Fig. 3.

I_pe-mediated Ca²⁺ and Na⁺ influx leads to the death of NMDA-exposed neurons. A–D,I_pe was triggered by NMDA application (10 min, 100 μm). A, Response ofI_pe to simultaneous removal of Ca²⁺_o and reduction of [Na⁺]_o for the postexposure phase (started 1 min postexposure). B, Response ofI_pe to removal of Ca²⁺_o for the postexposure phase.C, NMDA exposure triggers a gradually developingI_pe in nonrecorded cells. Healthy pyramidal cells within a field were identified before NMDA exposure and randomly selected at different times postexposure for point recording. Zero time indicates beginning of postexposure phase. Each circlerepresents a point recording from a different cell in the dish.D, Percentage of survival of neurons in sister dishes with the same treatment as those applied to recorded cells. NMDA application and manipulation of extracellular ionic composition were performed by bath perfusion. Healthy neurons in two fields per dish were identified before treatment. To evaluate the percentage of neuronal death after different treatments, trypan blue staining was performed at 60 min postexposure. The five barsrepresent average survival values obtained from (left toright) the control group (not exposed to NMDA), the NMDA group (exposed to NMDA), the NMDA + 0 Ca²⁺ group (exposed to NMDA in the presence of zero Ca²⁺_o), the low-Na⁺ + 0 Ca²⁺ postexposure group (exposed to NMDA and then bathed in the 20 mm NaCl solution during postexposure), and the 0 Ca²⁺ postexposure group (exposed to NMDA and then bathed in zero-calcium solution during postexposure). Consistent with data obtained from recorded cells, postexposure removal of Ca²⁺_o reduced neuronal death caused by NMDA exposure (0 Ca²⁺ postexposure group vs NMDA group,p < 0.01). Postexposure reduction of [Na⁺]_o in addition to removing Ca²⁺_o provided additional protection (low-Na⁺ + 0 Ca²⁺ postexposure group vs 0 Ca²⁺ postexposure group, p < 0.01) and was not significantly different from control (p > 0.05). Error bars represent SD (n = 12 fields, 2 fields from each of 6 animals). Student’s two-tailed t test was used to obtainp values.