Squeezing dendritic necks

Active dendritic spines isolate themselves from the outside world, say Brenda Bloodgood and Bernando Sabatini (Harvard Medical School, Boston, MA). The spine necks become a diffusion barrier, which may facilitate the localized build-up of changes needed for synaptic plasticity.

Bloodgood and Sabatini were “playing around” with a sensitive and photoactivatable fluorophore when they noticed that some dendritic spines seemed to be decoupled from the rest of the dendrite. Fluorophore activated inside these spines was slow to leak out, and fluorophore activated outside was slow to diffuse in. Large changes in this diffusion barrier occurred spontaneously in organotypic slice cultures, with more blockage being induced by drugs that favor excitatory transmission.

Sure enough, diffusion restriction was induced in individual dendrites by pairing two...