Sunday, November 20, 2011

Granule cells in awake animals - Strange results

SfN seems a distant past. Two days in Boston have seemed to eradicated all memory about Washington. Now, after one day in New York even Boston begins to fade. There is however, still so much to tell about the SfN. Especially the last afternoon poster session was very interesting for cerebellar physiologists. There were two sessions at the same time dedicated to the cerebellar cortex and nuclei. Unfortunately, I was presenting my own poster at the opposite side of the hall, which resulted in me sprinting across the whole thing twice to catch a glimpse of cerebellar research. Nice....

Mossy fibers seem to be much more active in awake animals than in anesthetized animals. This off course has two effects: granule cells receive both stronger excitatory input and stronger feedforward inhibitory input via Golgi cells. This causes granule cells on average to be more active, especially during movement when they could spike at sustained rates as high as ~5Hz! But, in my opinion, here are some serious concerns with the study as it is now. Clapping resulted in a strong excitatory response in all cells. The authors claimed this was a direct auditory response. This seem strange since in that case all granule cells should receive auditory information. And with only ~4 mossy fiber inputs per granule celll, this seems strange. The auditory input could of course evoke a startle response, which activated granule cells via movement.
Also, the firing rate during movements seems very high for granule cells. This was never recorded extracellularly with for example vestibular stimulation during rotation, where the average maximum firing rate was only 0.7Hz. There is a more scary interpretation of the results. It would be very interesting to see for how long after startle responses or after movement the cells could be recorded and with what quality. Maybe the movement is just too much for such a little cell, and it begins to leak during movement.

I wrote a long time ago a blogpost about patching in awake and getting your article in Science. I think this study would need a great deal of improvements before it can be published. Still, it is very exciting that some people can patch granule cells on a daily basis in awake animals. Much respect...

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