Fetal dexamethasone exposure alters macromolecular characteristics of rat brain development: a critical period for regionally selective alterations?

Prenatal prednisone exposure impacts liver development and function in fetal mice and its characteristics

Prednisone, a widely used glucocorticoid drug in human and veterinary medicine, has been reported to cause developmental toxicity. However, systematic studies about the effect of prednisone on fetal liver development are still unclear. We investigated the potential effects of maternal exposure to clinically equivalent doses of prednisone during different gestational stages on cell proliferation and apoptosis, cell differentiation, glucose and lipid metabolism, and hematopoiesis in the liver of fetal mice, and explored the potential mechanisms. Results showed that prenatal prednisone exposure (PPE) could suppress cell proliferation, inhibit hepatocyte differentiation, and promote cholangiocyte differentiation in the fetal liver. Meanwhile, PPE could result in the enhancement of glyconeogenesis and bile acid synthesis and the inhibition of fatty acid β-oxidation and hematopoiesis in the fetal liver. Further analysis found that PPE-induced alterations in liver development had obvious stage and sex differences. Overall, the alteration in fetal liver development and function induced by PPE was most pronounced during the whole pregnancy (GD0-18), and the males were relatively more affected than the females. Additionally, fetal hepatic insulin-like growth factor 1 (IGF1) signaling pathway was inhibited by PPE. In conclusion, PPE could impact fetal liver development and multiple functions, and these alterations might be partially related to the inhibition of IGF1 signaling pathway.

Prenatal amoxicillin exposure induces developmental toxicity in fetal mice and its characteristics

Amoxicillin, a widely used antibiotic in human and veterinary pharmaceuticals, is now considered as an "emerging contaminant" because it exists widespreadly in the environment and brings a series of adverse outcomes. Currently, systematic studies about the developmental toxicity of amoxicillin are still lacking. We explored the potential effects of amoxicillin exposure on pregnancy outcomes, maternal/fetal serum phenotypes, and fetal multiple organ development in mice, at different doses (75, 150, 300 mg/(kg·day)) during late-pregnancy, or at a dose of 300 mg/(kg·day) during different stages (mid-/late-pregnancy) and courses (single-/multi-course). Results showed that prenatal amoxicillin exposure (PAmE) had no significant influence on the body weights of dams, but it could inhibit the physical development and reduce the survival rate of fetuses, especially during the mid-pregnancy. Meanwhile, PAmE altered multiple maternal/fetal serum phenotypes, especially in fetuses. Fetal multi-organ function results showed that PAmE inhibited testicular/adrenal steroid synthesis, long bone/cartilage and hippocampal development, and enhanced ovarian steroid synthesis and hepatic glycogenesis/lipogenesis, and the order of severity might be gonad (testis, ovary) > liver > others. Further analysis found that PAmE-induced multi-organ developmental and functional alterations had differences in stages, courses and fetal gender, and the most obvious changes might be in high-dose, late-pregnancy and multi-course, but there was no typical rule of a dose-response relationship. In conclusion, this study confirmed that PAmE could cause abnormal development and multi-organ function alterations, which deepens our understanding of the risk of PAmE and provides an experimental basis for further exploration of the long-term harm.

Embryonic Amoxicillin Exposure Has Limited Impact on Liver Development but Increases Susceptibility to NAFLD in Zebrafish Larvae

Amoxicillin is commonly used in clinical settings to target bacterial infection and is frequently prescribed during pregnancy. Investigations into its developmental toxicity and effects on disease susceptibility are not comprehensive. Our present study examined the effects of embryonic amoxicillin exposure on liver development and function, especially the effects on susceptibility to non-alcoholic fatty liver disease (NAFLD) using zebrafish as an animal model. We discovered that embryonic amoxicillin exposure did not compromise liver development, nor did it induce liver toxicity. However, co-treatment of amoxicillin and clavulanic acid diminished BESP expression, caused bile stasis and induced liver toxicity. Embryonic amoxicillin exposure resulted in elevated expression of lipid synthesis genes and exacerbated hepatic steatosis in a fructose-induced NAFLD model, indicating embryonic amoxicillin exposure increased susceptibility to NAFLD in zebrafish larvae. In summary, this research broadens our understanding of the risks of amoxicillin usage during pregnancy and provides evidence for the impact of embryonic amoxicillin exposure on disease susceptibility in offspring.

