Integrins mediate cell adhesion to the extracellular matrix and initiate intracellular signaling. They play key roles in the central nervous system (CNS), participating in synaptogenesis, synaptic transmission and memory formation, but their precise mechanism of action remains unknown. Here we show that the integrin ligand-mimetic peptide GRGDSP induced NMDA receptor-dependent increases in intracellular calcium levels within seconds of presentation to primary cortical neurons. These were followed by transient activation and nuclear translocation of the ERK1/2 mitogen-activated protein kinase. RGD-induced effects were reduced by the NMDA receptor antagonist MK801, and ERK1/2 signaling was specifically inhibited by ifenprodil and PP2, indicating a functional connection between integrins, Src and NR2B-containing NMDA receptors. GRGDSP peptides were not significantly neuroprotective against excitotoxic insults. These results demonstrate a previously undescribed, extremely rapid effect of RGD peptide binding to integrins on cortical neurons that implies a close, functionally relevant connection between adhesion receptors and synaptic transmission.