23 April 2008

Great moments in crayfish research: Electrical synapses

If neurons are separate, how do they communicate?

The first early decades of the 20th century saw two major ideas emerging, which the great comparative physiologist Ted Bullock characterized as "soups versus sparks."

Bullock's "soups" were chemicals released by neurons, which are now called neurotransmitters. Bullock's "sparks" were electrical signals, which were thought to transmit directly from cell to cell.

Otto Loewi provided strong evidence for chemical neurotransmission between nerves and the heart. Loewi considered the matter conclusively proved. After he won the Nobel prize for his experiments, one might have reasonably considered the matter settled in favour of the "soups" camp.

So it was a bit of a surprise when two neurophysiologists, Ed Furshpan and David Potter, working on giant crayfish neurons found evidence for neurons communicating through sparks -- electrical synapses.

Furshpan and Potter were studying the giant neurons involved in escape responses. In particular, they were examining the connections between the lateral giant neurons and the motor neurons that go on to connect to muscle. Work on chemical synpases had shown short delays whenever there was a synapse between two neurons: the time needed for the chemicals to diffuse between the small gap between the cells. Furshpan and Potter found the delay between the crayfish neurons to be much, much shorter -- a small fraction of a millisecond (picture). But it was easy to see how such connections could be advantageous when the neurons were responsible for a rapid escape response.

Although some may have thought this would be peculiar to invertebrates, they were soon shown to be in vertebrates, too.

Thus, crayfish provided the first conclusive evidence for the existence of a different way that neurons could communicate.

References

Furshpan EE, Potter DD. 1957. Mechanism of nerve-impulse transmission at a crayfish synapse. Nature 180(4581): 342-343. http://dx.doi.org/10.1038/180342a0

Furshpan EE, Potter DD. 1959. Transmission at the giant motor synapses of the crayfish. Journal of Physiology 145(2): 289-325.

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