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Abstract. Aripiprazole is used clinically as an atypical antipsychotic. We evaluated the effect of in vivo treatment with aripiprazole on the proliferation and differentiation of neural stem/ progenitor cells in a mouse model, trimethyltininduced neuronal loss/selfrepair in the hippo campal dentate gyrus (referred as "impaired animals") [Ogita et al., J Neurosci Res. 82, 609 -621 (2005)]. In the impaired animals, an increased number of 5-bromo-2′-deoxyuridine (BrdU)-positive cells was seen in the dentate gyrus at the initial time window of the selfrepair stage. At the same time window, a single treatment with aripiprazole significantly increased the number of cells positive for both BrdU and nestin in the dentate gyrus of the impaired animals. Chronic treatment with aripiprazole promoted the proliferation/survival and neuronal differentiation of the cells newlygenerated following the neuronal loss in the dentate gyrus of the impaired animals. The chronic treatment with aripiprazole improved depressionlike behavior seen in the impaired animals. Taken together, our data suggest that aripiprazole had a beneficial effect on neuronal regeneration following neuronal loss in the dentate gyrus through indirectly promoted prolifera tion/survival and neuronal differentiation of neural stem/progenitor cells in the subgranular zone of the dentate gyrus.

The androgenic and the male-inducing (androtermonic) activities of 11-ketotestosterone were evaluated respectively by its abilities to stimulate a secondary sex character and to reverse gonadal sex differentiation in a teleost, the medaka (Oryzias latipes). The median effective dose (ED 50) of this steroid necessary to induce the formation of papillar process on the anal fin was 37 pg/g of food. The androgen is therefore about 8 times more potent than testosterone propionate and 17 times more potent than pure testosterone in the same test. The ED 50 for androtermonic activity (reversal of genetic females to phenotypic males) was found to be about 110 pg/g of food. Compared with testosterone propionate the 11-keto compound is about five times more potent. Thus, in teleosts, 11-ketotestosterone appears to be the most potent androgen of vertebrate origin for both androgenic and androtermonic potencies. The ratio of androtermonic to androgenic potencies (ED 50s) for Il-ketotestosterone is 3.0.

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Effects of androstenedione, 19-norethynyltestosterone, progesterone, and 17a-hydroxyprogesterone upon the manifestation of secondary sexual characters were studied in the orange-red variety of the medaka. The steroids were consecutively administered per os for 15 days.Androstenedione and 19-norethynyltestosterone induced formation of new segments in the fin rays and produced papillar processes on the anal fin of the female. 19-norethynyltestosterone proved to have a strong potency, estimated to be more than 300 times that of androstenedione.Progesterone and 17a-hydroxyprogesterone had neither androgenic nor estrogenic effect on the secondary sexual characters. This is quite in harmony with the fact that they have neither androtermonic nor gynotermonic potency.The administration of these steroids did not impair the fertility of females. The administered females produced offspring by mating with administered males.