PITTSBURGH, March 7 Generations of neuroscientists have been indoctrinated into believing that our senses, thoughts, feelings and movements are orchestrated by a communication network of brain cells, or neurons, each responsible for relaying one specific chemical message called a neurotransmitter. Either neurons release a neurotransmitter that excites a neighboring cell, thereby triggering an electrical discharge and enhancing brain activity, or they dispatch a signal that quells a neuron's activity. So, when researchers at the University of Pittsburgh discovered that immature rat brain cells could fire a simultaneous three-punch salvo three neurotransmitters bursting out of a single cell -- it was a finding they knew would excite more than just neurons.

Just as surprising, they report in the lead article of this month's Nature Neuroscience, is that by definition these three neurotransmitters are seemingly at odds with each other. One, glutamate, is a textbook excitatory neurotransmitter; while the other two, GABA and glycine, are quintessential inhibitory neurotransmitters.

Information is transmitted between neurons when one cell releases a neurotransmitter at a synapse, the point of contact between cells. When released from a cell, neurotransmitters are sent on a one-way ride that dead ends at the membrane of the adjacent cell. Like lock and key, they bind to specific receptors on the surface of the receiving cell, causing its electrical activity to be enhanced or inhibited.

The first week after birth marks a critical phase in the developing rat brain, a time period comparable to three months gestation in a human, when neurons are meticulously organizing and self-selecting to assemble into specific brain structures and neuronal networks. It has long been known that a specific receptor for glutamate, the NMDA receptor, plays a crucial role in these processes, but how inhibitory synapses, which account for about half of the brain'
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7-Mar-2005

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