The modulation of fragile X behaviors by the muscarinic M4 antagonist, tropicamide

Surabi Veeraragavan, Nghiem Bui, Jennie R. Perkins, Lisa A. Yuva-Paylor, Richard Paylor
2011 Behavioral Neuroscience  
Muscarinic acetylcholine receptors (mAChR) are G-protein coupled receptors (M1-M5), grouped together into two functional classes, based on their G protein interaction. Although ubiquitously expressed in the CNS, the M4 protein shows highest expression in the neostriatum, cortex, and hippocampus. Electrophysiological and biochemical studies have provided evidence for overactive mAChR signaling in the fragile X knock-out (Fmr1KO) mouse model, and this has been hypothesized to contribute to the
more » ... notypes seen in Fmr1KO mice. To address this hypothesis we used an M4 antagonist, tropicamide to reduce the activity through the M4 mAChR and investigated the behavioral response in the Fmr1KO animals. Data from the marble-burying assay has shown that tropicamide treatment resulted in a decreased number of marbles buried in the wild type (WT) and in the knockout (KO) animals. Results from the open field assay indicated that tropicamide increases activity in both the WT and KO mice. In the passive avoidance assay, tropicamide treatment resulted in the improvement of performance in both the WT and the KO animals at the lower doses (2 and 5 mg/kg) and the drug was shown to be important for the acquisition and not the consolidation process. Lastly, we observed that tropicamide causes a significant decrease in the percentage of audiogenic seizures in the Fmr1KO animals. These results suggested that pharmacological antagonism of the M4 receptor modulates select behavioral responses in the Fmr1 KO mice.
doi:10.1037/a0025202 pmid:21942438 pmcid:PMC3183989 fatcat:dewzjn6q4bgndomhevstnlcdlu