Postpubertal Exposure Research Articles

Gene expression profiles of multiple brain regions in rats differ between developmental and postpubertal exposure to valproic acid.

We have previously reported that the valproic acid (VPA)-induced disruption pattern of hippocampal adult neurogenesis differs between developmental and 28-day postpubertal exposure. In the present study, we performed brain region-specific global gene expression profiling to compare the profiles of VPA-induced neurotoxicity between developmental and postpubertal exposure. Offspring exposed to VPA at 0, 667, and 2000 parts per million (ppm) via maternal drinking water from gestational day 6 until weaning (postnatal day 21) were examined, along with male rats orally administered VPA at 0, 200, and 900 mg/kg body weight for 28 days starting at 5weeks old. Four brain regions-the hippocampal dentate gyrus, corpus callosum, cerebral cortex, and cerebellar vermis-were subjected to expression microarray analysis. Profiled data suggested a region-specific pattern of effects after developmental VPA exposure, and a common pattern of effects among brain regions after postpubertal VPA exposure. Developmental VPA exposure typically led to the altered expression of genes related to nervous system development (Msx1, Xcl1, Foxj1, Prdm16, C3, and Kif11) in the hippocampus, and those related to nervous system development (Neurod1) and gliogenesis (Notch1 and Sox9) in the corpus callosum. Postpubertal VPA exposure led to the altered expression of genes related to neuronal differentiation and projection (Cd47, Cyr61, Dbi, Adamts1, and Btg2) in multiple brain regions. These findings suggested that neurotoxic patterns of VPA might be different between developmental and postpubertal exposure, which was consistent with our previous study. Of note, the hippocampal dentate gyrus might be a sensitive target of developmental neurotoxicants after puberty.

Association of Prepubertal and Postpubertal Exposure to Childhood Maltreatment With Adult Amygdala Function

Abnormalities in amygdala response to threatening faces have been observed in anxiety disorders, autism, bipolar disorder, depression, posttraumatic stress disorder, and schizophrenia. Abnormally hyperactive and hypoactive responses have typically been associated with anxiety and inhibition vs risk taking and inappropriate social behaviors. Maltreatment is a major risk factor for most of these disorders and is associated with abnormal amygdala function. To identify the type and age of exposure to childhood maltreatment that are associated with hyperactive and hypoactive amygdala responses in young adulthood. Data collection for this retrospective cohort study took place from November 8, 2010, to August 23, 2012. Data analyses were conducted from September 20, 2012, to June 27, 2018. Participants were recruited from the urban and suburban Boston vicinity without diagnostic restrictions based on exposure history. The Maltreatment and Abuse Chronology of Exposure (MACE) scale was used to retrospectively assess type and age of exposure to childhood maltreatment. Activation and pattern information functional magnetic resonance imaging were used to assess bilateral amygdala response to angry and fearful faces vs neutral faces or shapes, and sensitive exposure periods were identified using cross-validated artificial intelligence predictive analytics (50 averaged randomized iterations with training on 63.3% and testing on 36.7% of the sample). Of the 202 participants (mean [SD] age, 23.2 [1.7] years; 118 [58.4%] female), 52 (25.7%) reported no exposure to maltreatment and 150 (74.3%) reported exposure to 1 or more maltreatment types. Eight participants (15.1%) with a MACE score of 0 and 51 (34.2%) with a MACE score of 1 or higher had a history of major depression (odds ratio, 2.40; 95% CI, 1.05-6.06; P = .03); 8 unexposed participants (15.1%) and 46 with MACE scores of 1 or higher (30.9%) had a history of 1 or more anxiety disorders (odds ratio, 2.45; 95% CI, 1.03-6.50; P = .03). Retrospective self-report of physical maltreatment between 3 and 6 years of age and peer emotional abuse at 13 and 15 years were associated with amygdala activation to emotional faces vs shapes. Early exposure was associated with blunted response (β = -0.17, P < .001), whereas later exposure was associated with augmented response (β = 0.16, P < .001). Prepubertal vs postpubertal maltreatment was associated with an opposite response on the voxelwise response pattern in clustering stimuli of the same type (eg, mean [SD] emotional ellipse areas for physical maltreatment at age 4 years vs nonverbal emotional abuse at 13 years: 1.41 [1.05] vs 0.25 [0.10], P < .001) and in distinguishing between stimuli of different types (eg, mean [SD] emotional vs neutral faces distance for peer emotional abuse at age 6 years vs 13 years: 1.89 [0.75] vs 0.80 [0.39], P < .001). The findings suggest that prepubertal vs postpubertal developmental differences in the association between maltreatment and amygdala response to threatening or salient stimuli exist. Understanding the role of adversity in different sensitive exposure periods and the potential adaptive significance of attenuated vs enhanced amygdala response may help explain why maltreatment may be a risk factor for many different disorders and foster creation of targeted interventions to preempt the emergence of psychopathology in at-risk youths.

