Bi-stable neural state switches : Article : Nature Neuroscience
Another channelrhodopsin breakthrough from Deisseroth’s lab. This time light is not required to keep the channel open. Light merely triggers opening and closing behavior. Blue-shifted light opens channels and red-shifted light closes them. This looks like another potentially powerful neurotechnology for interrogating circuits and systems.
Relevant fig:
The Circadian Clock in the Retina Controls Rod-Cone Coupling (Christophe Ribelayga, Yu Cao, and Stuart C. Mangel)
An amazing paper from Neuron demonstrating adaptive (circadian clock-governed) binning in the retina, based on dopamine modulation of gap junction (electrical) synapses between retinal photodetectors. During the day, abundant dopamine release weakens gap junctions coupling rods and cones together so that visual acuity is high. When light is scarce (at night), there is less dopamine and the electrical coupling between rods and cones is increased. This is analogous to on-chip binning in CCD (digital) cameras. Binning increases signal (in light-limited systems, eg. seeing at night) by increasing optical input area and by reducing single element noise (ie. noise at different photoreceptors should be independent) at the cost of resolution. So, the retina activates photoreceptor binning at night to boost low-light signals and deactivates it during the day to increase resolution. The dopamine comes from cells in the interplexiform layer, whose dopamine release is itself governed by melatonin projections.
Also, I never knew that gap junction strengths were directly modifiable. It looks like the D2 receptors are G-protein coupled to PKA, which acts on the gap junctions.
There has been a few articles recently in the NYT about the neural mechanisms used by mosquito repellents. What a wonderful idea: Do some ephys recordings to find which neurons are sensitive to DEET (the current standard for mosquito repellents, which I can attest both doesn’t work very well and eats holes in synthetic clothing) and then build targeted compounds for those receptors/neurons/pathways. I always like this type of simple and practical neuroengineering.
Right now, it appears that there’s a bit of controversy in the field. Earlier this year, in Science, a group from Rockefeller found that DEET masked sensitivity to human odors by interfering with a particular odorant receptor. This impressive result was recently question by entomologists from UC-Davis in a PNAS paper claiming that DEET acts directly on a particular olfactory receptor neuron and does not attenuate the response to the same human-emitted odorant, as found in the earlier paper. Although the results appear to be conflicting, the studies use different techniques and thus it is likely that DEET’s action might be more complex than either paper claims. Still, the idea of identifying a target for chemical intervention by looking at electrophysiological responses to DEET is smart.
In related work, earlier this year a group from Colorado State University, as described in this PNAS overview, “conducted a rigorous search of a library of N-acylpiperidines, using an artificial neural network to identify strong candidates, and then tested them in the laboratory on human volunteers.” They found a candidate molecule that has a ~4X longer repellency effect than DEET. Here’s a photo from the experiments (DEET vs. untreated hand)… ouch!
Plants Found to Show Preferences for Their Relatives – NYTimes.com
Two amazing things here:
It refreshing to see this kind of interesting behavior without any neurons involved. It makes me think (realize) that the idea of a neuron or a neural system has many components and there might not be any good reason to assume that a single cell must have all of those properties or none of them. Something like a neuron-like cell that’s not a neuron in the classical sense. Anyone know of other examples?
Saw this on the Confocal list… Several times in the last few years I and others in the lab have debated the advantages and disadvantages of different fluorescence microscopy techniques. As many of you know, fluorescence microscopy is becoming increasingly important for many cool neuroscience techniques. But equally important in knowing how to properly image fluorescence.
Here’s a really thorough 2007 article from J. Microscopy that does a nice job of comparing wide-field/deconvolution, spinning disk confocal, and laser scanning confocal microscopy. Punchline is after the jump. (more…)
This new technique from Cori Bargmann’s lab is one of the neatest that I’ve seen in a while. The authors split GFP into two pieces, expressing one piece presynaptically and the other postsynaptically. This creates functional (ie. fluorescing) GFP only at sites of synaptic contact where the protein can reconstitute. They call the technique GFP Reconstitution Across Synaptic Partners (GRASP). Check out an example labeling here:
The neurons are expressing mCherry in the cytoplasm but GFP is expressed only at the site of synaptic contacts where the split GFP peptides can be reconstituted into a complete GFP fluorophore.
We’ve certainly come a long way. (And I never knew about Music Portal behind that thing.)
Download MP3It’s hard to judge the merits of this particular interface but I’m sure this is just the first of many such devices that we’re about to see (demo starts 2:00):
This is an Emotiv headset. More than the gaming application, I like the idea of using it for IM emoticons.
Anyone know if the consumer version will require gel for the scalp electrodes? Hmmm… if gamers are the target audience, I think I have a good idea for a cross-promotional opportunity here.
Video-Rate Far-Field Optical Nanoscopy Dissects Synaptic Vesicle Movement
Just the optical engineering alone here deserves mention: 28 frames per second at 62nm resolution (well below the diffraction limit of 260nm for light of the wavelength used)! STED (or stimulated emission depletion, developed in Stefan Hell’s group) is ideal for visualizing synaptic vesicles, whose small size (~50nm) has typically confined them to the domain of electron microscopists. The ability to get high-speed STED allowed the researchers to track individual vesicles and their path dynamics. They conclude that vesicle movement has both motor-driven and diffusive components (ie. a biased random walk). I’m sure with more time and more analysis there will be a lot of interesting applications for this kind of real-time vesicle tracking. Perhaps in the near future we will have single vesicle “minis” monitored at multiple sites through microscopy instead of just one or two sites electrophysiologically…
Here’s the resolution difference between STED and confocal for a single vesicle:
And, for those of you with ~$1.25M lying around, you can now purchase a STED setup directly from Leica!
The relatively recently discovered cannabinoid receptors has me wondering how many other neuroreceptors may be left to discover. One way to estimate the number of these is to screen the genome and look for sequences that look like receptors. This paper says that people have done that for the special case of G protein-coupled receptors (GPCRs), and that the result is that, excluding receptors involved in “chemosensory responses such as taste and olfaction”, there are “367 receptors (1), of which some 200 have been shown to bind known transmitters (3). This leaves about 160 orphan GPCRs that are not activated by any known transmitters and thus are genes with unknown function.”