5a,6B-Dihydroxycholestanol-d7 is intended for use as an internal standard for the quantification of 5a,6B-dihydroxycholestanol (Item No. 25538) by GC- or LC-MS. 5a,6B-Dihydroxycholestanol is an oxysterol metabolite of cholesterol formed from conversion of cholesterol epoxides by 5,6-epoxysterol hydrolase.{41987,41988} It inhibits NMDA-mediated calcium influx in HEK293 cells expressing NR1/NR2B NMDA receptors in a concentration-dependent manner. It also binds to voltage-gated sodium (Nav) channels and decreases action potentials in hippocampal neurons in vitro when used at a concentration of 10 µM.{41988} It increases survival of spinal cord motoneurons, cortical neurons, and cerebellar granule neurons in vitro when used at concentrations ranging from 5 to 15 µM.{41989} 5a,6B-Dihydroxycholestanol is neuroprotective in a rat model of cerebral ischemia when administered at a dose of 12 mg/kg and increases latency to seizure onset and reduces severity of seizures induced by pentylenetetrazole (PTZ; Item No. 18682) in rats. 5a,6B-Dihydroxycholestanol has been used as a replacement for cholesterol in the study of cholesterol binding proteins.{41990}