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Each of us have our moods when we like to hum an old melody or suddenly feel like tapping our feet to the latest hit. It turns out that cells in our brains can be equally moody, changing the tune of their electrical signals from time to time. In a recent study, scientists Mohini Sengupta and Dr. Vatsala Thirumalai, from the National Centre for Biological Sciences (NCBS), Bangalore, reveal that nerve cells found in the cerebellum (at the base of the brain) send out electrical signals in either a constant hum or in sudden bursts. Which of the two tunes they choose depends on the voltage across their cell membranes and on input from a specific region of the brain.
Our balance, co-ordination and the capacity to learn new skills such as riding a bicycle or playing a piano depends on a small leaf-like structure at the base of our brain called the cerebellum. Within the cerebellum, are nerve cells named ‘Purkinje cells’ that are arranged neatly in a single layer and are vital for carrying out the aforementioned functions. These cells receive signals from many different regions of the brain and send out messages to the deeper layers of the cerebellum.
However, how Purkinje cells communicate with other nerve cells has thus far been a mystery, mainly because it is very difficult to ‘listen’ to these cells in animals that are awake and moving around. Since these nerve cells are very small, scientists employ fine glass capillaries to record their electrical signals using a technique called ‘whole cell patch clamping’. For this technique to work, most experimental animals must be anesthetised, as even small movements can knock the capillaries out of place. Unfortunately, anesthetics themselves alter the electrical signals generated by the brain. This means that previous studies aimed at determining the nature of electrical signals generated by Purkinje cells in awake and moving animals have largely been inconclusive.
The researchers at NCBS overcame these issues by using zebrafish, a fresh water fish found in the Ganga and Brahmaputra, for their experiments. The young zebrafish (called larvae) are transparent and have not yet developed a skull. Furthermore, specific nerve cells in the larvae can be made to glow by injecting DNA into them at the embryonic stage. This made it possible for scientists to insert and precisely place the fine recording equipment onto the Purkinje cells within the fish brains. To prevent the fish from moving, a paralytic agent that does not interfere with electrical signals in the brain was used. This combination of technical advances allowed the team to record electrical signals from Purkinje cells in an intact animal that was not anesthetized.
Results from these experiments showed that Purkinje cells sent out electrical signals in two different modes depending on the voltage at their cell surfaces. The first mode, called the ‘down’ state, occurred when the inside of the cell was more negative compared to the outside. In this state, cells were silent until signals from a different part of the brain arrived, at which time, they sent out a burst of impulses. In the second mode, called the ‘up’ state, the inside of the cell was less negative compared to the outside and the Purkinje cells sent out impulses at a constant rate. In this mode, these cells ignored any impulses coming from other parts of the brain. These states are reminiscent of a person attentively listening to directions and responding accordingly, or simply ‘zoning out’ and going their own way irrespective of instructions.
What does this phenomenon mean for the functioning of the cerebellum? To understand this, the NCBS scientists recorded the instructions of the nervous system to muscles. In normal fish, these instructions would result in swimming. However, since the experimental preparation is paralyzed, no movement is seen, yet the instructions to the muscle continue to be sent. The scientists discovered that such ‘fictive’ motor instructions were always accompanied by bursts of impulses in the Purkinje cells. Mostly, the impulses occurred after the start of these motor instructions and the timing of the bursts varied from cell to cell.
These results demonstrate that Purkinje cells receive a copy of the instructions sent by the nervous system to muscles and that they generate a burst of impulses in response. The researchers propose that the existence of the ‘up’ and ‘down’ states is a possible mechanism by which Purkinje cells choose to listen in on the instructions sent out to muscles or not. What do these cells do with such instruction copies? Do they alter their signals when the animal is learning a new motor task? The authors are excited to find out answers to these questions in ongoing experiments.
The paper titled “AMPA receptor mediated synaptic excitation drives state-dependent bursting in Purkinje neurons of zebrafish larvae” was published in the journal eLife on 29th September 2015 and can be accessed here.
Original news : NCBS News
News Update By – Nitali
Nectar is a primary food source for many animals but a few, including hummingbirds, honey eaters and sun birds and bats, possess mouthparts specifically designed to slurp up the sweet liquid found in flowers. Specialized nectar-feeding bats typically siphon nectar from flowers using extremely long, protruding tongues sprinkled with hair-like papillae. But some bats sport another type of grooved tongue — one that scientists haven’t studied in depth.
Marco Tschapka at the University of Ulm and colleagues show that grooved-tongued bats in the group of New World leaf-nosed bats known as the Lonchophyllinae display a unique feeding behavior. Using high-speed cameras focused on bats trained to obtain nectar from artificial “test tube” flowers containing honey water in the lab, the researchers’ video captured bats hovering in short flights (rarely lasting a second) over the feeders.
Unlike bats with hairy papillae, which moved their tongues in short lapping movements resembling a cat, the grooved-tongued bats lowered their tongues into the test tubes and did not move them during the entire visit. The bats’ grooved tongues appear to never separate from the liquid nectar, acting a bit like a conveyor belt to transport the food up the tongue and straight into the animals’ mouths.
The researchers aren’t exactly sure how the bats are able to do this, but suspect it occurs by some combination of tongue deformation and the ability of fluids like nectar to flow without external force in certain narrow spaces, a phenomenon known as capillary action.
