" this...could put researchers on the royal road to stroke treatment."

Johns Hopkins scientists have identified a new and unusual nerve transmitter in the brain, one that overturns certain long-cherished laws about how nerve cells behave.

Reporting in the current Proceedings of the National Academy of Sciences, the team led by neuroscientist Solomon H. Snyder, M.D., has also pinpointed the neurotransmitter's source -- itself a biologically unusual enzyme -- whose novelty as a drug target "could put researchers on a royal road to stroke treatment."

The neurotransmitter is an amino acid called D-serine. It's odd, Snyder says, because it differs in structure from any known molecule in its class found in mammals and other higher animals. D-serine is what chemists call a right handed amino acid. Normally, amino acids have atoms that extend from the left side of the molecule. These L-amino acids, as they're called, are the rule in vertebrates, whose biochemistry is set up to deal with these forms.

Some primitive organisms, however, notably bacteria, have a mixture of both L-amino acids and their mirror images called D-amino acids. But to find a D-amino acid in humans, Snyder says, "is unprecedented;" it's the equivalent of finding a Pterodactyl in your local pet shop.

Moreover, unlike dopamine, serotonin or other traditional nerve transmitters, D-serine isn't secreted at nerve cell endings in the brain. Instead, it comes from adjacent cells called astrocytes, which enclose nerve cells in the brain's gray matter like a glove.

The current study adds conclusive evidence to the idea that D-serine -- released from astrocytes -- activates receptors on key nerve cells in the brain. Activating these receptors, called NMDA receptors, has long been linked with learning, memory and higher thought. NMDA receptors are also known culprits in stroke damage in the brain, and have become a focus for anti-stroke research.

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Contact: Marjorie Centofanti
mcentofanti@jhmi.edu
410-955-8725
Johns Hopkins Medical Institutions
8-Nov-1999