Selective cortical VGLUT1 increase as a marker for antidepressant activity

The two recently characterized vesicular glutamate transporters (VGLUT) presynaptically mark and differentiate two distinct excitatory neuronal populations and thus define a cortical and a subcortical glutamatergic system (VGLUT1 and VGLUT2 positive, respectively). These two systems might be differentially implicated in brain neuropathology. Still, little is known on the modalities of VGLUT1 and VGLUT2 regulations in response to pharmacological or physiological stimuli. Given the importance of cortical neuronal activity in psychosis we investigated VGLUT1 mRNA and protein expression in response to chronic treatment with commonly prescribed psychotropic medications. We show that agents with antidepressant activity, namely the antidepressants fluoxetine and desipramine, the atypical antipsychotic clozapine, and the mood stabilizer lithium increased VGLUT1 mRNA expression in neurons of the cerebral cortex and the hippocampus and in concert enhanced VGLUT1 protein expression in their projection fields. In contrast the typical antipsychotic haloperidol, the cognitive enhancers memantine and tacrine, and the anxiolytic diazepam were without effect. We suggest that VGLUT1 could be a useful marker for antidepressant activity. Furthermore, adaptive changes in VGLUT1 positive neurons could constitute a common functional endpoint for structurally unrelated antidepressants, representing promising antidepressant targets in tracking specificity, mechanism, and onset at action.