Spines slow dendrite diffusion

Little bulbous neuronal protrusions known as spines slow diffusion along dendrites, say Fidel Santamaria, George Augustine (Duke University, Durham, NC), and colleagues. Based on their new data, they offer a new hypothesis for how active synapses are tagged during long-term potentiation (LTP).

Spines are thought to act locally by preventing the chemical messengers made at a synapse from leaking into the rest of the dendrite. But Augustine turned this idea around: he wondered whether spines affect the long-distance journey of chemicals along dendrites. Using fluorescent imaging, the group now shows that dendritic diffusion of both an inert dye and calcium-mobilizing IP₃ is slowed when spine density is high.

Slowing occurs because signals that enter a spine do not always escape quickly. How long...