Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Photoswitches shed light on spontaneous free swimming in zebrafish

18.09.2009
Technique targeting light-gated channels to enigmatic neurons proves role in burst swimming

A new way to select and switch on one cell type in an organism using light has helped answer a long-standing question about the function of one class of enigmatic nerve cells in the spinal cord.

Through targeted insertion of light-sensitive switches into these cells in awake zebrafish larvae, University of California, Berkeley, and UC San Francisco scientists have found that these mysterious cells trigger burst swimming – the periodic tail twitching typical of larvae.

While the finding could have implications for humans, because mammals have similar cells protruding into the spinal fluid, the discovery highlights the power of new techniques that employ photoswitches – light-gated ion channels – and gene targeting to non-invasively turn on small populations of cells as easily as flipping a light switch.

Claire Wyart, post-doctoral fellow at UC Berkeley's Department of Molecular and Cell Biology, and UCSF post-doctoral fellow Filippo Del Bene are the joint first authors of a paper describing these results that appears in the Sept. 17 issue of the journal Nature.

"With these optogenetic tools, we can activate single neurons in awake behaving animals and directly demonstrate the consequence of neuron activation on behavior," said Wyart. "This 'optogenetic' approach enabled us to learn something important about spinal circuits."

Wyart said that the strategy used here could be generalized to study all types of neurons, such as those in the smell, vision, touch and hearing centers of the brain.

"Optogenetics opens up a new and extremely exciting area of study, singling out one type of cell and finding out what it's doing," she said.

"This is a new way to do neuroscience," said coauthor Herwig Baier, professor of physiology at UCSF. "Instead of sticking electrodes into the brain to record and monitor activity in the nervous system, what we are doing is manipulating the function of neurons noninvasively with light, the gentlest way to make a manipulation."

"With these optically sensitive channels, it becomes possible to play back to the nervous system its normal innate activity and see what behavior results," added co-author Ehud Isacoff, UC Berkeley professor of molecular and cell biology.

Other coauthors of the Nature paper, in addition to senior authors Isacoff and Baier, are former UC Berkeley chemist Dirk Trauner, now at the University of Munich; Erica Warp, a graduate student in Isacoff's UC Berkeley lab; and Ethan Scott from Baier's UCSF laboratory. Scott is now at the University of Queensland in Brisbane, Australia.

Trauner, along with Isacoff and Richard Kramer, UC Berkeley professors of molecular and cell biology, worked for more than six years to perfect the technique of inserting optical switches into cells, and they formed the Nanomedicine Development Center for Optical Control of Biological Function to spearhead applications. One of the long-term goals of the joint UC Berkeley-Lawrence Berkeley National Laboratory center, which is funded by the National Institutes of Health, is to insert photoswitches into retinal cells to restore vision.

So far they have succeeded in engineering light-sensitive potassium ion channels and glutamate receptors to turn neurons on when zapped by ultraviolet light and turn the neurons off when zapped by green light, or vice versa. The researchers achieve this by attaching to the channel a chemical, called azobenzene, that changes shape when hit by light, opening or closing the ion channel. When the potassium channel opens, potassium ions flow through it and inhibit the cell; when the glutamate receptor channel opens, sodium, potassium and calcium ions flow through it and excite the cell.

Much of the early optogenetic work has confirmed results suggested by other approaches. Wyart and her UCSF and UC Berkeley colleagues have now applied the technique to search for a behaviorally relevant cell and found, to their surprise, a previously unknown function for the Kolmer-Agduhr (KA) cells in the spinal cord. The KA cells aren't standard relay neurons with dendrites and axons, but sensory neurons with cilia – small, movable hairs – that protrude into the spinal fluid, plus long axons extending up the spinal cord. They evidently sense something, but what, the researchers wondered.

Wyart and Isacoff teamed up with Baier's laboratory, where Del Bene and Scott produced 10 strains of zebrafish with photoswitches inserted in specific spinal cord nerve cell populations. When Wyart shined light on the fish with photoswitches in their KA neurons, the fish waggled their tails in a manner that exactly mirrored spontaneous slow forward swimming. Placing the transparent zebrafish larvae under a microscope, Wyart used a Digital Micromirror Device (DMD) to strongly focus light onto a small number of KA neurons, successfully switching on only a few KA cells at a time. She found that she had to switch on about 10 of the KA neurons to trigger swimming.

Knocking out these cells greatly reduced burst swimming, but did not eliminate it, suggesting that the KA neurons may be lowering the threshold for triggering reflex swimming.

"It came as a great surprise that these neurons played a role in locomotion at all," said Isacoff. "There is an apparent homologue of the KA neuron in mammals, so this may be a general modulatory principle for vertebrate locomotion, although it may change from positive drive early in development to negative drive later."

Earlier studies in lampreys by Sten Grillner, a professor in Stockholm at the Karolinska Institute's Nobel Institute for Neurophysiology, showed that nerve cells – including KA neurons – using GABA (gamma aminobutyric acid) as an inhibitory neurotransmitter were important modulators of swimming. The current study narrows this down to one kind of GABAergic neuron: the KA neuron.

Wyart continues to explore the role of KA neurons, but hopes to exploit the new optogenetic and gene targeting techniques to discover the roles of other types of neurons in the spinal cord.

Other researchers have developed an alternative optogenetic approach – inserting the gene for a light-sensitive ion channel isolated from algae – that also shows promise for directly showing the behavior triggered by activating cells. In fact, it is easier to use, though not as flexible as the approach developed by Isacoff, Trauner and Kramer, Baier said.

"Optogenetic targeting is a powerful approach, and we have really only started the work," he added. "We still have to learn how the KA neurons are connected to drive the muscles. Really, there is no way we could have done this experiment other than with optogenetics."

The work was supported by the National Institutes of Health.

Robert Sanders | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Life Sciences:

nachricht Rainbow colors reveal cell history: Uncovering β-cell heterogeneity
22.09.2017 | DFG-Forschungszentrum für Regenerative Therapien TU Dresden

nachricht The pyrenoid is a carbon-fixing liquid droplet
22.09.2017 | Max-Planck-Institut für Biochemie

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>