Sodium valproate: effects on social behaviour and physical development in the mouse

Autism spectrum disorder-like behaviors induced by hyper-glutamatergic NMDA receptor signaling through hypo-serotonergic 5-HT1A receptor signaling in the prefrontal cortex in mice exposed to prenatal valproic acid

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by repetitive behaviors, social deficits, and cognitive impairments. Maternal use of valproic acid (VPA) during pregnancy is associated with an increased risk of ASD in offspring. The prevailing pathophysiological hypothesis for ASD involves excitation/inhibition (E/I) imbalances and serotonergic dysfunction. Here, we investigated the association between glutamatergic-serotonergic neuronal interactions and ASD-like behaviors in mice exposed to prenatal VPA. Prenatal VPA exposure induced excessive repetitive self-grooming behavior and impaired social behavior and object recognition memory in young adult period. Prenatal VPA mice showed hyper-glutamatergic function (increase in basal extracellular glutamate levels and CaMKII phosphorylation) and hypo-serotonergic function (decrease in 5-hydroxyindoleacetic acid and stimulation-induced serotonin [5-HT] release, but an increase in 5-HT transporter expression) in the prefrontal cortex. Treatment with a low-affinity NMDA receptor antagonist (memantine), a selective 5-HT reuptake inhibitor (fluoxetine), and a 5-HT1A receptor agonist (tandospirone) attenuated both the increase in CaMKII phosphorylation and ASD-like behavior of prenatal VPA mice. Opto-genetic activation of the serotonergic neuronal system attenuated impairments in social behavior and object recognition memory in prenatal VPA mice. WAY-100635-a 5-HT1A receptor antagonist-antagonized the effect of fluoxetine on impaired social behavior and object recognition memory. These results suggest that E/I imbalance and ASD-like behavior are associated with hypo-serotonergic receptor signaling through 5-HT1A receptors in prenatal VPA mice.

The role of the endocannabinoid system as a therapeutic target for autism spectrum disorder: Lessons from behavioral studies on mouse models

Recent years have seen an impressive amount of research devoted to understanding the etiopathology of Autism Spectrum Disorder (ASD) and developing therapies for this syndrome. Because of the lack of biomarkers of ASD, this work has been largely based on the behavioral characterization of rodent models, based on a multitude of genetic and environmental manipulations. Here we highlight how the endocannabinoid system (ECS) has recently emerged within this context of mouse behavioral studies as an etiopathological factor in ASD and a valid potential therapeutic target. We summarize the most recent results showing alterations of the ECS in rodent models of ASD, and demonstrating ASD-like behaviors in mice with altered ECS, induced either by genetic or pharmacological manipulations. We also give a critical overview of the most relevant advances in designing treatments and novel mouse models for ASD targeting the ECS, highlighting the relevance of thorough and innovative behavioral approaches to investigate the mechanisms acting underneath the complex features of ASD.

The role of the endocannabinoid system in autism spectrum disorders: Evidence from mouse studies

A substantive volume of research on autism spectrum disorder (ASD) has emerged in recent years adding to our understanding of the etiopathological process. Preclinical models in mice and rats have been highly instrumental in modeling and dissecting the contributions of a multitude of known genetic and environmental risk factors. However, the translation of preclinical data into suitable drug targets must overcome three critical hurdles: (i) ASD comprises a highly heterogeneous group of conditions that can markedly differ in terms of their clinical presentation and symptoms, (ii) the plethora of genetic and environmental risk factors suggests a complex, non-unitary, etiopathology, and (iii) the lack of consensus over the myriad of preclinical models, with respect to both construct validity and face validity. Against this backdrop, this Chapter traces how the endocannabinoid system (ECS) has emerged as a promising target for intervention with predictive validity. Recent supportive preclinical evidence is summarized, especially studies in mice demonstrating the emergence of ASD-like behaviors following diverse genetic or pharmacological manipulations targeting the ECS. The critical relevance of ECS to the complex pathogenesis of ASD is underscored by its multiple roles in modulating neuronal functions and shaping brain development. Finally, we argue that important lessons have been learned from the novel mouse models of ASD, which not only stimulate game-changing innovative treatments but also foster a consensual framework to integrate the diverse approaches applied in the search of novel treatments for ASD.