Efficacy and safety of antenatal steroids

Antenatal steroids (ANS) are among the most important and widely utilized interventions to improve outcomes for preterm infants. A significant body of evidence demonstrates improved outcomes in preterm infants (24-34 wk) delivered between 1 and 7 days after the administration of a single course of ANS. Moreover, ANS have the advantage of being widely available, low cost, and easily administered via maternal intramuscular injection. The use of ANS to mature the fetal lung is, however, not without contention. Their use in pregnancy is not FDA approved, and treatment doses and regimens remain largely unoptimized. Their mode of use varies considerably between countries, and there are lingering concerns regarding the safety of exposing the fetus to high doses of exogenous steroids. A significant proportion of women deliver outside the 1- to 7-day therapeutic window after ANS treatment, and this delay may be associated with an increased risk of adverse outcomes for both mother and baby. Today, animal-based studies are one means by which key questions of dosing and safety relating to ANS may be resolved, allowing for further refinement(s) of this important therapy. Complementary approaches using nonhuman primates, sheep, and rodents have provided invaluable advances to our understanding of how exogenous steroid exposure impacts fetal development. Focusing on these three major model groups, this review highlights the role of three key animal models (sheep, nonhuman primates, rodents) in the development of antenatal steroid therapy, and provides an up-to-date synthesis of current efforts to refine this therapy in an era of personalised medicine.

The efficacy of antenatal steroid therapy is dependent on the duration of low-concentration fetal exposure: evidence from a sheep model of pregnancy

BACKGROUND

Antenatal corticosteroids are among the most important and widely used interventions to improve outcomes for preterm infants. Antenatal corticosteroid dosing regimens remain unoptimized and without maternal weight-adjusted dosing. We, and others, have hypothesized that, once a low concentration of maternofetal steroid exposure is achieved and maintained, the duration of the steroid exposure determines treatment efficacy. Using a sheep model of pregnancy, we tested the relationship among steroid dose, duration of exposure, and treatment efficacy.

OBJECTIVE

The study was conducted to investigate the relative importance of duration and magnitude of fetal corticosteroid exposure to mature the preterm fetal ovine lung.

STUDY DESIGN

Ewes with single fetuses at 120 days gestation received an intravenous bolus (loading dose) followed by a maintenance infusion of betamethasone phosphate to target 12-hour fetal plasma betamethasone concentrations of (1) 20 ng/mL, (2) 10 ng/mL, or (3) 2 ng/mL. In a subsequent experiment, fetal plasma betamethasone concentrations were targeted at 2 ng/mL for 26 hours. Negative control animals received sterile saline solution. Positive control animals received 2 intramuscular injections of 0.25 mg/kg Celestone Chronodose (betamethasone phosphate + betamethasone acetate) spaced at 24 hours. Preterm lambs were delivered surgically and ventilated 48 hours after treatment commenced. Maternal and fetal plasma betamethasone concentrations were confirmed by mass spectrometry in a parallel study of chronically catheterized, corticosteroid-treated ewes and fetuses.

RESULTS

The loading and maintenance doses were achieved and maintained the desired fetal plasma betamethasone concentrations of approximately 20, 10, and 2 ng/mL for 12 hours. Compared with the 12-hour infusion-treated animals, lambs from the positive control (2 intramuscular doses of 0.25 mg/kg Celestone Chronodose) group had the greatest functional lung maturation (compliance, gas exchange, arterial pH) and molecular evidence of maturation (glucocorticoid receptor signaling activation), despite having maximum fetal plasma betamethasone concentrations 2.5 times lower than animals in the 20 ng/mL betamethasone infusion group. Lambs from the 12-hour 2-ng/mL betamethasone infusion group had little functional lung maturation. In contrast, lambs from the 26-hour 2-ng/mL betamethasone infusion group had functional lung maturation equivalent to lambs from the positive control group.

CONCLUSION

In preterm lambs that were exposed to antenatal corticosteroids, high maternofetal plasma betamethasone concentrations did not correlate with improved lung maturation. The largest and most consistent improvements in lung maturation were in animals that were exposed to either the clinical course of Celestone Chronodose or a low-dose betamethasone phosphate infusion to achieve a fetal plasma betamethasone concentration of approximately 2 ng/mL for 26 hours. The duration of low-concentration maternofetal steroid exposure, not total dose or peak drug exposure, is a key determinant for antenatal corticosteroids efficacy. These findings underscore the need to develop an optimized steroid dosing regimen that may improve both the efficacy and safety of antenatal corticosteroids therapy.

Course-, dose-, and stage-dependent toxic effects of prenatal dexamethasone exposure on long bone development in fetal mice

Dexamethasone is routinely used for treating those mothers at risk for preterm delivery. However, overexposure to exogenous glucocorticoids induces bone loss in offspring, and the "critical window" and safe dose of this treatment are largely unknown. In this study, we found that femoral length, and the length of the primary ossification center were significantly reduced in fetal mice after repeated prenatal dexamethasone exposure (PDE). Compared with single-course exposure on gestational day (GD)15, newborn mice with repeated PDE (3 times, from GD15 to 17) showed a significant decrease in femoral trabecular bone mass with decreased trabecular number and thickness. For those newborn mice treated after repeated PDE at different doses (0, 0.2, 0.8, and 1.2 mg/kg/d), the toxic effect of dexamethasone on bone development was observed at 0.8 and 1.2 mg/kg/d. More severe retardation in bone development was observed in the fetal mice after PDE at 0.8 mg/kg/d during GD12-14, compared with that during GD15-17. Interestingly, stronger toxic effects were observed in male newborn mice after PDE than were observed in female newborn mice. In conclusion, PDE with multiple course, higher dose, or exposure at an early stage of pregnancy have stronger toxic effects on bone development of fetal mice.

