A, schematic of the experimental protocol. Cultures were treated with NMDA for 3 min, returned to the incubator for 27 min, and then treated with forskolin (forsk) to activate PKA. B, representative immunoblot for surface GluR1 showing that forskolin reverses the NMDA-induced loss of surface GluR1. C, NMDA reduces surface GluR1 to 48 ± 7% controls. Forskolin significantly reverses this effect (83 ± 8%; n = 8; *, p < 0.05 versus NMDA alone, Student's t test). D, blocking PKA activity with Rp-cAMPS (Rp) causes a reduction in surface GluR1. E, Rp-cAMPs significantly reduces surface GluR1 to 82 ± 6% control levels. (n = 6; *, p < 0.05 versus control, Student's t test).