Intraventricular Infusions of Enteric Short Chain Fatty Acids Induce Behavioural, Neuropathological and Epigenetic Changes in Rats- Further Development of a Novel Rodent Model of Autism

Background: Diverse cell-cell interaction, neuroinflammatory and metabolic processes are implicated in the pathophysiology of autism spectrum disorders (ASDs). Environmental agents may modulate these factors through epigenetic mechanisms. Propionic (PPA) or butyric acids (BA) are short chain fatty acids (SCFA) present in diet, and are also a product of enteric bacteria fermentation.  SCFA have widespread effects on many of the above systems and may thus be  possible environmental triggers in ASD.  We have shown that PPA can elicit consistent ASD related brain and behavioural changes in rodents, while BA can induce genes implicated in catecholamine, enkephalin and CREB related processes in vitro.

Objectives: To examine the effects of chronic intracerebroventricular infusions of SCFA on behaviour, neuropathology and gene expression in rats.

Methods: Adult rats received infusions of pH 7.5 buffered PPA or BA (.26M) or PBS vehicle (0.1M) twice daily for 7 treatment days.  Immediately following microinfusion, the animals were placed into an automated open field (Versamax,Ethovision) and a variety of locomotor/social activity variables were assessed for 30 minutes. After sacrifice brains were examined either neuropathologically for innate neuroinflammation, or via microarray analysis (Affymetrix Rat Genome GeneChip 230 2.0 microarrays/MetaCoreTM platform) for ASD related markers/genes.  

Results: SCFA infusions increased locomotor activity and induced social impairment. Only PPA produced increased innate neuroinflammation (GFAP,CD68) but both PPA and BA increased vimentin immunoreactivity. Comparison analyses of the microarray data was performed from three brain regions: hippocampus, neocortex and the caudate nucleus. While similar number of gene IDs were found differential regulated in both, hippocampus (BA- 1052; PA 1060, common gene IDs 769) and neocortex (BA- 1185, PA-862; common gene IDs 574), the expression of significantly less genes was affected in the caudate nucleus (BA-87, PA -61 common genes 22), suggesting region-specific responses to SCFA. The expression of autism candidate genes such as BDNF was down regulated in all three regions consistent with human data (Adegbola A. et al., 2008), TLR2 and TLR7 and ceruloplasmin (Fatemi et al., 2005), GCH1 (serotonin biosynthesis, Hranilovic D. et al., 2008) genes were up-regulated.  Enrichment analysis (MetaCore) based on common genes identified functional ontologies like immune response TLR signaling, classic complement pathway, cell adhesion – ECM remodeling, inflammatory response as major processes affected by SCFA infusion. 

Conclusions: SCFA produce behavioural, neuropathological and gene expression effects reminiscent of ASD when intraventricularly infused in rats, providing further evidence of a plausible dietary/gut/CNS link to this disorder