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Harding B, Conception K, Li Y, Zhang L. Glucocorticoids Protect Neonatal Rat Brain in Model of Hypoxic-Ischemic Encephalopathy (HIE). Int J Mol Sci 2016; 18:ijms18010017. [PMID: 28025500 PMCID: PMC5297652 DOI: 10.3390/ijms18010017] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 12/10/2016] [Accepted: 12/19/2016] [Indexed: 11/27/2022] Open
Abstract
Hypoxic-ischemic encephalopathy (HIE) resulting from asphyxia in the peripartum period is the most common cause of neonatal brain damage and can result in significant neurologic sequelae, including cerebral palsy. Currently therapeutic hypothermia is the only accepted treatment in addition to supportive care for infants with HIE, however, many additional neuroprotective therapies have been investigated. Of these, glucocorticoids have previously been shown to have neuroprotective effects. HIE is also frequently compounded by infectious inflammatory processes (sepsis) and as such, the infants may be more amenable to treatment with an anti-inflammatory agent. Thus, the present study investigated dexamethasone and hydrocortisone treatment given after hypoxic-ischemic (HI) insult in neonatal rats via intracerebroventricular (ICV) injection and intranasal administration. In addition, we examined the effects of hydrocortisone treatment in HIE after lipopolysaccharide (LPS) sensitization in a model of HIE and sepsis. We found that dexamethasone significantly reduced rat brain infarction size when given after HI treatment via ICV injection; however it did not demonstrate any neuroprotective effects when given intranasally. Hydrocortisone after HI insult also significantly reduced brain infarction size when given via ICV injection; and the intranasal administration showed to be protective of brain injury in male rats at a dose of 300 µg. LPS sensitization did significantly increase the brain infarction size compared to controls, and hydrocortisone treatment after LPS sensitization showed a significant decrease in brain infarction size when given via ICV injection, as well as intranasal administration in both genders at a dose of 300 µg. To conclude, these results show that glucocorticoids have significant neuroprotective effects when given after HI injury and that these effects may be even more pronounced when given in circumstances of additional inflammatory injury, such as neonatal sepsis.
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Affiliation(s)
- Benjamin Harding
- Division of Neonatology, Department of Pediatrics, Loma Linda University Children's Hospital, Loma Linda, CA 92354, USA.
| | - Katherine Conception
- Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.
| | - Yong Li
- Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.
| | - Lubo Zhang
- Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.
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Pinkas A, Turgeman G, Tayeb S, Yanai J. An avian model for ascertaining the mechanisms of organophosphate neuroteratogenicity and its therapy with mesenchymal stem cell transplantation. Neurotoxicol Teratol 2015; 50:73-81. [DOI: 10.1016/j.ntt.2015.06.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Revised: 06/16/2015] [Accepted: 06/21/2015] [Indexed: 12/29/2022]
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Abdul-Ghani S, Yanai J, Abdul-Ghani R, Pinkas A, Abdeen Z. The teratogenicity and behavioral teratogenicity of di(2-ethylhexyl) phthalate (DEHP) and di-butyl Phthalate (DBP) in a chick model. Neurotoxicol Teratol 2012; 34:56-62. [DOI: 10.1016/j.ntt.2011.10.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2011] [Revised: 09/12/2011] [Accepted: 10/05/2011] [Indexed: 02/02/2023]
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Yanai J, Brick-Turin Y, Dotan S, Langford R, Pinkas A, Slotkin TA. A mechanism-based complementary screening approach for the amelioration and reversal of neurobehavioral teratogenicity. Neurotoxicol Teratol 2009; 32:109-13. [PMID: 19217940 DOI: 10.1016/j.ntt.2009.02.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 12/10/2008] [Accepted: 02/05/2009] [Indexed: 10/21/2022]
Abstract
The identification of mechanisms and outcomes for neurobehavioral teratogenesis is critical to our ability to develop therapies to ameliorate or reverse the deleterious effects of exposure to developmental neurotoxicants. We established mechanistically-based complementary models for the study of cholinergic systems in the mouse and the chick, using both environmental neurotoxicants (chlorpyrifos, perfluoroalkyls) and drugs of abuse (heroin, nicotine, PCP). Behavioral evaluations were made using the Morris maze in the mouse, evaluating visuospatial memory related to hippocampal cholinergic systems, and imprinting in the chick, examining behavior dependent on cholinergic innervation of the IMHV. In both models we demonstrated the dependence of neurobehavioral deficits on impairment of cholinergic receptor-induced expression, and translocation of specific PKC isoforms. Understanding this mechanism, we were able to reverse both the synaptic and behavioral deficits with administration of neural progenitors. We discuss the prospects for clinical application of neural progenitor therapy, emphasizing protocols for reducing or eliminating immunologic rejection, as well as minimizing invasiveness of procedures through development of intravenous administration protocols.
