mGlu5 metabotropic glutamate receptors play a key role in mechanisms of activity-dependent synaptic plasticity underlying learning and memory processes, and are candidate drug targets for neurological and psychiatric disorders. Abnormalities in the expression or function of mGlu5 receptors are associated with most CNS disorders including autism spectrum disorders. mGlu5 receptor signaling proceeds through the hydrolysis of polyphosphoinositides (PI), a transduction mechanism that stimulate intracellular Ca2+ release and activation of protein kinase C as a result of inositol-1,4,5-trisphosphate (InsP3) and diacyglycerol formation, respectively. So far, mGlu5 receptor signaling has been assessed in brain slice preparation or cultured neurons by measuring the accumulation of radioactive inositolmonophosphate (InsP, the final product of InsP3 metabolism) in response to receptor activation with orthosteric agonists. These method is informative but not accurate and cannot be applied to the assessment of mGlu5 receptor signaling in living animals under physiological and pathological conditions. We have preliminary data indicating that mGlu5 receptor-mediated PI hydrolysis can be stimulated in vivo by treating animals with a brain permeant mGlu5 receptor PAM (positive allosteric modulator) combined with lithium salts (to inhibit the conversion of InsP into free inositol). The accumulation of non-radioactive InsP can then be measured in all CNS regions of individual animals by an ELISA method. Using this method we will perform a functional mapping of mGlu5 receptors in the mouse CNS during development and in the adult life and will examine how memory formation affects mGlu5 receptor-mediated PI hydrolysis in living mice. In addition, we will assess mGlu5 receptor signaling in the CNS of mutant mice modeling Fragile-X and Angeman's syndrome, two forms of monogenic autism which are characterized by abnormalities in mGlu5-dependent synaptic plasticity.
