Background: Despite significant progress in understanding the mechanisms underlying hippocampal involvement in neuropsychiatric systemic lupus erythematosus (NPSLE), our understanding of how neuroinflammation affects the brain neurotransmitter systems is limited. To date, few studies have investigated the role of neurotransmitters in pathogenesis of NPSLE with contradictory results.
Methods: Hippocampal tissue from NZB/W-F1 lupus-prone mice and age-matched control strains were dissected in both pre-nephritic (3-month-old) and nephritic (6-month-old) stages. High-Performance Liquid Chromatography (HPLC) was used to evaluate the level of serotonin (5-HT), dopamine (DA), and their metabolites 5-HIAA and DOPAC, respectively, in mouse hippocampi.
Results: Lupus mice exhibit decreased levels of serotonin at the early stages of the disease, along with intact levels of its metabolite 5-HIAA. The 5-HT turnover ratio (5-HIAA/5-HT ratio) was increased in the hippocampus of lupus mice at pre-nephritic stage suggesting that low hippocampal serotonin levels in lupus are attributed to decreased serotonin synthesis. Both DA and DOPAC levels remained unaffected in lupus hippocampus at both early and late stages.
Conclusion: Impaired hippocampal serotonin synthesis in the hippocampus of lupus-prone mice represents an early neuropsychiatric event. These findings may have important implications for the use of symptomatic therapy in diffuse NPSLE.
Keywords: Systemic lupus erythematosus; hippocampus; microglia; neuropsychiatric lupus; serotonin.