Twenty-eight-day repeated oral doses of sodium valproic acid increases neural stem cells and suppresses differentiation of granule cell lineages in adult hippocampal neurogenesis of postpubertal rats

Developmental exposure to valproic acid (VPA), a model compound for experimental autism, has shown to primarily target GABAergic interneuron subpopulations in hippocampal neurogenesis of rat offspring. The VPA-exposed animals had revealed late effects on granule cell lineages, involving progenitor cell proliferation and synaptic plasticity. To investigate the possibility whether hippocampal neurogenesis in postpubertal rats in a protocol of 28-day repeated exposure is affected in relation with the property of a developmental neurotoxicant by developmental exposure, VPA was orally administered to 5-week-old male rats at 0, 200, 800 and 900 mg/kg body weight/day for 28 days. At 900 mg/kg, GFAP+ cells increased in number, but DCX+ cells decreased in number in the granule cell lineages. Moreover, CHRNB2+ cells and NeuN+ postmitotic neurons decreased in number in the hilus of the dentate gyrus. Transcript level examined at 900 mg/kg in the dentate gyrus was increased with Kit, but decreased with Dpsyl3, Btg2, Pvalb and Chrnb2. These results suggest that VPA increased type-1 stem cells in relation to the activation of SCF-KIT signaling and suppression of BTG2-mediated antiproliferative effect on stem cells. VPA also decreased type-3 progenitor cells and immature granule cells probably in relation with PVALB+ interneuron hypofunction and reduced CHRNB2+ interneuron subpopulation in the hilus, as well as with suppression of BTG2-mediated terminal differentiation of progenitor cells. Thus, the disruption pattern of VPA by postpubertal exposure was different from developmental exposure. However, disruption itself can be detected, suggesting availability of hippocampal neurogenesis in detecting developmental neurotoxicants in a 28-day toxicity study.

Differential effect of parity on rat mammary carcinogenesis after pre- or post-pubertal exposure to radiation

Radiation exposure during the peri-pubertal period is a proven risk factor for breast cancer, whereas parity is an established protective factor. The present study investigated whether parity imposes differential protective effects against radiation-induced rat mammary carcinoma depending on the age at exposure. Pre- and post-pubertal female rats, irradiated or left unirradiated, were mated and allowed to nurse until weaning or left unmated. Appearance of mammary tumors was monitored, and serum concentrations of estradiol and progesterone were measured following weaning. Carcinomas were evaluated by immunohistochemistry for estrogen receptor, progesterone receptor, and the cell proliferation marker Ki-67. Parity reduced the risk of carcinoma in unirradiated and pre-pubertally irradiated rats but not post-pubertally irradiated rats. Although radiation exposure increased serum progesterone level, parity after pre-pubertal exposure significantly decreased the elevated progesterone to a normal level, reflecting a protective effect. Moreover, parity significantly decreased the proportion of hormone receptor–positive carcinomas after pre-pubertal exposure. Parity was also related to the observed positive association between progesterone receptor and Ki-67 indices in cancer tissue, implying progesterone receptor–dependent cell proliferation. Thus, parity protects against radiation-induced rat mammary carcinogenesis depending on the age at exposure; the mechanisms may involve changes in hormone levels and cancer tissue.

