FAST CONFOCAL IMAGING OF CALCIUM RELEASED FROM STORES IN DENDRITIC SPINES

The emerging significance of calcium stores in neuronal plasticity and the assumed involvement of dendritic spines in long-term plastic prop erties of neurons have led us to examine the presence and possible reg ulation of calcium stores in dendritic spines. Immunohistochemical sta ining for ryanodine receptors was found in dendritic spines of culture d hippocampal neurons. Confocal microscopic imaging of calcium transie nts in dendritic spines of these neurons in response to caffeine allow ed us to demonstrate an independent and unique calcium store in spines . The response to caffeine was blocked by thapsigargin and ryanodine, and maintained in calcium-free medium. The calcium stores were deplete d faster in the spines than the dendrites. Furthermore, when calcium w as released from stores under calcium-free conditions, and diffused pa ssively between the spine and the dendrite, the length of the spine ne ck determined the degree of spine independence. Finally, the caffeine- sensitive ryanodine receptor-linked calcium store was instrumental in regulating the response of neurons to glutamate, These results have im portant implications for understanding the roles of dendritic spines i n neuronal integration and plasticity.