NLRP1-Mediated Antidepressant Effect of Ketamine in Chronic Unpredictable Mild Stress Model in Rats

Abstract

Objective: NOD-like receptor protein 1 (NLRP1) inflammasome complex has been recently associated with chronic unpredictable mild stress (CUMS) model of depression. Our aim was to investigate whether ketamine-induced antidepressant effect is associated with suppression of NLRP1.

Methods: Wistar albino rats were divided into control, CUMS, CUMS+acute ketamine (a single 10 mg/kg dose) and CUMS+chronic ketamine (daily 10 mg/kg injections for 3 weeks) groups (n=10 for each group). Sucrose preference test and forced swimming test were performed to assess anhedonia and immobility time respectively for the severety of depression symptoms. Brain tissues were dissected and prefrontal cortex and hippocampus regions were used for real-time polymerase chain reaction (PCR) and immunohistochemical analysis.

Results: CUMS procedure significantly induced depressive-like symptoms whereas both acute and chronic ketamine treatment ameliorated them. mRNA expression levels of NLRP1, caspase 1, apoptosis-associated speck-like protein containing a CARD (ASC), NF-κB, endothelial nitric oxide synthase, IL-1β, IL-6, toll-like receptor 4 (TLR-4) and purinergic 2×7 receptor (P2X7R) and numbers of Iba- 1+and GFAP+glial cells were reduced by acute and/or chronic ketamine treatment.

Conclusion: In the present study for the first time upstream and downstream elements of the NLRP1 inflammasome complex are shown to be suppressed by ketamine thus reinforcing the involvement of NLRP1 in the physiopathology of depression.

Keywords: Depression; Glia; Inflammasome; Ketamine; NLRP1.

Figure 1.

The effect of chronic unpredictable mild stress (CUMS) procedure and acute or chronic ketamine (K) treatment on anhedonia-like behaviors of rats in sucrose preference test (upper panel) and on despair-like behaviors of rats in forced swimming test (lower panel). Vertical bars indicate standard errors. **p<0.01 vs. control group, ##p<0.01 and ###p<0.001 vs. CUMS group.

Figure 2.

The effect of chronic unpredictable mild stress (CUMS) procedure and acute or chronic ketamine (K) treatment on mRNA levels of NOD-like receptor protein (NLRP) inflammasome components and relevant neuroinflammatory mediators in the rat brain. *p<0.05, **p <0.01 and ***p<0.001 vs. control group. #p <0.05 and ##p <0.01 vs. CUMS group. ASC: apoptosis speck like protein, IL: interleukin, NF-kB: nuclear factor kappa B, eNOS: endothelial nitric oxide synthase. Vertical bars indicate standard errors.

Figure 3.

The effect of chronic unpredictable mild stress (CUMS) procedure and acute or chronic ketamine (K) treatment on microglia and astrocyte activation. (A) Number of Iba-1+ microglial cells in the hippocampus. (B) Number of GFAP+ astrocytes in the hippocampus. (C) Iba-1 (a-d) and GFAP (e-h) immunostaining of hippocampus: (a, e) control, (b, f) CUMS, (c, g) CUMS+acute K treatment, and (d, h) CUMS+chronic K treatment. Arrows, Iba-1 (a-d) or GFAP (e-h) immunoreactive microglia or astrocytes, respectively. Original magnification, ×400. **p <0.01 vs. control group, ##p <0.01 vs. CUMS group. Iba-1: ionized calcium-binding adapter molecule-1, GFAP: glial fibrillary acidic protein.

Figure 4.

The effect of chronic unpredictable mild stress (CUMS) procedure and acute or chronic ketamine (K) treatment on mRNA levels of toll-like receptor 4 (TLR-4) and purinergic 2X7 receptor (P2X7R). Vertical bars indicate standard errors. *p<0.05 vs. control group, #p <0.05 and ##p <0.01 vs. CUMS group.