Timing and Intertemporal Choice Behavior in the Valproic Acid Rat Model of Autism Spectrum Disorder

Comparison of predictive validity of two autism spectrum disorder rat models: Behavioural investigations

The valproic acid model has been shown to reproduce ASD-like behaviours observed in patients and is now widely validated for construct, face, and predictivity as ASD model in rat. The literature agrees on using a single exposition to 500 mg/kg of VPA at gestational day 12 to induce ASD phenotype with the intraperitoneal route being the most commonly used. However, some studies validated this model with repeated exposure by using oral route. The way of administration may be of great importance in the induction of the ASD phenotype and a comparison is greatly required. We compared two ASD models, one induced by a unique IP injection of 500 mg/kg of body weight at GD12 and the other one by repeated PO administration of 500 mg/kg of body weight/day between GD11 and GD13. The behavioural phenotypes of the offspring were assessed for the core signs of ASD (impaired social behaviour, stereotypical/repetitive behaviours, sensory/communication deficits) as well as anxiety as comorbidity, at developmental and juvenile stages in both sexes. The VPA IP model induced a more literature-compliant ASD phenotype than the PO one. These results confirmed that the mode of administration as well as the window of VPA exposure are key factors in the ASD-induction phenotype. Interestingly, the effects of VPA administration were similar at the developmental stage between both sexes and then tended to differ later in life.

Reinforced behavioral variability in the valproate rat model of autism spectrum disorder

Individuals diagnosed with autism spectrum disorder (ASD) tend to display restricted, repetitive behaviors and deficits in social interaction. Rats exposed to valproate (VPA) in utero have been shown to model symptoms of ASD. In previous research, VPA rats engaged in less social interaction and more repetitive responding than controls. The purpose of the present study was to further investigate behavioral variability in the VPA rat model of ASD by testing VPA and control rats in a reinforced-behavioral-variability operant task. In this procedure, rats emitted sequences of lever presses, some of which produced food. During baseline, food was delivered probabilistically, and variability was not required. Next, rats were exposed either to a variability contingency, in which food was only delivered following sequences that differed sufficiently from previous sequences (i.e., variability required), or to a yoked contingency, in which variability was not required. We hypothesized that VPA rats would behave less variably than controls in this task. However, VPA and control rats responded similarly variably when variability was required. Furthermore, VPA rats behaved slightly more variably than controls during baseline and yoked conditions, when variability was not required. These findings contribute to the complex literature surrounding the VPA rat model of ASD.

Preliminary evidence for timing abnormalities in the CNTNAP2 knockout rat

The CNTNAP2 gene has been implicated in several neuropsychological disorders, including autism spectrum disorder (ASD) and schizophrenia. The CNTNAP2 knockout (KO) rat model, rats without the CNTNAP2 gene, exhibits deficits in social interaction and increases in both repetitive and anxiety-like behaviors. However, deficits in time perception that may underlie several of the neuropsychological disorders implicated have not been investigated. The current study investigated timing in CNTNAP2 KO rats compared to control rats using a discrete-trial temporal bisection task. Results suggested deficits in the timing of relatively long durations in the CNTNAP2 KO rats. This finding is consistent with similar findings previously reported in humans diagnosed with ASD, and is promising for understanding the role that the CNTNAP2 gene may play in timing in certain neuropsychological disorders, and for developing targeted clinical therapies.