Paradigm of neuron/synapse model challenged

Transplantation of human astrocytes into mouse brain made the mice smarter

It has been assumed for decades that the brain learns and responds by virtue of the pattern of connection, via synapses, between wire-like axons of neurons which carry high-speed electrical signals. But recent experiments suggest that astrocytes, a different type of cell, previously thought to have only structural function, may play a powerful role in modulating signalling.

Read the New Scientist article here

The paradigm has been that repetitive firing, strengthening synaptic connections, is thought to be the cellular basis for memory, just as repetition in learning helps form lasting memories.

The recent research has shown that when human astrocytes were transplanted into the brains of young mice, the astrocytes integrated well into the mouse brain. This despite the fact that human astrocytes are much bigger than, and very different from mouse astrocytes. (Though mouse and human neurons are quite similar.)

When these mice were given standardized behavioral tests of learning and memory, the mice engrafted with human astrocytes outperformed mice injected with astrocytes from other mice as a control.

Hence the inference that astrocytes have a much more important role in human brain function than was thought previously. This seems to be by modulation of the synapse activity. A substance released from astrocytes (TNFalpha) was found to be increased after transplantation, and counteracting TNFalpha with drugs erased the enhanced performance of these chimeric mice in learning tests.

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