Steerable lasers give us a first look at firing neurons

April 28, 2008

A new technique that marries a fast-moving laser beam with a special microscope that look at tissues in different optical planes will enable scientists to get a 3-D view of neurons or nerve cells as they interact, said Baylor College of Medicine scientists in a report that appears today in the journal Nature Neuroscience.

“Most microscopes can only study cell function in two dimensions,” says Gaddum Duemani Reddy, an M.D./Ph.D. student at BCM at Houston and Rice Univ. and also first author of the study. “To look at different planes, you have move your preparation (of cells) or the objective lens. That takes time, and we are looking at processes that happen in milliseconds.”

To solve that problem, he said, they developed a “trick” to quickly move a laser beam in three dimensions and then adapted that laser beam to the multiphoton microscope they were using. That allowed them to “see” the neuron’s function in three dimensions, giving them a much better view of its activity.

A multiphoton microscope looks much like a conventional, upright microscope but it has an adaption that allows it to look at tissues in sections. A conventional multiphoton microscope does that very slowly, he says.

“With ours, you can do it very quickly. We are starting to see how a single neuron behaves in our laboratory,” he says. The next step, he says, will be to use to it to look a clusters or colonies of neurons. This will enable them to actually see the neuronal interactions.

“At present, the technology is applied in my lab to study information processing of single neurons in brain slice preparations by 3-D multi-site optical recording,” says Peter Saggau, professor of neuroscience at BCM and the paper’s senior author.

He is collaborating with two other labs on using the technology in other ways. In one, he says, researchers plan to use the technology to monitor nerve activity in the brains of lab animals in order study how populations of neurons communicate during visual stimulation. Another study attempts to use the technology to monitor stimulation of the acoustic nerve optically. Those scientists hope to reinstate hearing in lab animals whose inner ear receptors do not work.

Others who took part in the research include Keith Kelleher of the Univ. of Houston and Rudy Fink of BCM. Funding for this work comes from the National Institutes of Health and the National Science Foundation.

When the embargo lifts, the full article can be found at http://www.nature.com/neuro/index.html

Abstract of “Three-dimensional random access multiphoton microscopy for functional imaging of neuronal activity” available here:

“The dynamic ability of neuronal dendrites to shape and integrate synaptic responses is the hallmark of information processing in the brain. Effectively studying this phenomenon requires concurrent measurements at multiple sites on live neurons. Substantial progress has been made by optical imaging systems that combine confocal and multiphoton microscopy with inertia-free laser scanning. However, all of the systems developed so far restrict fast imaging to two dimensions. This severely limits the extent to which neurons can be studied, as they represent complex three-dimensional structures. Here we present a new imaging system that utilizes a unique arrangement of acousto-optic deflectors to steer a focused, ultra-fast laser beam to arbitrary locations in three-dimensional space without moving the objective lens. As we demonstrate, this highly versatile random-access multiphoton microscope supports functional imaging of complex three-dimensional cellular structures such as neuronal dendrites or neural populations at acquisition rates on the order of tens of kilohertz.”

http://www.nature.com/neuro/journal/vaop/ncurrent/abs/nn.2116.html

SOURCE: Baylor College of Medicine