The dumpy locus (dp) located on the chromosome 2 at map position 13.0 is among the loci intensively studied in Dyosophila.Its usefulness and suitability for mutational studies derive from the findings that (i) it is a complex locus (or a closely linked group of distinct genes) with no less than 7 mutational sites Grace 1970), events at which are phenotypically detectable in certain combinations; (ii) the locus is much more sensitive than others to radiation as well as chemical mutagens Carlson and Oster 1962;Oster 1963;Jenkins 1967;Corwin 1968) and (iii) the induced events at this locus involve presumed point mutations as well as those associated with chromosome breakage, the latter resulting in extreme phenotype Carlson and Oster 1962).In an attempt to shed more light on the nature of radiation-induced dumpy mutations, a comparison was recently made by Inagaki et al. (1974) for the dose-frequency patterns between the different kinds of dumpy exceptions induced by X-rays in mature sperm. The experimental data revealed that (a) the yield of dumpy exceptions of the o and v types increases with exposure up to 3,000 R beyond which there is no further increase; (b) the frequency of the of and the lv exceptions tends to increase faster than linearly with no evidence for a decrease at 4,500 R; (c) the exposure-frequency relationship for the ov and olv exceptions does not depart from linearity; (d) the over-all frequencies of o, v, of and lv at the three exposure levels (1,500, 3,000 and 4,500 R) are also consistent with linear increase with exposures and (e) the frequency of fractional dumpy mutants appears to remain approximately the same irrespective of the exposure. Although the data cannot be considered as more than preliminary results on which a more thorough analysis will have to be based, the authors were inclined to suggest that the exposurefrequency relationships for the different kinds of dumpy mutations are different. Definite evidence apparently supporting the above observations has been recently obtained in a large-scale study of Fujikawa et al. (1975). More information about the spectrum of X-ray-induced dumpy mutations especially in various experimental conditions under which mutagensis by ionizing radiation in Dyosophila may be well subject to modification seemed to be needed before the picture of dose-response curves for the different kinds of dumpy exceptions could be properly interpreted.In view of this it

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Dissociated cells of neonatal rat hypothalamus-preoptic area and cerebral cortex were grown in primary culture, and the effects of sex steroids on neurons were morphometrically studied. In cultures of the hypothalamus-preoptic area estradiol-17β or testosterone propionate significantly increased the total neuronal process length as compared with control cultures given no steroids in the medium. Significant stimulatory effects were detected on 1, 2 and 3 days after plating, while, 5a-dihydrotestosterone failed to show any stimulatory influence. In contrast, none of these steroids was effective in cultures of cerebral cortical cells. Based on the number of processes arising from the soma, neurons were divided into unipolar, bipolar and multipolar neurons. Percentage of multipolar neurons of the hypothalamus-preoptic area was more in cultures treated with estradiol-17β or testosterone propionate than the controls. Significant effect was not noted in cultures with 5α-dihydrotestosterone, while, in cultures of the cerebral cortical cells, effects on sprouting of these steroids were far less marked than in cultures of the hypothalamus-preoptic area. The present findings substantiate the importance of aromatization of androgen to exert its influence on neuronal process growth in cell culture.

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