MAPPING MINIATURE SYNAPTIC CURRENTS TO SINGLE SYNAPSES USING CALCIUM IMAGING REVEALS HETEROGENEITY IN POSTSYNAPTIC OUTPUT

The amplitudes and kinetics of miniature excitatory synaptic currents (MESCs) in mammalian central neurons vary widely. It is unclear whethe r this variability occurs at each synapse or arises from differences a mong st heterogeneous population of synapses. Furthermore, it is not k nown how variability in these currents would affect their associated p ostsynaptic Ca2+ transients. To address these questions, we conducted simultaneous Ca2+ imaging and patch-clamp recordings from cultured cor tical neurons and mapped individual MESCs to identified synapses displ aying coincident dendritic miniature synaptic Ca2+ transients (MSCTs). Measurements of MSCTs at dendritic sites that displayed multiple even ts revealed that MSCT amplitude varied considerably at each site. Simu ltaneous measurement of MESCs and MSCTs at these sites indicated that variability in coincident synaptic currents contributes to the differe nces in Ca2+ transient amplitude, The ability of single synapses to ex hibit variable output may enable them to engage intracellular signalin g pathways at different levels of intracellular Ca2+.