Course-, dose-, and stage-dependent toxic effects of prenatal dexamethasone exposure on fetal articular cartilage development

Dexamethasone, a synthetic long-acting glucocorticoid, is routinely used for treating mothers at risk for preterm delivery. However, intrauterine overexposure to glucocorticoids induces low birth weight and cartilage dysplasia in offspring. Also, the "critical window" and safe dose of this treatment are largely unknown. This study investigated the course-, dose-, and stage-dependent toxic effects and the possible mechanisms of prenatal dexamethasone exposure (PDE) on fetal development and articular cartilage development. Pregnant mice (C57BL/6) received subcutaneous injection of dexamethasone (0.8 mg/kg d) once on gestational day (GD) 15 or once a day from GD 15 to 17, or received various doses of dexamethasone (0, 0.2, 0.8, and 1.2 mg/kg d) on GD 15-17, or received dexamethasone (0.8 mg/kg d) at early stage (GD 12-14) or late stage of pregnancy (GD 15-17). Offspring's knee joints were harvested at birth for morphological analyses and detection of gene expression. Repeated PDE significantly suppressed fetal and articular cartilage development, which were characterized by decreased body weight and body length, coarse articular cartilage surfaces, and reduced gene and protein expression of Col2a1 and aggrecan. For those newborns treated with repeated PDE at different doses, the toxic effects on fetal and articular cartilage development were observed at doses of 0.8 and 1.2 mg/kg d, whereas no obvious toxic effects were observed at the dose of 0.2 mg/kg d. Moreover, PDE at 0.8 mg/kg d during the early embryonic stage induced stronger toxic effects on fetal and articular cartilage development, compared with PDE during the late embryonic stage. Detection of gene expression showed that the TGFβ signaling pathway in the articular cartilage was down-regulated after PDE. Taken together, PDE induces fetal developmental toxicity and articular cartilage developmental toxicity in a course-, dose-, and stage-dependent manner.

Antenatal dexamethasone exposure differentially affects distinct cortical neural progenitor cells and triggers long-term changes in murine cerebral architecture and behavior

Antenatal administration of synthetic glucocorticoids (sGC) is the standard of care for women at risk for preterm labor before 34 gestational weeks. Despite their widespread use, the type of sGC used and their dose or the dosing regimens are not standardized in the United States of America or worldwide. Several studies have identified neural deficits and the increased risk for cognitive and psychiatric disease later in life for children administered sGC prenatally. However, the precise molecular and cellular targets of GC action in the developing brain remain largely undefined. In this study, we demonstrate that a single dose of glucocorticoid during mid-gestation in mice leads to enhanced proliferation in select cerebral cortical neural stem/progenitor cell populations. These alterations are mediated by dose-dependent changes in the expression of cell cycle inhibitors and in genes that promote cell cycle re-entry. This leads to changes in neuronal number and density in the cerebral cortex at birth, coupled to long-term alterations in neurite complexity in the prefrontal cortex and hippocampus in adolescents, and changes in anxiety and depressive-like behaviors in adults.

Expanding the test set: Chemicals with potential to disrupt mammalian brain development

High-throughput test methods including molecular, cellular, and alternative species-based assays that examine critical events of normal brain development are being developed for detection of developmental neurotoxicants. As new assays are developed, a "training set" of chemicals is used to evaluate the relevance of individual assays for specific endpoints. Different training sets are necessary for each assay that would comprise a developmental neurotoxicity test battery. In contrast, evaluation of the predictive ability of a comprehensive test battery requires a set of chemicals that have been shown to alter brain development after in vivo exposure ("test set"). Because only a small number of substances have been well documented to alter human neurodevelopment, we have proposed an expanded test set that includes chemicals demonstrated to adversely affect neurodevelopment in animals. To compile a list of potential developmental neurotoxicants, a literature review of compounds that have been examined for effects on the developing nervous system was conducted. The search was limited to mammalian studies published in the peer-reviewed literature and regulatory studies submitted to the U.S. EPA. The definition of developmental neurotoxicity encompassed changes in behavior, brain morphology, and neurochemistry after gestational or lactational exposure. Reports that indicated developmental neurotoxicity was observed only at doses that resulted in significant maternal toxicity or were lethal to the fetus or offspring were not considered. As a basic indication of reproducibility, we only included a chemical if data on its developmental neurotoxicity were available from more than one laboratory (defined as studies originating from laboratories with a different senior investigator). Evidence from human studies was included when available. Approximately 100 developmental neurotoxicity test set chemicals were identified, with 22% having evidence in humans.

