Brexpiprazole (Rexulti®), a novel D2/3 receptor (R) partial agonist, was recently approved as monotherapy for schizophrenia, demonstrating effectiveness against both positive and negative symptoms, and also approved as add-on treatment to antidepressant drugs, inducing a potent antidepressant effect with a faster onset compared to an antidepressant given alone. Moreover, brexpiprazole has demonstrated pro-cognitive effects in preclinical studies. To explore whether the observed effects may be mediated via modulation of prefrontal glutamatergic transmission, we investigated the effect of brexpiprazole, alone and in combination with the SSRI escitalopram, on prefrontal glutamatergic transmission using in vitro electrophysiological intracellular recordings of deep layer pyramidal cells of the rat medial prefrontal cortex (mPFC). Nanomolar concentrations of brexpiprazole potentiated NMDAR-induced currents and electrically evoked EPSPs via activation of dopamine D1Rs, in similarity with the effect of the atypical antipsychotic drug clozapine. The effect of an ineffective concentration of brexpiprazole was significantly potentiated by the addition of escitalopram. When combined with escitalopram, brexpiprazole also potentiated AMPAR-mediated transmission, in similarity with the clinically rapid acting antidepressant drug ketamine. The effect on the AMPAR-mediated currents was also D1R dependent. In conclusion, our data propose that brexpiprazole exerts a clozapine-like potentiation of NMDAR-mediated currents in the mPFC, which can explain its efficacy on negative symptoms of schizophrenia and the pro-cognitive effects observed preclinically. Moreover, add-on brexpiprazole to escitalopram also potentiated AMPAR-mediated transmission, which may provide a neurobiological explanation to the faster antidepressant effect of add-on brexpiprazole in major depression.
Keywords: AMPA; Antidepressant; Antipsychotic; Dopamine D1 receptor; NMDA; mPFC.
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