Figure 2.

Optical detection of synaptic transmission. (A) CA1 pyramidal neuron, filled with fluorescent Ca²⁺ indicator. Presynaptic axons are activated by a SE in stratum radiatum (sr); evoked excitatory postsynaptic potentials (EPSPs) are recorded via a somatic microelectrode (not visible). Fluorescence changes due to calcium transients evoked by the same stimulus in an apical dendritic segment (region of interest indicated by the white box) are seen at higher magnification in (B). (B) Evoked postsynaptic calcium transients (EPSCaTs) are restricted to an individual dendritic spine (arrowhead), seen below at higher magnification in video frames at rest (bottom left) and immediately after synaptic activation (bottom right). (C) EPSCaTs monitored via line-scan (x-t) imaging across the spine (black arrowhead) and adjacent dendritic shaft. Successful synaptic transmission (left), visible as a fluorescence increase, can be clearly distinguished from transmission failure (right). EPSPs during transmission failure at this synapse are due to successful transmission at some of the other synapses activated by the same extracellular stimulus. Traces show (top to bottom) single-trial fluorescence from the spine, averaged EPSP, and averaged fluorescence from the spine, during success (red, left) and failure (black, right). sp, stratum pyramidale; so, stratum oriens. Figure adapted from Enoki et al. (2009).