Up to 85 percent of premature babies experience brief periods of apnea (pauses in breathing). A new study suggests that the resulting drops in blood oxygen levels can cause long-lasting changes in the release of dopamine from a key brain region, contributing to attention deficit hyperactivity disorder (ADHD) in later life.
Glenda Keating and Michael Decker exposed newborn rats to either 20-second bursts of a low-oxygen gas, or, as a control, 20 seconds of compressed air. When the rats were older, the researchers analyzed their activity patterns and the levels of dopamine in their brains. They found that the rats experiencing bouts of reduced oxygen intake during the first few days of life were hyperactive later in life. These rats also exhibited a 50 percent increase in the level of dopamine contained in the striatum and a corresponding reduction in the release of dopamine, meaning that their brains were abnormally storing the neurotransmitter.
Previous research by Decker had already revealed the link between repetitive apnea and ADHD-like behavior in rats, but the new study is the first to link brief, repeated periods of apnea to long-lasting reductions in the release of dopamine within the striatum, a brain region involved in behavior, learning, and memory.
Their findings, Keating and Decker say, could help to explain why drugs that increase dopamine levels in the brain, including amphetamine-like drugs such as Ritalin and non-amphetamine drugs such as Wellbutrin, are effective for children with ADHD. "So far scientists haven't sorted out which neurotransmitters are responsible for this effect," Decker says, "but if that could be narrowed down to just dopamine, as suggested by our data, it would provide a basis for developing drugs without the potential addictive properties of existing therapies."
The researchers plan to investigate methods of protecting the dopamine system in at-risk fetuses or children, saying these could include non-invasive dietary changes in mothers or infants.
"Low blood oxygen levels in newborns may contribute to ADHD development," news release, Emory University, Oct. 24, 2004. Findings presented at the annual meeting of the Society for Neuroscience, San Diego, Oct. 24, 2004.