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Affiliation(s)
- Joseph Yanai
- The Ross Laboratory for Studies in Neural Birth Defects, Department of Anatomy and Cell Biology The Hebrew University-Hadassah Medical School, Box 12272, 91120 Jerusalem, Israel.
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Flagel SB, Vázquez DM, Watson SJ, Neal CR. Effects of tapering neonatal dexamethasone on rat growth, neurodevelopment, and stress response. Am J Physiol Regul Integr Comp Physiol 2002; 282:R55-63. [PMID: 11742823 DOI: 10.1152/ajpregu.2002.282.1.r55] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dexamethasone is commonly used to lessen the morbidity of chronic lung disease in premature infants, but little is known regarding neurological consequences of its prolonged use. To study neurological effects of dexamethasone, we have developed a rat model in which newborn pups are exposed to tapering doses of dexamethasone at a time corresponding neurodevelopmentally to human exposure in the neonatal intensive care unit. On postnatal day (PD) 2, litters were divided into three groups: 1) handled controls, 2) saline-injected animals, and 3) animals injected with tapering doses of intramuscular dexamethasone between PD 3 and 6. Somatic growth and brain weight were decreased in dexamethasone-treated animals. Dexamethasone-treated animals demonstrated delays in gross neurological development on PD 7 and 14 but not PD 20. In late adolescence (PD 33), dexamethasone-treated animals were less active in light and dark environments, while demonstrating a blunted serum corticosterone response to a novel stress. The dissociation between behavioral and hormonal stress responsiveness suggests that neonatal dexamethasone exposure permanently alters central nervous system function, particularly within the neuroendocrine stress axis. This may lead to increased risk for learning impairment and maladaptive responses to the environment.
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Affiliation(s)
- Shelly B Flagel
- Department of Pediatrics, University of Michigan, Ann Arbor, Michigan 48109-0720, USA
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Brabham T, Phelka A, Zimmer C, Nash A, López JF, Vázquez DM. Effects of prenatal dexamethasone on spatial learning and response to stress is influenced by maternal factors. Am J Physiol Regul Integr Comp Physiol 2000; 279:R1899-909. [PMID: 11049876 DOI: 10.1152/ajpregu.2000.279.5.r1899] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study investigated the effect of prenatal dexamethasone (Dex) exposure on early perinatal events, hippocampal function, and response to stress. Pregnant rats received Dex in the evening water (2.5 microg/ml) or tap water (Veh) from gestational day 15 until delivery. On the day of parturition, pups were randomized, cross-fostered, and reduced to eight or nine per dam. Four groups resulted: Veh-Veh (offspring exposed to Veh in utero, rearing mother treated with Veh during gestation), Veh-Dex, Dex-Veh, and Dex-Dex. Spatial visual memory was evaluated with the Morris water maze. The corticosterone response to restraint stress was examined, and the expression of hippocampal glucocorticoid and mineralocorticoid receptors mRNA was determined by in situ hybridization. Exposure to Dex caused restlessness in mothers, low birth weights, and poor weight gain in the offspring. The Dex-Dex males had impaired spatial learning, inability to rapidly terminate the adrenocortical response to stress, and decreased hippocampal glucocorticoid receptor (GR) mRNA expression. In contrast, Dex-exposed animals reared by Veh-treated mothers had adequate spatial learning, enhanced glucocorticoid feedback, and increased hippocampal GR mRNA. We conclude that the environment provided by a healthy mother during the postnatal period can prevent the detrimental effects of prenatal Dex administration on cognition, GR mRNA expression of the hippocampus, and the quality of the stress response.
