Behavioral analysis of male and female Fmr1 knockout mice on C57BL/6 background

Abstract

Fragile X syndrome (FXS) is a monogenic disease caused by mutations in the FMR1 gene. The Fmr1 knockout (KO) mice show many aspects of FXS-related phenotypes, and have been used as a major pre-clinical model for FXS. Although FXS occurs in both male and female patients, most studies on the mouse model use male animals. Few studies test whether gender affects the face validity of the mouse model. Here, we examined multiple behavioral phenotypes with male hemizygous and female homozygous Fmr1 KO mice on C57BL/6 background. For each behavioral paradigm, we examined multiple cohorts from different litters. We found that both male and female Fmr1 KO mice displayed significant audiogenic seizures, hyperactivity in the open field test, deficits in passive avoidance and contextual fear memory, and significant enhancement of PPI at low stimulus intensity. Male and female Fmr1 KO mice also showed more transitional movement between the lit and dark chambers in the light-dark tests. The lack of gender effects suggests that the Fmr1 KO mouse is a reasonable tool to test the efficacy of potential FXS therapies.

Modeling fragile X syndrome in the <i>Fmr1</i> knockout mouse

“…A recent study revealed that individuals with FXS demonstrated less activation of the amygdala while viewing fearful faces than neurotypical subjects (165). Passive avoidance learning was not altered in Fmr1 KO mice in some studies (48,93,135,166) but was disrupted in others (90)(91)(92)129,167,168). Interestingly, passive avoidance extinction may occur more rapidly in Fmr1 KO mice (92,166), which is consistent with augmented extinction in Fmr1 KO mice in other assays (121).…”

“…Additionally, Fmr1 KO performance was disrupted by olfactory distracters, with mutant mice making more inaccurate responses during distracter presentations (122). A consistent behavioral finding in Fmr1 KO mice is their increased locomotor activity compared to wildtype controls in the open field test (48,52,89,90,(123)(124)(125)(126)(127)(128)(129)(130). It is important to note that the robust hyperactivity phenotype seen in Fmr1 KO mice could be a confounding factor for the assessment of sustained attention, given that the general activity of mutant mice may interfere with task engagement.…”

“…Seizures associated with FXS are infrequent, are often partial, and are typically controlled with medications (82,83). Fmr1 KO mice have not been reported to display spontaneous seizures, but are more susceptible to audiogenic seizures, induced by exposure to a 125 decibel, high-intensity siren (48,81,(84)(85)(86)(87)(88)(89)(90)(91)(92)(93). Audiogenic seizure vulnerability in Fmr1 KO mice may reflect seizure susceptibly in FXS, although audiogenic seizure severity in Fmr1 KO mice varied in degree depending on age and background strain (86,91,94,95).…”

“…Contextual and delaycued fear conditioning can be acquired during the same training session and assessed in independent settings to reveal hippocampus-dependent and hippocampusindependent memory effects, respectively. In amydgaladependent delay-cued fear conditioning, a deficit was reported in Fmr1 KO mice (75,90), but other studies did not observe this effect (173)(174)(175). In hippocampusdependent contextual fear conditioning, one report indicated a deficit (75) and another identified a contextdiscrimination deficit (176); other studies did not detect genotype differences in contextual fear conditioning in Fmr1 KO mice (52,173,175).…”

Deletion of Fmr1 results in sex‐specific changes in behavior

“…There is some evidence of a differential phenotype among the sexes, as male Fmr1 KOs exhibit a reduced anxiety phenotype, whereas females KOs show normal levels of anxiety (Qin, Kang, & Smith, 2005). However, previous studies show mainly similar deficits between male and female Fmr1 KOs on tests of activity levels, learning and memory (Baker et al., 2010; Ding, Sethna, & Wang, 2014), sensorimotor gating (Baker et al., 2010; Ding et al., 2014), and seizure susceptibility (Nguy & Tejada‐Simon, 2016; Qin et al., 2005) in adulthood. Recent experimental evidence has also shown that female Fmr1 KOs present normal fear learning and anxiety, but show impaired fear memory (Nguy & Tejada‐Simon, 2016).…”