Research has demonstrated that the simultaneous knockdown of Period 1 (Per1) and Period 2 (Per2) rhythm genes in the nucleus accumbens increases anxiety‐like responses in mice.[11] However, it remains unclear whether Per gene expression is aberrant in peripheral tissues and organs during the development of depression induced by CRD, and what role it plays in the pathogenesis of depression. The gene discussed is PER2; the disease is major depressive disorder.