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Affiliation(s)
- T Brabham
- Mental Health Research Institute, Department of Psychiatry, University of Michigan, Ann Arbor, Michigan 48109, USA
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Yanai J, Steingart RA, Snapir N, Gvaryahu G, Rozenboim I, Katz A. The relationship between neural alterations and behavioral deficits after prenatal exposure to heroin. Ann N Y Acad Sci 2000; 914:402-11. [PMID: 11085339 DOI: 10.1111/j.1749-6632.2000.tb05214.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The present studies employ multitudinous approaches in order to overcome the methodological obstacles in the understanding of the relationship between neurochemical alterations and behavioral deficits induced by heroin during prenatal development. Mice were exposed prenatally to heroin via daily subcutaneous injections of 10 mg/kg, on gestation days 9-18. At age 50 days, the heroin-exposed offspring displayed behavioral deficits as assessed in the eight-arm and Morris mazes, pointing to possible alteration in the septohippocampal cholinergic innervations. Biochemically there was increased presynaptic activity of these innervations as attested to by the increased [3H]hemicholinium-3 (HC-3) binding sites and by K+-stimulated inositol phosphate (IP) formation. Postsynaptically, there was global hyperactivation along the different components of the nerve conduction cascade, including an increase in M1 muscarinic receptor Bmax, a general increase in G-proteins (GP) including the most relevant, G subtype, and an increase in IP formation and in basal protein kinase C (PKC) activity. However, there was desensitization of PKC activity in response to cholinergic agonist in the heroin-exposed offspring. Transplantation of normal embryonic cholinergic cells to the impaired hippocampus reversed the behavioral deficits and both the pre- and postsynaptic hyperactivity and resensitized PKC activity. To support and further strengthen the findings of the neural grafting study, correlation of the heroin-induced behavioral deficits with the biochemical alterations, done within individuals, was applied. The results showed high r values for IP formation, basal PKC, and PKC desensitization. The r values for HC-3 binding were statistically significant but relatively low. Taken together, the findings of the neural grafting and correlation studies bring us closer to understanding the relationship between the prenatal heroin-induced biochemical and behavioral changes. However, mammalian models possess the inherent methodological hindrances, stemming from possible maternal effects. To provide a control for these confounding variables, a chick embryo model was applied in which filial imprinting, a behavior related to a specific hyperstriatal nucleus, served as an endpoint. Heroin was administered to developing chick embryos by injecting the eggs (20 mg/kg) on incubation days (ID) 0 or 5. Prehatch exposure to heroin markedly diminished the ability for filial imprinting in the hatched chicks.
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Affiliation(s)
- J Yanai
- The Ross Laboratory for Studies in Neural Birth Defects, Department of Anatomy and Cell Biology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel. yanai@
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Slotkin TA, Zhang J, McCook EC, Seidler FJ. Glucocorticoid administration alters nuclear transcription factors in fetal rat brain: implications for the use of antenatal steroids. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1998; 111:11-24. [PMID: 9804869 DOI: 10.1016/s0165-3806(98)00115-1] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A recent Consensus Conference endorsed antenatal steroid use in prematurity, but indicated the need for future work on molecular and cellular effects on the developing brain. In the current study, pregnant rats were given dexamethasone during late gestation, in doses spanning those recommended for use, and effects on nuclear transcription factors were evaluated. Within the first hour after a single dose of dexamethasone, and intensifying over 4 h, marked induction of brain c-fos was seen. With repeated administration, c-fos became suppressed in some brain regions, but remained elevated in others. Dexamethasone also elicited suppression of the AP-1 family of nuclear binding proteins, but with a slower time course than seen for c-fos induction. The magnitude of the effects of late gestational exposure to dexamethasone on these transcription factors was comparable to those seen when repeated doses were administered to midgestation embryos in the context of dysmorphogenesis. Similarly, the effects on brain c-fos expression were substantially greater than those in the liver, an archetypal glucocorticoid target tissue. These results indicate that even a single, low dose of glucocorticoids used in late gestation, can disrupt the transcription factors that regulate brain cell differentiation.
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Affiliation(s)
- T A Slotkin
- Box 3813, Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
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Celsi G, Kistner A, Aizman R, Eklöf AC, Ceccatelli S, de Santiago A, Jacobson SH. Prenatal dexamethasone causes oligonephronia, sodium retention, and higher blood pressure in the offspring. Pediatr Res 1998; 44:317-22. [PMID: 9727707 DOI: 10.1203/00006450-199809000-00009] [Citation(s) in RCA: 180] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Recent reports have shown that low birth weight infants have a higher incidence of adult hypertension. These observations have stimulated a number of studies designed to evaluate the mechanisms of this phenomenon. In this study, fetal growth retardation was induced by treating pregnant rats with dexamethasone. After birth, pups whose mothers were treated with dexamethasone had a lower body and kidney weight and a lower number of glomeruli than control pups. Immunohistochemistry on treated kidneys demonstrated a marked reduction in the number of cells undergoing mitosis in the cortical nephrogenic zone. In the treated group, body and kidney weight normalized by 60 d of age, but blood pressure was significantly higher compared with controls (130+/-4 versus 107+/-1 mm Hg). In addition, GFR was significantly lower, albuminuria was higher, urinary sodium excretion rate and fractional sodium excretion were lower, and sodium tissue content was higher. In contrast, when pregnant rats were treated with a natural glucocorticoid (hydrocortisone) which is metabolized by the placenta, fetal development and adult blood pressure were normal. In conclusion, we found that high levels of maternal glucocorticoids impair renal development and lead to arterial hypertension in offspring. Even though renal mass eventually normalizes, glomerular damage as well as sodium retention occur and these factors may contribute to the development of hypertension.
