Figure 2.

Biophysical and electrophysiological properties of CA1 neurons. (a₁) Superimposed sample traces of excitatory postsynaptic currents, evoked by stimulation of Schaffer collateral fibers, in voltage-clamped CA1 pyramidal cells from control (black) and 8-wk enriched mice (gray). Cells were held at −100 mV (lower traces) and +40 mV (upper traces). Arrows demarcate time points for measurements of current amplitudes shown in a₂ and a₃. The lower arrow indicates peak non-NMDA current, while the upper arrow, placed 35 msec after the peak, is the estimate of NMDA current amplitude. (a₂) I-V plot for peak current and the current at 35 msec after the peak in enriched and control cells. (a₃) Scatter plot of peak non-NMDA (V_M = −100 mV) versus NMDA (V_M = +40 mV) currents elicited at various stimulus intensities in CA1 pyramidal neurons from control (open triangles, 32 cells from 13 mice) and enriched mice (open circles, 21 cells from six mice). (a₄) The average ratio (±SEM) of NMDA to non-NMDA current amplitudes was derived from the scatter plot in a₃ and showed no significant difference between cells from control (C) and enriched (E) mice. (b₁) Action potentials in pyramidal CA1 neurons evoked by a 1-sec pulse of intracellular current injection. (b₂) Plot of average instantaneous spike frequency (Hz) versus time after the start of a current pulse. No significant differences in these curves were observed for CA1 pyramidal neurons from control (solid line, n = 16 cells from 12 mice) and enriched slices (broken line, n = 19 cells from six mice; P > 0.2). Inset bar graph: histogram showing the mean spike frequency measured during the last 400 msec of a spike train, expressed as a percentage of the average spike frequency measured during the initial 50 msec of the spike train. No significant difference was observed between the two groups (C = control, E = enriched).