mGlu3 Metabotropic Glutamate Receptors as a Target for the Treatment of Absence Epilepsy: Preclinical and Human Genetics Data

Abstract: Background: Previous studies suggest that different metabotropic glutamate (mGlu) receptor subtypes are potential drug targets for treating absence epilepsy. However, no information is
available on mGlu3 receptors.
Objective: To examine whether (i) changes of mGlu3 receptor expression/signaling are found in the
somatosensory cortex and thalamus of WAG/Rij rats developing spontaneous absence seizures; (ii)
selective activation of mGlu3 receptors with LY2794193 affects the number and duration of spike-
wave discharges (SWDs) in WAG/Rij rats; and (iii) a genetic variant of GRM3 (encoding the
mGlu3 receptor) is associated with absence epilepsy.
Methods: Animals: immunoblot analysis of mGlu3 receptors, GAT-1, GLAST, and GLT-1; real-
time PCR analysis of mGlu3 mRNA levels; assessment of mGlu3 receptor signaling; EEG analysis
of SWDs; assessment of depressive-like behavior.
Humans: search for GRM3 and GRM5 missense variants in 196 patients with absence epilepsy or
other Idiopathic Generalized Epilepsy (IGE)/ Genetic Generalized Epilepsy (GGE) and 125,748
controls.
Results: mGlu3 protein levels and mGlu3-mediated inhibition of cAMP formation were reduced in
the thalamus and somatosensory cortex of pre-symptomatic (25-27 days old) and symptomatic (6-7
months old) WAG/Rij rats compared to age-matched controls. Treatment with LY2794193 (1 or 10
mg/kg, i.p.) reduced absence seizures and depressive-like behavior in WAG/Rij rats. LY2794193
also enhanced GAT1, GLAST, and GLT-1 protein levels in the thalamus and somatosensory cortex.
GRM3 and GRM5 gene variants did not differ between epileptic patients and controls.
Conclusion: We suggest that mGlu3 receptors modulate the activity of the cortico-thalamo-cortical
circuit underlying SWDs and that selective mGlu3 receptor agonists are promising candidate drugs
for absence epilepsy treatment.