Figure 4.

Radiate neurons receive weaker and slower evoked synaptic inputs than planar neurons. (A,B) Example eEPSCs of radiate neurons (red) with graded amplitudes driven by stimuli with progressively increased strength. Arrow: onset of electric stimulation. Notice in (B) that a fast eEPSC component was recruited beyond a certain stimulus strength that changed the shape of eEPSCs. Black traces in (B), an example slow eEPSC evoked by weak stimulation and a fast eEPSC evoked by strong stimulation. Inset: the two black traces were normalized to the peak amplitude to show the temporal differences in eEPSCs driven by stimuli at different strength. (C) Example eEPSCs of a planar neuron (blue) driven by stimuli with progressively increased strength. The increase in eEPSC amplitude occurred over a narrow stimulus range, and grew in a stepwise fashion. Note the scale differences in eEPSC amplitudes among (A–C). (D) Summary plot of eEPSC amplitudes vs. normalized stimulation amplitudes in radiate and planar neurons. Each line represents one individual neuron. Thick red lines mark the example radiate neurons in (A,B), and the thick blue line marks the example planar neuron in (C). The stimulation amplitude was normalized to the threshold stimulus current used in the individual neuron, which is 1.0 in the x-axis. (E) Example eEPSCs of a radiate and a planar neuron that were blocked by CNQX (cells held at −77 mV). (F) Comparison of the time course of eEPSCs (normalized to peak) from example radiate and planar neurons. (G–I) Summary of the eEPSC amplitude (G), 10%–90% rise time (H), and 37% decay time (I). ***p < 0.001.