Using 1-ethyl-3(3-dimethyl-aminopropyl)-carbodiimide (EDAC) fixation and immunocytochemical confocal microscopic study, bright serotonin and histamine fluorescence appeared in the nucleus of rat peritoneal mast cells. In case of paraformaldehyde fixation, this was not observed. The phenomenon can be explained by the cross-linking effect of EDAC, which did not allow the efflux of biogenic amines from the nucleus. This means that biogenic amines are present in the nucleus of mast cells, and this is supported by the flow cytometric measurement data of the whole cell. Other hormones studied (triiodothyronine, insulin, and endorphin) were not present in the nucleus. Four pharmaca with biogenic amine-influencing character in the central nervous system were used for studying the relation between the external (surrounding and cytoplasmic) and nuclear biogenic amine content of mast cells. Fluoxetine, a serotonin reuptake inhibitor depleted nuclear as well as cytoplasmic serotonin content. Clorgyline, a MAO-A inhibitor, decreased cytoplasmic serotonin content and weakened nuclear serotonin fluorescence. The tryptophan hydroxylase inhibitor, para-chlorophenylalanine (PCPA), and the mast cell degranulator, Compound 48/80, reduced cytoplasmic serotonin content without influencing nuclear content. Histamine fluorescence was influenced solely by fluoxetine. The results show that nuclear 5-HT content is dependent firstly of serotonin uptake and reuptake. To our knowledge, this is the first exact report on the presence of non-steroid-type-receptor-transported hormones inside the nucleus of a cell. © 2005 Elsevier Inc. All rights reserved.
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