Figure 4.

D-aspartate and NMDA shift the kainate concentration–response curve to the right. (a) Superimposed current recordings obtained from the same isolated hippocampal neurons in response to different concentrations of kainate (KA, 30, 100, 300, 1000 and 3000 μM, open bar). In the presence of MK801, NMDA (1 mM) partially blocked kainate-induced current. (b) Kainate concentration–response curve in the control conditions (filled circles) and in the presence of NMDA (1 μM, open circles). The estimated EC₅₀ was significantly increased (control 0.17±0.02 mM vs in the presence of NMDA 0.26±0.01 mM, n=7, P<0.001). The estimated maximum currents were not changed. (c) Kainate concentration–response curves in the control conditions and in the presence of different concentrations of D-aspartate. Data were normalized to the maximum control kainate-induced current. The estimated maximum kainate-induced currents in the presence of different concentrations of D-aspartate were not different from those obtained from their corresponding maximum control kainate current in control conditions. (d) A Schild plot was constructed to show the antagonist action of D-aspartate on kainate-induced current was concentration dependent. Linear regression line (r²=0.997) was shown with a slope of 1.01±0.04 and an X-intercept at −3.03, giving K_b=0.93 mM for D-aspartate. Dose ratio r=(EC₅₀ in D-asp)/(EC₅₀ control).