A cytochrome P450 monooxygenase involved in neural cholesterol clearance through bile acid synthesis. Catalyzes 7-alpha hydroxylation of (24S)-hydroxycholesterol, a neural oxysterol that is metabolized to bile acids in the liver (PubMed:10748047). Mechanistically, uses molecular oxygen inserting one oxygen atom into a substrate, and reducing the second into a water molecule, with two electrons provided by NADPH via cytochrome P450 reductase (CPR; NADPH-ferrihemoprotein reductase) (PubMed:10748047). (24S)-hydroxycholesterol + O2 + reduced [NADPH--hemoprotein reductase] = (24S)-7alpha-dihydroxycholesterol + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Steroid metabolism; cholesterol degradation. Lipid metabolism; bile acid biosynthesis. Liver specific. Hepatic expression is sexually dimorphic (female > male). Belongs to the cytochrome P450 family.