Fig. 1.

NMDAR overstimulation evokes persistent elevation of [Ca²⁺]_i in hippocampal neurons. A, Time course of changes in [Ca²⁺]_i of a neuron in response to K⁺-induced membrane depolarization (35 mm KCl, 30 sec, K⁺), followed by 20 min exposure to 200 μm NMDA. Values are plotted as relative pixel fluorescence intensity (F) normalized to baseline fluorescence values (F₀); upward deflection denotes an increase in [Ca²⁺]_i. Horizontal bars(gray background) indicate duration of treatment.Numbers indicate critical points in the Ca²⁺signal and code panels 1 to 7 that are pseudocolor digital images of Fluo-3 fluorescence (Kao et al., 1989).Pseudocolor scale represents arbitrary fluorescence intensity values ranging from 0 to 255. The KCl control stimulus elicits a rapid and reversible increase of [Ca²⁺]_i (2). NMDA evokes a fast elevation of