Venlafaxine stimulates an MMP-9-dependent increase in excitatory/inhibitory balance in a stress model of depression
Emerging evidence suggests that there is a reduction in overall cortical excitatory to inhibitory balance in major depressive disorder (MDD), which afflicts approximately 14-20% of individuals. Reduced pyramidal cell arborization occurs with stress and MDD, and may diminish excitatory neurotransmission. Enhanced deposition of perineuronal net (PNN) components also occurs with stress. Since parvalbumin-expressing interneurons are the predominant cell population that is enveloped by PNNs, which enhance their ability to release GABA, excess PNN deposition likely increases pyramidal cell inhibition. In the present study we investigate the potential for matrix metalloprotease-9 (MMP-9), an endopeptidase secreted in response to neuronal activity, to contribute to the antidepressant efficacy of venlafaxine, a serotonin/norepinephrine reuptake inhibitor. Chronic venlafaxine increases MMP-9 levels in murine cortex, and increases both pyramidal cell arborization and PSD-95 expression in the cortex of wild-type but not MMP-9 null mice. We have previously shown that venlafaxine reduces PNN deposition and increases the power of ex vivo gamma oscillations in conventionally-housed mice. Gamma power is increased with pyramidal cell disinhibition and with remission from MDD. Herein we observe that PNN expression is increased in a corticosterone-induced stress model of disease and reduced by venlafaxine. As compared to mice that receive concurrent venlafaxine, corticosterone treated mice also display reduced ex vivo gamma power and impaired working memory. Autopsy-derived prefrontal cortex samples show elevated MMP-9 levels in anti-depressant treated MDD patients as compared to controls. These preclinical and postmortem findings highlight a link between extracellular matrix regulation and MDD.