Aβ25-35 Injection into the Temporal Cortex Induces Chronic Inflammation that Contributes to Neurodegeneration and Spatial Memory Impairment in Rats

Amyloid-beta (A beta)(25-35) is able to cause memory impairment and neurodegenerative events. Recent evidence has shown that the injection of A beta(25-35) into the temporal cortex (TCx) of rats increases the inflammatory response; however, it is unclear how the inflammatory process could be involved in the progression of A beta(25-35) toxicity. In this study we investigated the role of inflammation in the neuronal damage and spatial memory impairment generated by A beta(25-35) in rat TCx using immunohistochemistry, ELISA, and a behavioral test in the radial maze. Our findings show that A beta(25-35) -injection into the TCx induced a reactive gliosis (GFAP and CD11b-reactivity) and an increase of pro-inflammatory cytokines (IL-1 beta, IL-6, IL-17, and TNF-alpha) in the TCx and the hippocampus at 5, 15, and 30 days after injection. Thirty days after A beta(25-35) injection, we observed that the inflammatory reaction probably contributed to increase the immunoreactivity of inducible nitric oxide synthase and nitrite levels, as well as to the loss of neurons in TCx and hippocampus. Behavioral performance showed that the neurodegeneration evoked by A beta(25-35) delayed acquisition of learning and impaired spatial memory, because the A beta(25-35)-treated animals showed a greater number of errors during the task than the control group. Previous administration of an interleukin receptor antagonist (IL-1ra) (10 and 20 mu g/mu L, into TCx), an anti-inflammatory agent, suppressed the A beta(25-35)-induced inflammatory response and neurodegeneration, as well as memory dysfunction. This study suggests that the chronic inflammatory reaction could contribute to the progression of A beta(25-35) toxicity and cause cognitive impairment.