Neuropeptide Y (NPY), a 36 amino acid neurotransmitter, is involved in the regulation of emotional behavior and its role in the central responses to peripheral immune challenge is postulated. Plasma NPY levels rises in human sepsis and NPY improved survival in the experimental endotoxic shock induced by lipopolysaccharide (LPS) injection. Some of the behavioral effects of LPS, anorexia, depression and anxiety-like behavior are also modulated by NPY. Therefore, in the present study tried to fi nd out if LPS affected NPY neurons in mouse hippocampus, a structure most susceptible to damage and involved in the regulation of emotion. Male C57BL/6 mice were injected with LPS (1 m/kg, i.p.) and their brains were taken after 6 or 24 h. The brains were fi xed with paraformaldehyde, cut into frontal sections containing the dorsal hippocampus and processed by immunohistochemistry using an NPY antibody. NPY-immunoreactive neurons were counted stereologically in hippocampal subregions CA1+2, CA3 and DG+hilus, and results were statistically analysed. It was found that after 24 h LPS decreased by ca. 38% the number of NPY-positive neurons in the hippocampal CA regions. The effect was particularly signifi cant in the CA3 area. Moreover, staining intensity was diminished. The obtained results indicate a decrease in NPY expression in the hippocampus, which may be due to the peptide release induced by LPS infl ammatory action. Supported by MS&HE.28/E32/ BWSN-0053/2008.
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