Figure 2.

The input/output transfer function of DG cells is controlled by I_D. (A,B) Action potential (AP) output evaluated by number (A) and initial frequency (B) was evoked by somatic DC input in DG cells from naïve mice (Naï, circles) and KA-injected mice (KA, triangles) under control (CTRL) conditions and after DTX application (green symbols). The input/output (I/O) curve was shifted to higher input values in KA vs. Naï cells [(A), left panel, compare orange triangles with blue circles, respectively]. Application of DTX reduced this difference [(A,B), right panels, compare green triangles with green circles, respectively], although with higher input, the AP frequency did not reach naïve levels. (C) To test the effect of increased DTX-sensitive conductance on dendritic signal integration, the above changes in I/O curves were additionally verified with extracellular perforant path stimulation (5 pulses at 100 Hz, arrows in left panel) evoking excitatory postsynaptic synaptic potentials (EPSPs) in KA cells of which the first was measured as input (no such additional verification was performed in naïve cells). Synaptic input triggered no more than one AP at the end of five summating EPSPs in CTRL conditions (upper trace and orange triangles, respectively; scale bars, 20 mV, 50 ms). However, application of DTX shifted the I/O curve to lower input values and allows multiple APs to occur (lower trace, green triangles). (D–F) Application of DTX increased the AP width (D) and 1st AP precision (E,F) of the AP response to DC steps in Naï and KA DG cells. The AP jitter evaluated as SD of first spike (see Results for CV). Scale bars in (D), 10 mV, 1 ms; (E) 10 mV, 2 ms.