Viva post mortem

In December I submitted my first year dissertation, and last week I faced a viva on this dissertation. Opinions from colleagues and supervisors varied as to whether or not this was really an exam, and how much I should relax about it. Naturally (me being me) I did not relax about it. One feature I knew that this viva (exam or not) shared with real exams was that failure was a possibility, and that failure had consequences.

So this mattered.

I was lucky enough to be able to invite two scientists I like and get on with to examine me. But still - people can show a whole new side of their personality in this kind of role. And I hate the idea of making a fool of myself in front of people I respect. So I was tense for at least a week beforehand, and preparing diligently.

In the event, the whole thing was very amiable - enjoyable even. Defending my dissertation was a pretty minor part of it. Most of our time was spent chewing over the implications of different technical choices as I go forward with my project. Chemical LTP or glutamate uncaging? Organotypic or acute slices?

And I passed. And got some pretty nice feedback. So I can go on....

Journal club fun

McGuiness et al, "Presynaptic NMDARs in the Hippocampus Facilitate Transmitter Release at Theta Frequency", Neuron 68, 1109–1127, December 22, 2010

I go to two journal clubs, one nice the other nasty. Today was the nasty one, where we looked at the above article. It was the usual pattern - a paper that I thought was quite impressive, turned out to have feet of clay when subjected to the withering scrutiny of the assembled critical intelligences.

In this study, they used Ca-sensitive dyes to image Ca-transients in presynaptic boutons of the CA3-CA1 pathway, in response to action potentials. They claim that the distribution of Ca-transient amplitudes is bimodal. Various drug manipulations, including the use of norketamine to block (internally) only presynaptic NMDARs, demonstrate that the less frequent, large transients are dependent on presynaptic NMDARs. Trouble is, after fig 1 they don’t show us the data – just their opaque Bayesian analysis. And what is worse, they use the same control data in most of their figures.

Meeting Tim Bliss

I met Tim Bliss yesterday. What a lovely man - he was visiting UCL to give a lecture, and came up to the lab and spent at least 15 minutes with me chatting about my project, giving me some very helpful advice. For any non-neuroscientists reading, this is the LTP equivalent of hanging out with Bob Dylan. He wrote the songs that everyone else has been covering for the last 40 years.

Matsuzaki et al 2004

Matsuzaki M, Honkura N, Ellis-Davies GC, Kasai H (2004) Structural basis of long-term potentiation in single dendritic spines. Nature 429:761-766.

I've been re-reading this classic paper this week. Nice reassuringly fuzzy pictures of spines growing and shrinking, nice useful detail on how they measured spine heads, nice technique stimulating individual spines with 2-photon microscope and glutamate uncaging, nice findings with some spines growing very quickly (minutes) then fading back but still bigger than they started. Then the paper steps up another level when they perforated-patch the cell and use the post-synaptic response to the uncaging to map the size of the glatamate-sensitive area (ie the synapse presumably) on the spine, and find that this enlarges in step with the spine enlargement. Other headlines: LTP can be induced at an individual spine; neighbouring spines show no change; large spines resist LTP.

I NEED to get my hands on this technology

One of my highlight of Neuroscience 2010 - the huge bash for 31000 neuroscientists which I recently attended in San Diego - was a talk by Valentin Nagerl about nano-scale imaging of spines. I spend a lot of my time imaging dendritic spines on a confocal microscope, and pretty fuzzy they look sometimes - not because of any issues with our microscope I hasten to add, but just because I'm trying to image something whose size is of the same order as the wavelength of light. So I was just stunned to see the beautiful images of spines that Dr Nagerl obtained using STED. This all works with doughnuts apparently. Doughnuts of light, of a different wavelength, which you interleave at very high frequency with your actual illumination spot. This "prerelaxes" the electrons in your dye, with the result that you get a *very* small spot scanning your sample.

Here are some images from his latest paper (Nagerl UV, Bonhoeffer T (2010) Imaging living synapses at the nanoscale by STED microscopy. J Neurosci 30:9341-9346). Are they not lovely?

A rule of life

I love the varied rhythm of working in science:

• Experimenting. This is nicely practical, hands-on kind of work. Something I hardly ever experienced in my previous life as a software techie. Grappling with the cussedness of the physical world. Cleaning noise out of an electrical circuit. Getting a pump to pump at a consistent rate. Making a tiny grating with platinum wire and dental floss. Keeping living tissue healthy. (Endlessly) making up solutions.

• Reading. Another kind of grappling, with densely written, unapologetically expert papers. It gets easier with time, as I become more familiar with the field. Learning to read critically, not just accepting everything I read. Making time for reading (not just fag-ends like the daily tube).

• Writing. I've always liked writing. However, there is a certain fear-hurdle to be jumped with scientific writing. A feeling that I have to know everything before I can even start.

• Listening. At UCL there are many many opportunities to learn from the very best. Lectures, seminars, journal clubs, conferences, symposia. Fantastic. I just have to make space for at least some of this.

Softly, softly

With patching it really is "practice makes perfect". Yesterday I spent *hours* before I finally managed to get one. Today I was much much quicker. Softly, softly....that's the key. Being very careful about how much pressure you apply down the pipette. And it seems I can't talk and successfully patch at the same time. So from now on I have to cut out the running commentary for K's benefit.

So the neuron is nicely filled with dye now, and K is getting some images of lovely spiny dendrites.

Time for lunch.