BALB/c female subjected to valproic acid during gestational period exhibited greater microglial and behavioral changes than male mice: A significant contra intuitive result

Abstract

Most animal model studies of autism spectrum disorders (ASD) were performed in males. Thus, little is known about the mechanisms underlying disease progression in females. Here, we searched for potential influences of sex and environment on gestational valproic acid‐induced behavioral abnormalities using hippocampal‐dependent tasks, and on number and morphometry of microglia of the molecular layer of the dentate gyrus (Mol‐DG). We compared male and females BALB/c control mice with BALB/c mice gestationally exposed to VPA with regards to exploratory activity and risk assessment in novel environments. Pregnant females and males on gestational day 12.5 received VPA in saline (600 mg/kg body weight) or an equal volume of saline by gavage. After weaning, female and male offspring were housed separately either in standard laboratory cages (SE) or enriched cages (EE). At 5 months of age, these mice underwent behavioral testing and had their brains processed for microglia IBA1 immunolabeling. Compared with control mice, VPA‐exposed mice exhibited abnormal behavior in exploring novel environments and assessing risk, and these effects were significantly greater in females than in males and less intense among mice from enriched cages. Three‐way ANOVA revealed that environment, sex and valproic acid conditions interacted and altered the behavior results. Microglia number and volume of the Mol‐DG were significantly higher in VPA‐exposed groups raised in standard cages. The results of counting the intersects of microglia branching on Sholl's circles analyzed with permutational MANOVA, demonstrated that in comparison with males, there was a greater reduction in the number of intersections in females raised in standard cages. These findings suggest that the increased microglia and morphological changes might be associated with behavioral dysfunction in ASD. Moreover, the somatomotor and cognitive stimulation of environmental enrichment started at weaning may be beneficial for reducing behavioral abnormalities and reduction of microglia response in adulthood.

The Antiepileptic Drug and Toxic Teratogen Valproic Acid Alters Microglia in an Environmental Mouse Model of Autism

“…The reduction in microglia number close to the time of insult we observe in our experiments is also in contrast to other studies in young adult animals at a time point after remodeling occurs in the brain. For example, increased microglial density has been reported in the molecular layer of the dentate gyrus in female BALBc mice at 5 months [ 19 ]. This is in contrast to studies by Kazlauskas et al, who showed no change in microglial density in the same molecular layer of the dentate gyrus; however, this was carried out in early neonatal (PD-7) development and in a different strain Cr1Fcen:CF1 lineage showing age-specific and strain specific effects of the drug [ 18 ].…”

Epilepsy in Pregnancy—Management Principles and Focus on Valproate

“…Both, the volume of the molecular layer and the number of microglial cells were considerably higher in VPA mice from standard cages. Mice housed in enriched cages presented less intense behavioral and cellular abnormalities [81].…”

“…Considering that most studies of ASD in experimental animals were brought about in males, Dos Santos et al [81] have decided to compare the effects of prenatal VPA exposure (600 mg/kg on gestational day 12.5) on behavioral abnormalities in male and female offspring (housed either in standard or enriched cages) with the use of hippocampal-related tasks in five-month-old animals. Also, the number and morphometry of microglial cells located in the molecular layer of the dentate gyrus were evaluated.…”

Valproic Acid in Pregnancy Revisited: Neurobehavioral, Biochemical and Molecular Changes Affecting the Embryo and Fetus in Humans and in Animals: A Narrative Review

“…Numerous studies and reviews highlight the impaired behavioral phenotype in rodents prenatally exposed to VPA. Decreased exploration associated with locomotor hyperactivity and stereotypic-like behaviors and reduced social interactions were mainly observed in VPA-induced ASD-like behavior in rodents [ 144 , 147 , 148 , 149 , 150 , 151 , 152 , 153 ] in a sex-dependent manner, which is often observed in individuals with autism [ 154 ] ( Table 5 ).…”