In the para-chloro-DL-phenylalanine (PCPA)-induced insomnia rat model, the expression level of the apoptosis-related B-cell lymphoma 2 gene (Bcl-2) is reduced, while the expression levels of BCL2-associated X protein (Bax), B-cell lymphoma 2 gene-associated promoter (Bad), and caspase-3 (Caspase-3) are significantly upregulated, leading to a marked increase in the extent of apoptosis [44, 45]. Here, CASP3 is linked to insomnia.