MR imaging central thalamic deep brain stimulation restored autistic-like social deficits in the rat

BACKGROUND

Social deficit is a core symptom in autism spectrum disorder (ASD). Although deep brain stimulation (DBS) has been proposed as a potential treatment for ASD, an ideal target nucleus is yet to be identified. DBS at the central thalamic nucleus (CTN) is known to alter corticostriatal and limbic circuits, and subsequently increase the exploratory motor behaviors, cognitive performance, and skill learning in neuropsychiatric and neurodegenerative disorders.

OBJECTIVE

We first investigated the ability of CTN-DBS to selectively engage distinct brain circuits and compared the spatial distribution of evoked network activity and modulation. Second, we investigated whether CTN-DBS intervention improves social interaction in a valproic acid-exposed ASD rat offspring model.

METHODS

Brain regions activated through CTN-DBS by using a magnetic resonance (MR)-compatible neural probe, which is capable of inducing site-selective microstimulations during functional MRI (fMRI), were investigated. We then performed functional connectivity MRI, the three-chamber social interaction test, and Western blotting analyses to evaluate the therapeutic efficacy of CTN-DBS in an ASD rat offspring model.

RESULTS

The DBS-evoked fMRI results indicated that the activated brain regions were mainly located in cortical areas, limbic-related areas, and the dorsal striatum. We observed restoration of brain functional connectivity (FC) in corticostriatal and corticolimbic circuits after CTN-DBS, accompanied with increased social interaction and decreased social avoidance in the three-chamber social interaction test. The dopamine D2 receptor decreased significantly after CTN-DBS treatment, suggesting changes in synaptic plasticity and alterations in the brain circuits.

CONCLUSIONS

Applying CTN-DBS to ASD rat offspring increased FC and altered the synaptic plasticity in the corticolimbic and the corticostriatal circuits. This suggests that CTN-DBS could be an effective treatment for improving the social behaviors of individuals with ASD.

Predictable enriched environment prevents development of hyper-emotionality in the VPA rat model of autism

Understanding the effects of environmental stimulation in autism can improve therapeutic interventions against debilitating sensory overload, social withdrawal, fear and anxiety. Here, we evaluate the role of environmental predictability on behavior and protein expression, and inter-individual differences, in the valproic acid (VPA) model of autism. Male rats embryonically exposed (E11.5) either to VPA, a known autism risk factor in humans, or to saline, were housed from weaning into adulthood in a standard laboratory environment, an unpredictably enriched environment, or a predictably enriched environment. Animals were tested for sociability, nociception, stereotypy, fear conditioning and anxiety, and for tissue content of glutamate signaling proteins in the primary somatosensory cortex, hippocampus and amygdala, and of corticosterone in plasma, amygdala and hippocampus. Standard group analyses on separate measures were complemented with a composite emotionality score, using Cronbach's Alpha analysis, and with multivariate profiling of individual animals, using Hierarchical Cluster Analysis. We found that predictable environmental enrichment prevented the development of hyper-emotionality in the VPA-exposed group, while unpredictable enrichment did not. Individual variation in the severity of the autistic-like symptoms (fear, anxiety, social withdrawal and sensory abnormalities) correlated with neurochemical profiles, and predicted their responsiveness to predictability in the environment. In controls, the association between socio-affective behaviors, neurochemical profiles and environmental predictability was negligible. This study suggests that rearing in a predictable environment prevents the development of hyper-emotional features in animals exposed to an autism risk factor, and demonstrates that unpredictable environments can lead to negative outcomes, even in the presence of environmental enrichment.

Suppression of adipogenesis by valproic acid through repression of USF1-activated fatty acid synthesis in adipocytes

Valproic acid suppresses the accumulation of the intracellular lipids through suppression of fatty acid synthesis via repression of USF1-mediated expression of the fatty acid synthase gene in adipocytes.

