ABSTRACT
RATIONALE: Studies in the Fmr1 knockout (KO) mouse, a model of fragile X syndrome (FXS), suggest that excessive signaling through group I metabotropic glutamate receptors (mGluRs), comprised of subtypes mGluR1 and mGluR5, may play a role in the pathogenesis of FXS. Currently, no studies have assessed the effect of mGluR1 modulation on Fmr1 KO behavior, and there has not been an extensive behavioral analysis of mGluR5 manipulation in Fmr1 KO mice. OBJECTIVES: The goals for this study were to determine if pharmacologic blockade of mGluR1 may affect Fmr1 KO behavior as well as to expand on the current literature regarding pharmacologic blockade of mGluR5 on Fmr1 KO behavior. METHODS: Reduction of mGluR1 or mGluR5 activity was evaluated on a variety of behavioral assays in wild-type (WT) and Fmr1 KO mice through the use of antagonists: JNJ16259685 (JNJ, mGluR1 antagonist) and MPEP (mGluR5 antagonist). RESULTS: JNJ and MPEP decreased marble burying in both WT and Fmr1 KO mice without reductions in activity. Neither JNJ nor MPEP affected the prepulse inhibition in either WT or Fmr1 KO mice. JNJ did not affect Fmr1 KO motor coordination but did impair WT performance. MPEP improved a measure of motor learning in Fmr1 KO but not WT mice. While both JNJ and MPEP decreased the audiogenic seizures in the Fmr1 KO, MPEP completely abolished the manifestation of seizures. CONCLUSION: These data illustrate that, while the manipulation of either mGluR1 or mGluR5 can affect select behaviors in the Fmr1 KO, we observe greater effects upon mGluR5 reduction.
Subject(s)
Disease Models, Animal , Fragile X Mental Retardation Protein/genetics , Fragile X Syndrome/genetics , Receptors, Metabotropic Glutamate/antagonists & inhibitors , Acoustic Stimulation/methods , Animals , Dose-Response Relationship, Drug , Fragile X Syndrome/psychology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Quinolines/pharmacology , Receptor, Metabotropic Glutamate 5 , Receptors, Metabotropic Glutamate/physiology , Reflex, Startle/drug effects , Reflex, Startle/physiologyABSTRACT
INTRODUCTION: Genetic heterogeneity likely contributes to variability in the symptoms among individuals with fragile X syndrome (FXS). Studies in the Fmr1 knockout (KO) mouse model for FXS suggest that excessive signaling through group I metabotropic glutamate receptors (Gp1 mGluRs), comprised of subtypes mGluR1 and mGluR5, may play a role. Hence, Gp1 mGluRs may act as modifiers of FXS. Currently no studies have addressed whether manipulation of mGluR1 activity may alter Fmr1 KO behavioral responses, and only a few have reported the effects of mGluR5 manipulation. Therefore, the goals for this study were to extend our understanding of the effects of modulating Gp1 mGluR activity on Fmr1 KO behavioral responses. METHODS: The present study determined if genetically reducing mGluR1 or mGluR5 by 50% affects an extensive array of behaviors in the Fmr1 KO. RESULTS: Reduction of mGluR1 moderately decreased Fmr1 KO activity. Reduction of mGluR5 caused an analgesic response in the Fmr1 KO and decreased active social behavior. Modulation of either mGluR1 or mGluR5 did not significantly alter audiogenic seizures, anxiety- and perseverative-related responses, sensorimotor gating, memory, or motor responses. CONCLUSIONS: Genetic reduction of mGluR1 or mGluR5 modified a few select Fmr1 KO behaviors, although these modifications appeared to be subtle in nature and/or limited to select behaviors. This may indicate that 50% reduction of either mGluR1 or mGluR5 is insufficient to produce behavioral changes, and therefore, these receptors may not be dominant modifiers of a number of Fmr1 KO behavioral phenotypes.
