PKA activation is required for metaplasticity of LTP induced by β-AR stimulation. (A) One train of 100-Hz stimulation (1 sec) did not elicit robust long-lasting potentiation in area CA1 (white symbols, n = 8). In contrast, application of Iso (a β-AR agonist), followed by 100-Hz given 30 min after washout of Iso, induced stable, robust LTP (dark gray symbols, n = 6) that lasted for at least 110 min after induction by 100-Hz. (B) KT5720, a PKA inhibitor, blocked stabilization of LTP when applied during the priming Iso stimulus (n = 6). LTP induced by 100-Hz given 30 min after washout of Iso decayed to pre-100-Hz baseline within 100 min after 100-Hz stimulation. (C) Histogram showing mean fEPSP slopes measured at 100-min post-100-Hz. * represents different P values: P < 0.01 for 100-Hz versus Iso + 100-Hz; P < 0.05 for Iso + 100-Hz versus KT group (light gray bar). Sample fEPSP traces were obtained at time points marked “A” and “B” on x-axes of graphs.