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Affiliation(s)
- G Celsi
- Institute of Women's and Child's Health, Karolinska Institute, Stockholm, Sweden
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10
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McGrath KE, Seidler FJ, Slotkin TA. Convergent control of serotonin transporter expression by glucocorticoids and cocaine in fetal and neonatal rat brain. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1997; 104:209-13. [PMID: 9466725 DOI: 10.1016/s0165-3806(97)00144-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Serotonin plays a trophic role in brain cell differentiation. In this study, expression of the serotonin presynaptic transporter protein, which regulates the extracellular serotonin concentration, was measured with [3H]paroxetine in rats exposed to dexamethasone or cocaine prenatally. Within 24 h of a single dose of dexamethasone, significant increases were seen in fetal brain, and the effect persisted into the postnatal period. Chronic prenatal cocaine exposure elicited similar changes. These data indicate that exposures to apparently disparate drugs can elicit similar endpoints that may lead to behavioral teratogenesis.
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Affiliation(s)
- K E McGrath
- Department of Pharmacology, Duke University Medical Center, Durham, NC 27710, USA
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11
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Slotkin TA, Barnes GA, McCook EC, Seidler FJ. Programming of brainstem serotonin transporter development by prenatal glucocorticoids. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1996; 93:155-61. [PMID: 8804702 DOI: 10.1016/0165-3806(96)00027-2] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Prenatal stress or exposure to excess glucocorticoids are known to alter central nervous system function and to result in lasting changes in reactions to stress. The potential involvement of specific elements of brainstem serotonergic neurons was examined in the current study. Pregnant rats were given 0.05, 0.2 or 0.8 mg/kg of dexamethasone on gestational days 17, 18 and 19, and the effects on development of the serotonin presynaptic transporter were assessed from birth to young adulthood by measurement of [3H]paroxetine binding to membrane preparations. Dexamethasone produced a dose-dependent retardation of body and brainstem growth but evoked a significant elevation of [3H]paroxetine binding that persisted into adulthood. Effects on [3H]paroxetine binding were robust even at the lowest dose, which did not suppress growth, indicating that the programming of this transporter is more sensitive to glucocorticoids than is general development. At the highest dose, promotional effects on serotonin transporter expression were offset by impaired growth, so that the peak effect was seen at the intermediate dose of dexamethasone. There were no comparable effects on serotonin transmitter levels, indicating selectivity toward promotion of transporter expression as distinct from simply increasing the number of serotonergic nerve terminals or all nerve terminal components. As the effect of prenatal dexamethasone treatment on the serotonin transporter is more persistent than those on other monoamine transporters, and is not shared by postnatal treatment or by treatment in adulthood, it likely represents specific programming by glucocorticoids during the prenatal period. Aberrant serotonergic transporter expression may contribute to alterations of synaptic function that ultimately produce the physiological abnormalities seen after prenatal stress or glucocorticoid treatment.
