Preconditioning with TLR-3 agonists reduced infarct volume in P5 ischemic rat brain. P5 or P7 rats randomly received either a normal saline or poly I:C injection (n = 9-11 pups/group/age) as described in Methods. 48 h after poly I:C or normal saline injection, HI injury was induced and animals were then killed 1 week later and brains were immediately removed to assess tissue damage using H&E staining as described in Methods. The area of tissue damage (surrounded by dotted line) in the affected hemisphere is significantly greater in the untreated (a) compared to the poly I:C treated (b) P5 rat. Infarct volumes were compared between poly I:C treated and untreated P5 and P7 rat pups. The total area of brain tissue loss was measured on H&E stained sections using the Nikon NIS-Element Basic Research Image analysis software system, version 3.0. Total infarct volume was calculated using the formula V = ∑APt, where V is the total volume expressed as mm3, A is the sum of the areas measured, P is the inverse of the section sampling fraction (1/200), and T is the section thickness (5 μm) . Poly I:C ischemic preconditioning reduced infarct volume from 21.9 ± 4.0 (mean ± SEM) mm3 to 7.1 ± 2.0 (mean ± SEM) mm3 in P5 rats but had no protective effect in P7 rats (c). * P ≤0.002 when infarct volume compared to saline treated rats of the same age group.