In their experiments published online in the Journal of Neuroscience they also show that they could restore a significant degree of lost plasticity to the cells by giving treating mice with the commonly used antidepressant medication fluoxetine, also known as Prozac.
“Despite common belief, loss of neurons due to cell death is quite limited during normal aging and unlikely to account for age-related functional impairments,” wrote the scientists, including lead author Ronen Eavri and corresponding author Elly Nedivi, a professor of biology and brain and cognitive sciences. “Rather it seems that structural alterations in neuronal morphology and synaptic connections are features most consistently correlated with brain age, and may be considered as the potential physical basis for the age-related decline.”
Above: Tracking the growth of neuron arbors under the microscope over two weeks, researchers typically saw growth beyond the arrow marker in six-month-old mice (green), but none beyond the marker in 18-month old mice (red).
Nedivi and co-author Mark Bear, Picower Professor in the institute, are affiliated with MIT’s Aging Brain Initiative, a multidisciplinary effort to understand how aging affects the brain and sometimes makes the brain vulnerable to disease and decline.
In the study the researchers focused on the aging of inhibitory interneurons which is less well understood than that of excitatory neurons, but potentially more crucial to plasticity. Plasticity, in turn, is key to enabling learning and memory and in maintaining sensory acuity. In this study, while they focused on the visual cortex, the plasticity they measured is believed to be important elsewhere in the brain, as well.