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Affiliation(s)
- T A Slotkin
- Department of Pharmacology, Duke University Medical Center, Durham, NC 27710, USA
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12
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Bian X, Seidler FJ, Olsen C, Raymond JR, Slotkin TA. Effects of fetal dexamethasone exposure on postnatal control of cardiac adenylate cyclase: beta-adrenergic receptor coupling to Gs regulatory protein. TERATOLOGY 1993; 48:169-77. [PMID: 8211822 DOI: 10.1002/tera.1420480211] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In the adult, glucocorticoids have been shown to upregulate beta-adrenergic control of adenylate cyclase by a variety of mechanisms; glucocorticoids are also thought to play a role in development of cardiac adrenergic function. In the current study, pregnant rats were given 0.2 mg/kg of dexamethasone on gestational days 17, 18, and 19 and the effects on the development of cardiac beta-receptors and their linkage to the stimulatory G-protein, Gs, were examined at 4 days postpartum. beta-Receptor numbers and affinity were unaffected by dexamethasone exposure, nor was there any change in the ability of the GTP analog, Gpp(NH)p, to shift the affinity state of the receptor. Addition of Gpp(NH)p to cardiac membranes enhanced basal and isoproterenol-stimulated adenylate cyclase activity, but the total response to isoproterenol, with or without Gpp(NH)p, represented a very small fraction of total enzymatic activity. Quantitative analysis of Gs indicated no changes attributable to dexamethasone treatment. Although prenatal dexamethasone has been shown to increase adenylate cyclase reactivity to beta-adrenergic input, the effect appears to be at the level of the catalytic subunit of adenylate cyclase, rather than at receptor or G-protein stages.
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Affiliation(s)
- X Bian
- Department of Pharmacology, Duke University Medical Center/VA Medical Center, Durham, NC 27710
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Aszterbaum M, Feingold KR, Menon GK, Williams ML. Glucocorticoids accelerate fetal maturation of the epidermal permeability barrier in the rat. J Clin Invest 1993; 91:2703-8. [PMID: 8514877 PMCID: PMC443334 DOI: 10.1172/jci116509] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The cutaneous permeability barrier to systemic water loss is mediated by hydrophobic lipids forming membrane bilayers within the intercellular domains of the stratum corneum (SC). The barrier emerges during day 20 of gestation in the fetal rat and is correlated with increasing SC thickness and increasing SC lipid content, the appearance of well-formed lamellar bodies in the epidermis, and the presence of lamellar unit structures throughout the SC. Because glucocorticoids accelerate lung lamellar body and surfactant maturation in man and experimental animals, these studies were undertaken to determine whether maternal glucocorticoid treatment accelerates maturation of the epidermal lamellar body secretory system. Maternal rats were injected with betamethasone or saline (control) on days 16-18, and pups were delivered prematurely on day 19. Whereas control pups exhibited immature barriers to transepidermal water loss (8.16 +/- 0.52 mg/cm2 per h), glucocorticoid-treated pups exhibited competent barriers (0.74 +/- 0.14 mg/cm2 per h; P < 0.001). Glucocorticoid treatment also: (a) accelerated maturation of lamellar body and SC membrane ultrastructure; (b) increased SC total lipid content twofold; and (c) increased cholesterol and polar ceramide content three- to sixfold. Thus, glucocorticoids accelerate the functional, morphological, and lipid biochemical maturation of the permeability barrier in the fetal rat.
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Affiliation(s)
- M Aszterbaum
- Department of Dermatology, University of California, San Francisco 94143
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14
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Bian X, Seidler FJ, Slotkin TA. Fetal dexamethasone exposure interferes with establishment of cardiac noradrenergic innervation and sympathetic activity. TERATOLOGY 1993; 47:109-17. [PMID: 8446924 DOI: 10.1002/tera.1420470203] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Endogenous glucocorticoids provide natural differentiation signals for adrenergic neurons, and exposure to high exogenous steroid levels thus disrupts the timing of neuronal maturation. In the current study, pregnant rats were given 0.05, 0.2, or 0.8 mg/kg dexamethasone on gestational days 17, 18, and 19, and the effects on development of cardiac sympathetic function were assessed postnatally in the offspring. Dexamethasone produced a dose-dependent retardation of body and heart weight gains; at the highest dose, heart weight deficits were smaller than those for body weight, producing a relative cardiomegaly. The weight effects were accompanied by abnormalities of noradrenergic innervation, as assessed with measurements of norepinephrine levels and turnover. Norepinephrine levels were significantly reduced at all doses of dexamethasone, with the magnitude of effect exceeding that on heart or body weights; thus the levels were reduced even when corrected for tissue weight (ng norepinephrine/g heart weight). Norepinephrine turnover, a measure of neuronal impulse activity, showed delayed development at the lowest dose of dexamethasone and displayed profound suppression throughout development at the higher doses. Adverse effects of dexamethasone on norepinephrine turnover were still apparent in young adulthood, despite the recovery of weight variables to within 15% of normal values. In light of the release of steroids during maternal stress and the use of steroids in the therapy of neonatal respiratory distress, developing adrenergic neurons are likely to be targeted for adverse effects even when standard growth indices have normalized.
