BDNF and diabetes mellitus: b) Down-regulation of receptors of neurotrophins: Neurotrophins bind to two classes of receptors: tyrosine receptor kinases or trks (trk A, trk B, trk C) and a low-affinity receptor, “p75.” It was reported that the expression of p75NTR was decreased in DRG of STZ-induced diabetic rats compared with those of control rats,[42] whereas that of trk A was unchanged.[42] No increase in plasma p75NTR IR was observed after 4 weeks of diabetes, but significant increases were present at 10 and 12 weeks of diabetes.