抄録
A ubiquitous property of vertebrates is fluctuation of locomotor activity over the 24 h circadian cycle. It is also known that birds as well as other vertebrates exhibit a clear sex difference in locomotor activity. In particular, locomotor activity of males is much higher than that of females in Japanese quail. Only males exhibit marked diurnal changes in locomotor activity. Based on a series of experiments using Japanese quail, here we show that 7α-hydroxypregnenolone, a newly discovered avian neurosteroid, is a key factor inducing sex-dependent locomotor activity. We first identified 7α-hydroxypregnenolone in quail brain by using biochemical techniques. This neurosteroid has not previously been described in avian brain. We then demonstrated that 7α-hydroxypregnenolone acutely increased quail locomotor activity. Subsequently, we demonstrated a clear sex difference in 7α-hydroxypregnenolone synthesis in quail. Both 7α-hydroxypregnenolone synthesis and locomotor activity in males were much higher than in females. Only males exhibited marked diurnal changes in 7α-hydroxypregnenolone synthesis, and these changes occurred in parallel with changes in locomotor activity. In contrast, females showed constantly lower levels of 7α-hydroxypregnenolone synthesis and locomotor activity. Thus, the novel avian neurosteroid 7α-hydroxypregnenolone may be a key factor inducing sex-dependent locomotor activity. This is the first demonstration in any vertebrate of a clear sex difference in neurosteroid synthesis. [J Physiol Sci. 2008;58 Suppl:S41]
