Early-onset of social communication and locomotion activity in F2 pups of a valproic acid-induced mouse model of autism.

Autism spectrum disorder (ASD) is a heterogeneously pervasive developmental disorder that usually occurs before 3 years old. Animal models of psychiatric disorders are essential for elucidating the underlying preclinical neural mechanisms. Mice that are prenatally exposed to valproic acid (VPA, F1) are widely used as an ASD model. Epigenetics has recently been suggested as a contributor to ASD etiology with the hypothesis that epigenetic marks can be transgenerationally inherited. Previous studies have indicated that autism-like behavioral phenotypes detected in F1 VPA mice transgenetically appear in F2 and F3 generations. However, studies on the autism-like behavioral phenotypes during the early postnatal days in subsequent generations are scarce. Here, the behavioral deficit on postnatal day 5 of the F2 generation was examined to assess the onset of ASD symptoms. Communication disorders were examined by analyzing maternal separation-induced ultrasonic vocalizations (USVs). Although the duration and frequency of USVs were not significantly altered, the emission rate was significantly lower in F2 VPA pups. Furthermore, the locomotive activity with or without littermates was altered in F2 VPA pups. The data of the current study suggest that social deficit and impaired locomotion are inherited by the subsequent generation and were apparent on early postnatal day 5.

Oxytocin administration modulates the complex type of ultrasonic vocalisation of mice pups prenatally exposed to valproic acid.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterised by communication disability with no curative treatment. Maternal separation-induced ultrasonic vocalisation (USV) was widely used to assess communication disability between pups and dams. Particularly, USV calls in many genetically modified ASD model mice were altered. Previously, we demonstrated that mice pups exposed to valproic acid in utero (VPA pups) showed decreased number of USV calls on postnatal day 11 and were rescued by subcutaneous injection of oxytocin. However, the qualitative change of USV calls by oxytocin has not been evaluated in VPA pups. In the present study, we examined the duration of oxytocin effect and analysed the altered pattern of USV calls using VPA pups. The oxytocin administration increased the total number of USV calls and the effect persisted up to 120 min in VPA pups. The pattern analysis revealed that the increase in the number of complex calls also persisted up to 120 min. These results suggested that oxytocin had a prolonged effect on USV calls, mainly on complex calls, in VPA pup, showing that oxytocin could recover their social modality to respond to maternal separation.