BENZODIAZEPINE BINDING VARIES WITH STAGE OF ESTROUS-CYCLE IN UNWASHEDMEMBRANES FROM MOUSE-BRAIN

The influence of the stage of the estrous cycle on binding of [H-3]dia zepam was examined in membranes from brains of female mice. In order t o conserve endogenous factors such as progesterone, other steroids, or GABA, the assay was performed without the extensive washing procedure s typically employed in measurements of benzodiazepine binding. Signif icant variations in the apparent maximal numbers of binding sites (B-m ax) were noted during the estrous cycle in both hypothalamus and corte x. The B-max measured in membranes from proestrus female mice was sign ificantly higher than in membranes from mice at other stages in the es trous cycle. Variations in apparent equilibrium binding dissociation c onstants (K-d) were not statistically significant by stage of the estr ous cycle. The demonstrated variations in binding suggest the existenc e of a factor which varies with the estrous cycle in female mice and m odulates the activity of the GABA(A) receptor complex.