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Updated: Jun 18, 2026
Brain Ventricular Microinjections of Lipopolysaccharide into Larval Zebrafish to Assess Neuroinflammation and Neurotoxicity
Published on: August 23, 2022
Systemic administration of lipopolysaccharide induces cyclooxygenase-2 immunoreactivity in endothelium and increases
Dae Won Chung1, Ki-Yeon Yoo, In Koo Hwang
1Department of Anatomy and Cell Biology, College of Veterinary Medicine and BK21 Program for Veterinary Science, Seoul National University, Seoul, 151-742, South Korea.
Abstract:
In this study, we observed the effects of lipopolysaccharide (LPS) on neurodegeneration and immune response in the hippocampus. LPS is a gram-negative bacterial cell surface proteoglycan and known as a bacterial endotoxin. For this, we investigated the optimal concentration of LPS influencing the ICR mouse hippocampus to measure the LPS receptor, e.g., toll-like receptor 4 (TLR4), expression in mouse hippocampal homogenates. TLR4 expression was significantly and prominently increased in the hippocampal homogenates of the LPS (1 mg/kg)-treated group. Next, we examined pro-inflammatory response in the hippocampus using cyclooxygenase-2 (COX-2, a marker for inflammatory response) immunohistochemistry after LPS treatment. COX-2 immunoreactivity was significantly increased in the endothelium of blood vessels in the hippocampus 6 h after LPS treatment, judging from double immunofluorescence study with platelet-derived endothelial cell adhesion molecule-1 (PECAM-1, a marker for endothelial cells): it decreased 12 h and disappeared 24 h after LPS treatment. In addition, the ionized calcium-binding adapter molecule 1 (Iba-1)-immunoreactive ((+)) microglia were morphologically activated in the mouse hippocampus after LPS treatment. At 24 h after LPS treatment, Iba-1(+) microglia of activated forms were abundant in the hippocampus. However, NeuN (a neuron-specific soluble nuclear antigen)(+) neurons were not significantly changed in the hippocampus after LPS treatment. Fluoro-jade B (a marker for neuronal degeneration)(+) cells were not detected in the hippocampus at any time after LPS treatment. In addition, there were no significant differences in permeability of blood-brain barriers at any time points after LPS treatment. In brief, our results indicate that intraperitoneal administration of 1 mg/kg LPS effectively induces LPS receptor (TLR4) expression in the hippocampus, and the treatment increases corticosterone levels, inflammation in the blood vessels, and microglial activation in the hippocampus without any neuronal damage.
Insights
Lipopolysaccharide (LPS) administration in mice increases toll-like receptor 4 (TLR4) expression and activates microglia in the hippocampus, inducing inflammation without causing neuronal damage or blood-brain barrier issues.
Area of Science:
- Neuroscience
- Immunology
- Toxicology
Background:
- Lipopolysaccharide (LPS) is a potent bacterial endotoxin known to trigger immune responses.
- The hippocampus is a critical brain region involved in learning and memory, susceptible to inflammatory processes.
Purpose of the Study:
- To investigate the effects of LPS on neuroinflammation and neuronal integrity in the mouse hippocampus.
- To determine the optimal LPS concentration for inducing measurable changes in the hippocampus.
- To analyze the expression of LPS receptors and markers of inflammation and neuronal damage.
Main Methods:
- Mice were treated with varying concentrations of LPS to identify the optimal dose (1 mg/kg).
- Hippocampal homogenates were analyzed for toll-like receptor 4 (TLR4) expression.
- Immunohistochemistry was used to detect cyclooxygenase-2 (COX-2) and ionized calcium-binding adapter molecule 1 (Iba-1) as markers for inflammation and microglial activation.
- NeuN and Fluoro-jade B staining assessed neuronal survival and degeneration, respectively.
- Blood-brain barrier permeability was evaluated.
Main Results:
- LPS treatment (1 mg/kg) significantly upregulated TLR4 expression in the hippocampus.
- Increased COX-2 immunoreactivity was observed in hippocampal blood vessels, indicating vascular inflammation.
- Microglia (Iba-1 positive cells) showed morphological activation.
- No significant changes in neuron counts (NeuN positive cells) or neuronal degeneration (Fluoro-jade B positive cells) were detected.
- Blood-brain barrier permeability remained unaffected.
Conclusions:
- Intraperitoneal administration of 1 mg/kg LPS induces TLR4 expression, vascular inflammation, and microglial activation in the mouse hippocampus.
- Despite inflammatory changes, LPS at this dose does not cause significant neuronal damage or compromise the blood-brain barrier.
- The study provides insights into the early neuroinflammatory responses to LPS in the hippocampus.
