Does Prenatal Valproate Interact with a Genetic Reduction in the Serotonin Transporter? A Rat Study on Anxiety and Cognition

Intact maternal buffering of stress response in infant rats despite altered responsivity towards maternal olfactory cues in the valproic acid model of autism-like behavior

Disrupted processing of social cues and altered social behaviors are among the core symptoms of autism spectrum disorders (ASDs), and they emerge as early as the first year of life. These differences in sensory abilities may affect the ability of children with ASDs to securely attach to a caregiver and experience caregiver buffering of stress. Prenatal exposure to valproic acid (VPA) has been used to model some aspects of ASDs in rodents. Here, we asked whether prenatal VPA exposure altered infant rats’ behavioral responsivity to maternal olfactory cues in an Odor Preference Test (OPT) and affected maternal buffering of infants’ stress responsivity to shock. In the odor preference test, 1-week old rats treated with VPA during pregnancy appeared to have impaired social recognition and/or may be less motivated to approach social odors in early infancy. These effects were particularly prominent in female pups. In 2-week old rats, VPA-exposed pups and saline-exposed pups showed similar preferences for home cage bedding. Although VPA-exposed pups may initially have a deficit in this attachment-related behavior they do recover typical responses to home cage bedding in later infancy. Both control and VPA-exposed pups showed robust stress hormone responses to repeated shocks, an effect which was blocked when a calm mother was present during shock exposure. No sex differences in the effect of maternal presence on the stress response to shock and no interactions between sex and prenatal drug exposure were observed. Although VPA-exposed pups may show impaired responsivity to maternal cues in early infancy, maternal presence is still capable of regulating the stress response in VPA-exposed pups. In this study we demonstrate the importance of utilizing multiple batteries of tests in assessing behavior, dissecting the behavior on one test into different components. Our results inform about the underlying behavioral characteristics of some of the ASD phenotypes, including sex differences reported by clinical studies, and could shed light on potential opportunities for intervention.

Serotonin-related rodent models of early-life exposure relevant for neurodevelopmental vulnerability to psychiatric disorders

Mental disorders including depression and anxiety are continuously rising their prevalence across the globe. Early-life experience of individuals emerges as a main risk factor contributing to the developmental vulnerability to psychiatric disorders. That is, perturbing environmental conditions during neurodevelopmental stages can have detrimental effects on adult mood and emotional responses. However, the possible maladaptive neural mechanisms contributing to such psychopathological phenomenon still remain poorly understood. In this review, we explore preclinical rodent models of developmental vulnerability to psychiatric disorders, focusing on the impact of early-life environmental perturbations on behavioral aspects relevant to stress-related and psychiatric disorders. We limit our analysis to well-established models in which alterations in the serotonin (5-HT) system appear to have a crucial role in the pathophysiological mechanisms. We analyze long-term behavioral outcomes produced by early-life exposures to stress and psychotropic drugs such as the selective 5-HT reuptake inhibitor (SSRI) antidepressants or the anticonvulsant valproic acid (VPA). We perform a comparative analysis, identifying differences and commonalities in the behavioral effects produced in these models. Furthermore, this review discusses recent advances on neurodevelopmental substrates engaged in these behavioral effects, emphasizing the possible existence of maladaptive mechanisms that could be shared by the different models.

The long-term prognosis of hippocampal neurogenesis and behavioral changes of offspring from rats exposed to valproic acid during pregnancy

Aim

In pregnant women with epilepsy, it is essential to balance maternal safety and the potential teratogenicity of anticonvulsants. Recently, growing evidence has indicated that valproic acid (VPA) can produce postnatal congenital malformations and impair cognitive function. However, the mechanisms underlying cognitive dysfunction in long‐term prognoses remain unclear.

Methods

Pregnant Wistar rats received daily intraperitoneal injections of VPA (200 mg/kg/day) from embryonic day 12.5 until birth. On postnatal day (PD) 149, the rats received an injection of bromodeoxyuridine (BrdU). On PD 150, the rats were subjected to the open field (OF), elevated plus‐maze (EPM), and Y‐maze tests. After behavioral testing, perfusion fixation was performed and the brain was dissected for immunohistochemistry.

Results

A significant marked decrease was seen in the number of BrdU‐positive cells in the dentate gyrus of offspring of VPA‐treated dams compared to those of control. However, no significant differences in hyperactivity were found based on the results of the OF test among the offspring on PD 150 of 200 VPA‐treated dams. In addition, no significant differences were seen in the EPM test.

Conclusion

The behavioral abnormality observed in young offspring of VPA‐treated dams was not significantly different from that of controls in adult offspring on PD 150. However, compared with controls, the number of BrdU‐positive cells in VPA‐treated rats was halved. The findings suggest that the behavioral abnormality seems to improve as they grow, even if some structural abnormalities may remain in the central nervous system.

