Characterization of Spatial Learning and Sickness Responses in Aging Rats Following Recurrent Lipopolysaccharide...

Area of Science:

• Neuroscience
• Immunology
• Gerontology

Background:

• Infections in older adults can lead to cognitive decline.
• Limited research exists on the impact of recurrent infections on cognitive function.
• Immune system activation by infections triggers cytokine-mediated sickness responses.

Purpose of the Study:

• To investigate the effects of a recurrent infection model on sickness responses, spatial learning, and cytokine levels in aged rats.
• To examine the dissociation between cognitive and metabolic effects during recurrent immune challenges.

Main Methods:

• A pilot study using aged, male Brown Norway rats.
• Modeled recurrent infection using lipopolysaccharide (LPS) or saline administration over two weeks.
• Assessed spatial learning and memory using the Morris water maze (directional heading error, swim time latency, retention, probe trials).
• Measured plasma cytokine levels (Interleukin-6) at 5 and 24 hours post-injection.

Main Results:

• LPS-injected rats showed decreased food intake and weight, and increased directional heading error in Week 1.
• Despite reduced sickness behaviors in Week 2, LPS-injected rats exhibited persistent spatial learning deficits.
• Probe trials revealed memory deficits in the LPS-exposed group.
• Interleukin-6 levels were elevated post-LPS, particularly at 5 hours on Day 1 of Week 2.

Conclusions:

• Recurrent LPS exposure in aged rats leads to persistent cognitive impairment, dissociating from metabolic effects.
• Cognitive deficits, including spatial learning and memory impairment, occur despite diminished sickness responses.
• Further research is warranted to understand these effects in older human populations.