Major depressive disorder (MDD) afflicts approximately 17 percent of the population and is one of the leading causes of total disability and economic burden[1]. Although there are medications that alleviate depressive symptoms, these have serious limitations. Most notably, available treatments require weeks or months to produce a therapeutic response, and only about one third of patients respond to the first medication prescribed [2]. In contrast, recent studies demonstrate that a single, low dose of a glutamate N-methyl-Daspartic acid (NMDA) receptor antagonist produces a rapid (within hours) antidepressant response that lasts for up to 7 days [3, 4], and is effective in MDD patients who are resistant to traditional antidepressants [5]. The mechanisms underlying rapid antidepressant actions are likely more complicated than simple NMDA receptor blockade, and so far have not been identified. We carried out a series of studies to examine the cellular signaling pathways that mediate the behavioral actions of NMDA receptor blockade, focusing on signaling cascades known to rapidly influence synaptic plasticity[6].
The drug used for clinical trials is ketamine, a nonselective NMDA receptor antagonist [7]. A low dose of ketamine (10 mg/kg), which is reported to have antidepressant actions in behavioral models of depression[7], rapidly activated the mammalian target of rapamycin(mTOR) signaling pathway in the prefrontal cortex (PFC) of rats. Activation of mTOR signaling was observed in a preparation enriched in synaptoneurosomes, and included increased levels of the phosphorylated and activated forms of eukaryotic initiation factor 4E binding protein 1 (4E-BP1), p70S6 kinase (p70S6K), and mTOR. Increased phosphorylation of 4E-BP1, p70S6K, and mTOR is transient, returning to basal levels by two hours after ketamine administration. In contrast, other antidepressants tested, including electroconvulsive seizure, imipramine, or fluoxetine, did not significantly influence mTOR signaling. Ketamine produced a similar rapid and transient increase in the phosphorylated and activated forms of extracellular signal-regulated kinase (ERK, including ERK1 and ERK2) and protein kinase B (PKB/Akt), growth factor signaling pathways that have been linked to activation of mTOR signaling[8]. The activation of 4E-BP1, p70S6K, mTOR, ERK, and Akt was dose dependent, occurring at relatively low doses (5 to 10 mg/kg) that produce antidepressant behavioral actions, but not at a higher anesthetic dose[7].
Major Depressive Disorder (MDD) is a serious medical issue however, the most commonly prescribed first-line pharmacological therapy for MDD, selective serotonin reuptake inhibitors (SSRIs), are effective only after several weeks of treatment. The delayed onset of therapeutic efficacy has been an unresolved issue and, despite decades of research, the molecular mechanisms underlying this delayed onset of antidepressant effects remains unknown.
A better understanding of the mechanism of temporal antidepressant efficacy is necessary to discover new and more effective therapeutic targets. The overall goal of an ongoing project in the Blendy Lab is to determine the translating state of serotonin neurons in the cell body and terminals following administration of an SSRI or a novel antidepressant. This approach utilizes a mouse-line that expresses enhanced green fluorescent protein (eGFP)-tagged ribosomes to track their location in the cell body and axon terminals of serotonin neurons. This method also enables identification of mRNA that are actively translating. Collectively, this unique combination of behavioral pharmacology, molecular techniques (RNA isolation, real-time PCR, immunohistochemistry), and bioinformatics analysis will identify potential new targets for the treatment of depression.
The purpose is to research the antidepressant effects of ketamine in a chronic unpredictable stress model. I will establish the chronic unpredictable stress model for 21 days stress. After 21 days chronic unpredictable stress test. I will evaluate the level of stress from stress mice and no stress mice from the coat score and weight change in 21 days. After 21 days, I will do the NIH test to evaluate the level of stress. If the mice are depressed, they will not as interested as other mice about the sweet food. I will do the male first and then will finish the female test. Since there could be some sexy difference of the behavior, I will also analyze the sexy difference. When the stress model establish, we will begin do the perfusion of the mice and stock their brain. I will do the brain slicing and observe the expression of gene in the brain. Since our lab has Pre-cre mice, we will use them to detect the gene expression better. I will do the genotyping first. And then, basing on the genotyping, I will do the research. After finishing the chronic unpredictable stress model, I will inject the ketamine and do the marble burying test. According to the number of marbles which the mice bury some of them in 5 minutes, we will analyze the degree of stress.
Genotyping Pet-cre mice
Materials:
Stock Number: 012712
Strain name: B6;Cg-Tg(Fev-cre)1Esd/J
Primers:
