The image shows a partially cut stack of discs from a mouse rod photoreceptor. The rhodopsin molecules in the disc membrane form dimers, the dimers form rows, and the rows are arranged in pairs, referred to as “tracks”. The tracks, with pre-assembled G protein transducin (green), are oriented parallel to the slit-shaped incisure of discs.

Rhodopsin on track – Biological pigment aligns in double rows


Scientists from the caesar research center, an Institute of the Max Planck Society, have explained, with the help of electron microscopy, how the pigment rhodopsin is arranged in the rod cells of the retina. This question has long been subject of a heated scientific debate. The findings have been published in the scientific journal Structure. Future research on diseases causing blindness will be facilitated by this discovery.

Seeing starts in the rods and cones, two different types of sensory cells in the retina of the eye. The rods are responsible for dark vision and are particularly sensitive to light as a result. A single photon activates the pigment rhodopsin and initiates the process of vision. The rhodopsin molecules are found in flat membrane disks in the outer segment of photoreceptors. The biochemical processes on which vision is based have been known for many years: rhodopsin triggers a highly-reinforced cascade of enzymatic reactions which give rise to electrical excitation. However, it was unclear up to now how the rhodopsin is arranged in these disks. For example, scientists debated whether rhodopsin arises as dimers, or whether the rhodopsin molecules wander around freely on the discs and thus encounter their interaction partners at random – like billiard balls following a wild hit with the cue.

Working in cooperation with Ashraf Al-Amoudi from the German Center for Neurodegenerative Diseases (DZNE), the researchers from the caesar research center used cryo-electron microscopy to examine the arrangement of rhodopsin in the rods of mice. This method involves the vitrification of the samples by shock-freezing, which conserves their natural structure. The actual examination of the sample is carried out using a cryo-transmission electron microscope which provides the resolution necessary to make individual molecules visible.

The team of scientists headed by Benjamin Kaupp and Ashraf Al-Amoudi succeeded in demonstrating that the rhodopsin molecules arise as dimers. In addition, the rhodopsin shows a supramolecular structure: the dimers are arranged in rows consisting of around 50 molecules. Two rows align to form double rows – like railway tracks. All rows are parallel in their arrangement.

The physiological function of such a regular arrangement is currently unclear. It is possible that the double rows form a platform, on which other molecules that participate in the electrical signal transformation, are also arranged regularly. The parallel arrangement could possibly explain polarisation vision, which is used by some vertebrates – for example amphibians and birds – to orient themselves in their environment. Unlike the polarisation vision of insects, the corresponding mechanisms in vertebrates are still inadequately understood. Whether this capacity also exists in mammals remains a matter of dispute. The results on the mouse model will lead to further studies


 

Original publication:

Gunkel, M., Schöneberg, J., Alkhaldi, W., Irsen, S., Noé, F., Kaupp, U.B. &  Al-Amoudi, A. (2015) “Higher-order architecture of rhodopsin in intact photoreceptors and its implication for phototransduction kinetics” Structure, [Epub ahead of print]

DOI: http://dx.doi.org/10.1016/j.str.2015.01.015

 

Sam Young, Max Planck Florida Institute for Neuroscience

New insights into underlying cellular mechanisms of information processing in the brain

Researchers at the Max Planck Florida Institute for Neuroscience and the Pasteur Institute have uncovered a key factor in regulating information transmittal during the early stages of auditory processing

• The human body consists of almost 100 billion neurons that contain synapses, point-to-point contacts for information transfer. Every function, feeling and action depends on the ability of synapses within neurons to maintain continuous communication with each other.
• Synapses transmit information in the form of synaptic vesicles that contain specific chemical messengers called neurotransmitters. The continuous release of neurotransmitters is essential to maintain communication between neurons.
• To better understand and address a number of neurological disorders, we need a better understanding of how synapses can continuously relay information between neurons.
• A new study has discovered that a key factor in regulating this continual communication is the proximity of synaptic vesicles next to voltage gated calcium channels within synapses.