Cuprizone decreases intermediate and late-stage progenitor cells in hippocampal neurogenesis of rats in a framework of 28-day oral dose toxicity study

Developmental exposure to cuprizone (CPZ), a demyelinating agent, impairs intermediate-stage neurogenesis in the hippocampal dentate gyrus of rat offspring. To investigate the possibility of alterations in adult neurogenesis following postpubertal exposure to CPZ in a framework of general toxicity studies, CPZ was orally administered to 5-week-old male rats at 0, 120, or 600mg/kg body weight/day for 28days. In the subgranular zone (SGZ), 600mg/kg CPZ increased the number of cleaved caspase-3+ apoptotic cells. At ≥120mg/kg, the number of SGZ cells immunoreactive for TBR2, doublecortin, or PCNA was decreased, while that for SOX2 was increased. In the granule cell layer, CPZ at ≥120mg/kg decreased the number of postmitotic granule cells immunoreactive for NEUN, CHRNA7, ARC or FOS. In the dentate hilus, CPZ at ≥120mg/kg decreased phosphorylated TRKB+ interneurons, although the number of reelin+ interneurons was unchanged. At 600mg/kg, mRNA levels of Bdnf and Chrna7 were decreased, while those of Casp4, Casp12 and Trib3 were increased in the dentate gyrus. These data suggest that CPZ in a scheme of 28-day toxicity study causes endoplasmic reticulum stress-mediated apoptosis of granule cell lineages, resulting in aberrations of intermediate neurogenesis and late-stage neurogenesis and following suppression of immediate early gene-mediated neuronal plasticity. Suppression of BDNF signals to interneurons caused by decreased cholinergic signaling may play a role in these effects of CPZ. The effects of postpubertal CPZ on neurogenesis were similar to those observed with developmental exposure, except for the lack of reelin response, which may contribute to a greater decrease in SGZ cells.

Effects of Crude Aqueous Extract of Origanum vulgaris in Developing Ovary of Rabbits Following in Utero, Adolescent, and Postpubertal Exposure

We evaluated the impact on rabbits after having been treated with Origanum vulgaris (Lamiaceae) (OV) at a dose level known to adversely affect ovarian functions in rodents without causing systemic toxicity. The choice of rabbits has been guided by the fact that rabbits have a relatively long phase of reproductive development and hence simulation of reproductive development is better as opposed to dealing with rodents. The use of rabbits facilitates multiple evaluations of mating ability. An attempt has also been made at determining whether OV affected ovarian development and hence the use of animal model. Rabbits were exposed to 80 mg OV/kg/day in utero (gestation days [GD] 0 to23) or during adolescence (postnatal weeks [PNW] 4 by breast feeding and orally from 4w to 12 w), and the offspring were examined at the end of the 12 W period. Another group was treated after puberty (for 12 weeks) till age of 24 [PNW] of age and examined at the conclusion of exposure and follicles were categorized as primordial, primary, small preantral, large preantral or small antral follicles. The most pronounced reproductive effects were in female rabbits group which had been exposed from in utero till post-puberty period, in weights of ovaries (at 12 and 24 weeks, down 23%; p < 0.05). Serum Gonadotropin levels were down (at 24 weeks, 32%; p < 0.05); a slight increase in histological alterations of the ovaries (p < 0.05) at 24 weeks, of abnormal follicles;Â

Hormonally Active Doses of Isoflavone Aglycones Promote Mammary and Endometrial Carcinogenesis and Alter the Molecular Tumor Environment in Donryu Rats

Our research is focused on modifying effects of an isoflavone aglycones (IAs)-rich extract at a hormonally active dose of 150 mg/kg body weight/day on mammary and endometrial carcinogenesis in female Donryu rats. IA administered for 2 weeks in a phytoestrogen-low diet exerted estrogenic activity and induced cell proliferation in the uterus of ovariectomized rats. Furthermore, administration for 4 weeks resulted in elevation of cell proliferation in the mammary glands of 7,12-dimethylbenz[a]anthracene (DMBA)-treated animals. Forty weeks of postpubertal administration of IA to 5-week-old rats after initiation of mammary and endometrial carcinogenesis with DMBA and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) caused significant increase of incidence and multiplicity of mammary adenocarcinoma, multiplicities of endometrial atypical hyperplasia, adenomatous polyps, and an increased trend of uterine adenocarcinomas. Liquid chromatography with tandem mass spectrometry and immunohistochemical analyses revealed significant elevation of tumorigenesis-related proteins such as S100 calcium-binding protein A8, kininogen 1, and annexins 1 and 2 in mammary adenocarcinomas and cadherin EGF LAG seven-pass G-type receptor 2, DEAD box polypeptide 1, and cysteine- and glycine-rich protein 1 in uterine proliferative lesions of IA-treated animals. Those changes are likely to be related to modulation of estrogen receptor (ER), AP1, nuclear factor-kappa B, and actin signaling pathways. Our results indicate that the postpubertal exposure of Donryu rats to IA at an estrogenic dose results in promotion of mammary and uterine carcinogenesis induced by DMBA and ENNG, which might be related to the activation of ER-dependent signaling and alteration of the molecular tumor environment in the mammary gland and endometrium.

