Location-Dependent Excitatory Synaptic Interactions in Pyramidal Neuron Dendrites
Figure 5
Proximal-distal interactions: experimental results.
A, Somatic responses evoked by 50 Hz double pulse stimulation with bipolar theta electrode at distal site (210 µm from the soma), including a clearly visible dendritic spike. B, Somatic responses to proximal input alone at 120 µm, evoked by laser flash photolysis of caged glutamate. C, Distally evoked responses in the presence of constant proximal modulation activated simultaneously; modulatory input alone is indicated by asterisked trace in (B). D, Summary plot: each successive curve corresponds to a higher proximal modulation. Modulator-alone peaks are given by y-intercepts. Triangle indicates just-suprathreshold response to distal input, also shown in (E). Circle marks just-suprathreshold response for the distal stimulus when the proximal bias was simultaneously just-subthreshold for its own spike. E, Same cell as (D), with proximal and distal roles reversed. Square and pentagon correspond to just sub- and just supra-threshold response peaks, respectively, also shown in (D). F, G, Combined results of 294 stimulus pairs in 6 cells (cell-by-cell results shown in Figure S2 in Text S1). Inset, stimulus sites are indicated by black triangles (electrical stimulation) and purple clouds (laser uncaging), dendrite length in ball-and-stick cartoon is 275 µm. Blue case is same as in (A–E). Red case included TTX (1 µM) perfused from an electrode near the soma to prevent somatic spiking which would have masked the subthreshold integration process being studied. Grey and orange cases used electrical stimulation at proximal site instead of uncaging, and included CNQX (10 µM) in the bath to block AMPAR responses in order to prevent somatic spiking due to fast AMPA currents.