Size anomaly and alteration of GABAergic enzymes expressions in cerebellum of a valproic acid mouse model of autism

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by social communication deficit and repetitive behaviour. In the past few years, increasing clinical evidence has shown that the cerebellum may contribute to the neuropathology of ASD. However, studies in the mechanism for the involvement of the cerebellum in autism remained speculative. Although some have suggested the possibility of a change of glutamate decarboxylases in the cerebellum of autistic patients, this remains controversial and is limited to the alteration in transcriptional level. This study aimed to investigate the cerebellar structure and determine the expression of rate-limiting GABAergic enzymes in GABA signalling of the autism cerebellum. Pregnant C57BL/6 J mice were intraperitoneally injected with a dosage of 500 mg/kg valproic acid (VPA) on embryonic day 10.5 for autistic behavioural induction. This study found that early prenatal exposure to VPA led to tail deformation and decreased cerebellar weight and size. Early adult mouse models with autistic behaviour showed reduced expression of both isoforms of glutamate decarboxylases (GAD) 65 and 67 in the cerebellum. Also, protein expressions of cerebellar type 1 GABA transporter (GAT-1) and GABA transaminase (GABAT) were reduced in VPA mice. It indicated that abnormal GABA production, recycling, and metabolism could alter the excitatory-inhibitory balance in the autistic cerebellum. Thus, our findings provide supporting evidence that cerebellum impairment could be an etiology of environmentally induced autism. Changes in cerebellar structure and the altered GABAergic enzymes in the cerebellum provide targets for future therapeutic studies in idiopathic autism.