Glue Sniffing and Time Stamping with Roger Tsien

Yesterday I went to a UPENN neuroscience retreat at The College of Physicians of Philadelphia, which happens to be the same building that houses the Mütter Museum. The highlight was an introductory lecture by Dr. Roger Tsien, inventor of calcium-sensitive dyes and Nobel favorite.

Recently his lab developed two novel techniques for imaging brain activity. First, Tsien discussed the Glutamate Sensitive Fluorescent Reporter (GluSnFR aka “Glue Sniffer”). The probe works by Fluroresence Resonance Energy Transfer (FRET). This technique involves two fluoresecent proteins that are matched so that the emission wavelength of the first is the excitation wavelength of the second. If the molecules are close together and oriented properly, then exciting the first protein (say, one that normally fluoresces blue) will in turn excite the second protein (say, one that normally fluoresces yellow). When the fluorescent proteins are separated, only blue light is emitted because FRET cannot take place. When they are oriented in the right way, only yellow light is emitted because all the energy is transferred via FRET.

GluSnFR works by linking blue and yellow fluorescent proteins with a third protein that changes conformation when it binds glutamate. Normally the two fluorescent proteins are close enough to engage in FRET, so excitation results in only yellow light. But glutamate released from neurons can bind the linker domain in GluSnFR and disrupt FRET, causing only blue light to be emitted. The ratio of blue to yellow light emission can be measured with high spatial resolution, facilitating time-lapse movies of glutamate spillover from synapses. This is a cool new tool for imaging neuronal activity. The graduate student who performed the work has a better explanation than I can provide. Paper here.

Tsien began the second half of his lecture by discussing competing theories for memory storage in the brain. The dominant theory has been that learning involves modulation of synaptic strength. However, Tsien stressed new evidence showing that learning depends on the formation of new synapses. TimeSTAMP is a new way of monitoring synapse formation.

Tsien’s lab engineered animals to express modified versions of the proteins normally expressed at the synapse, such as PSD-95. This version of the protein is linked to a hemagglutinin (HA) tag via another protein. The linker protein is actually a cis-acting protease, meaning that it spontaneously cleaves itself. Normally, the linker cleaves immediately after PSD-95 is translated, thus separating it from the HA tag. But when a protease inhibitor is added, all the newly translated PSD-95 will have the HA tag. After the experiment is over, the brain can be stained with anti-HA antibodies to see only the synapses that formed after the addition of the protease inhibitor. The ultimate goal is to administer the inhibitor before a learning experience and then observe the when and where of synapse formation compared to an animal that did not have that learning experience.

TimeSTAMP isn’t quite as cool as GluSnFR becasue the results are obtained retroactively with immunohistology instead of real time optical imaging. However, this approach is advantageous because it allows you to view the whole brain instead of just the superficial areas that light can penetrate. Another problem is that there may be high turnover of proteins like PSD-95 even at old synapses. The perfect marker will use a synaptic protein that is only translated during synapse formation, although it is unclear whether such a master molecule exists.

Needless to say, Tsien’s research is pretty awesome.

It’s over.

Is this what postpartum depression feels like? I just took the MCAT on Saturday, and now I don’t know what to do with myself. I thought most of it was manageable, but I definitely made a couple dumb mistakes along the way. My scores on the practice tests rarely correlated with my subjective impression of how I did, so I guess I’ll just have to wait a month in order to find out. Speaking of which, what part of grading a (mostly) multiple choice exam takes 30 days?

To those who plan on taking this test one day, here are my two cents:

  • Start Early. I began studying about 3 months ago, though I only got serious about it 2 months ago. I also took last week off work, which was probably unnecessary. Anyway, the longer you have to study, the more comfortable you will be with the test’s format and timing.
  • Expect the unexpected. While the scope of material on the exam is relatively limited, the questions are always applying these concepts in unfamiliar settings.
  • It’s in the passage, dummy! It’s true that a good chunk of the questions can be answered without reference to the passage. But if you stumble across one that doesn’t make any sense, you probably skimmed over a subtle clue in the text. This is also true for VR, where the correct answers are usually paraphrased literally from the text.
  • Practice, practice, practice. I used a combination of Kaplan Full Lengths and AAMC exams to prepare. The actual test was somewhere in between in terms of difficulty.

Signs of Life

It’s been a long time since my last post, so I figured that my loyal readers (are you out there?) deserve some kind of explanation. As I may have mentioned before, I am about to apply to a bunch of Medical Scientist Training Programs (MSTP) in the hopes of earning both an MD and a PhD in neuroscience. Unfortunately, that means that every moment of free time that used to go here now goes toward the behemoth that is the MCAT.  Now I’m one month away from Test Day, and I look forward to resuming my normal posting schedule after this is all over. In the meantime…


…Wish me luck.

