NPPA and Anxiety: The neurobiological mechanisms underpinning the effect of physical activity on anxiety are not yet fully elucidated, but potentially involve modulating activity of 5-HT neurons in the dorsal ralph nucleus (DRN), modulation of the autonomic nervous system (ANS) and regulation of various neuroactive agents, including brain derived neurotrophic factor [108] and beta-endorphins [109], and atrial natriuretic peptide [110].