Changes in behaviour and cytokine expression upon a peripheral immune challenge.

Area of Science:

• Neuroscience
• Immunology
• Psychiatry

Background:

• Depression is linked to inflammation, but mechanisms are unclear.
• Peripheral inflammation can cause sickness and depressive behaviors in animals.
• A distinction between sickness and depression behavior is proposed, possibly due to central immune mediator changes.

Purpose of the Study:

• To investigate the role of central immune mediators in distinguishing sickness and depressive behaviors induced by peripheral inflammation.
• To examine the temporal and regional changes in brain cytokines and COX enzymes following lipopolysaccharide (LPS) administration.

Main Methods:

• Rats were administered lipopolysaccharide (LPS) intraperitoneally for 4 days.
• Sickness and depressive-like behaviors were assessed.
• Protein and mRNA levels of cytokines (IL-1β, IL-6, TNF-α) and cyclooxygenase (COX) enzymes were measured in serum, CSF, and brain regions (frontal cortex, hippocampus, striatum).

Main Results:

• LPS induced sickness behavior and elevated peripheral and central cytokine levels within 2 hours.
• Specific brain regions showed altered cytokine mRNA transcription (IL-1β, IL-6, TNF-α).
• Depressive-like behavior emerged at 24 hours with normalized peripheral cytokines but increased central IL-1β and CSF levels, indicating persistent neuroinflammation.

Conclusions:

• Peripheral inflammation induces region-specific central cytokine and COX enzyme transcription in the brain.
• Distinct temporal patterns of central immune mediator changes correlate with sickness and depressive behaviors.
• Persistent central inflammation in the brain parenchyma occurs even after peripheral inflammation and sickness behavior subside.