Sleep and spine loss

Sleep and waking modulate spine turnover in the adolescent mouse cortex

Maret et al 2011 (Nature Neuroscience)

This is an intriguing little paper just appeared in Nature Neuroscience, looking at spine turnover in sensorimotor (a bit of a vague word this) cortex of adolescent (P23-44) YFP-expressing mice. They imaged the same section of dendrite through the skull of the same mouse on two separate occasions - quite a technical achievement - at the end of a period of wakefulness, and then again after the mouse's next sleeping period. In this situation they found a net loss of spines after the sleeping period, whereas if they reversed the order, imaging after sleep first, then after waking, they found a net gain of spines. These differences disappeared in adults.

So sleep seems to be an important period of synaptic pruning in adolescent mice. I wonder if this applies to humans as well. Teenagers seem to go through these periodic bouts of excessive sleeping. Perhaps they're not being lazy after all - they're engaging in important synaptic pruning, remodelling their brain circuits in preparation for adult life?

How to write a neuroscience textbook

I've been leaving the trusty old iPod at home and instead carrying "Dendritic Spines" (Rafael Yuste, MIT Press, 2010) with me for on-tube entertainment. Also for propping up in front of my sandwiches during my lunch "break". It's a long time since I have come across such a readable science text. My previous big purchase, "Barrel Cortex" by Woolsey and Fox, had large tracts of impenetrable dullness. But Yuste's book, as well as being less than half the price, just whizzes along. Considering the fairly technical nature of its subject matter, it's superbly readable.

I think part of the secret is that Dr Yuste has a big idea, and his writing buzzes with the excitement of getting this across to you. After all, if spines are the physical substrate of memory and cognition, then it's pretty important to understand how they work.

Plus it has a great chapter on Ramon y Cajal, my neuroscience hero....

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?