Decreased expression of mGluR5 within the dorsolateral prefrontal cortex in autism and increased microglial number in mGluR5 knockout mice: Pathophysiological and neurobehavioral implications Gursharan Chana a,b,⇑,1 , Liliana Laskaris a,b,1 , Christos Pantelis b,c , Piers Gillett a,b , Renee Testa c,d , Daniela Zantomio e , Emma L. Burrows f , Anthony J. Hannan f,g , Ian P. Everall b,1 , Efstratios Skafidas a,b,1 a Centre for Neural Engineering, The University of Melbourne, Parkville, Victoria, Australia b Department of Psychiatry, The University of Melbourne, Parkville, Victoria, Australia c Melbourne Neuropsychiatry Centre, Department of Psychiatry, The University of Melbourne & Melbourne Health, Parkville, Victoria, Australia d Department of Psychology, Monash University, Clayton, Victoria, Australia e Department of Haematology, Austin Health, Heidelberg, Victoria, Australia f Florey Institute of Neuroscience and Mental Health, University of Melbourne Parkville, Victoria, Australia g Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria, Australia article info Article history: Received 13 January 2015 Received in revised form 16 May 2015 Accepted 28 May 2015 Available online xxxx Keywords: Autism Glutamate Microglia Neuroinflammation Neuropathology Stereology abstract Metabotropic glutamate receptor 5 (mGluR5) and microglial abnormalities have been implicated in aut- ism spectrum disorder (ASD). However, controversy exists as to whether the receptor is down or upreg- ulated in functioning in ASD. In addition, whilst activation of mGluR5 has been shown to attenuate microglial activation, its role in maintaining microglial homeostasis during development has not been investigated. We utilised published microarray data from the dorsolateral prefrontal cortex (DLPFC) of control (n = 30) and ASD (n = 27) individuals to carry out regression analysis to assess gene expression of mGluR5 downstream signalling elements. We then conducted a post-mortem brain stereological investigation of the DLPFC, to estimate the proportion of mGluR5-positive neurons and glia. Finally, we carried out stereological investigation into numbers of microglia in mGluR5 knockout mice, relative to wildtype littermates, together with assessment of changes in microglial somal size, as an indicator of activation status. We found that gene expression of mGluR5 was significantly decreased in ASD versus controls (p = 0.018) as well as downstream elements SHANK3 (p = 0.005) and PLCB1 (p = 0.009) but that the pro-inflammatory marker NOS2 was increased (p = 0.047). Intensity of staining of mGluR5-positive neurons was also significantly decreased in ASD versus controls (p = 0.016). Microglial density was signif- icantly increased in mGluR5 knockout animals versus wildtype controls (p = 0.011). Our findings provide evidence for decreased expression of mGluR5 and its signalling components representing a key patho- physiological hallmark in ASD with implications for the regulation of microglial number and activation during development. This is important in the context of microglia being considered to play key roles in synaptic pruning during development, with preservation of appropriate connectivity relevant for nor- mal brain functioning. Ó 2015 Elsevier Inc. All rights reserved. 1. Introduction To date, the aetiology of autism spectrum disorder (ASD) remains poorly understood with diagnosis relying solely on clinical interview. Evidence linking the metabotropic glutamate receptor (mGluR5) to ASD pathogenesis has come from studies demonstrat- ing that mGluR5 is strongly linked to fragile X syndrome (FXS) and tuberous sclerosis (Tsc); two genetically defined disorders with significantly increased prevalence of ASD and similar core http://dx.doi.org/10.1016/j.bbi.2015.05.009 0889-1591/Ó 2015 Elsevier Inc. All rights reserved. Abbreviations: CAK b, cell adhesion kinase-b; CREB, cyclic AMP response binding protein; DAG, diacylglycerol; ER, endoplasmic reticulum; GKAP, guanylate kinase associated protein; Gq/Gq11, guanine nucleotide binding protein q/q11; IP3, inositol 1,4,5 trisphosphate; NMDA, N-methyl-D-aspartate; GRM5/mGluR5, meta- botropic glutamate receptor-5; MAPK, mitogen activated protein kinase; PIP2, Phosphatidylinositol 4,5-bisphosphate; PKC, protein kinase C; PLCB1, phospholi- pase C-beta 1; PSD95, post-synaptic density 95; SHANK3, SH3 and multiple ankyrin repeat domain. ⇑ Corresponding author at: Centre for Neural Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia. E-mail address: gchana@unimelb.edu.au (G. Chana). 1 These authors contributed equally. Brain, Behavior, and Immunity xxx (2015) xxx–xxx Contents lists available at ScienceDirect Brain, Behavior, and Immunity journal homepage: www.elsevier.com/locate/ybrbi Please cite this article in press as: Chana, G., et al. Decreased expression of mGluR5 within the dorsolateral prefrontal cortex in autism and increased microglial number in mGluR5 knockout mice: Pathophysiological and neurobehavioral implications. Brain Behav. Immun. (2015), http://dx.doi.org/ 10.1016/j.bbi.2015.05.009