P-cresol Alters Brain Dopamine Metabolism and Exacerbates Autism-Like Behaviors in the BTBR Mouse

Abstract

Background: Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social interaction/communication, stereotypic behaviors, restricted interests, and abnormal sensory-processing. Several studies have reported significantly elevated urinary and foecal levels of p-cresol in ASD children, an aromatic compound either of environmental origin or produced by specific gut bacterial strains. Methods: Since p-cresol is a known uremic toxin, able to negatively affect multiple brain functions, the present study was undertaken to assess the effects of a single acute injection of low- or high-dose (1 or 10 mg/kg i.v. respectively) of p-cresol in behavioral and neurochemical phenotypes of BTBR mice, a reliable animal model of human ASD. Results: P-cresol significantly increased anxiety-like behaviors and hyperactivity in the open field, in addition to producing stereotypic behaviors and loss of social preference in BTBR mice. Tissue levels of monoaminergic neurotransmitters and their metabolites unveiled significantly activated dopamine turnover in amygdala as well as in dorsal and ventral striatum after p-cresol administration; no effect was recorded in medial-prefrontal cortex and hippocampus. Conclusion: Our study supports a gene x environment interaction model, whereby p-cresol, acting upon a susceptible genetic background, can acutely induce autism-like behaviors and produce abnormal dopamine metabolism in the reward circuitry.

Keywords: autism spectrum disorder (ASD), biomarker; dopamine; mouse social behavior; p-cresol.

Figure 1

P-cresol enhances anxiety-like behaviors, stereotypies, locomotor parameters and hinders social preference in BTBR mice. (A) Total entries, % of time spent and entries in open arms in the Elevated Plus Maze. (B) Distance travelled and speed in the Open Field Test after acute p-cresol treatment. (C) Schematic representation of the Object Recognition Test. (D) Time spent grooming during the first session of the Object Recognition Test. (E) Time spent exploring the novel or familiar object during the test session of the Object Recognition Test. (F) Schematic representation of the three-chamber Social Interaction Test. (G) Time in object and subject zones during the Social Interaction Test session. (H) Time spent in contact with the object or with the social intruder during the Social Interaction Test. Results are shown as mean ± sem. *, **, *** p < 0.05, p < 0.01, p < 0.001 P-C1 or P-C10 vs. CNTR. ^^ p < 0.01 P-C10 vs. P-C1, ^## p < 0.01 old vs. new, ^§§, ^§§§ p < 0.01, p < 0.001 subject vs. object.

Figure 2

P-cresol enhances tissue levels of dopamine and its metabolites in the amygdala, caudate putamen and nucleus accumbens of BTBR mice. (A) Tissue levels of DA, DOPAC, HVA, NE, 5-HT and 5-HIAA, measured in medial pFC, NAc, CP, HIP, AMY. (B) Tissue levels of DA, DOPAC, HVA, measured in NAc, CP and AMY. CNTR, n = 9–10; P-C1, n = 6, P-C10 n = 6. Data are expressed as mean ± sem ng/g wet weight. *, **, *** p < 0.05, 0.01, 0.001 P-C1 or P-C10 vs. CNTR group. ^##, ^### p < 0.01, 0.001 P-C10 vs. P-C1 (treatment effect) by Duncan’s post-hoc test following one-way ANOVAs. Abbreviations: AMY: Amygdala; CP: Caudate Putamen; DA: dopamine; DOPAC: 3,4-Dihydroxyphenylacetic acid; HIP: Hippocampus; HVA: Homovanillic acid; NAc: Nucleus Accumbens; pFC: preFrontal Cortex.