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 ([Ca2+]d) are frequently not parallelled in the spine ([Ca2+]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.