Differential effects of theta phase on CA3-CA3 and mPP-CA3 synaptic responses during initial exploration of a novel environment. Left, Mean percent change (±SEM) in cCA3-CA3 field EPSP slopes (dV/dt) compared with baseline synaptic responses collected in the home cage (defined as 100% response magnitude for each animal). A comparison of responses evoked during the initial exploration of a novel environment show cCA3-CA3 synaptic responses are reduced during CA3 theta peaks when compared with both baseline responses collected in the home cage (home), and responses evoked on local theta troughs (*p < 0.05, Tukey's test; n = 5). Right, Mean percent change (±SEM) in mPP-CA3 synaptic responses relative to baseline responses collected in the home cage (defined as 100% of response amplitude) during the initial exploration of a novel environment. mPP-CA3 synaptic responses are reduced during local CA3 theta troughs when compared with both baseline responses collected in the home cage (home) and responses evoked on CA3 theta peaks (*p < 0.05, Tukey's test; n = 5). Calibration: 0.5 mV, 5 ms.