Deficits in Seizure Threshold and Other Behaviors in Adult Mice without Gross Neuroanatomic Injury after Late Gestation Transient Prenatal Hypoxia

Abstract

Intrauterine hypoxia is a common cause of brain injury in children resulting in a broad spectrum of long-term neurodevelopmental sequela, including life-long disabilities that can occur even in the absence of severe neuroanatomic damage. Postnatal hypoxia-ischemia rodent models are commonly used to understand the effects of ischemia and transient hypoxia on the developing brain. Postnatal models, however, have some limitations. First, they do not test the impact of placental pathologies on outcomes from hypoxia. Second, they primarily recapitulate severe injury because they provoke substantial cell death, which is not seen in children with mild hypoxic injury. Lastly, they do not model preterm hypoxic injury. Prenatal models of hypoxia in mice may allow us to address some of these limitations to expand our understanding of developmental brain injury. The published rodent models of prenatal hypoxia employ multiple days of hypoxic exposure or complicated surgical procedures, making these models challenging to perform consistently in mice. Furthermore, large animal models suggest that transient prenatal hypoxia without ischemia is sufficient to lead to significant functional impairment to the developing brain. However, these large animal studies are resource-intensive and not readily amenable to mechanistic molecular studies. Therefore, here we characterized the effect of late gestation (embryonic day 17.5) transient prenatal hypoxia (5% inspired oxygen) on long-term anatomical and neurodevelopmental outcomes in mice. Late gestation transient prenatal hypoxia increased hypoxia-inducible factor 1 alpha protein levels (a marker of hypoxic exposure) in the fetal brain. Hypoxia exposure predisposed animals to decreased weight at postnatal day 2, which normalized by day 8. However, hypoxia did not affect gestational age at birth, litter size at birth, or pup survival. No differences in fetal brain cell death or long-term gray or white matter changes resulted from hypoxia. Animals exposed to prenatal hypoxia did have several long-term functional consequences, including sex-dichotomous changes. Hypoxia exposure was associated with a decreased seizure threshold and abnormalities in hindlimb strength and repetitive behaviors in males and females. Males exposed to hypoxia had increased anxiety-related deficits, whereas females had deficits in social interaction. Neither sex developed any motor or visual learning deficits. This study demonstrates that late gestation transient prenatal hypoxia in mice is a simple, clinically relevant paradigm for studying putative environmental and genetic modulators of the long-term effects of hypoxia on the developing brain.

Intrauterine inflammation leads to some sex and age-specific behavior and molecular differences in mice

“…Our data, obtained using the OF test, revealed that exposure to prenatal inflammation caused increased anxiety in LPS-exposed mature (P68), but not pre-adolescent (P27), male pups, while female pups from both age groups remained unaffected. An increase in anxiety levels in LPS-exposed male pups detected in our study is consistent with previously published data which were obtained using both systemic immune activation [51-59], intrauterine exposure to infectious agents or their ligands [21, 60], and prenatal hypoxia [35]. For instance, using the OF test, Dada and co-authors showed that mouse offspring that received intrauterine LPS injections at E17 had elevated anxiety levels at P60, although a sex-specific effects were not tested [60].…”

“…Statistics were performed as described previously using R-studio [35]. Briefly, we used mixed models with generalized estimating equations in the geepack package in R with cohort as the random effect [36].…”

Sex and age differences in social and cognitive function in offspring exposed to late gestational hypoxia

“…However, there were differences between these prior studies and our current study, in which sustained hypoxia impaired cognitive function in young adult female offspring [114], decreased repetitive behaviors in young adult male offspring [76,111], and increased anxiety-like behaviors in young adult male offspring [76,111], indicating that the type of hypoxic exposure during this critical period of brain development is important.…”

“…have found equivocal ndings that range from social impairments in male offspring with no effects in female offspring [109,110] to social impairments in female offspring with no effects in male offspring [76,111] or social impairments in both sexes [112]. Reports of sex differences in cognition due to gestational hypoxia have been observed, with impairment observed in male offspring [109,113], female offspring [114], or neither sex [76,112,115].…”

“…Although no other study has used gestational intermittent hypoxia exposure targeting brain development stage 3, prior studies using a sustained hypoxia protocol during this time have been conducted (Supplemental Table 4). Speci cally, sustained hypoxia during this time period (GD 15-22) impaired social behaviors displayed by young adult female offspring and not young adult male offspring [76, 111], had no impact on anxiety-like behaviors in young adult male and female offspring [76,116], and decreased repetitive behaviors in young adult female offspring [111].…”