FOS and Anxiety: For example, administration of Lactobacillus rhamnosus was effective in decreasing both depressive- and anxiety-like phenotypes in mice, an effect that was mediated by an increased firing rate of VN terminals.11 Similarly, supplementation with Campylobacter jejuni increased VN c-Fos expression in the vagal ganglia, leading to activation of neurons in the solitary nucleus of the brainstem.30 Additionally, another study showed that C. jejuni treatment in mice promoted anxiety-related behavior.31 The interactions between the vagus nerve, the gut epithelium and the ENS are summarized in Figure 2.