BDNF has been found to promote neuronal survival and differentiation and to guide axon extension both in vitro and in vivo. (17) Evidence suggests that BDNF may act as a stress-responsive intercellular messenger modifying HPA axis activity. (17) Short-term acute stress induces a significant increase in BDNF mRNA and protein in both younger and older groups but changes in the younger group are substantially greater. (18) BDNF has interactions with both inflammation and pain. BDNF knock out mice show a weaker visceral response to colorectal distention. (19) A human study compared 40 adults with IBS to 21 healthy controls. (20) Biopsies from patients with IBS revealed significant upregulation of BDNF as compared to controls. (20)