A technique that shows colorful connections in the brain

A neuron looks a bit like a tree: its branches are dendrites, which accept input and its roots are the axon, which send output. Where axons and dendrites of different neurons come together, they can make connections -- or synapses -- that relay signals and form circuits in the brain.

To study these connections, scientists have traditionally grown networks of neurons in petri dishes -- but there, networks are limited in their ability to mimic brain cells in a living, developing creature. Daniel Kerschensteiner, of Washington University School of Medicine in St. Louis, is one of the first to study connections in the nervous system of living mice, by inserting genes into neurons that cause them to produce fluorescent molecules.

"The novel thing is that we can label specific pairs of pre- and post-synaptic cells and their connections in an intact circuit," said Kerschensteiner. "No one has really done that before."

When energized by the imaging technique called two-photon microscopy, the molecules fluoresce in different colors and reveal the structure and connectivity of brain circuits.

This approach has already yielded some surprising insights. For instance, studies of the neurons in the mouse retina have shown that neural connections can change dramatically fairly late in an animal's development -- in its second week of life, long after the arrangement of axons and dendrites has already been laid down.

In ongoing experiments, Kerschensteiner hopes to further refine science's understanding of how a developing brain reorganizes its connections as it grows -- as well as the internal mechanisms behind this rearrangement and how much it is influenced by an animal's experiences and external environment.

The presentation, "Imaging the Development of Neural Circuits in the Mammalian Retina," takes place on Oct. 25 at the Frontiers in Optics (FiO) 2010/Laser Science XXVI -- the 94th annual meeting of the Optical Society (OSA), which is being held together with the annual meeting of the American Physical Society (APS) Division of Laser Science at the Rochester Riverside Convention Center in Rochester, N.Y., from Oct. 24-28.