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Updated: Oct 7, 2025
A Chronic Immobilization Stress Protocol for Inducing Depression-Like Behavior in Mice
Published on: May 15, 2019
Monophosphoryl Lipid A Tolerance Against Chronic Stress-Induced Depression-Like Behaviors in Mice
Fu Li1, Xu Lu2, Yaoying Ma2
1Department of Pharmacy, Changzhou Geriatric Hospital Affiliated to Soochow University, Changzhou No.7 People's Hospital, Changzhou, Jiangsu, China.
Backgrounds:
Our recent studies reported that a single injection with lipopolysaccharide (LPS) before stress exposure prevents depression-like behaviors in stressed mice. Monophosphoryl lipid A (MPL) is a derivative of LPS that lacks the undesirable properties of LPS. We hypothesize that MPL can exert a prophylactic effect on depression.
Methods:
The experimental mice were pre-injected with MPL before stress exposure. Depression in mice was induced through chronic social defeat stress (CSDS). Behavioral tests were conducted to identify depression-like behaviors. Real-time polymerase chain reaction and biochemical assays were performed to examine the gene and protein expression levels of pro-inflammatory cytokines.
Results:
A single MPL injection 1 day before stress exposure at the dosages of 400, 800, and 1600 μg/kg but not 200 μg/kg prevented CSDS-induced depression-like behaviors in mice. This effect of MPL, however, vanished with the extension of the interval time between drug injection and stress exposure from 1 day or 5 days to 10 days, which was rescued by a second MPL injection 10 days after the first MPL injection or by a 4× MPL injection 10 days before stress exposure. A single MPL injection (800 μg/kg) before stress exposure prevented CSDS-induced increases in the gene expression levels of pro-inflammatory cytokines in the hippocampus and prefrontal cortex. Pre-inhibiting the innate immune stimulation by minocycline pretreatment (40 mg/kg) abrogated the preventive effect of MPL on CSDS-induced depression-like behaviors and neuroinflammatory responses in animal brains.
Conclusions:
MPL, through innate immune stimulation, prevents stress-induced depression-like behaviors in mice by preventing neuroinflammatory responses.
Insights
Monophosphoryl lipid A (MPL) prevents depression-like behaviors in mice exposed to stress. This prophylactic effect is mediated by innate immune stimulation and reduced neuroinflammation, offering a potential therapeutic strategy.
Area of Science:
- Neuroscience
- Immunology
- Pharmacology
Background:
- Lipopolysaccharide (LPS) pre-exposure can prevent stress-induced depression-like behaviors.
- Monophosphoryl lipid A (MPL), a less toxic LPS derivative, is investigated for similar prophylactic effects.
- Depression is a complex disorder with significant neuroinflammatory components.
Purpose of the Study:
- To investigate the prophylactic effect of Monophosphoryl lipid A (MPL) on depression-like behaviors induced by chronic social defeat stress (CSDS).
- To determine the role of innate immune stimulation and neuroinflammation in MPL's preventive effects.
- To explore optimal dosing and timing for MPL administration.
Main Methods:
- Mice were pre-injected with varying doses of MPL before CSDS exposure.
- Behavioral tests were used to assess depression-like phenotypes.
- Gene and protein expression of pro-inflammatory cytokines were analyzed using RT-PCR and biochemical assays.
- The role of innate immunity was assessed using minocycline pretreatment.
Main Results:
- A single MPL injection (400-1600 μg/kg) 1 day before CSDS prevented depression-like behaviors.
- The preventive effect diminished with longer intervals (10 days) but was restored with a second injection or increased frequency.
- MPL suppressed CSDS-induced pro-inflammatory cytokine expression in the hippocampus and prefrontal cortex.
- Minocycline pretreatment blocked MPL's preventive effects, indicating involvement of innate immune stimulation.
Conclusions:
- Monophosphoryl lipid A (MPL) demonstrates prophylactic efficacy against stress-induced depression-like behaviors in mice.
- MPL exerts its effects by modulating innate immune responses and reducing neuroinflammation.
- These findings suggest MPL as a potential therapeutic agent for preventing stress-related depression.
