The discovery by scientists at UCSF is reported today in the December 22 issue of the journal Neuron and is featured on the journal's cover.
Memory formation is thought to involve a strengthening of the communication between neurons in the part of the brain known as the hippocampus. Researchers know that this increased communication results from a surge in the number of receptors on one neuron that is available to bind to the neurotransmitter glutamate released from another neuron. The two neurons meet at a synapse.
But how and from where the brain gains fresh supplies of these crucial receptors has remained unclear. Known as AMPA receptors, they are essential for the rapid connections made between nerves during learning.
The scientists sought to answer this question by studying the basal trafficking of receptors -- the normal process by which receptors are replaced from fresh stores that are synthesized and located inside the cell. Focusing on live neurons cultured from rats, they discovered clear evidence to dispel the prevailing view that receptors at the synapse are constantly being replaced by stores inside the cell. Rather, the scientists found that the synaptic receptors are relatively stable, lasting about 16 hours before they are replaced.
The study also supports an unsuspected route by which new receptors make their way to the synapse: Fresh AMPA receptors appear to be placed on the cell surface at the cell body and then migrate along the arms or dendrites of the cell to synapses, rather than moving within the cell to the synapse as had been thought.
The scientists suspect the trafficking process their research revealed also occurs during learning and memory formation, but at a much faster rate. The study may provide insight into how to treat memory disorders, said Pam England, PhD,
Contact: Wallace Ravven
University of California - San Francisco