General developmental health in the VPA-rat model of autism

Autism is a neurodevelopmental condition diagnosed by impaired social interaction, abnormal communication and, stereotyped behaviors. While post-mortem and imaging studies have provided good insights into the neurobiological symptomology of autism, animal models can be used to study the neuroanatomical, neurophysiological and molecular mediators in more detail and in a more controlled environment. The valproic acid (VPA) rat model is an environmentally triggered model with strong construct and clinical validity. It is based on VPA teratogenicity in humans, where mothers who are medicated with VPA during early pregnancy show an increased risk for giving birth to an autistic child. In rats, early embryonic exposure, around the time of neural tube closure, leads to autism-like anatomical and behavioral abnormalities in the offspring. Considering the increasing use of the VPA rat model, we present our observations of the general health of Wistar dams treated with a single intraperitoneal injection of 500 or, 600 mg/kg VPA on embryonic day E12.5, as well as their male and female offspring, in comparison to saline-exposed controls. We report increased rates of complete fetal reabsorption after both VPA doses. VPA 500 mg/kg showed no effect on dam body weight during pregnancy or, on litter size. Offspring exposed to VPA 500 mg/kg showed smaller brain mass on postnatal days 1 (P1) and 14 (P14), in addition to abnormal nest seeking behavior at P10 in the olfactory discrimination test, relative to controls. We also report increased rates of physical malformations in the offspring, rare occurrences of chromodacryorrhea and, developmentally similar body mass gain. Further documentation of developmental health may guide sub-grouping of individuals in a way to better predict core symptom severity.

Suppression of adiponectin gene expression by histone deacetylase inhibitor valproic acid

Valproic acid (VPA) has been used for the treatment of epilepsy and bipolar disorders for more than 30 yr. Obesity and insulin resistance are common side effects of VPA treatment. Adiponectin is an adipocyte-derived protein that plays an important role in controlling insulin sensitivity and glucose homeostasis. In this report, we examined the effects of VPA on adiponectin gene expression in C57BL/6J mice and in differentiated 3T3-L1 adipocytes. VPA treatment significantly decreased adiponectin protein and mRNA levels in both mice and 3T3-L1 adipocytes. The adipocyte study showed that VPA inhibited adiponectin gene expression in a dose- and time-dependent manner. Repression of adiponectin expression by VPA occurred at the transcription level and correlated with inhibition of histone deacetylase activity. Therapeutic concentrations of VPA increased overall histone acetylation and increased adiponectin promoter-driven luciferase expression in fibroblasts, but decreased adiponectin promoter activity in differentiated 3T3-L1 adipocytes. VPA treatment decreased adipogenic transcription factor CCAAT/enhancer binding protein-alpha (C/EBPalpha) levels and binding of C/EBPalpha to the adiponectin promoter without altering the levels of peroxisome proliferator-activated receptor-gamma and steroid regulatory element binding protein-1. Furthermore, VPA did not suppress adiponectin gene expression in C/EBPalpha gene-deficient adipocytes that stably expressed exogenous peroxisome proliferator-activated receptor-gamma2. Together, these results demonstrate that histone deacetylase inhibitor VPA suppresses adiponectin gene expression in mature adipocytes. The study also provides evidence that diminished C/EBPalpha protein level and decreased binding at the adiponectin promoter mediate the inhibitory effects of VPA on adiponectin gene transcription.

Valproic acid inhibits leptin secretion and reduces leptin messenger ribonucleic acid levels in adipocytes