Synaptic vesicles in cell-to-cell communication

While synapses contain hundreds to thousands of synaptic vesicles, when a specific signal is received by the neuron, only a fraction of synaptic vesicles that exist in what is called the readily releasable pool are discharged from one neuron to another. Previous studies have demonstrated that within the readily releasable pool, synaptic vesicles have different specific kinetic properties of release that impact the type and bandwidth of information that can be relayed in response to stimulation. What was not known was the cellular mechanisms that regulate the release of synaptic vesicles from the readily releasable pool to support the early stages of auditory processing.

New findings

In their February publication in the Journal of Neuroscience, the authors of the manuscript report that a dominant factor regulating the properties of synaptic vesicle release supporting the early stages of auditory processing is the distance between the synaptic vesicles and voltage gated calcium channels within a synapse.

The authors characterized the readily releasable pool of synaptic vesicles at the calyx of Held, a critical component of auditory processing, employing several different techniques that allowed them to investigate the pre-synaptic mechanisms of informational transmittal. This study identifies the critical mechanism is the regulation of Ca2+ influx through voltage gated calcium channels and release of neurotransmitters by synaptic vesicles. These findings are important for understanding the mechanisms of synaptic transmission, specifically for neuronal circuits that rely on fast, continuous synaptic transmission.

“It is becoming apparent that the underlying cause of most neuropsychiatric or neurodegenerative diseases is a dysfunction of the synapse,” explained Dr. Young. “Identifying what factors are involved in proper synaptic transmission and neural circuit function have tremendous potential as therapies for neurological disorders or brain injury.”

Future directions

According to Dr. Young, the future goals of this project are to uncover molecular mechanisms that allow synapses to sustain synaptic transmission over a wide range of activity levels to allow for proper information processing by the neuronal circuit in which they are embedded.

Gordon Smith, David Fitzpatrick, Max Planck Florida Institute for Neuroscience

New research sheds light on neural circuit development

Researchers report substantial postnatal changes in the functional properties of brain circuits that enhance their ability to encode information

– The brain undergoes a series of dramatic changes following birth, many of which are shaped by sensory experience, such as exposure to various sights and sounds.
– Previous studies have shown that during development, individual brain cells become more selective for specific features in the environment dependent upon early experiences.
– Using multiphoton imaging, researchers are now able to move beyond characterizing the properties of individual cells to investigate how communication among neurons changes over the course of development.
– In their paper published in Nature Neuroscience in January, researchers at Max Planck Florida Institute for Neuroscience (MPFI) and Frankfurt Institute for Advanced Studies (FIAS) report substantial developmental changes in communication among cells that significantly improve the information processing capabilities of the brain.

Advancing our understanding of neural circuits

Previous work, including studies performed in the Fitzpatrick Lab at MPFI, has shown that individual brain cells refine their responses to stimuli with experience so they can better discriminate between similar features in their environments. However, the signals of individual brain cells can be noisy and imprecise – which means our brains cannot rely solely on the activity of single neurons to make accurate decisions about our world. Instead, we combine the activity of thousands to millions of neurons to ensure a more accurate message, which makes effective communication amongst large populations of neurons a central feature of the brain.

This study demonstrates that, over development, neural circuits reorganize themselves to decrease noise and improve the fidelity of communication amongst each other. The critical role these changes play in brain development highlights the importance and urgency in understanding neural circuits in more detail and suggests new avenues for investigating the underlying causes of developmental disorders such as autism.

Future Directions

The authors of the study said the key question moving forward is to understand what specific changes in brain circuitry give rise to the effects observed in this study. Where do these changes manifest themselves within the circuit and what molecular processes do they utilize? We know that a number of structural changes also occur during this developmental period, and we now can attempt to link those changes to the changes in circuit function.

About the research institutions

The Max Planck Florida Institute for Neuroscience (Florida, USA) specializes in the development and application of novel technologies for probing the structure, function and development of neural circuits. It is the first research institute of the Max Planck Society in the United States.

The Frankfurt Institute for Advanced Studies (Frankfurt, Germany), founded by the Goethe University Frankfurt, is focused on the theoretical analysis of complex structures in nature. In addition to brain research, the institute carries out fundamental research in life sciences, computer science, chemistry and physics.


