Supersensitive Ras activation in dendrites and spines revealed by two-photon fluorescence lifetime imaging

Nat Neurosci. 2006 Feb;9(2):283-91. doi: 10.1038/nn1635. Epub 2006 Jan 22.


To understand the biochemical signals regulated by neural activity, it is necessary to measure protein-protein interactions and enzymatic activity in neuronal microcompartments such as axons, dendrites and their spines. We combined two-photon excitation laser scanning with fluorescence lifetime imaging to measure fluorescence resonance energy transfer at high resolutions in brain slices. We also developed sensitive fluorescent protein-based sensors for the activation of the small GTPase protein Ras with slow (FRas) and fast (FRas-F) kinetics. Using FRas-F, we found in CA1 hippocampal neurons that trains of back-propagating action potentials rapidly and reversibly activated Ras in dendrites and spines. The relationship between firing rate and Ras activation was highly nonlinear (Hill coefficient approximately 5). This steep dependence was caused by a highly cooperative interaction between calcium ions (Ca(2+)) and Ras activators. The Ras pathway therefore functions as a supersensitive threshold detector for neural activity and Ca(2+) concentration.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Cell Line
  • Dendritic Spines / physiology*
  • Diagnostic Imaging* / instrumentation
  • Diagnostic Imaging* / methods
  • Enzyme Activation
  • Hippocampus / physiology*
  • Humans
  • Microscopy, Confocal
  • Microscopy, Fluorescence / instrumentation
  • Microscopy, Fluorescence / methods
  • Organ Culture Techniques
  • Patch-Clamp Techniques
  • Photons
  • Rats
  • ras Proteins / metabolism*


  • ras Proteins
  • Calcium