Treatment of epilepsy or bipolar disorder with valproic acid (VPA) induces weight gain and increased serum levels for the satiety hormone, leptin, through an unidentified mechanism. In this study we tested the effects of VPA, a short-chain branched fatty acid (C8:0), on leptin biology and fatty acid metabolism in 3T3-L1 adipocytes. VPA significantly reduced leptin secretion in a dose-dependent manner. Because fatty acid accumulation has been hypothesized to block leptin secretion, we tested the effect of VPA on fatty acid metabolism. Using 14C-radiolabeled VPA, we found that the 14C was mainly incorporated into triacylglycerol. VPA did not alter lipogenesis from acetate, nor did it change the amount of intracellular free fatty acids available for triacylglycerol synthesis. Decreased leptin secretion was accompanied by a reduction in leptin mRNA, even though VPA treatment did not alter the protein levels for known transcription factors affecting leptin transcription including: CCAAT/enhancer binding protein-alpha, peroxisome proliferator-activated receptor-gamma, or steroid regulatory element binding protein 1a. VPA altered levels of leptin mRNA independent of de novo protein synthesis without affecting leptin mRNA degradation. This report demonstrates that VPA decreases leptin secretion and mRNA levels in adipocytes in vitro, suggesting that VPA therapy may be associated with altered leptin homeostasis contributing to weight gain in vivo.

Inhibition of histone deacetylase activity by valproic acid blocks adipogenesis

Adipogenesis is dependent on the sequential activation of transcription factors including the CCAAT/enhancer-binding proteins (C/EBP), peroxisome proliferator-activated receptor gamma (PPARgamma), and steroid regulatory element-binding protein (SREBP). We show that the mood stabilizing drug valproic acid (VPA; 0.5-2 mm) inhibits mouse 3T3 L1 and human preadipocyte differentiation, likely through its histone deacetylase (HDAC) inhibitory properties. The HDAC inhibitor trichostatin A (TSA) also inhibited adipogenesis, whereas the VPA analog valpromide, which does not possess HDAC inhibitory effects, did not prevent adipogenesis. Acute or chronic VPA treatment inhibited differentiation yet did not affect mitotic clonal expansion. VPA (1 mm) inhibited PPARgamma induced differentiation but does not activate a PPARgamma reporter gene, suggesting that it is not a PPARgamma ligand. VPA or TSA treatment reduced mRNA and protein levels of PPARgamma and SREBP1a. TSA reduced C/EBPalpha mRNA and protein levels, whereas VPA only produced a decrease in C/EBPalpha protein expression. Overall our results highlight a role for HDAC activity in adipogenesis that can be blocked by treatment with VPA.

An ethological study of the effects of buspirone and the 5-HT3 receptor antagonist, BRL 43694 (granisetron) on behaviour during social interactions in female and male mice

Buspirone (12.8 mg/l; 2.3-2.6 mg/kg daily) and the 5-HT3 receptor antagonist, BRL 43694 (granisetron) (40 micrograms/l; 10 micrograms/kg daily), were each given in drinking fluid to male and female DBA/2 mice for 5-10 days. Controls received tap water. Effects on behaviour were examined by ethological procedures during 5 min encounters with unfamiliar BKW partners. One group of DBA/2 males acted as intruders in a resident-intruder paradigm and another group encountered oestrous females in a neutral cage. The DBA/2 females each encountered a group-housed male in a neutral cage. Both buspirone and BRL 43694 decreased flight in females and increased the duration of their active social investigation. In females, BRL 43694 also reduced the occurrence of "scan" and prolonged the bout length of exploration. In male mice, buspirone increased social investigation, including the specific elements "sniff" and "follow" in encounters with female partners, but its only effect on behaviour during encounters with isolated resident males, was to decrease duration of the element, "attend". In males, BRL 43694 did not significantly affect behaviour in heterosexual encounters and had only a slight effect on behaviour during encounters with resident males, decreasing the occurrence of "eat". Overall, these results suggest that records of effects of drugs on flight responses of female mice, in encounters with male partners, may provide a sensitive index of the anxiolytic profile of novel compounds.

