FURUKAWA Yasuo FAC.SCI., HIROSHIMA UNIVERSITY ASSOCIATE PROFESSOR, 理学部, 助教授 (40209169)
YAMAZAKI Takeshi FAC.INTEGRATETD ARTS AND SCI., HIROSHIMA UNIVERSITY RES.ASSOCIATE, 総合科学部, 助手 (30192397)
KOMINAMI Shiro FAC.INTEGRATED ARTS AND SCI., HIROSHIMA UNIVERSITY PROFESSOR, 総合科学部, 教授 (10106776)
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Fiscal Year 1997 : ¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1996 : ¥5,600,000 (Direct Cost : ¥5,600,000)
Steroid hormones supplied by peripheral steroidogenic glands regulate neuronal functions during development and in adulthood. Peripheral steroids cross the blood-brain barrier as a result of their lipid solubility and act on brain tissues through intracellular receptor-mediated mechanisms that regulate the transcription of specific genes. Therefore, the brain is considered to be a target site of peripheral steroids. Recently, we obtained new findings that the avian brain also possesses a steroidogenic enzyme, cytochrome P450scc, and produces pregnenolone and its sulfate ester, by biochemical and immunochemical approaches. In addition, our immunohistochemical studies with avian brain indicated that an intense immunoreaction with the polyclonal antibody directed against the purified bovine adrenal P450scc is present in soma and dendrites of the Purkinje cell, a typical cerebellar neuron. We further demonstrated that steroidogenic enzyme P450scc appears in the rat Purkinje cell immediatel
y after its differentiation.
To understand the mode of action of pregnenolone and its sulfate ester, we examined the effects of these neurosteroids on synaptic currents in cerebellar Purkinje neurons. Inhibitory postsynaptic currents (IPSCs) in Purkinje neurons were recorded in a cerebellar slice by the patch-clamp method. Pregnenolone sulfate increased, in a dose-related way, the frequency of IPSCs within 1 min of perfusion, indicating that this effect is unlikely to be induced via gene transcription. In contrast, pregnenolone had no effect on the frequency of IPSCs. The IPSCs recorded in the Purkinje neurons were completely blocked by bicuculine, a gamma-aminobutyric acid A (GABAA) receptor antagonist, suggesting that they are mediated by GABAA receptors. It is therefore possible that pregnenolone sufate, produced in Purkinje neurons, may modulate GABAergic transmission by paracrine acitons on GAGAergic neurons rather than by genomic mechanisms. Behavioral studies are now in progress to clarify the neurosteroidal function.
More recently, we demonstrated that Purkinje neurons possess not only P450scc but also 3beta-HSD and produces progesterone by molecular and biochemical approaches. Interestingly, expression of the P450scc mRNA was relatively constant during neonatal life and in adulthood, whereas the 3beta-HSD mRNA expression was evident in early in early neonatal life. It is considered that progesterone, a product of 3beta-HSD activity, may play a role in the development of cerebellar nervous system structures in this period. Less