Gordon B SmithAudrey SederbergYishai M ElyadaStephen D Van HooserMatthias Kaschube David Fitzpatrick

Nature Neuroscience 18, 252–261 (2015) doi:10.1038/nn.3921

Received 05 November 2014 Accepted 10 December 2014

Published online 19 January 2015
Joan Lora, Florida Atlantic University

Second Annual SYNAPSE 2015 Brings Local Neuroscientists Together

Local Universities and Research Institutions Collaborate for the Popular Neuroscience Networking Event

Over 200 of the brightest scientific minds in the region gathered in the sunshine-filled Alexander and Renate Dreyfoos Atrium of the Max Planck Florida Institute for Neuroscience (MPFI) to share their research findings with the local neuroscience community. In collaboration with Florida Atlantic University (FAU) and Scripps Florida, MPFI was honored to be this year’s host of the well-attended, highly popular second annual networking event that included representatives from nearby Nova Southeastern University, Torrey Pines Institute, Vaccine and Gene Therapy Institute and Palm Beach State College.

SYNAPSE 2015’s happy hour and poster session forum was specifically designed to fuel local scientific collaboration within a relaxed, enjoyable setting. The late afternoon session offered over 200 students, guests, faculty and neuroscientists the opportunity to enjoy more than 60 posters covering an impressive range of topics including behavioral studies, neural computations and molecular neuroscience.

“This is a great opportunity for us to see what’s going on in the Jupiter neuroscience community. We have three different institutions here tonight that are all leading key neuroscience initiatives along with representatives from many other research programs,” explained Dr. David Fitzpatrick, Scientific Director and CEO at Max Planck Florida Institute for Neuroscience.

The multi-institutional committee that carefully designed the event to be interactive, informative, inclusive and highly welcoming was planned this year by MPFI’s Research Coordinator and Public Engagement Scientist Dr. Rebekah Corlew, “This really started as a way for local institutions and schools to come together in an social setting to get to know each other and start talking about science that we can do together and ways to collaborate as we strengthen our network.”

Dr. Corlew explained that the informal, laid-back venue encourages interaction since the posters are all carefully intermingled. Scientists from completely different specialty areas are strategically placed right next to each other to spark conversations. The open, relaxed submission process is designed to be grassroots in nature so that scientists and students of all levels have an equal opportunity to present their work.

“When collaboration happens at a grassroots level, students start talking and recognize common interests. Poster sessions provide a level of communication that doesn’t always happen when you are giving a presentation because of the immediate feedback you can get and the questions you can ask. At a poster session you can really explain your science at a fundamentally deep level,” shared Dr. Fitzpatrick.

For two hours scientists and guests talked excitedly and milled around the packed room, freely asking each other to share their posters. Joan Lora is a fourth year doctoral candidate at FAU’s Jupiter campus within the Integrative Biology and Neuroscience (IBAN) program. IBAN students work alongside world-renowned neuroscientists at FAU, MPFI and the Scripps Research Institute.

When asked what an event like SYNAPSE 2015 means to students, Joan Lora explained, “It’s a great opportunity for us to show our work and what we’ve been doing the last couple of years as we build relationships.” Lora was excited to share that he and another scientist had just been able to discuss another project they were both interested in and make plans to work together soon.

Dr. Brenda Claiborne, Program Director for Neuroscience at FAU’s Jupiter campus, was one of the organizers of the first annual SYNAPSE event held in 2014 and sponsored by the Palm Beach Chapter of the Society for Neuroscience. “The students all go off to the national meetings which is fabulous, but when they come back and present to their peers locally it really gives them the chance to interact and show off their hard work,” shared Claiborne who was very pleased with the collaborative nature of Synapse 2015 thanks to the partnership between MPFI, Scripps and FAU.

Regarding this supportive relationship, Dr. Ron L. Davis, the Founding Chair of the Department of Neuroscience at the Scripps Research Institute added, “We’re terrifically excited about the ‘Jupiter Three.’ There’s every reason for us to be complementary in our science and really work together. It’s a win for the community and a win for Palm Beach County as well. It’s an ideal situation to be a neuroscientist or a scientist student here right now in this environment,” he concluded.