Is spine head growth an "artifact"?

A visiting seminar speaker to my department recently told that he thought that the rapid and permanent increase in spine head size we have reported was an artifact of 2-photon uncaging (of glutamate). At this years SfN annual conference in San Diego, two labs are finally catching up and reporting similar phenomena. Karel Svoboda gave the Presidential address on the saturday evening (3rd November) of the conference. In the final part of his talk he showed all unpublished data using 2-photon uncaging of MNI-Glu. Using a Ras indicator, he showed that tetanic photo-stimulation of single spine heads a la Matsuzaki, produced enlargement (see pic). Activated Ras was seen to spread from the spine into the dendrite and remain active for several minutes. Hayashi's lab (MIT) had a poster (363.11/M23) showing spine head enlargement using photochemical tetanus as well.

So now with a n=3, perhaps spine head enlargement is not an "artifact" after all?

Matsuzaki et al. Nature Neurosci. (2001) 4: 1086-1092, & Nature (2004) 429:761-766.

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