Fig. 5. Changes in intracellular calcium levels in cultured cortical neurons after bath application of N -methyl-d-aspartate (NMDA) in the absence or presence of propofol or okadaic acid (OA). The [Ca2+]ilevels were measured by somatic fura-2 ratio fluorescence. In the presence of propofol, NMDA induced a significantly less increase in [Ca2+]ilevels. Propofol (100 μm) was incubated 15 min before addition of NMDA (50 μm). The values are expressed as mean fold changes of basal levels in terms of the peak amplitude of Ca2+responses measured within 30 s after the start of NMDA treatment from 16–24 neurons. * P < 0.05 versus basal levels. + P < 0.05 versus NMDA given in the absence of propofol. # P < 0.05 versus NMDA given in the presence of propofol .