24(S)-Hydroxycholesterol (24S-OHC), the major brain cholesterol metabolite, plays an important role to maintain homeostasis of cholesterol in the brain. 24(S)-Hydroxycholesterol (24S-OHC) is one of the most efficient endogenous LXR agonist known and is present in the brain and in the circulation at relatively high levels. 24(S)-Hydroxycholesterol (24S-OHC) is a very potent, direct, and selective positive allosteric modulator of NMDARs with a mechanism that does not overlapthat of other allosteric modulators.