BDNF and major depressive disorder: Interestingly, we have recently shown that the expression of Bdnf, a neurotrophin involved in psychiatric disorders, is significantly downregulated in PNS rats only after adolescence,39 thus supporting the idea that exposure to ELS may influence life-long genome adaptation thus resulting in behavioral disorders, such as bipolar disorder, depression and schizophrenia, that frequently become manifest during adolescence.13, 70, 71, 72