FOS and Anxiety: Given that the activation of excitatory neurons in the BNST (BNSTEXT neurons) promotes anxiety-like behaviors (Kim et al., 2013; Ch'ng et al., 2018; Kim and Kim, 2021), and that the increase in c-Fos expression was the most significant in the BNST after formalin injection (Figures 2B,C), we hypothesized that the activation of BNSTEXT neurons is responsible for acute pain-induced anxiety-like behaviors.