LPS + LT injections increase hippocampal neurodegeneration in young animals. (A) Fluoro-Jade B staining of brain slices of animals 72 hours after saline + LPS, saline + LT or LPS + LT injection. Images correspond to the CA1, CA3 and dentate gyrus (DG) of the hippocampal formation. Note the absence of neurodegeneration in saline + LPS rats, agreeing with biochemical data. Saline + LT injection produced a moderate neurodegeneration, but the number of positive Fluoro-Jade B cells was clearly increased in rats injected with LPS + LT. Representative photographs with cresyl violet staining are shown in the middle panel: (a) saline + LPS; (b) saline + LT; and (c) LPS + LT. In the lower panel is shown the immunohistochemistry detection of the neuronal marker NeuN in hippocampal slices from rats injected with (d)saline + LPS; (e) saline + LT and (f) LPS + LT. Note the strong diminution in the immunolabeling intensity for this neuronal marker in rats injected with LPS + LT. For orientative purposes, dotted lines represent the localization of the stratum pyramidale and granular layer, where somata of principal neurons are located. (B) Representative western blot of caspase-3. The amount of processed caspase-3 was higher in the LPS + LT rats in agreement with biochemical and cellular data. Image corresponding to the processed fragments is overexposed for a better visualization. Experiments were done in parallel and repeated at least three times with similar results. DG: dentate gyrus; gl: granular layer; LPS: lipopolysaccharide; LT: lactacystin; sp: stratum pyramidale.