title: N-methyl-N-nitrosourea during late gestation results in concomitant but reversible progenitor cell reduction and delayed neurogenesis in the hippocampus of rats.
abstract: N-Methyl-N-nitrosourea (MNU) is an alkylating agent having genotoxic potential to cause gene mutations and antiproliferative cytotoxic activity on developing brains to cause microcephaly by mid-gestational exposure in rodents. This study investigated the transient genotoxic and cytocidal effect of MNU at the beginning of the subgranular zone (SGZ) formation in the hippocampal dentate gyrus on neurogenesis in later life using rats. Pregnant rats were injected with MNU at 0 (vehicle controls), 1 or 3mg/kg body weight intraperitoneally from gestational day (GD) 18 to GD 20 once a day. In offspring, effects were observed at 3mg/kg. Fetal brains on GD 21 after the last MNU injection increased TUNEL(+) apoptotic cells in the tertiary germinal matrices. At postnatal day (PND) 21 on weaning, offspring displayed decrease of doublecortin (Dcx)(+) cells and cell proliferation in the SGZ and increase of calbindin (Calb1)(+) interneurons in the dentate hilus. Postnatal single bromodeoxyuridine (BrdU) injection on PND 3 resulted in an increase of BrdU(+)/Dcx(+) cells. On PND 77, Dcx(+) cells recovered in number, but cell proliferation increased in the SGZ. Thus, late-gestational maternal MNU exposure may induce reversible reductions of type-3 progenitor and/or immature granule cells and cell proliferation on weaning in response to progenitor cell apoptosis, as well as delayed neurogenesis due to cell cycle arrest. Increases of Calb1(+) interneurons on weaning and SGZ cell proliferation later on may reflect compensatory mechanism for MNU-induced aberrant neurogenesis. Considering the lack of effects on PND 77, MNU may mainly target transient populations of highly proliferative progenitor cells without affecting their stem cells to undergo progenitor production. Protective and plasticity mechanism may be operated against genotoxic agents on hippocampal neurogenesis.
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan; Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan. Electronic address: itahashi@cc.tuat.ac.jp.
authors.forename: Megu
authors.initials: M
authors.lastname: Itahashi
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan. Electronic address: waly2009@cc.tuat.ac.jp.
authors.forename: Liyun
authors.initials: L
authors.lastname: Wang
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan; Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan. Electronic address: shirakia@cc.tuat.ac.jp.
authors.forename: Ayako
authors.initials: A
authors.lastname: Shiraki
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan; Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan. Electronic address: abeichi@cc.tuat.ac.jp.
authors.forename: Hajime
authors.initials: H
authors.lastname: Abe
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan; Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan. Electronic address: tatanaka@cc.tuat.ac.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: Laboratory of Veterinary Toxicology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan. Electronic address: mrkmt@cc.tuat.ac.jp.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Murakami
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan. Electronic address: yoshida7@cc.tuat.ac.jp.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Yoshida
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan. Electronic address: mshibuta@cc.tuat.ac.jp.
authors.forename: Makoto
authors.initials: M
authors.lastname: Shibutani
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D064026:Calbindins / Q000032:analysis; D049109:Cell Proliferation / Q000187:drug effects; D000089622:Doublecortin Domain Proteins; D000089662:Doublecortin Protein; D005260:Female; D005333:Fetus / Q000187:drug effects*; D006624:Hippocampus / Q000187:drug effects* / Q000473:pathology; D007395:Interneurons / Q000187:drug effects; D008297:Male; D008770:Methylnitrosourea / Q000633:toxicity*; D008869:Microtubule-Associated Proteins / Q000032:analysis; D058953:Neural Stem Cells / Q000187:drug effects*; D055495:Neurogenesis / Q000187:drug effects*; D009479:Neuropeptides / Q000032:analysis; D011247:Pregnancy; D051381:Rats
chemical_list: D064026:Calbindins; C000714848:Dcx protein, rat; D000089622:Doublecortin Domain Proteins; D000089662:Doublecortin Protein; D008869:Microtubule-Associated Proteins; D009479:Neuropeptides; D008770:Methylnitrosourea
keywords: Hippocampal dentate gyrus; N-Methyl-N-nitrosourea (MNU); Neurogenesis; Subgranular zone (SGZ); γ-Aminobutyric acid (GABA) ergic interneuron