A new study into the hippocampus - the brain's memory formation circuit, has revealed key insights to the function of a region that has remained largely elusive for over 75 years of Neuroscience research. The work undertaken allows scientists to consider a whole new route of electrical signalling in the hippocampus, further to the previously considered 'tri-synaptic pathway'.

Previous studies of the hippocampus have focussed on the following three synapses:

• the perforant path (cortex input to hippocampus) and dentate gyrus granule cells;
• the mossy fibres (dentate gyrus granule cell axons) - CA3 connections;
• the Schaffer collaterals (CA3 axons) - CA1 pyramidal cell inputs.

In each of these cases, in vitro slice preparations and in vivo recordings show an enhancement of activity following strong excitation protocols. This increase in activity at the synapses is known as long-term potentiation (LTP), which, along with the opposite, long-term depression (LTD), is thought to represent a function of learning and memory in the mammalian brain.

In this latest study by Chevaleyre and Siegelbaum, the CA2 region was shown to have little impact upon this tri-synaptic pathway, and underwent no LTP from any of these fibres. However, these cells did show LTP when their more distal inputs (from the cortex) were stimulated. Furthermore, they were also shown to have an inverse synaptic drive, with the proximal synapses having little input on the firing rate of the CA2 pyramidal neurons.

Also of crucial interest was the role that these cells play, since they appear not to be involved in the main circuit of memory formation. Previous studies had shown that the output of the hippocampus - the CA1 cells, were still capable of firing strongly, even when their main inputs (from CA3) were severed. Here, the team from the Howard Hughes Medical Institute proved that not only do CA2 cells form synapses with CA1 cells, but that they are also capable of driving them to fire, thus providing a separate moderation of hippocampal output from the usually considered circuitry.

Image taken from MRC Centre for Synaptic Plasticity. Paper reference: Chevaleyre & Siegelbaum, Neuron, 66, 560-572, 2010.

Whilst many of the most significant drivers of climate change are thought to be of man's making, a recent publication in PNAS has shown that the success of one rapidly spreading vine is leading to a reduction in air quality.

The study focussed on the deep rooted vine, kudzu (Pueraria montana), and its spreading through south-eastern America (at up to 120,000 hectares per annum) after being introduced from Asia to prevent soil erosion on farmland in the early 20th Century.

The Nitrogen-fixing legume increases the soil's nitrogen content, allowing for a greater quantity of nitric oxide (NO) emissions, which in turn could raise ozone levels in the affected region. The sites in Georgia showed at least a 100% increase in NO emissions and up to 1000% increase in the rate of nitrogen mineralisation. Models of NO levels factoring in the spread of kudzu showed that the number of high levels of ozone events recorded could increase by up to 7 per summer, or more than double in areas where the vine is currently absent.

One of the biggest wonders in the natural world is that of the brain. How does it compute the vast quantities of data that it does? Over the past couple of centuries, Neuroscientists have begun to understand some of the means by which the brain can process information. However, there is still great debate as to how neurons deal with their inputs.

In an article recently published in Nature, a German team has studied the firing of neurons in the mouse primary visual cortex under different rotations and movements of the same visual stimulus - a grid of adjacent lines. The researchers found that, in line with previous studies of cats, various neurons within the mice fired at different orientations of the visual stimulus. Some of these were highly preferential, some less so.

More surprisingly, regardless of whether or not a neuron was highly tuned to a specific orientation (in terms of its overall output), it still receives hotspots of excitatory inputs in different locations under a variety of rotations of the visual stimulus. The same was even true of single dendrites - the branches of neuronal cells, which, without fail, received hotspots of activity in response to multiple orientation stimuli. Not only were adjacent inputs not the same, but looking at any one rotation associated response set showed a spread of locations across the entire neuron.

One of the most surprising aspects of this work was when comparing those neurons that fire in response to a specific rotation of the stimulus, and those that were less specific. Researchers found that both of these categories had the same sort of input sets, with highly active regions for each rotation, in spite of the fact that some resulted in the neuron firing more predominantly than others. This points to the computational aspect of neuronal cells, rather than simply adding up the inputs they receive.

Images from article: Jia et al., Nature, 464, 1307-1312, 2010.

An international group has reported in Nature Genetics that they have discovered the secret to how the woolly mammoth coped with the freezing temperatures of Siberia. Utilising modern genetic techniques, including the insertion of RNA into E. coli, they have discovered a specific mutation within the mammoths' haemoglobin which would allow the elephants to cope with the extremes of the last ice age.

Whilst cold conditions usually inhibit haemoglobin's ability to release oxygen to the rest of the body, the mammoth's genes for the protein feature three key sections not witnessed in any present lineage of elephant, allowing for this lower temperature functionality.

The researchers utilised ~43,000-year-old preserved DNA samples to generate RNA. This was then used in the bacteria to produce a replica of the haemoglobin that the animals would have naturally formed in animals of the species, even up to a billion years ago. These proteins were shown to have relatively small temperature dependent-oxygen affinity. This is a key factor for cold inhabiting mammals and is absent in modern elephants. These different amino acid residues enabled minimal heat loss and as such were evolutionarily favourable during the ice age and for the animals that migrated towards the pole from their ancestors' home in equitorial Africa.

Image: ecoworld.com.

Over the weekend, one of the most significant unmanned space missions reached its 20th Anniversary. After being plagued by errors and malfunctions during the first three years of observation, the Hubble Space Telescope has since provided images of our solar system, stars, galaxies, nebulae and much, much more.

At an orbit of 600 Km above Earth, Hubble suffers none of the diffractory problems experienced by telescopes observing from the surface. As such, Hubble is able to observe in both the ultraviolet and infrared frequency ranges, which are unfiltered in space, but blocked by our atmosphere. Among its discoveries over the past two decades, have been that of dark energy, which accelerates the expansion of the universe, and pinpointing the origins of the universe to between 13 and 14 billion years ago.

A full history of the mission, including details of specific findings, press releases, functionality of the microscope and much more, can be found at: NASA's hubble pages.

A site entirely devoted to the Hubble Mission is also available featuring even more information, as well as a full catalogue of the images that Hubble has taken over the years. This includes a special 20th Anniversary section, featuring documentaries and downloads to celebrate the images and discoveries of the mission.

For an introduction to Astronomy, I recommend the BBC's Solar System pages, including video contributions from Brian Cox and Patrick Moore.

Images: hubblesite.org.