ITHACA, N.Y., March 5 -- Combining the bright laser light of multiphoton microscopy with specially developed dyes and a phenomenon called second-harmonic generation, biophysicists have made high-resolution images of millisecond-by-millisecond signaling through nerve cells. The first demonstration of the new technique was in neurons of the lowly sea slug, Aplysia. But researchers say the technique could eventually be used in brain tissues of higher animals to help decipher the wiring of the brain and could possibly explain consequences of degenerative brain diseases such as Alzheimer's. The research was conducted at Cornell University and the Universite de Rennes, France, and was reported recently in The Journal of Neuroscience. Multiphoton microscopy, including second-harmonic generation, produces high-resolution, 3-D pictures of tissue with minimal damage to living cells, using a laser that produces a stream of extremely short, intense pulses. When two or three photons strike a biological molecule at the same time, their energies combine. This has the cumulative effect of delivering one photon -- with nearly twice the energy -- to the sample. By adjusting the plane of focus, a multiphoton microscope can produce a vivid image deep within living tissue. And by "stacking" multiple images at various depths of focus, the system produces 3-D images or movies. "This technique gives us the ability to look at membrane potential in nerve-cell signaling with high-resolution deep in intact tissue, where previous methods were not applicable," said Daniel A. Dombeck, lead author on the journal paper and a graduate student in the Developmental Resource for Biophysical Imaging Opto-Electronics laboratory of Watt W. Webb, professor of applied physics at Cornell. "With submillisecond resolution, we're beginning to see how much the electrical signals can vary between different places of a single neuron," said Dombeck. "With further development, we should be able to see how pathology affects electrical signals. We'd like to know, for example, how much Alzheimer's plaques affect the signal transmission in axons." For more information, visit: www.drbio.cornell.edu