EFFECT OF ZINC, COPPER AND GLUCOCORTICOIDS ON METALLOTHIONEIN LEVELS OF CULTURED NEURONS AND ASTROCYTES FROM RAT-BRAIN

The knowledge of brain metallothionein (MT) regulation and especially of MT presence in specific cell types is scarce. Therefore; the effect of several well-known MT inducers, measured by radioimmunoassays usin g antibodies that cross-react with MT-I and MT-II or specific for MT-I and which do not cross-react with human growth inhibitory factor (GIF or MT-III), has been studied in primary cultures of neurons or astroc ytes obtained from rat cerebrum. MT-I levels in glial cells were about ten times higher than those in neuronal cells (538 +/- 194 vs. 49 +/- 16 pg MT-I/mu g protein, mean +/- S.D. from three separate cell prepa rations). Increasing the concentration of Zn in the bovine serum album in (BSA)-containing culture medium up to 50 mu M significantly increas ed MT-I levels by up to 3.5-fold in neurons and 2.5-fold in astrocytes . In contrast, Cu up to 50 mu M increased MT-I levels in a saturable m anner in both neurons (up to 5-fold) and astrocytes (up to 1.5-fold), the maximum effect occurring at 5 mu M Cu. In general, the combination of Zn and Cu further increased MT-I levels. The effect of the metals on MT-I appeared to reflect metal uptake, since MT-I induction was les s marked when the BSA concentration in the medium was increased from 2 to 10 mg/ml. Dexamethasone increased MT-I levels in both neurons and astrocytes in vitro in a concentration-dependent manner. Endotoxin, IL -1 and IL-6 did not have a significant effect on glial MT levels at th e concentrations studied. The administration of dexamethasone to rats increased MT-I levels in non-frontal cortex, cerebellum, pens + medull a, midbrain and hippocampus, but not in hypothalamus, frontal cortex a nd striatum. Endotoxin increased liver but not brain MT-I levels. Immu nocytochemical studies in adult rat brain preparations with a polyclon al antibody that cross-reacts with MT-I and MT-II indicated that immun ostaining was always nuclear in glial cells, whereas in neurons it was nuclear in the cerebral cortex, hippocampus and the granular layer of the cerebellum, and nuclear plus cytoplasmic in Purkinje cells in the cerebellum, hypothalamic nuclei and gigantocellular reticular nucleus in the brain stem. Meninges, choroidal plexus, ependymal and endothel ial cells were also MT-immunoreactive.