FOS and Anxiety: Our results revealed an increased percentage of c-Fos+ + FG+ cells (calculated as c-Fos+FG+ double-labeled cells/total FG positive cells) in the BLA of Mor-A mice compared with the saline control mice (p = 0.0020, Figure 2E), verifying that the BLA to vHip projections were involved in the process of anxiety-like behaviors following morphine withdrawal.