Pregnant Wistar rats received daily intraperitoneal injections of VPA (200 mg/kg/d) from embryonic day 12.5 until birth. On postnatal day (PD) 149, the rats received an injection of bromodeoxyuridine (BrdU). A significant marked decrease was seen in the number of BrdU‐positive cells in the dentate gyrus of offspring of VPA‐treated dams compared to those of control.

Prenatal exposure to valproic acid is associated with altered neurocognitive function and neurogenesis in the dentate gyrus of male offspring rats

In pregnant women with epilepsy, it is imperative to balance the safety of the mother and the potential teratogenicity of anticonvulsants, which could cause impairments such as intellectual disability and cleft lip. In this study, we examined behavioral and hippocampal neurogenesis alterations in male offspring of rats exposed to valproic acid (VPA) during pregnancy. Pregnant Wistar rats received daily intraperitoneal injections of VPA (100 mg/kg/day or 200 mg/kg/day) from embryonic day 12.5 until birth. At postnatal day 29, animals received an injection of bromodeoxyuridine (BrdU). At postnatal day 30, animals underwent the open field (OF), elevated plus-maze, and Y-maze tests. After behavioral testing, animals were decapitated, and their brains were dissected for immunohistochemistry. Of the offspring of the VPA200 mothers, 66.6% showed a malformation. In the OF test, these animals showed locomotor hyperactivity. In the elevated plus-maze, offspring of VPA-treated mothers spent significantly more time in the open arms, irrespective of the treatment dose. The number of BrdU-positive cells in the dentate gyrus of the offspring of VPA-treated mothers increased significantly in a dose-dependent manner compared with the control. A significant positive correlation between spontaneous locomotor activity in the OF and BrdU-positive cell counts was observed across groups. In conclusion, VPA administration during pregnancy results in malformations and attention-deficit/hyperactivity disorder-like behavioral abnormalities in the offspring. An increase in cell proliferation in the hippocampus may underlie the behavioral changes observed. Repeated use of high doses of VPA during pregnancy may increase the risk of neurodevelopmental abnormalities dose dependently and should be carefully considered.

Current Enlightenment About Etiology and Pharmacological Treatment of Autism Spectrum Disorder

Autistic Spectrum Disorder (ASD) is a complex neurodevelopmental brain disorder characterized by two core behavioral symptoms, namely impairments in social communication and restricted/repetitive behavior. The molecular mechanisms underlying ASD are not well understood. Recent genetic as well as non-genetic animal models contributed significantly in understanding the pathophysiology of ASD, as they establish autism-like behavior in mice and rats. Among the genetic causes, several chromosomal mutations including duplications or deletions could be possible causative factors of ASD. In addition, the biochemical basis suggests that several brain neurotransmitters, e.g., dopamine (DA), serotonin (5-HT), gamma-amino butyric acid (GABA), acetylcholine (ACh), glutamate (Glu) and histamine (HA) participate in the onset and progression of ASD. Despite of convincible understanding, risperidone and aripiprazole are the only two drugs available clinically for improving behavioral symptoms of ASD following approval by Food and Drug Administration (FDA). Till date, up to our knowledge there is no other drug approved for clinical usage specifically for ASD symptoms. However, many novel drug candidates and classes of compounds are underway for ASD at different phases of preclinical and clinical drug development. In this review, the diversity of numerous aetiological factors and the alterations in variety of neurotransmitter generation, release and function linked to ASD are discussed with focus on drugs currently used to manage neuropsychiatric symptoms related to ASD. The review also highlights the clinical development of drugs with emphasis on their pharmacological targets aiming at improving core symptoms in ASD.

Impaired repair of DNA damage is associated with autistic-like traits in rats prenatally exposed to valproic acid

Prenatal exposure to the antiepileptic and mood stabilizer valproic acid (VPA) is an environmental risk factor for autism spectrum disorders (ASD), although recent epidemiological studies show that the public awareness of this association is still limited. Based on the clinical findings, prenatal VPA exposure in rodents is a widely used preclinical model of ASD. However, there is limited information about the precise biochemical mechanisms underlying the link between ASD and VPA. Here, we tested the effects of increasing doses of VPA on behavioral features resembling core and secondary symptoms of ASD in rats. Only when administered prenatally at the dose of 500mg/kg, VPA induced deficits in communication and social discrimination in rat pups, and altered social behavior and emotionality in the adolescent and adult offspring in the absence of gross malformations. This dose of VPA inhibited histone deacetylase in rat embryos and favored the formation of DNA double strand breaks (DSB), but impaired their repair. The defective DSB response was no more visible in one-day-old pups, thus supporting the hypothesis that unrepaired VPA-induced DNA damage at the time of neural tube closure may underlie the autistic-like traits displayed in the course of development by rats prenatally exposed to VPA. These experiments help to understand the neurodevelopmental trajectories affected by prenatal VPA exposure and identify a biochemical link between VPA exposure during gestation and ASD.