For example, hydrogen sulfide, an antidepressant-like compound for diabetic rats, could improve the depression-like behavior of rats by enhancing hippocampal autophagy through BDNF-TrkB pathway [46], but the similar improvement was explained by opposite mechanism in another research, in which the upregulating BDNF-TrkB pathway was along with the decreasing autophagy in hippocampus [47]. This evidence concerns the gene NTRK2 and major depressive disorder.