The use of intranasal insulin to correct the neurodegenerative disorders and in experimental T2DM [117,119,120,122,124]; the use of BBB-penetrating analogs of leptin in experimental obesity and T2DM [185,206,207]; the use of SSRI and intranasal 5-HT to treat diabetic patients and in experimental conditions [34,258–262]. This evidence concerns the gene LEP and type 2 diabetes mellitus.