NGF and major depressive disorder: Based on the comorbidity of diabetes, depression, and dementia and recognizingthat a deficiency of the nerve growth factor (NGF) is involved in all of thesekinds of pathologies, we studied the effect of the mimetic of dimeric dipeptideNGF loop 4, GK-2, on a model of streptozotocin-induced type 2 diabetes inC57Bl/6 mice.