Astroglial Plasticity Is Implicated in Hippocampal Remodelling in Adult Rats Exposed to Antenatal Dexamethasone

The long-term effects of antenatal dexamethasone treatment on brain remodelling in 3-month-old male Sprague Dawley rats whose mothers had been treated with dexamethasone were investigated in the present study. Dorsal hippocampus, basolateral amygdala and nucleus accumbens volume, cell numbers, and GFAP-immunoreactive astroglial cell morphology were analysed using stereology. Total brain volume as assessed by micro-CT was not affected by the treatment. The relative volume of the dorsal hippocampus (% of total brain volume) showed a moderate, by 8%, but significant reduction in dexamethasone-treated versus control animals. Dexamethasone had no effect on the total and GFAP-positive cell numbers in the hippocampal subregions, basolateral amygdala, and nucleus accumbens. Morphological analysis indicated that numbers of astroglial primary processes were not affected in any of the hippocampal subregions analysed but significant reductions in the total primary process length were observed in CA1 by 32%, CA3 by 50%, and DG by 25%. Mean primary process length values were also significantly decreased in CA1 by 25%, CA3 by 45%, and DG by 25%. No significant astroglial morphological changes were found in basolateral amygdala and nucleus accumbens. We propose that the dexamethasone-dependent impoverishment of hippocampal astroglial morphology is the case of maladaptive glial plasticity induced prenatally.

Prenatal corticosteroid exposure alters early developmental seizures and behavior

In humans, corticosteroids are often administered prenatally to improve lung development in preterm neonates. Studies in exposed children as well as in children, whose mothers experienced significant stress during pregnancy indicate behavioral problems and possible increased occurrence of epileptic spasms. This study investigated whether prenatal corticosteroid exposure alters early postnatal seizure susceptibility and behaviors. On gestational day 15, pregnant rats were injected i.p. with hydrocortisone (2×10mg/kg), betamethasone (2×0.4mg/kg) or vehicle. On postnatal day (P)15, seizures were induced by flurothyl or kainic acid (3.5 or 5.0mg/kg). Horizontal bar holding was determined prior to seizures and again on P17. Performance in the elevated plus maze was assessed on P20-22. Prenatal exposure to betamethasone decreased postnatal susceptibility to flurothyl-induced clonic seizures but not to kainic acid-induced seizures. Prenatal hydrocortisone decreased postnatal weight but did not affect seizure susceptibility. Hydrocortisone alone did not affect performance in behavioral tests except for improving horizontal bar holding on P17. A combination of prenatal hydrocortisone and postnatal seizures resulted in increased anxiety. Prenatal exposure to mineralocorticoid receptor blocker canrenoic acid did not attenuate, but surprisingly amplified the effects of hydrocortisone on body weight and significantly worsened horizontal bar performance. Thus, prenatal exposure to excess corticosteroids alters postnatal seizure susceptibility and behaviors. Specific effects may depend on corticosteroid species.

Toxicity of corticosteroids and catecholamines for mice neuronal cell cultures: Role of preservatives

OBJECTIVE

To confirm previous reports on dexamethasone and sulfite neurotoxicity, and to investigate methylprednisolone, dopamine, and dobutamine neurotoxicity.

METHODS

Pure dexamethasone, injectable dexamethasone containing sodium metabisulfite (Soludecadron), pure methylprednisolone, injectable methylprednisolone (Solu-Medrol), pure dopamine, injectable dopamine containing potassium metabisulfite (Revivan), pure dobutamine, injectable dobutamine containing sodium metabisulfite (Dobutrex), and sodium metabisulfite were added to the medium of mixed glial-neuronal cell cultures at concentrations of 0.1, 1, 10, and 100 microM. Cell damage induced by glucocorticoids was assessed by measuring the release of lactate dehydrogenase (LDH) from the injured cells into the extracellular fluid during the 24 hours of exposure to drugs. Cell damage induced by catecholamines was assessed using the fluorescent dye propidium iodide (PI) method 24 hours after exposure to the drugs.

RESULTS

Methylprednisolone and Solu-Medrol did not affect neuronal death, which was increased by dexamethasone and Soludecadron at 100 microM and sodium metabisulfite at 10 and 100 microM. Neuronal death was significantly increased by dopamine, Revivan, dobutamine, Dobutrex, and sulfites at 10 and 100 microM concentrations.

CONCLUSIONS

In vitro dexamethasone, Soludecadron, and sulfites increase neuronal cell death, while methylprednisolone and Solu-Medrol are not neurotoxic; dopamine and dobutamine were found neurotoxic independently from sulfite toxicity.

Antenatal steroid therapy: have we undervalued the risks?

Antenatal corticosteroid therapy to enhance fetal lung maturation in pregnancies at risk for preterm delivery is used commonly, based on the assumption that its established benefits outweigh associated risks. Corticosteroid treatment does confer some risks, particularly with respect to restricted brain growth and disordered neuronal development. These alterations have the potential for long-term effects on health. They deserve further study, and should not be undervalued. Corticosteroid therapy should be applied selectively in those situations in which the risk of preterm birth is very high and the likelihood of severe respiratory distress syndrome substantial.

