Sigma-1 Receptor Activation by Fluvoxamine Ameliorates ER Stress, Synaptic Dysfunction and Behavioral Deficits in a Ketamine Model of Schizophrenia

Abstract

Endoplasmic reticulum (ER) stress and misfolded proteins accumulation are recognized as central factors in the development of psychiatric disorders. This study evaluated the potential therapeutic effect of fluvoxamine, a potent sigma-1 receptor agonist in alleviating protein misfolding and the subsequent ER stress in ketamine-induced model of schizophrenia. NE100 hydrochloride, a sigma-1 receptor blocker, was used to investigate the role of this receptor in fluvoxamine-mediated effects. Rat model of schizophrenia was induced by intraperitoneal administration of ketamine (30 mg/kg/day) for 5 consecutive days. Then, rats were treated with fluvoxamine (30 mg/kg/day, p.o), with or without NE100 (1 mg/kg/day, i.p), for 14 days. Fluvoxamine improved the learning abilities, cognitive flexibility, and sociability functions of ketamine-subjected rats as evidenced in Morris water maze and three-chamber social interaction tests. It mitigated ketamine-induced inhibition of nNOS/PSD-95/NMDAR signaling pathway, thus augmented the function of parvalbumin-GABAergic neurons as indicated by increasing the prefrontal cortical levels of parvalbumin and GAD67. Fluvoxamine also attenuated the prefrontal cortical production of unfolded protein response markers, namely, IRE-1, PERK, and ATF-6, highlighting its ability to alleviate ER stress. Further, it exerted anti-apoptotic and anti-inflammatory effects as shown by lowering Iba-1, tumor necrosis factor-α (TNF-α), Bax, and caspase-12 levels contrary to elevating Bcl-2. Additionally, it attenuated the histopathological alterations in prefrontal cortical neurons. Noteworthy, the co-administration of NE100 reduced the advantageous effects of fluvoxamine, indicating the involvement of sigma-1 receptor in mediating the observed antipsychotic effects. Thus, sigma-1-mediated signaling pathways could be therapeutic targets for preventing or slowing schizophrenia progression.