Neuronal death and sex hormones during brain sexual differentiation

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During the process of brain sexual differentiation, sex steroids regulate the number of certain neuronal groups. Recently, we have found that the anteroventral periventricular nucleus of the preoptic area (AVPVN-POA) is sexually dimorphic and perinatal treatment of female rats with androgen decreases the neuronal number of the AVPVN-POA, resulting in malefemale difference in nuclear volume.In the present study, we injected Bromodeoxyuridine (BrdU) into pregnant rats at day 15 of pregnancy in order to label the proliferating neurons with BrdU. Pregnant mothers were also injected with androgen from days 14 to 18. Animals were sacrificed at day 17 or 21Exposure of androgen to female fetuses from. !days 14 to 18 markedly reduced BrdU-labeled neurons in the AVPVN area, compared to control female fetuses, when sacrificeed, . at day : 21 of pregnancy, whereas there- was no differenced when. sacrificed at day 17. BrdU labelled neurons in the AVPVN-POA was also significantly smaller than that in control females at day 21.Incidence of pycnotic figures in the AVPVN-POA was significaltly higher in males and androgenized females than control females, when sacrificed at day 21.These results suggest that gndrogengiven prenatally regulates the neuron number of the AVPVN=POA through enhancing neuronal death.other than the regulation of neuronal number by cell death, neuronal migration phenomenon is one of the influencing factors for neuronal number of. the nuclear groups. In the present study, we have studied the origin and migration phenomenon of LHRH neurons from the olfactory placode to the forebrain area in the chick embryos. In this study, the possible participation of a highly polysialylated NCAM in migration of LHRH neurons from the nasal region to the forebrain area.