Pre‐ and postpubertal irradiation induces mammary cancers with distinct expression of hormone receptors, ErbB ligands, and developmental genes in rats

Childhood exposure to carcinogens renders a higher risk of breast cancer. The molecular mechanisms underlying cancer development after such exposure are not, however, well understood. Here we examined how the mechanism of cancer development relates to the age at exposure to ionizing radiation (IR) or the carcinogen 1-methyl-1-nitrosourea (MNU). Pre- and postpubertal (3- and 7-wk-old, respectively) female Sprague-Dawley rats were whole-body γ-irradiated (2 Gy), injected intraperitoneally with MNU (20 mg/kg) or left untreated and were autopsied at 50 wk of age. Mammary carcinomas were examined for estrogen receptor (ER) α, progesterone receptor (PR) and ErbB ligand expression and for expression microarrays. Early histological changes of the ovaries were also evaluated. The incidence of mammary cancer was higher after postpubertal, rather than prepubertal, IR exposure; the inverse was true for MNU. Most cancers were positive for both ERα and PR except for the prepubertal IR group. Cancers of the prepubertal IR group expressed a different set of ErbB ligands from those of the other groups and did not overexpress Areg, which encodes an estrogen-regulated ErbB ligand, or other developmentally related genes including those for hormonally regulated mammary gland development. Prepubertal IR exposure resulted in ovarian dysfunction as revealed by a reduced follicular pool. Evidence thus suggests that mammary carcinogenesis induced by prepubertal IR exposure is independent of ovarian hormones but requires certain ErbB ligands; induction by postpubertal exposure depends on ovarian hormones and different ErbB ligands. In contrast, the mechanism of MNU-induced carcinogenesis was less influenced by the age at exposure.

Fetal origins of breast cancer

Susceptibility to breast cancer might be pre-determined in utero. Alterations in the fetal hormonal environment, caused by either maternal diet or exposure to environmental factors with endocrine activities, can modify the epigenome, and these modifications are inherited in somatic daughter cells and maintained throughout life. These epigenetic modifications might lead to changes in mammary gland development, such as increased vulnerability of epithelial targets for malignant transformation. According to this hypothesis, on post-pubertal exposure to an initiating factor, such as a carcinogen, high levels of hormones and radiation, the mammary epithelial targets, perhaps stem cells, in terminal end buds/terminal ductal lobular units would be at an increased risk of malignant transformation. The increased susceptibility for cancer initiation might result from high levels of cell proliferation, reduced apoptosis and/or altered stromal regulation. Thus, maternal diet and environmental exposure might increase the risk of breast cancer by inducing permanent epigenetic changes in the fetus that alter the susceptibility to factors that can initiate breast cancer. Identifying the epigenetically altered target genes and their ligands might lead to strategies to prevent this disease in some women.

Effects of dibutyl phthalate in male rabbits following in utero, adolescent, or postpubertal exposure.

