Location-Dependent Excitatory Synaptic Interactions in Pyramidal Neuron Dendrites
Figure 2
Location independence of the dendritic spike-threshold nonlinearity.
A, Experimental setup. Whole-cell recordings were performed from the soma of a layer 5 pyramidal neuron. The cell was loaded with OGB-1 (200 µM) and was visualized using fluorescence confocal microscopy. Purple “clouds” denote sites of glutamate uncaging. B, Somatic responses to increasing stimulus intensity using UV laser focal uncaging of glutamate 60 µm from the soma. Black dashed trace shows extrapolated response based on linear fit to series of subthreshold response peaks. Ratio of actual to extrapolated response at local spike threshold defines the “Nonlinearity Relative to Linear Extrapolation” (NRLE) ratio (see Materials and Methods). C, Same as (B), but for stimulus site 160 µm from soma. D, NRLE values at proximal and distal sites were equivalent (∼3) under control conditions, and were reduced to equivalent values (<1) by NMDA channel blockers APV and MK-801. Bars indicate mean ±SD. E, Model responses at soma to increasing stimulus intensity (# of synapses) at 70 µm. F, Same as (E) but for stimulus at 160 µm. G, As in the experimental data, model NRLE values under control and NMDA block conditions were nearly constant along the proximal-distal axis. Error bars indicate SD across four different dendritic branches in the model, highlighted in the inset in (E). H, Red data are same as in (G). When the NMDA-AMPA ratio is made uniformly higher or lower over the length of the dendrite (magenta and cyan dashed lines, respectively), the NRLE measure roughly follows suit (magenta and cyan points). Similarly, if the NMDA-AMPA ratio increases or decreases linearly along the length of the dendrite (diagonal green and blue dashed lines, respectively), the NRLE ratio also varies roughly linearly (green and blue points).