Supported by a $1.7 million National Institutes of Health (NIH) grant, Fox and his group set out to find possible reasons for this supernormal retinal response in children. The researchers employed rat and mice models that covered the three levels of lead found in the blood of the Mexico City mothers some below, some right at and some higher than the CDC "safe level." The researchers exposed rodents to lead throughout pregnancy and the first 10 days of life, which is a time period equivalent to human gestation.
Fox said that the early-born retinal progenitor cells give rise to four neuron types, which were not affected by lead exposure. The later-born retinal progenitor cells, he said, give rise to two types of neurons and a glial cell. Surprisingly, only the late-born neurons increased in number. The glial cells, which nurture neurons and sometimes protect them from disease, were not changed at all. The rats and mice both had "bigger, fatter retinas," according to Fox. Interestingly, the lower and moderate doses of lead produced a larger increase in cell number than the high lead dose.
"This is really a novel and highly unexpected result, because lead exposure after birth or during adulthood kills retinal and brain cells, but our study showed that low-level lead exposure durin
|Contact: Lisa Merkl|
University of Houston