N-methyl D-aspartate receptor-mediated bidirectional control of extracellular signal-regulated kinase activity in cortical neuronal cultures

N-Methyl D-aspartate (NMDA) receptor activation of extracellular-signal reg ulated kinase (ERK) was examined in primary cortical cultures. Tetrodotoxin , NMDA receptor antagonists, or reduced extracellular calcium (0.1 mM) grea tly decreased basal levels of phospho-ERK2, indicating that activity-depend ent activation of NMDA receptors maintained a high level of basal ERK2 acti vation. This activity-dependent activation of phospho-ERK2 was blocked by p ertussis toxin and inhibition of calcium/calmodulin-dependent kinase II and phosphatidylinositol 3-kinase but not by inhibition of protein kinase C or cAMP-dependent protein kinase, Addition of a calcium ionophore or 100 muM NMDA decreased phospho-ERK2 in the presence of 1 mM extracellular calcium b ut enhanced phospho-ERK2 in 0.1 mM extracellular calcium. The reduction in basal phospho-ERK2 by 100 muM NMDA was also reflected as a decrease in phos pho-cAMP response element-binding protein, Inhibition of tyrosine phosphata ses and serine/threonine phosphatases protein phosphatase 1 (PP1), PP2A, an d PP2B did not prevent the inhibitory effect of NMDA. In the presence of te trodotoxin, NMDA produced a bell-shaped dose-response curve with stimulatio n of phospho-ERK2 at 10, 25, and 50 muM NMDA and reduced stimulation at 100 muM NMDA. NMDA (50 muM) stimulation of phospho-ERK2 was completely blocked by pertussis toxin and inhibitors of phosphatidylinositol 3-kinase and was partially blocked by a calcium/calmodulin-dependent kinase II inhibitor. T hese results suggests that NMDA receptors can bidirectionally control ERK s ignaling.