In this most recent experiment, Svoboda's team was looking to see if persistent changes in connectivity occurred after a long-term change in experience. They focused on the formation of new long-lasting spines that indicate robust connections between a neuron's highly branched dendrites and nearby axons. Dendrites are the input side of neurons and axons the output side. Spines stipple the surface of dendrites, like twigs from a branch, and form the receiving ends of synapses, which are the junctions between neurons where neurotransmitters are released.
The researchers induced a long-term change in the sensory experience of mice by trimming the animals' whiskers, selectively cutting some but leaving neighboring whiskers, in a chessboard pattern. Over time, this selective grooming caused the animals' neurons to rewire themselves to adapt to loss of the whiskers ?a strategy that reduces dependence on lost whiskers and enhances input from intact whiskers.
"We knew from previous work that a subpopulation of dendritic spines appears and disappears over time, but we didn't know the biological meaning of this process," said Svoboda. "In these experiments, we found that over about a month new spines appeared, and in particular a subset of these new spines stabilized to form new circuits," he said.
He said that the researchers were most excited to find that after this long-term change in experience there were many new spines that were large, robust and "persistent," meaning that they remained over long periods of time. "Under normal conditions, most new spines are faint and small, and disappear after a couple of days," said Svoboda. "What we think they are doing is reaching out and probing for potential neuronal partners. And while most of them
Source:Howard Hughes Medical Institute