Scientists working to understand more about the brains ability to learn and change in relation to the age of the cells have reported a new finding that they were able to prompt a new period of plasticity in the brain of juvenile mice. Their study involved the transplant a specific type of immature neuron from embryonic mice to the visual cortex of juvenile mice. The visual cortex has a period of very high plasticity during the earliest stages of development. During the period of plasticity, cells in this region react strongly to visual cues and respond with rapid synaptic transmissions produce the neural circuitry that is crucial for proper visual function.

In the release from the University of California at San Francisco they write "In mice this critical period of plasticity occurs around the end of the fourth week of life." To judge the efficacy of transplanting they applied a "process called monocular visual deprivation, in which they blocked the visual signals in one eye in each animal for four days." By doing monocular visual deprivation during this critical period the cells in the visual cortex begin favoring the non-deprived eye creating what is called ocular dominance plasticity.

From UCSF:
The team wanted to see if the transplanted cells would affect the visual system’s response to the visual deprivation after the critical period. They studied the cells’ effects after allowing them to mature for varying lengths of time. When the cells were as young as 17 days old or as old as 43 days old, they had little impact on the neural circuitry of the region. However, when they were 33-39 days old, their impact was significant. During that time, monocular visual deprivation shifted the neural responses away from the deprived eye and toward the non-deprived eye, revealing the state of ocular dominance plasticity.

Naturally occurring, or endogenous, inhibitory neurons are also around 33-39 days old when the normal critical period for plasticity occurs. Thus, the transplanted cells’ impact occurred once they had reached the cellular age of inhibitory neurons during the normal critical period.

The finding, the team says, suggests that the normal critical period of plasticity in the visual cortex is regulated by a developmental program intrinsic to inhibitory neurons, and that embryonic inhibitory neuron precursors can retain and execute this program when transplanted into the postnatal cortex, thereby creating a new period of plasticity.

“The findings suggest it ultimately might be possible to use inhibitory neuron transplantation, or some factor that is produced by inhibitory neurons, to create a new period of plasticity of limited duration for repairing damaged brains,” says author Sunil P. Gandhi, PhD, a postdoctoral fellow in the lab of Michael Stryker, PhD, professor of physiology and a member of the Keck Center for Integrative Neurosciences at UCSF. “It will be important to determine whether transplantation is equally effective in older animals.”

Likewise, “the results raise a fundamental question: how do these cells, as they pass through a specific stage in their development, create these windows of plasticity?” says author Derek G. Southwell, PhD, a student in the lab of Arturo Alvarez-Buylla, PhD, Heather and Melanie Muss Professor of Neurological Surgery and a member of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at UCSF.

The findings could be relevant to understanding why learning certain behaviors, such as language, occurs with ease in young children but not in adults, says Alvarez-Buylla. “Grafted MGE cells may some day provide a way to induce cortical plasticity and learning later in life.”

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Source article: http://news.ucsf.edu/releases/new-period-of-brain-plasticity-created-wit...

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Related links:
Science paper: “Cortical Plasticity Induced by Inhibitory Neuron Transplantation”
http://www.sciencemag.org/cgi/content/full/327/5969/1145

Alvarez-Buylla lab
http://neurosurgery.ucsf.edu/index.php/about_us_faculty_alvarez_buylla.html

Stryker lab
http://www.neuroscience.ucsf.edu/neurograd/faculty/stryker.html

Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research at UCSF
http://stemcell.ucsf.edu/