A repetitive drop in blood oxygen levels in newborn rats, similar to that caused by apnea (brief pauses in breathing) in some human infants, is followed by a long-lasting reduction in the release of the brain neurotransmitter dopamine, according to an Emory University research study. Because dopamine promotes attention, learning, memory and a variety of higher cognitive functions, the researchers believe repetitive apnea during neonatal development may be one factor leading to the development of attention deficit hyperactivity disorder (ADHD). This research will be reported at the Society for Neuroscience annual meeting in San Diego on October 24 by Glenda Keating, PhD, and Michael Decker, PhD, of the Department of Neurology at Emory Universitys School of Medicine. The research was funded by the National Heart Lung and Blood Institute and conducted by the Program in Sleep Medicine and the Department of Neurology at Emory University.
Apnea of prematurity occurs in up to 85 percent of all prematurely born human infants, and obstructive sleep apnea occurs in 3 to 27 percent of all children. Data from previous studies suggests that diminished release of brain dopamine may be responsible for behaviors such as impulsiveness and distractibility, reduced self control, and impaired learning, which are hallmark traits associated with ADHD. Previous studies in Dr. Deckers laboratory at Emory have shown that newborn rats who experience repetitive drops in blood oxygen levels go on to develop behavioral traits similar to those seen in humans with ADHD. This is the first time, however, that researchers have linked repetitive reductions in blood oxygen levels during a period of critical brain development to long-lasting deficiencies in release of dopamine specifically within the striatum, which is one of the brain regions important in modulating behavior, learning and memory.
The scientists exposed newborn rats from 7 to 11 days old to either 20-second bursts of a gas containing low oxygen content or to bursts of compressed air. Once the rats matured into juveniles, the scientists studied their locomotive activity and brain dopamine levels. They found that juvenile rats exposed to brief reductions in oxygen during their neonatal period had a 50 percent reduction in release of dopamine and were hyperactive.
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