Figure 4. NMDA spike initiation with LOT and IC inputs.

(a) Pyramidal neuron was loaded with the fluorescent dye CF-633 (200 µm) via the somatic patch recording electrode. Glutamate (MNI-glutamate) was uncaged at three sites as indicated by red circles (346 µM, 245 µM and 157 µm from soma). Bellow, is somatic action potential firing patter in response to somatic step current injection (500 ms). (b) Somatic voltage responses evoked by increasing laser intensity at the dendritic locations indicated in A, in Control (left, red) and with the blocker APV (right, black). (c) Summary plot of dendritic spike peak amplitudes as recorded at the soma, as a function of distance from the soma (n = 11). (d) Reconstruction of a pyramidal neuron showing a focal stimulation electrode at a distal LOT receiving zone (244 µm from soma). Bellow, is somatic action potential firing patter in response to somatic step current injection (500 ms). (e) NMDA spike in Control (red), after sequential addition of Baclofen (100 µM; blue) and APV (50 µM; black). Bottom, plot of peak voltage response as a function of stimulus intensity for Control (red), in the presence of baclofen (blue) and sequential addition of APV (black). (f) Reconstruction of a pyramidal neuron showing focal stimulating electrode at a proximal IC dendritic receiving zone (148 µm from soma). Bellow, is somatic action potential firing patter in response to somatic step current injection (500 ms). (g) NMDA spike in Control (red), after sequential addition of Baclofen (100 µM; blue) and APV (50 µM; black). Bottom, plot of peak voltage response as a function of stimulus intensity for Control (red), in the presence of baclofen (blue) and sequential addition of APV (black). (h) Summary plot of mean percent reduction in voltage amplitude measured at NMDA spike threshold in control conditions (mean % reduction peak voltage ± SEM) in the presence of baclofen and APV, for distal (n = 7), middle (n = 6) and proximal (n = 6) spike locations. *p < 0.05; **p < 0.01.