BDNF and type 2 diabetes mellitus: New evidence indicates that hippocampal neurogenesis and neuronal density elevation, blood–brain barrier (BBB) permeability reduction, and gene expression modulation (an elevation in the expression of genes that belong to the synaptic modulation and signal transduction categories, such as BDNF, Orexin-1, and claudin-5) are likely involved in the promotion of brain abilities in response to exercise training in type 2 diabetic patients [55–58].