This study investigated the expression of nitric oxide (NO)-synthesizing enzymes and the glial reaction in the rat hippocampal formation following sleep deprivation for 5 days. Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) reactivity was markedly reduced in the hippocampal CA1, CA2 and CA3 sectors as well as in the dentate gyrus, suggesting a suppression of NO production in these areas. Microglial cells were hypertrophic and showed an up-regulation of complement type 3 receptors as determined by antibody OX-42. However, expression of major histocompatibility complex class I and II antigens, and antigen of monocyte/macrophage lineage marked by OX-18, OX-6 and ED1, respectively, was undetected. Astrocytes also displayed hypertrophied processes with enhanced glial fibrillary acidic protein (GFAP) immunoreactivity. Western blots of hippocampal tissues corroborated the above-mentioned morphological findings in that expression of NO-synthase (NOS) was decreased while that of OX-42 and GFAP was increased in the sleep-deprived rats. Since NO is thought to be involved in memory consolidation processes in the hippocampus during sleep, the inhibition of NADPH-d and NOS reactivities may account for the memory decline after long-term sleep deprivation. The concomitant reactions in microglia and astrocytes suggest the involvement of these cells in the deleterious effect of prolonged sleep deprivation.
Copyright 2003 S. Karger AG, Basel