Estradiol- and Progesterone-Associated Changes in microRNA-Induced Silencing and Reduced Antiseizure Efficacy of an Antagomir in Female Mice.

About one-third of individuals living with epilepsy have treatment-resistant seizures. Alternative therapeutic strategies are thus urgently needed. One potential novel treatment target is miRNA-induced silencing, which is differentially regulated in epilepsy. Inhibitors (antagomirs) of specific microRNAs (miRNAs) have shown therapeutic promise in preclinical epilepsy studies; however, these studies were mainly conducted in male rodent models, and research into miRNA regulation in females and by female hormones in epilepsy is scarce. This is problematic because female sex and the menstrual cycle can affect the disease course of epilepsy and may, therefore, also alter the efficacy of potential miRNA-targeted treatments. Here, we used the proconvulsant miRNA miR-324-5p and its target, the potassium channel Kv4.2, as an example to test how miRNA-induced silencing and the efficacy of antagomirs in epilepsy are altered in female mice. We showed that Kv4.2 protein is reduced after seizures in female mice similar to male mice; however, in contrast to male mice, miRNA-induced silencing of Kv4.2 is unchanged, and miR-324-5p activity, as measured by the association with the RNA-induced silencing complex, is reduced in females after seizure. Moreover, an miR-324-5p antagomir does not consistently reduce seizure frequency or increase Kv4.2 in female mice. As a possible underlying mechanism, we found that miR-324-5p activity and the silencing of Kv4.2 in the brain were differentially correlated with plasma levels of 17ß-estradiol and progesterone. Our results suggest that hormonal fluctuations in sexually mature female mice influence miRNA-induced silencing and could alter the efficacy of potential future miRNA-based treatments for epilepsy in females.

When can embryos learn? A test of the timing of learning in embryonic amphibians.

Learning is crucial to the survival of organisms across their life span, including during embryonic development. We set out to determine when learning becomes possible in amphibian development by exposing spotted salamander (Ambystoma maculatum) embryos to chemical stimuli from a predator (Ambystoma opacum), nonpredator (Lithobates clamitans), or control at developmental stages 16-21 or 36-38 (Harrison 1969). Once exposures were completed and embryos hatched, we recorded the number of movements and time spent moving of individuals in both groups and all treatments. There was no significant difference in number of movements or time spent moving among any of the treatments. The groups that were exposed to predator stimuli and a blank control at stages 36-38 were also tested to determine whether there was a difference in refuge preference or difference in survivorship when exposed to a predator (marbled salamander). There was no difference in survival or refuge preference between individuals; however, all individuals preferred vegetated over open areas regardless of treatment type. We discuss hypotheses for the absence of embryonic learning in this species and suggest it may be the result of the intensity of the predator-prey interaction between the predator, large marbled salamander larvae, and the prey, spotted salamander larvae.