Functional
dyspepsia (FD) is associated with chronic gastrointestinal distress and with anxiety and depression. Here, we hypothesized that aberrant gastric signals, transmitted by the vagus nerve, may alter key brain regions modulating affective and
pain behavior. Using a previously validated rat model of FD characterized by gastric
hypersensitivity, depression-like behavior, and anxiety-like behavior, we found that vagal activity - in response to gastric distention - was increased in FD rats. The FD phenotype was associated with gastric mast cell
hyperplasia and increased expression of
corticotrophin-releasing factor (Crh) and decreased
brain-derived neurotrophic factor genes in the central amygdala. Subdiaphragmatic
vagotomy reversed these changes and restored affective behavior to that of controls.
Vagotomy partially attenuated
pain responses to gastric distention, which may be mediated by central reflexes in the periaqueductal gray, as determined by local injection of
lidocaine.
Ketotifen, a
mast cell stabilizer, reduced vagal
hypersensitivity, normalized affective behavior, and attenuated gastric
hyperalgesia. In conclusion, vagal activity, partially driven by gastric mast cells, induces long-lasting changes in Crh signaling in the amygdala that may be responsible for enhanced
pain and enhanced anxiety- and depression-like behaviors. Together, these results support a "bottom-up" pathway involving the gut-brain axis in the pathogenesis of both gastric
pain and psychiatric comorbidity in FD.