LIPOPOLYSACCHARIDE AND INTERLEUKIN-1-BETA AUGMENTED HISTIDINE-DECARBOXYLASE ACTIVITY IN CULTURED-CELLS OF THE RAT EMBRYONIC BRAIN

We investigated the effect of lipopolysaccharide (LPS) and various inf lammatory cytokines on the histidine decarboxylase (HDC) activity in c ultured cells of the rat embryonic brain. Histaminergic neuronal cell bodies were supposed to exist in cultured cells of the diencephalon bu t not in those of the cortex. The HDC activity was elevated by adding LPS and interleukin-1 beta (IL-1 beta) but not by tumor necrosis facto r-alpha (TNF-alpha) and IL-6 to the mixed primary cultures of dienceph alon. In the adherent cell fraction of the cultured diencephalon coils , HDC activity was also enhanced by LPS and IL-I beta, In a similar ma nner, LPS augmented HDC activity in the mixed primary culture of cereb ral cortical cells and in its adherent cell fraction, The effects of I L-1 beta but not LPS in the mixed primary culture of diencephalon were canceled by a prior exposure to cytosine-beta-D-arabinofuranoside. Th e changes in HDC activity after exposure to LPS for 12 h were not acco mpanied by increased mRNA levels. In these cell cultures, mast cells w ere not detected by Alcian Blue staining. These results indicated the presence of the third type of HDC-bearing cell besides neurons and mas t cells in the brain. The increase of HDC activity by IL-1 beta might be due to cell proliferation.