|Reorganizing the Plastic Brain|
|SciMed - Neuroscience|
|TS-Si News Service|
|Sunday, 20 March 2011 14:00|
Ann Arbor, MI, USA. Scientists have shown how the plasticity of their brains allowed mice to restore critical functions related to learning and memory after their ability to make certain new brain cells were disrupted.
The new findings bring scientists one step closer to isolating the mechanisms by which the brain compensates for disruptions and reroutes neural functioning — which could lead to an improved understanding of how the innate body plan is implemented in humans and posit treatments for cognitive impairments (such as those caused by disease and aging.
Neurons are most actively generated during the foundational period of pre-natal development. However, the neuron population process continues throughout adulthood.
More generally stated, the regrowth or repair of cell tissues (neuroregeneration is a continuous process throughut the human life cycle.
The extent and speed of neuroregeneration can vary, depending on whether it takes place within the central nervous system (CNS) or the peripheral nervous system (PNS).
In either case, the functional mechanisms are very similar.
The discovery of such neuroplasticity eclipsed old ideas that fixed brain locations supported specific functions exclusive of other areas."It's amazing how the brain is capable of reorganizing itself in this manner," says Geoffrey Murphy, Ph.D., is the co-senior author of the study and a researcher at the Molecular and Behavioral Neuroscience Institute (MBMI) of the University of Michigan (U-M).
The mice, exhibiting neuroplasticity, were able to shift key functions associated with learning and memory. "Right now, we're still figuring out exactly how the brain accomplishes all this at the molecular level, but it's sort of comforting to know that our brains are keeping track of all of this for us."
Murphy, also an associate professor of molecular and integrative physiology at the University of Michigan Medical School, put his lab in collaboration with the Neurodevelopment and Regeneration Laboratory run by Jack Parent, M.D. to examine the effects of neurgenerative disruption. Their findings appear in the Proceedings of the National Academy of Sciences (PNAS).
In previous research, the scientists had found that restricting cell division in the hippocampuses of mice using radiation or genetic manipulation resulted in reduced functioning in a cellular mechanism important to memory formation known as long-term potentiation.
But in this study, the researchers demonstrated that the disruption is only temporary and within six weeks, the mouse brains were able to compensate for the disruption and restore plasticity, says Parent, the study's other senior co-author, a researcher with the VA Ann Arbor Healthcare System, and an associate professor of neurology at the U-M Medical School.
After halting the ongoing growth of key brain cells in adult mice, the researchers found the brain circuitry compensated for the disruption by enabling existing neurons to be more active. The existing neurons also had longer life spans than when new cells were continuously being made.
"The results suggest that the birth of brain cells in the adult, which was experimentally disrupted, must be really important — important enough for the whole system to reorganize in response to its loss," Parent says.
FundingThe research was supported by grants from the National Institutes of Health (NIH), National Institute of Neurological Disorders and Stroke (NINDS). Temme is a National Science Foundation (NSF) Graduate Research Fellow and was also supported by a U-M.
ParticipationAdditional Authors: Benjamin H. Singer, Ph.D., Amy E. Gamelli, Ph.D., Cynthia L. Fuller, Ph.D., Stephanie J. Temme, all of U-M.
CitationCompensatory network changes in the dentate gyrus restore long-term potentiation following ablation of neurogenesis in young-adult mice. Benjamin H. Singera, Amy E. Gamelli, Cynthia L. Fuller, Stephanie J. Temme, Jack M. Parent, and Geoffrey G. Murphy. Proceedings of the National Academy of Sciences 2011; ePub ahead of print. doi:10.1073/pnas.1015425108
It is now well established that neurogenesis in the rodent subgranular zone of the hippocampal dentate gyrus continues throughout adulthood. Neuroblasts born in the dentate subgranular zone migrate into the granule cell layer, where they differentiate into neurons known as dentate granule cells. Suppression of neurogenesis by irradiation or genetic ablation has been shown to disrupt synaptic plasticity in the dentate gyrus and impair some forms of hippocampus-dependent learning and memory. Using a recently developed transgenic mouse model for suppressing neurogenesis, we sought to determine the long-term impact of ablating neurogenesis on synaptic plasticity in young-adult mice. Consistent with previous reports, we found that ablation of neurogenesis resulted in significant deficits in dentate gyrus long-term potentiation (LTP) when examined at a time proximal to the ablation. However, the observed deficits in LTP were not permanent. LTP in the dentate gyrus was restored within 6 wk and this recovery occurred in the complete absence of neurogenesis. The recovery in LTP was accompanied by prominent changes within the dentate gyrus, including an increase in the survival rate of newborn cells that were proliferating just before the ablation and a reduction in inhibitory input to the granule cells of the dentate gyrus. These findings suggest that prolonged suppression of neurogenesis in young-adult mice results in wide-ranging compensatory changes in the structure and dynamics of the dentate gyrus that function to restore plasticity.
Keywords: adult neurogenesis, thymidine kinase, metaplasticity, miniature inhibitory postsynaptic currents.
|Last Updated on Sunday, 20 March 2011 14:02|