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Affiliation(s)
- X Bian
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710
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Longo LD, Packianathan S, McQueary JA, Stagg RB, Byus CV, Cain CD. Acute hypoxia increases ornithine decarboxylase activity and polyamine concentrations in fetal rat brain. Proc Natl Acad Sci U S A 1993; 90:692-6. [PMID: 8421708 PMCID: PMC45730 DOI: 10.1073/pnas.90.2.692] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The cellular responses to hypoxia are poorly understood. To test the hypothesis that ornithine decarboxylase (ODC; L-ornithine carboxy-lyase; EC 4.1.1.17) activity and polyamine concentrations change in response to acute hypoxia, we performed the following studies. Pregnant Sprague-Dawley rats inspired various O2 concentrations (9-21%) for various time periods (0.5-48 h) from days 15 to 21 of gestation. In fetal brains we measured the activity of ODC, ODC mRNA, and polyamines. In response to 4-h acute mild hypoxia, ODC activity in fetal rat brain (cerebrum, cerebellum, and hippocampus) increased to 330-450% from control values (P < 0.001), after which it declined to control levels in 6-8 h. The 4-h ODC response varied inversely with inspired O2 concentration and was not mimicked by beta 2 agonist or blocked by beta 2-antagonist administration. The ODC response was associated with an increase in fetal brain putrescine concentration to 190% above control at 4-6 h (P < 0.01) and an increase in the polyamines spermidine and spermine to about 115% above control at 6-8 h. We also observed that ODC mRNA increased significantly after 2-4 h of hypoxia. ODC activity and polyamine concentrations appear to be useful enzymatic markers for fetal brain hypoxia. The magnitude and time course of the acute hypoxic ODC increase were similar to responses to extracellular signals that result in differentiation or cell growth. Thus, the well-defined and regulated ODC activity response may represent a protective mechanism in brain to hypoxia.
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Affiliation(s)
- L D Longo
- Department of Physiology, Loma Linda University, CA 92350
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Slotkin TA, McCook EC, Seidler FJ. Glucocorticoids regulate the development of intracellular signaling: enhanced forebrain adenylate cyclase catalytic subunit activity after fetal dexamethasone exposure. Brain Res Bull 1993; 32:359-64. [PMID: 8221125 DOI: 10.1016/0361-9230(93)90200-u] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Although glucocorticoids cause growth retardation and interfere with cell development, selective promotion of some aspects of cell function also has been reported. The current study examines whether glucocorticoids enhance intracellular transduction mechanisms mediated by adenylate cyclase in the developing forebrain, a region in which steroids have been shown to interfere with cell replication, maturation, and growth. Pregnant rats were given dexamethasone at doses spanning the threshold for growth impairment (0.05, 0.2, and 0.8 mg/kg) on gestational days 17, 18, and 19, and development of adenylate cyclase was evaluated in membrane preparations, using four different activity measures; basal adenylate cyclase in the absence or presence of GTP, maximal G-protein activation by fluoride in the presence of GTP, and stimulation mediated by forskolin-Mn2+, which bypasses the G-proteins. Prenatal exposure to dexamethasone produced a dose-dependent impairment of body growth, with smaller deficits in forebrain weights (brain sparing) indicative of systemic toxicity. Basal adenylate cyclase activity was unaffected by dexamethasone treatment, regardless of whether GTP was present in the assay. Similarly, fluoride stimulation developed normally in all dexamethasone groups. However, forskolin-Mn(2+)-stimulated activity was significantly enhanced in a dose-dependent fashion. These results suggest that glucocorticoids serve as positive factors for the development of adenylate cyclase catalytic subunit activity, independently of their adverse effects on general growth and development; thus, these hormones may be a primary regulator of cell signaling during early development.
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Affiliation(s)
- T A Slotkin
- Department of Pharmacology, Duke University Medical Center, Durham, NC 27710
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Carlos RQ, Seidler FJ, Slotkin TA. Fetal dexamethasone exposure alters macromolecular characteristics of rat brain development: a critical period for regionally selective alterations? TERATOLOGY 1992; 46:45-59. [PMID: 1641811 DOI: 10.1002/tera.1420460108] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Fetal glucocorticoid exposure retards postnatal growth and evokes abnormalities of nervous system structure and function. To examine the underlying mechanisms, we administered 0.2 or 0.8 mg/kg of dexamethasone to pregnant rats on gestational days 17, 18, and 19 and assessed brain region cell development with indices of DNA content (total cell numbers), DNA concentration (cell packing density), and protein/DNA ratio (relative cell size). Dexamethasone evoked deficits of pup body and brain region weights, but the brain regions displayed growth-sparing associated initially with preservation of cell numbers (normal or elevated DNA content and concentration), at the expense of relative cell size (decreased protein/DNA). Subsequently, brain cell acquisition lagged behind that of controls, with deficits in DNA and elevations of protein/DNA. In midbrain + brainstem and in cerebellum, cell markers returned to normal by weaning. However, the forebrain showed persistent elevations of DNA and reduced protein/DNA, indicative of replacement of neurons with glia. Because the treatment period coincided with the timing of neuronal cell replication in the forebrain, but not in the other regions, these results suggest that the critical period for lasting deficits of dexamethasone coincides with the peak of neuronal mitosis.
