Pathophysiological and neurobehavioral characteristics of a propionic acid-mediated autism-like rat model

<div><p>Autism spectrum disorder (ASD) is induced by complex hereditary and environmental factors. However, the mechanisms of ASD development are poorly understood. The purpose of this study was to identify standard indicators of this condition by comparing clinical, pathophysiological, and neurobehavioral features in an autism-like animal model. A total of 22 male Sprague-Dawley rats were randomly divided into control and 500 mg/kg propionic acid (PPA)-treated groups. Rats were subjected to behavioral tests, gene expression analyses, and histological analyses to detect pathophysiological and neurobehavioral alterations. Exploratory activity and non-aggressive behavior were significantly reduced in PPA-treated rats, whereas enhanced aggressive behavior during adjacent interactions was observed on day 14 after PPA administration. To evaluate gene expression after PPA administration, we analyzed hippocampal tissue using reverse transcription PCR. Glial fibrillary acidic protein was augmented in the PPA-treated group on day 14 after appearance of ASD-like behaviors by PPA administration, whereas octamer-binding transcription factor 4 expression was significantly decreased in the PPA-treated group. Histological evaluation revealed significantly reduced diameter and layer thickness of granule cells in PPA-treated rats compared with control rats. We conclude that PPA administration induced abnormal neural cell organization, which may have led to autism-like neurobehaviors, including increased aggressive behavior, reduced exploratory activity, and isolative and passive behaviors.</p></div

Schematic representation of experimental design.

<p>Schematic representation of experimental design.</p

Changes in gene expression in the hippocampus between early and the late post- induction day following PPA administration.

<p>Gene expression of a neuron-specific microtubule associated protein (<i>MAP2</i>) (A), an astrocyte marker (<i>GFAP</i>) (B), a neural stem cell marker (<i>OCT4</i>) (C), and a pro-inflammatory cytokine (<i>TNF-α</i>) (D) following PID 0 and during the late PID period (days 7 and 14). Data are shown as the mean ± SD. Cont, control rats; ASD, PPA-treated rats. ^<i>*</i><i>p</i> < 0.05, ^<i>**</i><i>p</i> < 0.01: <i>vs</i>. Cont.</p

Immunostaining of hippocampal tissue with GFAP following PPA administration during early and late post-induction day.

<p>GFAP-positive cells (red) in the hippocampus in control (A) and PPA-treated (B) rats. To quantify the number of GFAP-positive cells, we obtained a 3D surface plot using Image-Pro Plus software. Cont, control rats; ASD, PPA-treated rats. Scale bar = 200 μm, <i>p</i> < 0.01: <i>vs</i>. Cont.</p

Comparison of exploratory activity in a non-social environment between control and PPA-treated groups.

<p>PPA-treated rats showed significantly reduced exploratory activity (A) and inner-square exploratory activity (B) during the whole PID period (days 0 to 14). (C) The locomotor activity of the control and PPA-treated rats was observed using a video tracking system. Data are presented as the mean ± SD. Cont, control rats; ASD, PPA-treated rats. ^<i>*</i><i>p</i> < 0.01: <i>vs</i>. Cont.</p

Structural changes of hippocampal tissue in the control and PPA-treated rats.

<p>Histological changes in the dentate gyrus of the hippocampus between the early and late PID period following PPA administration (A, B). Quantitative results for GCL thickness (C) and GC diameter (D). Data are shown as the mean ± SD. Cont, control rats; ASD, PPA-treated rats; GCL, granule cell layer; GC, granule cell. ^<i>**</i><i>p</i> < 0.01: <i>vs</i>. Cont.</p

Alterations in social interaction between early and late post-induction day following PPA administration.

<p>(A, C, D) PPA-treated rats showed significantly reduced non-aggressive behavior, but (B) increased aggressive behavior during the late PID period (days 7 and 14). (E) All social interactions between the control and PPA-treated rats are shown. Data are presented as the mean ± SD. Cont, control rats; ASD, PPA-treated rats. ^<i>*</i><i>p</i> < 0.01: <i>vs</i>. Cont.</p