Prenatal exposure to betamethasone decreases anxiety in developing rats: hippocampal neuropeptide y as a target molecule

Repeated antenatal administration of betamethasone is frequently used as a life-saving treatment in obstetrics. However, limited information is available about the outcome of this therapy in children. The initial prospective studies indicate that there are behavioral impairments in children exposed to repeated courses of prenatal betamethasone during the third trimester of pregnancy. In this study, pregnant rats received two betamethasone injections on day 15 of gestation. Using immunohistochemistry, the expression of a powerful anxiolytic molecule neuropeptide Y (NPY) was determined on postnatal day (PN) 20 in the hippocampus and basolateral amygdala (structures related to anxiety and fear) of the offspring. Prenatal betamethasone exposure induced significant increases in NPY expression in the hippocampus but not in the amygdala. Indeed, behavioral tests in the offspring, between PN20 and PN22 in the open field, on the horizontal bar, and in the elevated plus maze, indicated decreases in anxiety, without impairments in motor performance or total activity. Decreased body weight in betamethasone-exposed rats confirmed long-lasting effects of prenatal exposure. Thus, prenatal betamethasone treatment consistently increases hippocampal NPY, with decreases in anxiety-related behaviors and hippocampal role in anxiety in rats. Animal models may assist in differentiation between pathways of the desired main effect of the antenatal corticosteroid treatment and pathways of unwanted side effects. This differentiation can lead to specific therapeutic interventions directed against the side effects without eliminating the beneficial main effect of the corticosteroid treatment.

Prenatal corticosteroid impact on hippocampus: implications for postnatal outcomes

Prenatal administration of corticosteroids is common in obstetrics to improve the outcome of premature deliveries. Many pregnant women receive multiple corticosteroid courses. Long-term follow-up studies in humans are limited, but those available suggest detrimental effects on the behavior of those children. Animal data also show adverse effects of prenatal corticosteroids mainly in the hippocampus, a structure sensitive to corticosteroid action. Several molecules involved in neuronal survival, seizure susceptibility, and behavior have been identified as possible targets of prenatal corticosteroid effects. These molecules include hippocampal glucocorticoid receptors, brain-derived neurotrophic factor, corticotropin-releasing hormone, and neuropeptide Y. Prenatal corticosteroid treatment permanently reprograms expression of these molecules. The future goals of research in this area include development of specific antagonists of corticosteroid activation pathways that would help differentiate between positive main effects and undesired adverse effects of prenatally administered corticosteroids.

RETRACTED: Maternal adversity, glucocorticoids and programming of neuroendocrine function and behaviour

The fetus may be exposed to increased endogenous glucocorticoid or synthetic glucocorticoid in late gestation. Approximately 7% of pregnant women in Europe and North America are treated with synthetic glucocorticoid to promote lung maturation in fetuses at risk of preterm delivery. Very little is known about the mechanisms by which synthetic glucocorticoid or prenatal stress influence neurodevelopment in the human, or whether specific time windows of increased sensitivity exist. Glucocorticoids are essential for many aspects of normal brain development, but exposure of the fetal brain to excess glucocorticoid can have life-long effects on neuroendocrine function and behaviour. Both endogenous glucocorticoid and synthetic glucocorticoid exposure have a number of rapid effects in the fetal brain, including modification of neurotransmitter systems and transcriptional machinery. Such fetal exposure permanently alters hypothalamo-pituitary-adrenal (HPA) function in prepubertal, postpubertal and aging offspring, in a sex-dependent manner. Prenatal glucocorticoid manipulation also leads to modification of behaviour, brain and organ morphology, as well as altered regulation of other endocrine systems. Permanent changes in endocrine function will impact on health, since elevated cumulative exposure to endogenous glucocorticoid is linked to the premature onset of pathologies associated with aging.

Effects of maternally administered dexamethasone and acute hypoxemia at 0.7 gestation on blood pressure and placental perfusion in sheep

Glucocorticoid administration to women in premature labor significantly decreases preterm infant morbidity and mortality. Fetal exposure to maternally administered glucocorticoids in late gestation causes fetal hypertension. We determined the effects of a single course (4 injections at 12-hr intervals) of dexamethasone (DM; 2 mg, a weight-adjusted dose equivalent to one-third the dose administered to pregnant women) or saline (S) in sheep at 103-104 days of gestation (dGA; term 149 dGA) on maternal and fetal blood pressure (BP). We also determined the BP and placental perfusion effects of acute maternal hypoxemia. Venous and arterial catheters were placed in 10 ewes and fetuses (DM = 6, S = 4) at 96 +/- 1 dGA. Maternal and fetal placental perfusion was determined with fluorescent microspheres. Dexamethasone increased fetal but not maternal BP; maternal and fetal placental blood flow and vascular resistance (VR) were unchanged. At 105 dGA, hypoxemia was induced for 1 hr by maternal nitrogen gas inhalation to decrease fetal PaO2 by 40%. Hypoxemia increased BP in DM but not S fetuses or mothers in either group. Hypoxemia decreased maternal placental blood flow by 39 +/- 7% and 51 +/- 9% and increased maternal placental VR by 65 +/- 7% and 69 +/- 6% in S and DM mothers, respectively. Hypoxemia did not alter fetal placental blood flow or VR in either treatment group. In summary, at 0.7 gestation, DM induces a hypertensive response to fetal hypoxemia that is characteristic of older fetuses but does not alter hypoxemia-induced reductions in maternal placental blood flow.

