Hypo-anxious phenotype of adolescent offspring prenatally exposed to LPS is associated with reduced mGluR5 expression in hippocampus.

Many studies have reported long-term modulation of metabotropic glutamate receptor 5 (mGluR5) by inflammatory processes and a pharmacological modulation of mGluR5 is known to regulate anxiety level. However, it is not known if non-pharmacological modulation of mGluR5 by inflammation impaired the unconditional level of anxiety. In this study, we investigated this relation in LPS prenatal immune challenge (120μg/kg, 3x i.p. injection in late gestation), a developmental model of neuroinflammation in which some studies have reported hypo-anxious phenotype. Using positron emission tomographic imaging (PET) approaches, we have demonstrated a decrease in the binding potential of [18F]fluoro-5-(2-pyridinylethynyl)benzonitrile ([18F]FPEB, a radioligand for mGluR5) in hippocampus of adolescent offspring prenatally exposed to LPS, without significant change in the binding of [11C]peripheral benzodiazepine receptor 28 ([11C]PBR28), an inflammatory marker. In addition, dark-light box emergence test revealed a lower level of anxiety in LPS-exposed offspring and this behavioural phenotype was associated with the binding potential of [18F]FPEB in hippocampus. These results confirm that neuroinflammation during developmental phase modulates the physiology of mGluR5 and this alteration can be associated with behavioural phenotype related to anxiety. In addition, this study supports a hypotheses that mGluR5 could be used as a diagnostic target in anxiety.