New bearers of nerve tidings?

New bearers of nerve tidings?

Something repeatedly by one person and then another often becomes a garbled message. But in the nervous system, a crowd of chemical messengers accurately transmits signals from cell to cell. The neurotransmitters passed between nerve cells, along withthe intracellular "second messengers" they frequently enlist, can work to keep open the lines of communication, instructing cells how to respond to a specific stimulus. Now scientists at Columbia University in New York City report a newly identified class of second messengers, which may play a double role in carrying signals both within and between cells. The finding eventually may further the understanding of certain neurological disorders.

Using the marine mollusk Aplysia -- chosen because of its large, easily accessible neurons--the researchers found that one or more products formed during the breakdown of intracellular arachidonic acid apparently act as second messengrs within cells, which are stimulated when neurotransmitters attach to receptors on their surface. The arachidonic-acid metabolites, called eicosanoids, may go beyond the usual second-messenger job of carrying out instructions brought by the neurotransmitter released from another cell, says Columbia's Daniele Piomelli.

"We think we have found a second messenger tht allows the [message-receiving] cell to regulate the amount of neurotransmitter it itself releases," Piomelli told SCIENCE NEWS. The possibility of such a double-duty mechanism--first postulated by other scientists about 10 years ago -- would require that the eicosanoids work outside, as well as inside, the nerve cell, says Piomelli, coauthor of a report on the study in the July 2 NATURE.

Eicosanoids are known to carry messages between cells other than nerve cells. In order to determine whether this also holds for nerve cells, the scientists studied the effect of various eicosanoids on the Aplysia neurons, whose electrical-impulse responses were measured after each application. In addition, they are working to identify which of the various metabolites is either directly responsible for signal transmission or is itself further changed into the mysterious second messenger, says Piomelli.

He says that in the past five years, scientists have found receptors for eicosanoids on the surface of mammalian brain cells, and that there is an increased release of the metabolites during epileptic seizures. Although such clinical implications are "worth investigating," he says that more basic research questions must first be answered.