Prenatal and postnatal steroid therapy and child neurodevelopment

In recent years, scientific evidence has accumulated on the potential neuro-toxic effects of perinatal steroid therapy on the incompletely developed brain; therefore, much effort has been directed toward finding the optimal regimen that may reduce lung disease without incurring significant brain injury in fetuses and preterm infants. Current recommendations of the NIH endorse a single course of prenatal steroids in cases of imminent preterm delivery. Postnatal steroid therapy should be limited, according to the American Association of Pediatrics Guide-lines, to selected clinical cases after the first week of life. These cautions aim to decrease possible harmful effects that could affect short- and long-term neuro-developmental outcome in this high-risk population.

Perinatal corticosteroids: A review of research. Part I: Antenatal administration

The premature infant may receive therapeutic glucocorticoid drugs while in utero or in the postnatal period. This article (part I of a two-part series) discusses the benefits and risks of in utero, or antenatal, corticosteroids (ACS) for the premature infant. Part II addresses the benefits and risks of postnatal corticosteroid (PCS) use. There are numerous clinical studies on the therapeutic use of these steroids for the prevention of respiratory distress syndrome and chronic lung disease in the premature infant, although research results on the efficacy of repeated steroid exposure among premature infants vary. Premature infants who are exposed to repeated courses of ACS and/or high-cumulative-dose PCS may show no neurologic side effects until later in life. Research in newborn animal models focused on the timing, duration, and amounts of ACS and PCS. Current clinical research includes examination of the neurodevelopment of infants who are therapeutically exposed to perinatal corticosteroids, to identify safer minimal dose protocols. Over the past 30 years, corticosteroids have been increasingly prescribed before and after birth. Understanding the potential treatment benefits and risks to human fetuses and neonates is vital to clinical practice. This review presents historic and pharmacokinetic information about prenatal use of corticosteroids. It also offers scientific evidence of the benefits and risks identified in animal models and clinical trials, to stimulate thought that gtiides neonatal clinical practice.

Effects of three courses of maternally administered dexamethasone at 0.7, 0.75, and 0.8 of gestation on prenatal and postnatal growth in sheep

OBJECTIVES

To evaluate the effects of repeated low doses of maternally administered dexamethasone (DM) on growth in sheep during fetal life and the first 2 years of postnatal life.

METHODS

Ewes received 3 courses of DM (1 course: four 2-mg intramuscular injections at 12-hour intervals) or saline beginning at 103, 110, and 117 days of gestation (dGA). At 119 dGA, fetal BW and organ weight were recorded. Total placentome number, weight, and morphologic distributions were recorded. Placentome glucocorticoid receptor expression was determined by immunocytochemistry. Newborn BW and organ weight were recorded within 12 hours of birth. Duration of gestation was recorded. Measurements were collected on body weight (BW), biparietal diameter (BPD), crown-to-rump length, thoracic girth circumference, abdominal girth circumference, and radial bone length for 2 months. Maternal estradiol and progesterone levels were measured daily from 135 dGA.

RESULTS

At 119 dGA, DM significantly decreased BW. Placentome glucocorticoid receptor expression increased after DM exposure. DM did not significantly decrease BW at birth but did prolong gestation length. DM decreased maternal estradiol before lambing. DM decreased newborn brain weight and BPD. After 2 weeks of age, no effect of DM on postnatal growth could be found.

CONCLUSIONS

This study shows that repeated maternal DM treatment at doses threefold lower than what women in preterm labor receive results in decreased fetal BW, prolonged gestation length, decreased newborn brain weight, and BPD.

Connexin 43 ontogeny in fetal sheep adrenal glands

We examined fetal sheep adrenal glands from 99 to 130 days of gestational age (dGA) to see how connexin 43 (Cx43), the major if not the only adult adrenal gap junction protein, changes expression as the adrenal cortex emerges from the well-documented refractory period to participate in labor and delivery. Immunocytochemical technique and Western blot were used to examine changes in the quantity and quality of Cx43. In addition, adrenal glands of ACTH infused fetuses or of fetuses from dexamethasone injected ewes underwent image analysis quantification after Cx43 immunostaining. Finally, fetal adrenal glands, from fetuses splanchnic nerve sectioned (SPLX) at 125 dGA, were examined for the pattern of Cx43 immunostaining at 131 days of gestation. From 100 to 130 dGA, the amount of Cx43 in cells of the adrenal cortex increased steadily while the pattern of immunoreactivity changed from predominantly cytoplasmic to membrane bound. At 100-103 dGA, ACTH infusion increased the size of the cortex, but decreased the expression of Cx43 per unit area while dexamethasone had no effect on either parameter. Lastly, the expression of Cx43 as a membrane bound protein was not delayed or reversed by SPLX. We conclude that the described changes in Cx43 are most intriguing given their temporal relationship to the described preparturient increases in ACTH and cortisol in peripheral fetal plasma as term approaches and deserve further investigation.

