Figure 4. Feedback inhibition appears normal in GD17-MAM rats.

A) The dentate gyrus is a complex circuit with both feedforward and feedback inhibition. Responses of control and GD17-MAM rats to pairs of pulses are shown at various inter-stimulus intervals (ISI). The response to the first stimulus is shown in black and the response to the second stimulus is shown in blue or red. The lighter lines are voltage responses and the darker responses are CSD, i.e. after correction for volume conduction. Calibration is the same for both control and GD17-MAM. There are no group differences in ratios of the second second response to the first response for B) population spiking activity (Group: F_1,7 = 0.26, p = 0.63; ISI: F_7,1 = 2.98×10⁴, p < 0.01; Interaction: F_7,1 = 9.20×10³, p = 0.03). Post hoc analyses indicated no group differences at any inter stimulus interval. Additionally, there are no group differences in fEPSP measured at C) the granule cell layer (Group: F_1,7 = 1.71, p = 0.23; Inter stimulus interval: F_7,1 = 2238.25, p = 0.02; Interaction: F_7,1 = 22.23, p = 0.16) and D) the molecular layer (Group: F_1,7 = 1.76, p = 0.23; ISI: F_7,1 = 228.14, p = 0.05; Interaction: F_7,1 = 4.86, p = 0.34). There are two phases to the inhibition, an early strong inhibition that occurs until 20 ms, and a persistent inhibition that lasts up to 0.5 s, as seen by the fact that the response ratios do not recover to 1. Values are average ± SEM. Calibration is the same for B, C and D. For B and C: Control n = 5, GD17-MAM n = 5. For D: Control n = 4, GD17-MAM n = 5. mol = molecular layer of DG, grc = granule cell layer of DG.