Loss of Glial Glutamate and Aspartate Transporter (Excitatory Amino Acid Transporter 1) Causes Locomotor Hyperactivity and Exaggerated Responses to Psychotomimetics: Rescue by Haloperidol and Metabotropic Glutamate 2/3 Agonist

Background: Recent data suggest that excessive glutamatergic signaling in the prefrontal cortex may contribute to the pathophysiology of schizophrenia and that promoting presynaptic glutamate modulation via group II metabotropic glutamate 2/3 (mGlu2/3) receptor activation can exert antipsychotic efficacy. The glial glutamate and aspartate transporter (GLAST) (excitatory amino acid transporter 1 [EAAT1]) regulates extracellular glutamate levels via uptake into glia, but the consequences of GLAST dysfunction for schizophrenia are largely unknown. Methods: We examined GLAST knockout mice (KO) for behaviors thought to model positive symptoms in schizophrenia (locomotor hyperactivity to novelty, exaggerated locomotor response to N-methyl-D-aspartate receptor [NMDAR] antagonism) and the ability of haloperidol and the mGlu2/3 agonist LY379268 to normalize novelty-induced hyperactivity. Results: Glial glutamate and aspartate transporter KO consistently showed locomotor hyperactivity to a novel but not familiar environment, relative to wild-type (WT) mice. The locomotor hyperactivity-inducing effects of the NMDAR antagonist MK-801 was exaggerated in GLAST KO relative to WT. Treatment with haloperidol or LY379268 normalized novelty-induced locomotor hyperactivity in GLAST KO. Conclusions: Schizophrenia-related abnormalities in GLAST KO raise the possibility that loss of GLAST-mediated glutamate clearance could be a pathophysiological risk factor for the disease. Our findings provide novel support for the hypothesis that glutamate dysregulation contributes to the pathophysiology of schizophrenia and for the antipsychotic potential of mGlu2/3 agonists.