Figure 2.

PKA, RNA synthesis, and protein synthesis in IL are necessary for extinction learning. A, Before extinction, rats were infused (arrow) with either the PKA inhibitor Rp-cAMPS (n = 11) or saline (n = 11). Rats infused with Rp-cAMPS into IL showed decreased expression of freezing during extinction training, but could not recall extinction on day 3. Rp-cAMPS-infused rats matched for similar levels of freezing to saline-infused rats at the start of extinction training still showed significantly impaired extinction recall on day 3 (see inset). B, Rats were infused with either the RNA synthesis inhibitor actinomycin D (n = 16), the protein synthesis inhibitor anisomycin (n = 9), or saline (n = 15) before extinction. Rats infused with actinomycin or anisomycin showed normal within-session extinction, but deficient recall of extinction on day 3. C, Summary of infusion findings showing that fear extinction is mediated by noradrenergic β-receptor signaling initiated early in extinction. Percent freezing is shown for the first two trials on day 3. *p < 0.05, ***p < 0.001 compared with saline. Error bars indicate SEM.