January 4, 2008
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Researchers at Northwestern University’s Feinberg School of Medicine have identified the protein that acts as the foreman in the construction and support of neurons. Kalirin-7 and its construction projects are what allow us to remember and learn.
Kalirin-7 is found in high concentrations in the spines of dendrites, the signal-receiving ends of synapses between neurons. Kalirin-7 is also involved in the construction of cell cytoskeletons. These two facts suggested to physiology professor Peter Penzes and his colleagues at Northwestern that kalirin-7 might be involved in building and maintaining the dendritic spines that are so important in transmission between nerve cells. If true, it would mean kalirin-7 helps build and reinforce the network that allows us to learn and remember.
To test their hypothesis, Penzes and his colleagues cultured neurons in the lab and subjected them to neurotransmitters. They found that when neurons were activated, kalirin-7 molecules triggered the growth of the spines along the dendrites, thereby making them more likely to receive further transmissions at full strength. They also saw that kalirin-7 controlled the number of receptors on dendritic spines, which in turn controlled the strength of the nerve signals. The overall trend was that the more activity the neurons had, the more kalirin-7 triggered further growth and development. “Synaptic activity turns on the function of kalirin-7, and kalirin-7 in turn makes synapses larger and stronger,” Dr. Penzes explained. “A synapse is like a volume dial between two cells. If you turn up the volume, communication is better. Kalirin makes the synaptic spines grow.”
In addition to determining the identity and role of this protein, this discovery could pave the way for treatments of cognitive diseases and disorders such as Alzheimer’s, autism, drug addiction, and mental retardation, all of which involve defects or degradations of the receptors of neurons. If kalirin-7 can be activated or enhanced, perhaps neural circuitry could be healed or rewired. “The extension of this is that maybe we can make drugs and thereby fortify the synapses and perhaps delay or reverse some of these cognitive diseases,” Penzes said.