Chronic administration of the 5-HT3 receptor antagonist BRL 43694; effects on reflex epilepsy and social behaviour of the Mongolian gerbil

The 5-HT3 receptor antagonist BRL 43694 was administered in drinking fluid to Mongolian gerbils, previously selected for their propensity to exhibit seizures on mild stimulation, for 11 days at doses of 1.5 micrograms/kg, 150 micrograms/kg and 1 mg/kg daily, while controls received tap water. Effects upon behaviour during encounters under white light with an untreated resident gerbil were assessed using ethological procedures. Effects upon seizure susceptibility and severity were also examined. All doses of BRL 43694 significantly increased the time spent by gerbils in the social activity "attend", and acts of social investigation involving physical contact between animals were significantly increased only by the highest dose of 1 mg/kg, as was occurrence of the specific element, "groom". The duration of flight was increased in gerbils receiving the drugs at 1.5 micrograms/kg. The treatment had no effect upon seizure susceptibility or severity. It is suggested that BRL 43694 increases the sensitivity of gerbils to their social environment. At the lower dose this was seen as an increase in flight, at all doses it was associated with increase of the social activity "attend" and at the high dose it was manifested as an increase in active social interaction. Further investigations are required to assess the relevance of these findings to the purported anxiolytic activity of 5-HT3 receptor antagonists.

Effects of sodium valproate on development and social behaviour in the Mongolian gerbil

Sodium valproate is an anticonvulsant widely prescribed because of its broad spectrum of activity. While acute toxicity from high doses is well recognized, there have been few animal studies of its chronic toxicity at therapeutic dose levels. Sodium valproate given continuously in drinking fluid (600 mg/l) throughout pregnancy and lactation to breeding gerbils caused developmental delay of the self-righting reflex in their pups. Dams ingested 97 mg/kg daily during gestation and 151 mg/kg on average during lactation, a dose in the lower range of anticonvulsant effectiveness. Reproductive performance, birth weights and subsequent growth of the pups remained normal, as did brain weights in adulthood. Drug-treated offspring, continuing to receive valproate as drinking fluid after weaning (600 mg/l; 82 to 111 mg/kg) showed negligible behavioural alteration at 6 weeks of age as assessed by ethological procedures, although behavioural change did occur at 20 weeks in the female animals. These females were characterised by significant enhancement of exploration and scanning during dyadic encounters in an unfamiliar cage, and showed a concomitant reduction of other nonsocial activities. Short-term administration of this dose of the drug did not affect behaviour. These results suggest an increased reactivity to the environment which becomes evident only after long-term treatment with valproate and to which female animals are more susceptible than males. These findings of developmental delay and of modifications to behaviour later in life points to the need for more detailed clinical assessments of the effects of valproate in human patients.

Sodium valproate: effects on maternal behaviour in the mouse

The behaviour of lactating mice in their home cages was examined by ethological procedures at 1, 7, 14 and 21 days postpartum. Early in lactation, maternal behaviour was more frequent in the light phase of the 24 hr cycle, whereas non-social activity occupied a greater amount of time during the dark phase. As the pups became older, maternal behaviour declined, and at 21 days the dams showed a marked increase of solitary immobility. Behavioural alterations produced by the administration of sodium valproate at 600 mg/l as drinking fluid during pregnancy and lactation (group SVP), and during lactation only, (group PN) were assessed. (Intake of drug amounted to 153 mg/kg during gestation and 186 mg/kg in lactation). Dams of group PN showed behavioural differences from controls in late lactation, pup nursing being prolonged at day 14 postpartum and the frequency of all categories of active behaviour, other than nursing and nestbuilding, was increased at day 21 postpartum in the dark phase of their daily cycle. There was not significant effect on categories of behaviour in dams of the SVP group. Overall, sodium valproate, at this dose, did not reduce maternal care.

Prenatal antiepileptic drug exposure alters seizure susceptibility in rats

An animal model is used to address the issue of prenatal exposure to certain antiepileptic drugs and seizure susceptibility in the offspring. Administration of doses established as median therapeutic doses in humans of phenobarbital, valproate and clonazepam to pregnant rats during the last third of gestation produced sexually dimorphic alterations in pentylenetetrazol (PTZ)-induced seizures as well as in non-convulsive (spontaneous alternation and cliff avoidance) behaviors in the offspring. Altered seizure susceptibility occurred in the absence of overtly recognizable morphological abnormalities and did not appear to reflect differences in the status of circulating drug-binding plasma proteins. Possible neural and/or metabolic mechanisms responsible for these behavioral changes are discussed.