokers the first cigarette of the day is always the most enjoyable and now doctors think they know why.
Nicotine, like other addictive drugs, effects neurons in the brain that respond to dopamine, a chemical that regulates mood and shapes human behavior.In a report in the scientific journal Nature, John Dani and colleagues at Baylor College of Medicine in Houston, Texas, showed that nicotine first activates and then gradually desensitizes the receptors in the brain that regulate dopamine neurons.
"Initial application of nicotine can increase activity of the dopamine neurons, which could mediate the rewarding aspects of tobacco use," Dani said.
Amounts of nicotine in the body drop overnight during sleep which makes the blast of nicotine in the first cigarette so pleasurable.
But prolonged smoking during the day desensitizes the dopamine neurons so that doses of nicotine in all subsequent cigarettes would need to be larger to get the same enjoyment as that first cigarette.