We evaluated sequelae in male rabbits following exposure to dibutyl phthalate (DBP) at a dose level known to adversely affect testicular function in rodents without causing systemic toxicity. Because rabbits have a relatively long phase of reproductive development simulating better than rodents the reproductive development of humans, and because the use of rabbits facilitates multiple evaluations of mating ability and seminal quality, we used this animal model. Rabbits were exposed to 0 or 400 mg DBP/kg/day in utero (gestation days [GD] 15-29) or during adolescence (postnatal weeks [PNW] 4-12), and male offspring were examined at 6, 12, and 25 weeks of age. Another group was exposed after puberty (for 12 weeks) and examined at the conclusion of exposure. The most pronounced reproductive effects were in male rabbits exposed in utero. Male offspring in this group exhibited reduction in numbers of ejaculated sperm (down 43%; p < 0.01), in weights of testes (at 12 weeks, down 23%; p < 0.05) and in accessory sex glands (at 12 and 25 weeks, down 36%; p < 0.01 and down 27%; p < 0.05, respectively). Serum testosterone levels were down (at 6 weeks, 32%; p < 0.05); a slight increase in histological alterations of the testis (p < 0.05) and a doubling in the percentage (from 16 to 30%, p < 0.01) of abnormal sperm; and 1/17 males manifesting hypospadias, hypoplastic prostate, and cryptorchid testes with carcinoma in situ-like cells. In the DBP group exposed during adolescence, basal serum testosterone levels were reduced at 6 weeks (p < 0.01) while at 12 weeks, testosterone production in vivo failed to respond normally to a GnRH challenge (p < 0.01). In addition, weight of accessory sex glands was reduced at 12 weeks but not at 25 weeks after a recovery period; there was a slight increase in the percentage of abnormal sperm in the ejaculate; and 1/11 males was unilaterally cryptorchid. In both of these DBP-treated groups, daily sperm production, epididymal sperm counts, mating ability, and weights of body and nonreproductive organs were unaffected. Thus, DBP induces lesions in the reproductive system of the rabbit, with the intrauterine period being the most sensitive stage of life.

Hormonal regulation of rat liver microsomal enzymes. Role of gonadal steroids in programming, maintenance, and suppression of delta 4-steroid 5 alpha-reductase, flavin-containing monooxygenase, and sex-specific cytochromes P-450.

Neonatal gonadectomy studies and hormonal replacement regimens were employed to characterize the regulation of delta 4-steroid 5 alpha-reductase, microsomal flavin-containing monooxygenase, and several forms of rat hepatic microsomal cytochrome P-450, including three that are sexually differentiated. Rats of both sexes that had been gonadectomized at birth were either untreated or were administered testosterone propionate or estradiol benzoate neonatally (subcutaneous injection on days 1 and 3 of life), postpubertally (an implant of a hormone-packed capsule at 5 weeks of age), or both neonatally and postpubertally. At the age of 10 weeks, all rats were killed, and several liver microsomal enzymes were assayed using immunochemical and catalytic techniques. Expression in the 10-week-old male and female rats of two male-specific cytochrome P-450 forms, termed P-4502c/UT-A and P-4502a/PCN-E, and their associated respective 16 alpha- and 6 beta-steroid hydroxylase activities could either be imprinted (programmed) by androgen exposure during the early neonatal period or, alternatively, could be stimulated by continuous hormone treatment after the age of 5 weeks. By contrast, hepatic expression of two female-specific enzymes, P-4502d/UT-1 and delta 4-steroid 5 alpha-reductase, was only partially dependent on estradiol; birth-gonadectomized rats expressed as much as 30-50% of the enzyme levels present in untreated adult females. Expression of both female-specific enzymes was fully suppressed upon postpubertal exposure to testosterone. In another study, birth sham-operated female rats were administered testosterone using the same regimens described above for the birth-gonadectomized rats. Although neonatal testosterone treatment alone did not affect the expression in these females of the four sex-specific enzymes examined in this study, it did enhance significantly the masculinization effected by postpubertal androgen exposure. This resulted in expression of the male-specific enzymes P-4502c/UT-A and P-4502a/PCN-E in these females at levels comparable to those found in adult males, while simultaneously suppressing the two female-specific enzymes, P-4502d/UT-I and delta 4-steroid 5 alpha-reductase, by approximately 70-75% to levels characteristic of prepubertal rats of either sex. The levels of another microsomal enzyme, flavin-containing monooxygenase, were also measured and found to be regulated by testosterone, but the ontogenic profiles and the effects of gonadectomy and hormone replacement indicated clear differences in its regulation when compared to the other male-specific enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)