Endotoxin elicits ambivalent social behaviors

Area of Science:

• Neuroscience
• Behavioral Biology
• Immunology

Background:

• The acute phase response to infection typically reduces social investigation.
• Previous studies often used inescapable environments and unfamiliar social stimuli, potentially confounding results.

Purpose of the Study:

• To investigate the effects of lipopolysaccharide (LPS) on social behavior in a controlled, semi-naturalistic setting.
• To determine if LPS induces social avoidance or ambivalence in rats familiar with their social partners.

Main Methods:

• Male Wistar rats were housed with familiar conspecifics from weaning.
• Radiotelemetry devices tracked spatial activity after LPS or saline injection in a novel arena.
• Social interaction time and spatial distribution relative to cagemates were analyzed.

Main Results:

• LPS induced expected thermoregulatory responses (hypothermia then fever).
• No significant change in the proportion of time spent in social interaction was observed.
• LPS-treated rats significantly increased distance from familiar cagemates, altering spatial activity.

Conclusions:

• LPS challenge results in a transient state of social ambivalence, not simple avoidance.
• Sickness responses may involve a persistent motivation for social contact coupled with increased avoidance of social environments.
• This plasticity in sickness behavior expression could be adaptive for social species.