Video Game Doping

Performing-enhancing drugs have seen a lot of recent media attention because of the Mitchell Report. But while most people are busy criticizing the use of such substances, others are trying achieve broader acceptance for them. A German company is selling a product called FPSBrain, where FPS stands for First-Person Shooter. From their website:

FpsBrain was developed doing extensive research to cater to the growing demand for performance improvement in electronic sports. It accelerates neural processes and heightens perception and capacity of reaction and concentration – because not just a first-rate computer or a team well set up are the key to winning a competition, but also the physical and mental condition of each player.

These pills won’t make your muscles huge, rather the ingredients resemble the contents of most energy drinks:

1. L-glutamine 100,00 mg
2. L-tyrosine 100,00 mg
3. Betaine 50,00 mg
4. Vitamin C 75,00 mg
5. Vitamin E 10,00 mg
6. Niacin amide 18,00 mg
7. Selenium 30,00 µg
8. Calcium pantothenate 6,00 mg
9. Vitamin B6 2,00 mg
10. Vitamin B2 1,60 mg
11. Vitamin B1 1,40 mg
12. Vitamin B12 1,00 µg
13. Folic acid 200,00 µg
14. Biotin 150,00 µg
15. Caffeine 5,00 mg
16. Soy lecithin 250,00 mg

FPSBrain may not contain any novel ingredients, but at the very least it represents a marketing breakthrough. Bringing doping to video games seems to legitimize them as an actual sport while also promising players an elusive edge. Are you concerned that these people are just snake oil salesmen?  Don’t worry, the website assures customers “All our staff use FpsBrain at least four times a week to enhance their mental performance and their work efficieny [sic].”  So the whole company is hopped up on caffeine pills…and that’s supposed to make me trust them more?

Mirror Neurons Discovered in Birds

A new paper by Prather et al. identifies song-specific neurons in the swamp sparrow that are active during song perception and song performance. These properties suggest that the neurons might be part of mirroring system analagous to those identified in primates. As far as I can tell, this is the first paper on mirror neurons that Nature has published, though its sibling journals have been kinder to the emerging field (see here and here; note the infamous Iacaboni is an author on both). Because mirror neurons have received extraordinary media attention, sometimes it’s hard to separate the facts from the hype. This Nature paper lends credibility to the field by establishing a small-animal model for future investigation.

Prather et al. measured action potential activity using motorized microdrives that precisely positioned electrodes in the telencephalic nucleus HVC, a brain region known to be involved in singing and song perception. They found that the pattern activity in these regions was nearly identical for auditory perception and song vocalization (see figure below). The authors do note one difference between the neural correlates of action and perception: HVC neurons fired single action potentials during song perception but fired in bursts during song vocalization.


The authors also prove that activity during song vocalization cannot be explained in terms of auditory feedback. For instance, the authors show that HCV activity is not influenced by auditory distractions while a bird is singing. This suggests that activity during singing reflects a corollary discharge from motor systems.

I think the most exciting aspect of this research is the translational potential. Now that we have a small-animal model, it will be easier to test the effects of genetic and pharmacological manipulations on mirror neuron systems. Further research might provide important insights about language acquisition and how it is disrupted in certain pathologies (i.e. autism).

Cookie Scent Makes Women Buy Sweaters

A new paper in the Journal of Consumer Research looks at subliminal influences on consumer decisions, and Science Daily has a great write-up.  In the first study, experimenters tested the effect of visual stimuli on preferences regarding delayed gratification:

Li asked participants to act as “photo editors of a magazine” and choose among either appetite stimulating pictures of food or non-appetite stimulating pictures of nature. A control group was shown no pictures at all. All were then asked to participate in a lottery that would either pay them less money sooner or more money later.

Those who had been exposed to the photos of food were almost twenty percentage points more likely to choose the lottery with the chance of a smaller, more immediate payoff than those who were exposed to the photos of nature (61 percent vs. 41.5 percent) and eleven percentage points more likely to choose the short-term gain than those who had not been exposed to any stimulus (61 percent vs. 50 percent).

 The second study tested the effect of odor on consumer spending:

Another experiment used a cookie-scented candle to further gauge whether appetitive stimulus affects consumer behavior. Female study participants in a room with a hidden chocolate-chip cookie scented candle were much more likely to make an unplanned purchase of a new sweater — even when told they were on a tight budget — than those randomly assigned to a room with a hidden unscented candle (67 percent vs. 17 percent).

I have a feeling J.Crew is stocking up on cookie candles as we speak…

The PCR Song