Amygdala NMDAR neuronal signaling and metaplasticity in C57BL/6J and DBA/2J. A, B, Measurement of temporal summation of NMDAR EPSCs evoked by 10 Hz local stimulation showed that stress significantly increased amplitudes in DBA/2J (A) but not C57BL/6J (B). C, D, NMDAR-EPSC amplitudes evoked by 20 Hz stimulation were significantly increased by stress in DBA/2J (C), but not C57BL/6J (D). E, F, Stress did not alter amplitudes evoked by 40 Hz stimulation in either strain probably because of saturation. Under nonstressed conditions, amplitude was significantly lower in DBA/2J than C57BL/6J after 10 Hz (pulses 5–10) and 20 Hz (pulses 8–10), but not 40 Hz. Data are expressed as mean ± SEM. Representative traces for each stimulation frequency are depicted (insets) Scale bars, 250 ms. *p < 0.05 versus the same pulse number in nonstressed DBA/2J; ^#p < 0.05 versus nonstressed C57BL/6J at the same pulse number.