Independent regulation of calcium revealed by imaging dendritic spines

THE dendritic spine is a basic structural unit of neuronal organization. It is assumed to be a primary locus of synaptic plasticity, and to undergo long-term morphological and functional changes 1–6 , at least some of which are regulated by intracellular calcium concentrations 7–11 . It is known that physiological stimuli can cause marked increases in intracellular calcium levels in hippocampal dendritic shafts 12,13 , but it is completely unknown to what extent such changes in the dendrites would also be seen by calcium-sensing structures within spines. Will calcium levels in all spines change in parallel with the dendrite or will there be a heterogeneous response? This study, through direct visualization and measurement of intracellular calcium concentrations in individual living spines, demonstrates that experimentally evoked changes in calcium concentrations in the dendritic shaft ([Ca 2+ ] d ) are frequently not parallelled in the spine ([Ca 2+ ] s ). This isolation is not caused by a physical diffusion barrier. This report provides, to our knowledge, the first direct demonstration of autonomous spine function.