Fig. 2. Effect of extinction training on conditioning-induced Akt phosphorylation. A, Behavioral procedure used in experiment B. B, Time course of PI-3 kinase activation in paired as opposed to those of unpaired and naive rats. Shown are the representative blots and mean ± SE ratios of P-Akt/Akt immunoreactivities from rats decapitated at 30, 60, 90, 120, 150, and 180 min (n = 6 rats in each time point) after pretests. The −10 min time point represents the level of Akt phosphorylation 24 hr after training but before test, whereas the 0 min time point is the value taken from naive rats. *p< 0.01 versus unpaired control. C, Behavioral procedure used in experiment D. D, Rats received fear training in a paired or unpaired manner and were tested 24 hr later (pretest). Shown are the representative blots and mean ± SE percentage of P-Akt immunoreactivities from unpaired (lane 1) and paired (lane 2) rats decapitated at 60 min after pretest. Ten minutes after pretest, paired rats were given light-alone trials (lane 3) or exposed to the context (lane 4), and the amygdala was removed for biochemical assay. The degree of Akt phosphorylation was significantly reduced in the light-alone group. Bilateral infusion of FK-506 (10 μg dissolved in 1.6 μl of DMSO, 0.8 μl per side) before light-alone trials blocked dephosphorylation (lane 5). *p < 0.01 versus pretest.