Fig. 7.

Most CA1 pyramidal neuron dendritic spines have presynaptic partners. A, Confocal microscopy image of a representative segment of the apical dendrite of a CA1 pyramidal neuron filled with Alexa-594 (red) via the patch electrode during whole-cell recording in a control slice subsequently processed for synaptobrevin immunoreactivity (green). Note that most dendritic spines colocalize with synaptobrevin-positive puncta [yellow (overlap)]. B, Higher magnification view of an Alexa-filled spine with a synaptobrevin-positive presynaptic terminal. C, Scatterplot of the number of spines identified solely by Alexa-filling (left) and the number of synapses identified by Alexa-filling and subsequent immunolabeling of presynaptic terminals with anti-synaptobrevin antibodies (right). The numbers of spines and synapses (normalized per 10 μm of apical dendrite) in each analyzed segment are connected by lines to show the proportion of spines with presynaptic partners (∼65%).