IMAGING OF CALCIUM VARIATIONS IN LIVING DENDRITIC SPINES OF CULTURED RAT HIPPOCAMPAL-NEURONS

1. Cultured rat hippocampal neurons were loaded with the Ca2+ indicato r fura-2 through micropipettes and visualized with an inverted microsc ope equipped with a high power objective and a cooled CCD camera. The responses of dendritic spines and their parent dendrites to stimuli wh ich evoke a rise of [Ca2+](i) were monitored. 2. NMDA caused a rapid a nd transient rise in [Ca2+](i), which was more evident in the spine th an in the parent dendrite. The recovery in both compartments had the s ame time course, and was dependent on normal [Na+](0). 3. Application of alpha-latrotoxin, which causes release of neurotransmitters from te rminals, produced a rise of [Ca2+](i) in the dendritic spines, more th an in their parent dendrites. Prolonged exposure to the drug eliminate d the spine/dendrite disparity. 4. The presence of voltage-gated calci um channels in dendritic spines is indicated by the enhanced calcium r ise in spines rather than dendrites of cells depolarized by either int racellular current injection or by raising [K+](0). This rise was atte nuated by nifedipine or verapamil, both L-type channel blockers.5. It is suggested that the dendritic spine constitutes an independent calci um compartment that is closely linked to the parent dendrite.