DURHAM, N.C. - Immune system cells of the brain, which scavenge pathogens and damaged neurons, are also key players in memory and learning, according to new research by Duke neuroscientists.
Earlier studies by Staci Bilbo, an assistant professor in psychology & neuroscience, had shown that laboratory rats experiencing an infection at an early age have an aggressive immune response to subsequent infections, which also harms their learning and memory.
In a study published in the Oct. 26 Journal of Neuroscience, Bilbo's team identifies the source of the learning difficulties and traces it back to the immune system itself.
The researchers found that specialized immune system cells in the brain called microglia release a signaling molecule called Interleukin-1, or IL-1, in response to an infection. IL-1 is also crucial to normal learning and memory in the hippocampus region of the brain. But too much IL-1 can impair learning and memory in laboratory animals.
"These same molecules go up in response to any brain infection. I don't really understand why you would build a brain that way, except that there are clearly benefits in other aspects of immunity, outside the brain," Bilbo said.
In a series of experiments she has been conducting for nearly a decade, very young rats are exposed to infection and then challenged again later with a second infection consisting of only harmless, dead bacteria. The "second hit" has been shown to affect learning and memory while these rats mount a highly effective immune response.
"The microglia remember that infection and respond differently," she said. "The infection itself wasn't doing permanent damage. It was changing the immune system somehow."
The second infection doesn't even have to be directly involved with the brain. A bacterial lesion on a limb produces enough of a signal to make the glia in the brain pump out extra IL-1. "These rats handle peripheral
|Contact: Karl Leif Bates|