Maternal dexamethasone increases endothelin-1 sensitivity and endothelin a receptor expression in ovine foetal placental arteries

Despite National Institutes of Health recommendations to administer antenatal steroids as a single course to women threatening preterm delivery, repeated treatments are often given. We investigated effects of repeated dexamethasone (DM) administered to the ewe on small maternal and foetal placental arteries. We hypothesized that DM would increase responsiveness to endothelin-1 (ET-1) and norepinephrine (NE) and that foetal arteries would react differently to ET-1 and NE compared to maternal arteries. Ewes received three treatments beginning at 103, 110, and 117 days of gestation (dGA). Each treatment consisted of four IM injections of 2mg DM or saline at 12-h intervals. At 119 dGA, in vitro functional studies were performed using Mulvany wire myography and endothelin receptor (ETR) expression was quantified using real-time RTPCR and receptor ligand autoradiography. Foetal placental arteries demonstrated greater maximal contractility to ET-1 and lesser maximal contractility to NE compared to maternal arteries. DM increased the maximal contraction elicited by ET-1 and NE in foetal but not maternal placental arteries. DM also increased the abundance of type-A ETR but not type-B ETR mRNA in foetal but not maternal placental arteries. However, within the whole placentome, DM increased the abundance of type-B ETR and decreased type-A ETR mRNA, which was confirmed by similar changes in ETR binding specifically within the labyrinth region. In summary, repeated DM treatment results in agonist and vascular bed specific responses within the placenta.

Antenatal glucocorticoids and the developing brain: mechanisms of action

Glucocorticoids are critical for normal brain development. There is no doubt that prenatal treatment with synthetic glucocorticoid affords great benefit to the preterm infant. However, animal studies, now carried out in many species, indicate that there may be some long-term physiological costs of early exposure to excess glucocorticoid, and that these appear sex-dependent. Further, the effects may not become apparent until later life. Given the dynamics of corticosteroid receptor systems in late gestation, it is likely that there are critical windows of development when specific regions of the brain are more sensitive to the influence of synthetic glucocorticoid. Once such windows have been identified it will be possible to target prenatal treatments, so as to maximize benefit and reduce risk of long-term effects. Notwithstanding, the data reviewed below indicate that caution should be exercised in the use of multiple course glucocorticoid therapy during pregnancy.

Repeated prenatal corticosteroid administration delays myelination of the corpus callosum in fetal sheep

Glucocorticoids regulate oligodendrocyte maturation and the myelin biosynthetic pathways. Synthetic glucocorticoids, the corticosteroids have been successfully used in clinical practice as a single course to enhance lung maturation and reduce mortality and morbidity in preterm infants with no long-term neurologic or cognitive side effects. However, a trend has arisen to use repeated courses despite an absence of safety data from clinical trials. We examined the effects of clinically appropriate, maternally administrated, repeated courses of corticosteroids on myelination of the corpus callosum using sheep as a large animal model. The corpus callosum is a major white matter tract that undergoes protracted myelination, underpins higher order cognitive processing and developmental damage to which is associated with, for example, cerebral palsy, mental retardation and attention deficit hyperactivity disorder. Pregnant ewes were given saline or betamethasone (0.5 mg/kg) at 104,111,118 and 124 days gestation, stages equivalent to the third trimester in humans. Lambs were delivered at 145 days (term), perfused and the corpus callosum examined light and electron microscopically. Total axon numbers were unaffected (P>0.05). However, myelination was significantly delayed. Myelinated axons were 5.7% in the experimental group and 9.2% in controls (P<0.05); conversely, unmyelinated axons were 88.3 and 83.7% (P<0.05). Myelinated axon diameter and myelin sheath thickness were also reduced (0.68 vs. 0.94 and 0.11 vs. 0.14 microm, P<0.05). Our data suggest that repeated prenatal corticosteroid administration delays myelination of the corpus callosum and that further safety data are needed to evaluate clinical practice.

Antenatal therapies and the developing brain

This chapter presents a review of basic science and human studies of two commonly used pharmacologic agents (antenatal steroids and magnesium sulfate), in pregnancies at risk of preterm delivery, and examines the effects of these therapies on the developing brain. Very low birthweight (VLBW) infants are known to be at risk of both short-term and long-term neurodevelopmental sequelae; therefore, an understanding of the mechanisms contributing to both neuroprotective and neurotoxic effects of antenatal therapies on the immature brain and potential effects on long-term outcome are critical. Although the short-term beneficial effects of a single course of antenatal steroids are well documented, the experimental animal literature suggests detrimental effects on neurodevelopment of multiple doses. In addition, clinical studies of repeat doses suggest a negative impact on head and brain growth. The animal and human data on the effects of MgSO(4)are also mixed with both beneficial effects or no effects on neurodevelopment. This review will discuss the potential impact of single versus multiple doses and timing of doses on the brain.