Both methods for obtaining nectar were effective, but the researchers think that the grooved-tongue bats may have an advantage in acquiring nectar from flowers of certain shapes that hold the sweet liquid differently.
For example, some flowers have diffusely distributed nectar, while others offer one small pool of nectar. Different nectar extraction mechanisms might be useful depending on the flower. The pumping mechanism of Lonchophyllinae bats might work more efficiently in flowers that allow a more complete submersion of the tongue in the nectar pool, the authors suggest.
Another important factor might be nectar viscosity. Nectar from bat-visited flowers is generally dilute, but the sugar concentration in nectar varies between flowers. Nectar with a low sugar concentration that is less viscous and more free-flowing might be more easily harvested by the pumping mechanism compared to nectar of high sugar concentration and viscosity.
Original News : Science Advances
Like many other life forms, bacteria too are prone to viral infections. Many bacteria harbor restriction endonuclease enzymes, which help check the infection by selectively cutting and destroying the viral genomic DNA. The perpetual tussle between bacteria and viruses to gain an upper hand has resulted in a battery of restriction enzymes of different complexities. There are the simple nucleases that cut DNA at target sites – two copies of the nuclease come together, each cutting a strand to slice the double-stranded DNA. And there are motor-driven nucleases that are massive in size and use chemical energy to cut DNA only upon collision with another such nuclease and away from the target sites. A collaborative study between a team of scientists at IISER Pune and the University of Bristol, UK, of these energy-driven nucleases, published this week in Nature Chemical Biology, reveals a new mechanism of DNA break formation involving a compound damage caused by DNA shredding rather than slicing.
Dr. Saikrishnan Kayarat’s team at IISER Pune has solved the first atomic resolution x-ray crystal structure of a motor-driven restriction endonuclease bound to DNA. They found that contrary to the prevalently understood mode of action, the nuclease domain of this class of enzyme is positioned such that when two enzymes collide on a DNA, the nuclease domains are distant from each other. This structure also happens to be of one of the largest single-polypeptide chain bound to nucleic acid determined to date.
Guided by the structure, Prof. Mark Szczelkun and colleagues at the University of Bristol used single-molecule biophysical approaches, to find that the nucleases use the energy derived from the cellular fuel, ATP, to run along the DNA. Using biochemical approaches they found that upon collision, the distantly spaced nucleases make multiple nicks on the individual strands, thus shredding the double stranded DNA. This is in contrast to a clean-cut slicing brought about by the action of an enzyme with an apposed pair of nuclease domains. Unlike a sliced-DNA, a shredded DNA cannot be easily repaired.
The paper titled “Translocation-coupled DNA cleavage by the Type ISP restriction-modification enzymes” and authored by Mahesh K. Chand, Neha Nirwan, Fiona M Diffin, Kara van Aelst, Manasi Kulkarni, Christian Pernstich, Mark D. Szczelkun and Kayarat Saikrishnan has appeared as an advance online publication of Nature Chemical Biology.
This work received funding from Wellcome Trust-DBT India Alliance; Wellcome Trust, UK; DBT India; and CSIR India.
Original News : IISER Pune.
– By Anusha Krishnan
Beatboxing is the art of vocal percussion, and one could say that birds are the masters of beatboxing. In a contemporary approach to music and social awareness, a bird ecologist, a photographer and a musician have collaborated to create the unique #SkyislandBeatbox project. The trio – V. V. Robin (the ecologist), Prasenjeet Yadav (the photographer) and Ben Mirin (the musician) – enthralled their audience at the National Centre for Biological Sciences (NCBS) with their Birdsong Beatbox performance.
“The overwhelming response was unexpected and I was not sure what to make of it. It wasn’t just in NCBS – our shows in Cochin, Kodi, Trivandrum and Ooty rocked!” says V. V. Robin.
“The experience was all about portraying the birds as the heroes. We wanted to draw attention to the music, not the musician; the science, not the scientist and the photos, not the photographer”, says Aparna Banerjee, one of the curators of the #SkyislandBeatbox initiative from NCBS.
Ben’s music on a beatbox with bird calls from the Western Ghats coupled with Prasenjeet’s footage of these birds created a smorgasbord of audio-visual excitement. “The NCBS show was a really strong capstone to our team’s tour through the Western Ghats. We ended up modifying our structure to make the pieces more integrated and I think it really paid off. It was obvious that everyone in the room really enjoyed the music but also had a deep interest in our process and the science behind it. I’m really excited to see where this model can go, it’s as much about the team as it is about the message,” says Ben Mirin.
Current research by V.V. Robin in collaboration with Uma Ramakrishnan of NCBS shows that some of the birds featured in the program are very special – they are endemic to (which means they live only on) areas called sky-islands. Sky-islands are essentially the tops of mountains that are separated from each other by a “sea” of valleys. They are unique habitats that are in danger of disappearing due to deforestation and climate change. The presentation takes an innovative approach to spreading awareness about the very real dangers of extinction that loom over the wondrous bird life in the Western Ghats.
The effort has been funded by National Geographic, the Indian Bird Conservation Network (IBCN) and the Shola Trust.
For an example of Ben Mirin’s musical work, please click here.
A Must watch Video : Music Made from Real Bird Songs By Ben.
Original News : NCBS News
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