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Affiliation(s)
- R Q Carlos
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710
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18
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Carlos RQ, Seidler FJ, Slotkin TA. Fetal dexamethasone exposure sensitizes neonatal rat brain to hypoxia: effects on protein and DNA synthesis. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1991; 64:161-6. [PMID: 1786639 DOI: 10.1016/0165-3806(91)90220-d] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Fetal exposure to glucocorticoids is known to produce long-term alterations in cell development within the central nervous system. The current study examines whether some of the adverse effects of prenatal dexamethasone treatment on brain development represent sensitization to hypoxia-induced damage. Pregnant rats were given 0.2 or 0.8 mg/kg of dexamethasone on gestational days 17, 18 and 19 and their offspring were challenged by exposure to 7% O2 on postnatal days 1 and 8. In control rats at 1 day of age, hypoxia evoked an acute decrease in protein synthesis, assessed by [3H]leucine incorporation, in both the midbrain + brainstem and forebrain. The decrease was also seen in animals receiving the low dose of dexamethasone, but was of smaller magnitude in the midbrain + brainstem than in the control cohort. At the higher dose of dexamethasone, hypoxia failed to evoke a decrease in protein synthesis; instead, protein synthesis was significantly increased. By 8 days of age, the animals receiving the lower dose of dexamethasone also displayed the anomalous increment in [3H]leucine incorporation during hypoxic challenge, whereas the effect in the high dose group was less notable. Similarly, parallel examination of incorporation of [3H]thymidine into DNA on postnatal day 1 indicated that control animals would reduce their macromolecule synthetic rate in a hypoxic environment, but that animals exposed to the high dose of dexamethasone would not; unlike the case with protein synthesis, however, the dexamethasone group never showed an increase in DNA synthesis during hypoxia. By 8 days of age, the interaction between the high dose of dexamethasone and hypoxia was no longer apparent for DNA synthesis.2
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Affiliation(s)
- R Q Carlos
- Department of Pharmacology, Duke University Medical Center, Durham, NC 27710
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19
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Koegler SM, Seidler FJ, Spencer JR, Slotkin TA. Ischemia contributes to adverse effects of cocaine on brain development: suppression of ornithine decarboxylase activity in neonatal rat. Brain Res Bull 1991; 27:829-34. [PMID: 1786562 DOI: 10.1016/0361-9230(91)90217-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Exposure to cocaine during development has been shown to cause structural and functional alterations in the nervous system. In the current study, the mechanisms underlying these effects were examined in neonatal rats through measurement of ornithine decarboxylase activity, a key regulatory enzyme in the control of neural cell differentiation. Animals were given cocaine (30 mg/kg SC) and ornithine decarboxylase measured 1 and 4 h later in midbrain + brainstem, cerebral cortex and cerebellum. Cocaine caused inhibition of ornithine decarboxylase activity that was not secondary to local anesthesia, as lidocaine was ineffective. The effect of cocaine was independent of direct central actions, as introduction of the drug into the central compartment via intracisternal injection failed to inhibit ornithine decarboxylase. In contrast, prevention of cocaine-induced ischemia by peripheral alpha-adrenergic blockade (phenoxybenzamine) reversed the ornithine decarboxylase inhibition caused by cocaine, and actually unmasked potential stimulatory actions. These data indicate that cocaine-induced ischemia is a major contributor to the net effect of the drug on central nervous system cellular development.
