Cytochemical and cell biological study on the mechanism of synthesis and action of neurosteroids in the olfactory bulb.

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This study aims to clarify the mechanism of synthesis and action of neurosteroid in the rat and mouse olfactory bulbs, and to know the physiological roles of neurosteroids in this organ. The results obtained are as follows :1)Steroid synthesixzing enzymes (P450scc, 3beta-HSD, 17beta-HSD, P450c17, aromatase, 5alpha-reductase) and estrogen receptor (ER) were immunocytochemically localized in the olfactory bulb. The enzymes except 5alpha-reductase and ER were present in neurons but 5alpha-reductase was present in glial cells.2)The results of RT-PCR, Northern-blotting, and Western-blotting showed the presence of the enzymes and ER at the DNA, mRNA and pretein level in the olfactory bulb.3)The enzyme actibvities of P450scc, 17beta-HSD and 5alpha-reductase were demonstrated in the olfactory bulb.4)Whe mice were administered with estradiol, the ecpressions of P450scc, P450c17, 3beta-HSD and aromatase were suppressed in the olfactory bulb. However, the expression of the other enzymes and ER did not change.5)Olfactory ensheathing cells were themain 5alpha-reductase immunopositive cells in the olfactory nerve layer of the olfactory bulb. However, in the other layer of the olfactory bulb, the 5alpha-reductase immunopositive cells were astrocytes and oligodendorcytes.6)In order to compare the results, immunohisitochemistry was achieved in the cerebellum and hippocampus. The results showed that 5alpha-reductase was present in astrocytes and oligodendrocytes in these brain areas, too.7)When mice were treated with estradiol or progesterone, mRNAs of P450c17 and aromatase in the olfactory bulb were decreased, but they were increased by the treatment with dihydorotestosterone.8)The present results showed that all the enzymes required for the sex-steroid synthesis were present in the olfactory bulb, and that the expression of the enzymes was controlled by sex-steroids.