Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New microscope decodes complex eye circuitry

10.03.2011
Retinal ganglion cells can recognise directions thanks to amacrine cells

The properties of optical stimuli need to be conveyed from the eye to the brain. To do this efficiently, the relevant information is extracted by pre-processing in the eye.


Cells and synapses reconstructed from serial block face electron microscopy data. A single starburst amacrine cell (yellow, note synaptic varicosities) and two direction-selective ganglion cells (green). Even though there is substantial dendritic overlap with both cells, all connections (magenta) go to the right ganglion cell. © Kevin Briggman

For example, some of the so-called retinal ganglion cells, which transmit visual information to the brain via the optic nerve, only react to light stimuli moving in a particular direction. This direction selectivity is generated by inhibitory interneurons that influence the activity of the ganglion cells through their synapses. Using a novel microscopy method developed at the Institute, scientists from the Max Planck Institute for Medical Research in Heidelberg have now discovered that the distribution of the synapses between ganglion cells and interneurons follows highly specific rules. Only those dendrites that extend from the cell body of the amacrine cell in a direction opposite to the preferred direction of the ganglion cell connect with the ganglion cell.

The sensory cells in the retina of the mammalian eye convert light stimuli into electrical signals and transmit them via downstream interneurons to the retinal ganglion cells which, in turn, forward them to the brain. The interneurons are connected to each other in such a way that the individual ganglion cells receive visual information from a circular area of the visual field known as the receptive field. Some ganglion cells are only activated, for example, when light falls on the centre of their receptive fields and the edge remains dark (ON cells). The opposite is the case for other ganglion cells (OFF cells). And there are also ganglion cells that are activated by light that sweeps across their receptive fields in a particular direction; motion in the opposite (null-) direction inhibits activation.

Starburst amacrine cells, which modulate the activity of the ganglion cells through inhibitory synaptic connections, play an important role in this direction selectivity. The same research group at the Max Planck Institute in Heidelberg demonstrated a number of years ago that starburst amacrine cells are activated by moving stimuli. Each branch in the circular dendrite tree reacts preferentially to stimuli that move away from the cell body; movements in the opposite direction, towards the cell body, inhibit its activity. In the central area around the cell body dendrites function only as receivers of synaptic signals, while the dendrites on the periphery act as transmitters as well – and, therefore, double as axons. Whether these dendrites cause the direction selectivity in the ganglion cells or whether the ganglion cells “compute” it using other signals was unclear up to now.

Max Planck researchers Kevin Briggman, Moritz Helmstaedter and Winfried Denk have now discovered that, although the cells themselves are symmetrical, the synapses between retinal ganglion cells and starburst amacrine cells are distributed asymmetrically: seen from the ganglion cell, the starburst cell dendrites connected with it run in the direction opposite to the preferred direction of motion. “Ganglion cells prefer amacrine-cell dendrites that run along the null-direction,” says Winfried Denk.

According to previous studies by Winfried Denk and his research group, the electrical characteristics of the dendrites, which emerge starlike from the cell bodies of amacrine cells, play a crucial role here. The further they are located from the centre of the cell toward the edge, the easier they are to excite; therefore, stimuli are transmitted preferentially in this direction. This mechanism does not require but is helped by inhibitory influences between neighbouring amacrine cells, known as lateral inhibition. “A ganglion cell can thus differentiate between movements from different directions simply by making connections with certain starburst amacrine cell dendrites - namely those that prevent activation of the ganglion cell in null-direction through their inhibitory synapses. These are precisely the amacrine cell dendrites that run along this direction,” explains Winfried Denk.

Functional and structural analysis

This discovery was made possible by combining two different microscopy methods. The scientists succeeded, first, in determining the preferred motion direction of the ganglion cells using a two-photon fluorescence microscope. A calcium-sensitive fluorescent dye indicated in response to which stimuli calcium flows into the cells - a process that signals electrical activity in cells.

They then measured the exact trajectory of all of the dendrites of these ganglion cells and those of connected amacrine cells with the help of a new electron microscopy method known as serial block face electron microscopy. This process enabled them to produce a volumetric image by repeatedly scanning the surface of a tissue sample using the electron beam of a scanning electron microscope. A thin “slice” is shaved off the sample surface after each scan is complete, using an extremely sharp diamond knife. These slices are thinner than 25 nanometers, just about one thousandth of the thickness of a human hair.

The high three-dimensional resolution of this method enabled the scientists to trace the fine, densely packed branched dendrites of retinal neurons and clearly identify the synapses between them. The complete automation of the imaging process enables them to record data sets with thousands and even tens of thousands of sections “while on holiday or attending a conference,” says Winfried Denk. “For the first time, minute cell structures can now be viewed at a high resolution in larger chunks of tissue. This procedure will also play an indispensable role in the clarification of the circuit patterns of all regions of the nervous system in the future.”

Contact
Prof. Dr. Winfried Denk
Max Planck Institute for Medical Research, Heidelberg
Phone: +49 6221 486-335
Fax: +49 6221 486-325
Email: denk@mpimf-heidelberg.mpg.de
Publication reference
Kevin L Briggman, Moritz Helmstaedter, Winfried Denk
Wiring specificity in the direction-selectivity circuit of the retina
Nature, March 10 2011

Prof. Dr. Winfried Denk | EurekAlert!
Further information:
http://www.mpg.de
http://www.mpg.de/1200127/direction_selective_ganglion_cells

More articles from Health and Medicine:

nachricht Antibiotic effective against drug-resistant bacteria in pediatric skin infections
17.02.2017 | University of California - San Diego

nachricht Tiny magnetic implant offers new drug delivery method
14.02.2017 | University of British Columbia

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Biocompatible 3-D tracking system has potential to improve robot-assisted surgery

17.02.2017 | Medical Engineering

Real-time MRI analysis powered by supercomputers

17.02.2017 | Medical Engineering

Antibiotic effective against drug-resistant bacteria in pediatric skin infections

17.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>