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

Abstract

Background: Gestational sleep apnea is a hypoxic sleep disorder that affects 8-26% of pregnancies and increases the risk for central nervous system dysfunction in offspring. Specifically, there are sex differences in the sensitivity of the fetal hippocampus to hypoxic insults, and hippocampal impairments are associated with social dysfunction, repetitive behaviors, anxiety, and cognitive impairment. Yet, it is unclear whether gestational sleep apnea impacts these hippocampal-associated functions and if sex and age modify these effects. To examine the relationship between gestational sleep apnea and hippocampal-associated behaviors, we used chronic intermittent hypoxia (CIH) to model late gestational sleep apnea in pregnant rats. We hypothesized that late gestational CIH would produce sex- and age-specific social, anxiety-like, repetitive, and cognitive impairments in offspring.

Methods: Timed pregnant Long-Evans rats were exposed to CIH or room air normoxia from GD 15-19. Behavioral testing of offspring occurred during either puberty or young adulthood. To examine gestational hypoxia-induced behavioral phenotypes, we quantified hippocampal-associated behaviors (social function, repetitive behaviors, anxiety-like behaviors, and spatial memory and learning), hippocampal neuronal activity (glutamatergic NMDA receptors, dopamine transporter, monoamine oxidase-A, early growth response protein 1, and doublecortin), and circulating hormones in offspring.

Results: Late gestational CIH induced sex- and age-specific differences in social, repetitive, and memory functions in offspring. In female pubertal offspring, CIH impaired social function, increased repetitive behaviors, and elevated circulating corticosterone levels but did not impact memory. In contrast, CIH transiently induced spatial memory dysfunction in pubertal male offspring but did not impact social or repetitive functions. Long-term effects of gestational CIH on social behaviors were only observed in female offspring, wherein CIH induced social disengagement and suppression of circulating corticosterone levels in young adulthood. No effects of gestational CIH were observed in anxiety-like behaviors, hippocampal neuronal activity, or circulating testosterone and estradiol levels, regardless of sex or age of offspring.

Conclusions: Our results indicate that hypoxia-associated pregnancy complications during late gestation can increase the risk for behavioral and physiological outcomes in offspring, such as social dysfunction, repetitive behaviors, and cognitive impairment, that are dependent on sex and age.

Keywords: Chronic intermittent hypoxia; Hippocampus; Marble burying behaviors; Morris water maze; Open field; Prenatal programming; Sex differences; Social behaviors.

Fig. 1

Social and exploratory behaviors. Gestational CIH decreased social behaviors in female rats during puberty (A) but not during young adulthood (B). No effect of gestational CIH was observed on male rats during puberty (A) or young adulthood (B). No effect of sex was observed on social behaviors (A, B). No effect of gestational CIH or sex was observed in exploratory behavior (C, D). Analyzed by Two-way ANOVA with Fisher’s LSD multiple comparisons tests. ANOVA significance indicated by: ** = CIH; Post-hoc significance indicated by: # versus normoxic female; p ≤ 0.05

Fig. 2

Social disengagement. No effect of gestational CIH or sex was observed on social disengagement in pubertal rats (A). Gestational CIH only increased percentage of young adult female rats that exhibited social disengagement (B). Social withdrawal was significantly associated with gestational CIH only in pubertal females (C). Social disengagement analyzed by Two-way ANOVA with Fisher’s LSD multiple comparisons tests (A, B). Relationship between social engagement and CIH measured by Fisher’s exact test (C). Significance indicated by: ** = CIH, *** = interaction; p ≤ 0.05

Fig. 3

Repetitive behaviors. Gestational CIH increased marble burying in pubertal females (A) and young adult females (B). Males buried more marbles than females, regardless of age (A, B). Normalized by square-root transformation (A, B). Analyzed by Two-way ANOVA with Fisher’s LSD multiple comparisons tests. ANOVA significance indicated by: * = sex, ** = CIH; Post-hoc significance indicated by: # versus normoxic female, p ≤ 0.05

Fig. 4

Anxiety-like behaviors. Females spent less time in the center of the open field compared to males, irrespective of age or gestational CIH (A, B). No effect of gestational CIH or sex was observed on center entries, regardless of age (C, D). Normalized by square-root transformation (C, D). Analyzed by Two-way ANOVA with Fisher’s LSD multiple comparisons tests. ANOVA significance indicated by: * = sex; Post-hoc significance indicated by: # versus normoxic female, ### versus CIH female; p ≤ 0.05

Fig. 5

Spatial memory. Pubertal males had longer pathlength to target during Morris water maze probe trial (A), with the sex difference observed primarily in gestational CIH exposed pubertal males. No effect of sex or gestational CIH was observed on pathlength in young adult rats (B). Analyzed by Two-way ANOVA with Fisher’s LSD multiple comparisons tests. ANOVA significance indicated by: * = sex; Post-hoc significance indicated by: ### = versus CIH female; p ≤ 0.05

Fig. 6

Spatial learning. No effect of gestational CIH on latency to target was observed in females, regardless of age (A). Age improved latency to target during day 2 of learning in males with no effect of age observed on other days (B). Learning index was not affected by gestational CIH or sex during puberty (C). Males had shorter learning index than females during young adulthood (D). Analyzed by Two-way ANOVA with Fisher’s LSD multiple comparisons tests. ANOVA significance indicated by: * = sex; ** = age; Post-hoc significance indicated by: # = versus normoxic female, ## = versus normoxic male; ### = versus CIH female; p ≤ 0.05; P = Puberty; YA = Young Adult