Neurones have a small central body and long arms called axons which connect them to between 1,000 and 10,000 other cells, forming a very complex set of competing networks in the brain. (For a diagram,
click here). Most communication between neurones happens via junctions at the ends of the axons, called synapses. However, the electrical activity of some types of neurone doesn't match the activity we'd expect if this were the only form of communication occurring.

In some brain cells, a structure called a gap junction also allows cells to pass on messages. A gap junction consists of a pore on an axon's wall through which chemical and electrical messages can be passed between two cells lying next to each other. It allows neurones to communicate with other neurones lying next to them, in addition to those further away, connected via synapses.

A research collaboration between scientists at the State University of New York, Mount Sinai School of Medicine in New York, Colorado State University, and the University of Newcastle, UK, and led by Professor Roger Traub, has produced images of these junctions in cells in the hippocampus using a form of very high magnification microscopy. The images are published in the Proceedings of the National Academy of Sciences USA and are free to view in the article here.

Interestingly the gap junctions are in an unexpected part of these cells, right at the top of the axon (the long arm). Hence the importance of the electron microscopy ("photograph") evidence.

This may be important in epilepsy. Previous research had established that some inhibitory cells in the brain communicate in part via gap junctions, but the same type of communication among excitatory cells, as in this study, had not been demonstrated. It now appears that most types of neurones communicate via gap junction-coupling, but that the nature of the coupling differs depending on the type of neurone and where in the brain it is.

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