Salmonella lipopolysaccharide (LPS) mediated neurodegeneration in hippocampal slice cultures

Neuroinflammation has been suggested to play an integral role in the pathophysiology of various neurodegenerative diseases. Bacterial lipopolysaccharide (LPS) endotoxins are general activators of immune-cells, including microglial cells, which induce expression of pro-inflammatory factors. The aim of this study was to characterize neurodegenerative effects of exposure to LPS, derived from Salmonella abortus equi bacteria, in an in vitro brain slice culture system. Quasi-monolayer cultures were obtained using roller-drum incubations of hippocampal slices from neonatal Sprague Dawley rats for three weeks. Microglia/macrophages were identified in the monolayer cultures by CD11b immunostaining, while neuronal populations identified included N-methyl-D-aspartate (NMDA-R1) receptor immunoreactive pyramidal neurons and smaller GABA-immunoreactive cells. Following exposure to LPS (100 ng/ml) an increased density of CD11b positive cells was found in the cultures. In addition, the LPS exposure produced a concentration-dependent loss of the NMDA-R1 immunoreactive neurons in the cultures which was substantial at 100 ng/ml LPS. The loss of NMDA-R1 cells was apparent already after 24 h exposure to LPS and seemed to be primarily due to necrotic-like cell death. However, a continued loss of cells was found when cultures were analyzed at 72 h, concomitant with an increase in the expression of p53 in the NMDA-R1 cells and TUNEL labeling of a few cells. Also the number of GABA-immunoreactive cells decreased rapidly and to a substantial extent after 24 h exposure to LPS, with a continued decrease up to 72 h. The findings show that Salmonella LPS increases the density of CD11b positive cells and acts as a potent neurotoxin in hippocampal roller-drum slice cultures. The LPS-induced neurodegeneration has both necrotic- and apoptotic-like properties and appears to be non-selective, affecting both pyramidal and GABA neurons. LPS-induced neurotoxicity in slice cultures may be a useful system to study processes involved in inflammatory-mediated neurodegeneration.