Research reportEffects of the enteric bacterial metabolic product propionic acid on object-directed behavior, social behavior, cognition, and neuroinflammation in adolescent rats: Relevance to autism spectrum disorder
Research highlights
▶ Effects of propionic acid (ICV) in an adolescent rat model of ASD were studied. ▶ Propionic acid increased restricted/repetitive behavior toward objects. ▶ Propionic acid impaired social behavior in a novel rat–novel object choice test. ▶ Propionic acid impaired reversal learning, but not acquisition, in a T-maze. ▶ Results broaden the relevance of the propionic acid rat model of ASD.
Introduction
The prevalence of autism spectrum disorders (ASD) is approximately 1 in 110 children [17]. Behavioral symptoms of ASD include restrictive and/or repetitive interests and behaviors, impaired social behavior, cognitive impairment, and convulsions, suggesting broad neurodevelopmental abnormality in ASD [7], [22]. Although there is a strong genetic component to the etiology of ASD [22], [43], recent research suggests that ASD can be exacerbated by a number of environmental factors in sensitive sub-populations [28]. Recent studies suggest a link between dietary factors or gastrointestinal disturbances and ASD symptoms, but the exact mechanisms by which such factors might contribute to ASD are not clear [7], [29], [32]. Some clinical studies have also found that a subset of ASD patients have high levels of Clostridia or Bacterioidetes in the gut, which produce propionic acid (PPA) and other fatty acids by anaerobic fermentation of dietary carbohydrates and some amino acids [26], [54]. PPA is a short chain fatty acid that is endogenous to the human body as both an intermediary of fatty acid metabolism and a metabolic endproduct of enteric gut bacteria such as clostridia and propionibacteria [4], [40], [58], [67]. Parents of some ASD children report that ASD symptoms are exacerbated when the children crave and consume processed wheat or dairy products that contain PPA as a food preservative [29], [32]. Rat models of propionic acidemia based on administration of PPA or 3-nitropropionic acid (3NP), a derivative of PPA, have revealed behavioral symptoms and brain markers consistent with human ASD, including developmental delay with cognitive impairments, and neuroinflammation [6], [12], [48], [59]. Consistent with such effects on brain and behavior, PPA readily crosses the gut–blood and blood–brain barriers by both passive and active means [33], thus potentially gaining access to the brain where it can accumulate in cells and alter multiple neurophysiological processes, including neurotransmitter release, gene expression, mitochondrial function, immune modulation, gap junction gating, and ultimately behavior [15], [35], [47].
There is a need for a defined set of behavioral tasks relevant to the symptoms of ASD in animal models of the disorder (see [20], [53]). Earlier studies with PPA in our laboratory found that intraventricular administration of PPA to adult rats induced repetitive behaviors, impairments in cognition and social behavior, and brain events including epileptiform spiking in neocortex, hippocampus and caudate nucleus, seizures with convulsions, increases in oxidative stress markers, reductions in glutathione, alterations of brain phospholipids/acylcarnitines and an innate neuroinflammatory response [35], [36], [51], [52], [57]. These outcomes appear to be consistent with ASD behavioral symptoms and brain events [6], [18], [20], [22], [59]. Adolescence is a key developmental period, with exacerbation of many ASD associated symptoms [42]. As part of a systematic investigation of PPA with young rats, this study examined the effects of PPA in adolescent rats. Data were obtained using a test of interaction with multiple objects to study restricted/repetitive behavior, a test of object vs. rat interaction to study social impairment, a T-maze test of cognition, and a measure of locomotor activity. We hypothesized that PPA treatment would increase restricted/repetitive behaviors, and impair social behavior and cognition [51], [52] in adolescent rats. At the completion of the study brain tissue was examined using neuropathological markers for innate neuroinflammation [59].
Section snippets
Subjects
Long–Evans male hooded rats were obtained at age 26 days from Charles River Laboratories (Quebec, Canada) and housed in groups of 3 or 4 at 21 ± 1 °C in acrylic cages (26 cm × 48 cm × 21 cm) for 8 days for acclimation to the animal colony, with lights on from 7:00 to 19:00 h and access to food (LabDiet RMH 3000) and water ad libitum. Post-surgical housing was individual for 7 days to allow recovery. Procedures complied with Canadian Council on Animal Care guidelines and were approved by the University
Object-directed behavior
Preliminary analysis revealed no consistency within or across groups in the specific novel object that was interacted with the most. Therefore for graphing and analysis purposes, for each rat the objects were rank ordered from 1 through 3 on each behavioral measure to indicate greater-to-less interaction/interest in the objects. Thus, Object 1 was, for each rat, the object that the rat interacted with the most, Object 2 was the object that the rat interacted with second most, and Object 3 was
Discussion
The results show that PPA treatment increased restrictive/repetitive behaviors in an object choice test, impaired social behavior in a rat vs. object choice test, and impaired reversal learning in a T-maze task in adolescent rats relative to PBS controls. PPA significantly increased GFAP immunoreactivity in hippocampal areas CA1/CA2 and in white matter adjacent to hippocampus, and there was a nonsignificant trend for similar increases in CD68 immunoreactivity in the same brain structures. These
Acknowledgements
We thank Karen Jameson and Lisa Tichenoff for excellent technical assistance in immunohistochemistry quantification. This research was supported by GoodLife Children's Foundations (to DFM) and The Natural Sciences and Engineering Research Council of Canada (to DPC).
