Fig. 4: Robust LTP was induced by simultaneous activation of pCA1-dSUB inputs and MEC^CCK-SUB projections.

A Viral injections were delivered to the pCA1 and MEC area of CCK Cre mice (pCA1: 6.50 E + 12 vg/ml, 200 nl; MEC: 6.15E + 12 vg/ml, 300 nl in each of two sites). B Viral expression in the pCA1 and MEC area. Green: Chronos-GFP expressed in MEC-dSUB projections. Red: ChrimsonR-Td protein expressed in the pCA1 neurons and their pCA1-dSUB projections (scale bar, 1,000 µm). C Viral expression in the pCA1area (1, scale bar: 100 µm); A magnified view of the square area (2; scale bar, 100 μm). D Two color - light for activation of both pCA1-dSUB projections and MEC^CCK-dSUB projections in the dSub area of the CCK-Cre mice. E Laser power determination of 473 nm and 635 nm to prevent cross-talk between the Chronos and ChrimsonR. Slices with either ChrimsonR expressing pCA1 area or Chronos expressing MEC area were prepared. 473 nm and 635 nm laser were both applied to stimulate their projections in the dSub area, and their corresponding L-fEPSPs were recorded. To minimize the non-specific activation, the maximum power of the 473 nm laser was controlled under 3.70 mW (arrow). F Two color L-TBS for simultaneous activation of pCA1-dSUB projections and MEC^CCK-dSUB projections. G Normalized slopes of L-fEPSPs of pCA1-dSUB projections responding to 635 nm light stimulation before and after two color L-TBS (Red dots). Normalized slopes of L-fEPSP of MEC-dSUB projections responding to 473 nm light stimulation before and after two color L-TBS (Green triangle). Normalized slopes of L-fEPSP of pCA1-dSUB projections responding to 635 nm light stimulation before and after two color L-TBS with perfusion of APV (Red dots); N = 5 animals, n = 10 recording sites in three groups. Scale, 0.2 mV by 20 msec. H Comparison of L-fEPSPs before and after different manipulations. *p < 0.05, **p < 0.01, ***p < 0.001; ns not significant. Data are reported as mean ± SEM.