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Affiliation(s)
- S M Koegler
- Department of Pharmacology, Duke University Medical Center, Durham, NC 27710
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20
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Smith WT, Seidler FJ, Slotkin TA. Acute stimulation of ornithine decarboxylase in neonatal rat brain regions by nicotine: a central receptor-mediated process? BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1991; 63:85-93. [PMID: 1790600 DOI: 10.1016/0165-3806(91)90069-u] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Nicotine exposure during development alters central nervous system structure and function. In the current study, we examined the acute effects of nicotine (3 mg/kg) on developing rat brain by monitoring ornithine decarboxylase (ODC), a marker for perturbed cell development; ODC controls polyamine biosynthesis and thus regulates cell differentiation. Three brain regions were selected that differ both in their timetables for maturation and in nicotinic receptor concentrations: midbrain + brainstem (earliest development, highest receptor concentration), forebrain (intermediate profiles) and cerebellum (latest development and lowest receptor concentration). Nicotine caused stimulation of ODC within 1 h after drug administration, an effect that displayed both age- and region-dependence corresponding to the development of central nicotinic receptors: effects appeared earliest and were largest in magnitude in midbrain + brainstem and forebrain, and appeared last and with smaller magnitude in the cerebellum. Central receptor involvement was confirmed at 8 days postpartum by demonstrating desensitization of the response after repeated nicotine administration, and by evoking equivalent effects with direct introduction of a small dose of nicotine into the central nervous system. Later in development, acute stimulation of ODC by nicotine became less selective, reflecting secondary actions mediated through systemic hypoxia caused by the drug; this conclusion was confirmed by the absence of desensitization after repeated nicotine administration, and by the failure of centrally administered nicotine to evoke a full stimulatory response. Nicotine-induced ischemia did not contribute to stimulation of ODC seen at the 1 h time point: pretreatment with chlorisondamine, a ganglionic nicotinic antagonist, failed to alter the central stimulatory response.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- W T Smith
- Department of Pharmacology, Duke University Medical Center, Durham, NC 27710
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21
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Slotkin TA, Seidler FJ, Kavlock RJ, Bartolome JV. Fetal dexamethasone exposure impairs cellular development in neonatal rat heart and kidney: effects on DNA and protein in whole tissues. TERATOLOGY 1991; 43:301-6. [PMID: 2048038 DOI: 10.1002/tera.1420430404] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Fetal glucocorticoid exposure causes postnatal growth retardation. To examine the mechanisms underlying effects on specific organ systems, we administered 0.2 or 0.8 mg/kg of dexamethasone to pregnant rats on gestational days 17, 18, and 19 and assessed three biochemical markers of cell development in heart and kidney of the offspring: DNA content per organ as an index of total cell numbers, DNA per g tissue as an index of cell packing density, and protein/DNA ratio as an index of relative cell size. In both tissues, DNA content became markedly subnormal during the first postnatal week, the ontogenetic period of rapid cell division. Partial recovery occurred by the end of the first postnatal month. In the heart, cell packing density was subnormal initially and the cells were significantly enlarged. In contrast, packing density was slightly elevated in the kidney; protein/DNA was increased by the low dose of dexamethasone, but markedly decreased by the high dose. These results suggest that tissue growth impairment caused by prenatal dexamethasone treatment reflects primary deficits in cell proliferation that extend to a variety of different cell types; however, consequent effects on cell packing density and cell size are dose-specific, possibly reflecting actions of glucocorticoids selective for certain cell types or phases of cell development.
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Affiliation(s)
- T A Slotkin
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710
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22
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Navarro HA, Kudlacz EM, Eylers JP, Slotkin TA. Prenatal dexamethasone administration disrupts the pattern of cellular development in rat lung. TERATOLOGY 1989; 40:433-8. [PMID: 2623631 DOI: 10.1002/tera.1420400504] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
To examine whether prenatal exposure to glucocorticoids could adversely affect subsequent cellular development of the lung, we administered 0.2 mg/kg of dexamethasone to pregnant rats on gestational days 17, 18, and 19. Lungs of the offspring were then examined for patterns of cell acquisition (DNA) and growth (protein). DNA concentration (a marker of cell packing density) and DNA content (a measure of total cell numbers) were reduced during gestation, and the shortfalls in concentration persisted past weaning. Disruption of development was also apparent in the protein/DNA ratio, which was consistently elevated, a finding consistent with cellular hypertrophy. In addition, lung ODC became coupled to beta-adrenergic receptors prematurely in the dexamethasone group, suggesting that neural control of tissue differentiation is altered. These data indicate that prenatal glucocorticoids may compromise lung development through effects on cell replication and differentiation, which derive, in part, from alterations in the reception of trophic neural signals.
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Affiliation(s)
- H A Navarro
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710
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