[ 3 H] Diazepam Displacing Activity in Human Cerebrospinal Fluid

Pooled human cerebrospinal fluid was separated by Sephadex G‐50 chromatography. The presence of three peaks, A, B and C, was demonstrated by monitoring absorbance at 254 and 280 nm. All peaks showed [ 3 H]diazepam displacing activity in the membrane receptor test. Peak B was further separated on Bio‐Gel P‐4. At least two major fractions free of salt and GABA in the molecular weight range of approximately 700‐3600 were shown to displace [ 3 H]diazepam in the receptor test. This activity was enhanced by a factor of 3 in the presence of 10 μ m ‐GABA.