TNF and major depressive disorder: Chronic stimulation of the innate immune response can lead to inflammation-mediated depression; however, pre-stimulation of the innate immune response has been effective in preventing depression-like phenotypes in rodent models, while 24 h pre-stress exposure to a single dose (20 mg/kg) of β-glucan prevented a chronic-stress-induced increase in TNF-α in the HPC and mPFC.