BDNF and Anxiety: It has been found that BDNF could be up- regulated by a lentivirus-based silencing RNA system using short hairpin RNA (shRNA)-hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1), which reduced the expression of HCN1 protein, increased the neuronal excitability, and produced anxiety- and depressive-like behavior (12).