An investigation team in MIT's Picower Institute for Learning and Memory and the Department of Brian and Cognitive Sciences, have identified tiny molecular signals that administer how the connections between brain cells mature when they eyes first see light.
The study's 12 authors carried out their work in the laboratory of Mriganka Sur, the Paul E. Newton (1965) Professor of Neuroscience at MIT, and at many other research centers overseas.
Micro RNA molecules whose presence helped develop the links between cells responsible for perceiving and processing signals from light, where identified by the investigators while working on the brains of mice.
In normal brain development, these micro-RNAs permit visual brain regions to strengthen specific connections in response to light received from their surroundings. This process is called synaptic plasticity. If one or both eyes are deprived of light, levels of these micro-RNAs are reduced, resulting in underdevelopment of the connections.
Postdoc Nikolaos Mellios, the lead author of a research report appearing in the current issue of the scientific journal Nature Neuroscience, explained:
"Our study is the first to demonstrate the existence of numerous experience-dependent micro-RNAs in the visual cortex, and to demonstrate that inhibition of one of these small RNAs causes a profound loss in the ability of neurons to adjust to changes in their input."
This type of investigation is crucial as neuroscientists are observing increased evidence that abnormalities during brain development play some role in brain disorders. Levels of micro-RNA molecules that are either too-high or too-low may contribute to these abnormalities.
Their investigation concentrated on a micro-RNA molecule called miR-132, which as the brain region responsible for vision, primary visual cortex, matured, the miR-132 molecule was shown to gradually increase in abundance.
In order to examine how this molecule could impact the ability of this area of the brain to adapt to changing conditions, one eyelid in mice was stitched together by the investigators to prevent nerve signals from that eye reaching neurons in the visual cortex. Since one eye remained open, transmitting data to the cortex normally, they were able to examine how the visual cortex responded to the mixed signals, providing clues regarding the brain's capacity to adjust to changes in input.
Conducted by co-first author Hiroki Sugihara, they used an innovative method to evaluate real-time activity in the brains of live mice, to show that a reduction in miR-132 neurons delayed their maturation and made the mice not able to respond to the changes in signals from each eye.
Researchers know that micro-RNAs orchestrate gene expression and coding proteins in cells, although not much is known regarding how these molecules contribute to processes of brain development that are dependent on experience and external surroundings. This investigation demonstrates that micro-RNA's do, in fact, play an crucial role in synaptic plasticity, particularly during sensitive periods of early maturation.
Micro-RNA was discovered only twelve years ago, however, investigating these molecules has led to a greater understanding of how genes and genetic systems communicate with one another inside living organisms.
Written by Grace Rattue