text: DREAM/calsenilin/KChIP3 modulates strategy selection and estradiol-dependent learning and memory.
  Downstream regulatory element antagonist modulator (DREAM)/calsenilin(C)/K⁺ channel interacting protein 3 (KChIP3) is a multifunctional Ca²⁺-binding protein highly expressed in the hippocampus that inhibits hippocampus-sensitive memory and synaptic plasticity in male mice. Initial studies in our lab suggested opposing effects of DR/C/K3 expression in female mice. Fluctuating hormones that occur during the estrous cycle may affect these results. In this study, we hypothesized that DR/C/K3 interacts with 17β-estradiol, the primary estrogen produced by the ovaries, to play a role in hippocampus function. We investigated the role of estradiol and DR/C/K3 in learning strategy in ovariectomized (OVX) female mice. OVX WT and DR/C/K3 knockout (KO) mice were given three injections of vehicle (sesame oil) or 17β-estradiol benzoate (0.25 mg in 100 mL sesame oil) 48, 24, and 2 h before training and testing. DR/C/K3 and estradiol had a time-dependent effect on strategy use in the female mice. Male KO mice exhibited enhanced place strategy relative to WT 24 h after pre-exposure. Fear memory formation was significantly reduced in intact female KO mice relative to intact WT mice, and OVX reduced fear memory formation in the WT, but had no effect in the KO mice. Long-term potentiation in hippocampus slices from female mice was enhanced by circulating ovarian hormones in both WT and DR/C/K3 KO mice. Paired-pulse depression was not affected by ovarian hormones but was reduced in DR/C/K3 KO mice. These results provide the first evidence that DR/C/K3 plays a timing-dependent role in estradiol regulation of learning, memory, and plasticity.