References (67)
- et al.
The spontaneously-hypertensive rat as an animal model of ADHD: evidence for impulsive and non-impulsive subpopulations
Neurosci Biobehav Rev
(2003) - et al.
Biological effects of propionic acid in humans; metabolism, potential applications and underlying mechanisms
Biochim Biophys Acta
(2010) Molecular genetics and animal models in autistic disorder
Brain Res Bull
(2002)- et al.
The teratology of autism
Int J Dev Neurosci
(2005) - et al.
Reactive microglia in hippocampal sclerosis associated with human temporal lobe epilepsy
Neurosci Lett
(1995) - et al.
Contribution of sex differences in the acute stress response to sex differences in water maze performance in the rat
Behav Brain Res
(2004) - et al.
Regulation of type-II calmodulin kinase: functional implications
Brain Res Rev
(1993) - et al.
Effect of chemically induced propionic acidemia on neurobehavioral development of rats
Pharmacol Biochem Behav
(1999) - et al.
Thalamic and hippocampal mechanisms in spatial navigation: a dissociation between brain mechanisms for learning how versus learning where to navigate
Behav Brain Res
(2006) - et al.
[3H]-DA release evoked by low pH medium and internal H+ accumulation in rat hypothalamic synaptosomes: involvement of calcium ions
Neurochem Int
(2003)
The many faces of CREB
Trends Neurosci
Oxidative stress in autism
Pathophysiology
Methylmalonic and propionic acids increase the in vitro incorporation of 32P into cytoskeletal proteins from cerebral cortex of young rats through NMDA glutamate receptors
Brain Res
Motivational systems in adolescence: possible implications for age differences in substance abuse and other risk-taking behaviors
Brain Cogn
Pyrosequencing study of fecal microflora of autistic and control children
Anaerobe
Valproic acid induces up- or down-regulation of gene expression responsible for the neuronal excitation and inhibition in rat cortical neurons through its epigenetic actions
Neurosci Res
Gastrointestinal abnormalities in children with autistic disorder
J Pediatr
Properties of gap junction blockers and their behavioral, cognitive and electrophysiological effects: animal and human studies
Prog Neuropsychopharmacol Biol Psychiatry
Functional characterization of human receptors for short chain fatty acids and their role in polymorphonuclear cell activation
J Biol Chem
Neurobiological effects of intraventricular propionic acid in rats: possible role of short chain fatty acids on the pathogenesis and characteristics of autism spectrum disorders
Behav Brain Res
Developments of a water-maze procedure for studying spatial learning in the rat
J Neurosci Methods
Differential regulation of the tyrosine hydroxylase and enkephalin neuropeptide transmitter genes in rat PC12 cells by short chain fatty acids: concentration-dependant effects on transcription and RNA stability
Brain Res
Intracerebroventricular injection of propionic acid, an enteric bacterial metabolic end-product, impairs social behavior in the rat: implications for an animal model of autism
Neuropharmacology
Intracerebroventricular injections of the enteric bacterial metabolic product propionic acid impair cognition and sensorimotor ability in the Long–Evans rat: further development of a rodent model of autism
Behav Brain Res
The adolescent brain and age-related behavioral manifestations
Neurosci Biobehav Rev
Sources of propionate in inborn errors of propionate metabolism
Metabolism
Social interactions in adolescent adult Sprague–Dawley rats: impact of social deprivation and test context familiarity
Behav Brain Res
Plasma fatty acid profiles in autism: a case–control study
Prostaglandins Leukot Essent Fatty Acids
Elevated levels of impulsivity and reduced place conditioning with d-amphetamine: two behavioral features of adolescence in mice
Behav Neurosci
Windows of vulnerability to psychopathology and therapeutic strategy in the adolescent rodent model
Behav Pharmacol
Diagnostic and Statistical Manual of Mental Disorders
Inhibition of oxidative metabolism by propionic acid and its reversal by carnitine in isolated rat hepatocytes
Biochem J
Epilepsy, electroencephalographic abnormalities and regression in children with autism
J Child Neurol
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