Multiple courses of antenatal glucocorticoid treatment and fetal outcome

Thanks to the US National Institutes of Health Consensus Conference, the odds of antenatal use of glucocorticoids for preventing severe neonatal complications of premature delivery have significantly increased these last years. The belief that neonatal benefits last up to 7 days after the first course and administration of further courses is safe has led many obstetricians to prescribe multiple antenatal glucocorticoid courses. Whether multiple courses offer an advantage over a single course has not been demonstrated. In contrast, there are accumulating evidence suggesting that this practice may have short and long-term side effects. The potential benefits and side effects of multiple antenatal courses of glucocorticoids, extrapolated from experimental data and observational studies, are detailed in this review. Until the results of ongoing randomized trials with long term follow-up are available, the practice of giving multiple courses of glucocorticoids to women should be considered with the greatest caution.

Effects of prenatal dexamethasone on spatial learning and response to stress is influenced by maternal factors

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.

Fetal sciatic nerve growth is delayed following repeated maternal injections of corticosteroid in sheep

AIMS

A single course of prenatal corticosteroid reduces the mortality and morbidity of preterm birth. Repeated courses of prenatal corticosteroids are widely prescribed despite a lack of safety data. Repeated corticosteroids delay myelination in the ovine central nervous system at the time of preterm delivery but with catch-up at term. We aimed to evaluate their effect in the peripheral nervous system.

METHODS

Thirty date-mated ewes were administered either saline, a single injection of betamethasone, or four injections of betamethasone between 104 and 124 days' gestation, with delivery on day 125 or 145 (term = 150 days). Sciatic nerves were dissected and fixed in modified Karnovsky's fixative and prepared for light and electron microscopy to determine the proportion of myelinated axons and mean axon diameter.

RESULTS

Repeated, but not single, corticosteroid administration resulted in significant decreases in the total cross-sectional and fascicle-containing areas of the sciatic nerve, and in the mean diameter of myelinated and unmyelinated axons. Deficits persisted at term. The proportion of myelinated axons was unaffected.

CONCLUSION

Repeated prenatal corticosteroids have the capacity to affect the growth of peripheral nerve axons in sheep. Documentation of their effects in human pregnancy await randomized trials.

An animal model of adolescent nicotine exposure: effects on gene expression and macromolecular constituents in rat brain regions

Nearly all smokers begin tobacco use in adolescence, and approximately 25% of US teenagers are daily smokers. Prenatal nicotine exposure is known to produce brain damage, to alter synaptic function and to cause behavioral anomalies, but little or no work has been done to determine if the adolescent brain is also vulnerable. We examined the effect of adolescent nicotine exposure on indices of cell damage in male and female rats with an infusion paradigm designed to match the plasma levels found in human smokers or in users of the transdermal nicotine patch. Measurements were made of DNA and protein as well as expression of mRNAs encoding genes involved in differentiation and apoptosis (p53, c-fos) in cerebral cortex, midbrain and hippocampus. Following nicotine treatment from postnatal days 30-47.5, changes in macromolecular constituents indicative of cell loss (reduced DNA) and altered cell size (protein/DNA ratio) were seen across all three brain regions. In addition, expression of p53 showed region- and gender-selective alterations consistent with cell damage; c-fos, which is constitutively overexpressed after gestational nicotine exposure, was unaffected with the adolescent treatment paradigm. Although these measures indicate that the fetal brain is more vulnerable to nicotine than is the adolescent brain, the critical period for nicotine-induced developmental neurotoxicity clearly extends into adolescence. Effects on gene expression and cell number, along with resultant or direct effects on synaptic function, may contribute to increased addictive properties and long-term behavioral deficits.

Effect of single versus multiple courses of antenatal corticosteroids on maternal and neonatal outcome

OBJECTIVE

Treatment of pregnant mothers with a single course of antenatal corticosteroids significantly reduces neonatal mortality and morbidity. Multiple weekly courses are often given. However, the safety and efficacy of repeated courses of antenatal corticosteroids have not been adequately studied.

STUDY DESIGN

A retrospective study was performed for 609 mothers and their 713 infants who were treated with 1 to 12 courses of antenatal corticosteroids. Data for 369 singleton preterm infants born at < or =34 weeks' gestation, 210 multiple gestations, and 134 infants delivered at > or =35 weeks' gestation were analyzed separately.

RESULTS

The incidence of respiratory distress syndrome was 45% for single-course and 35% for multiple-course groups (P =.005; odds ratio, 0.44; 95% confidence interval, 0.25-0.79). The multiple-course group also had significantly less patent ductus arteriosus (20% vs 13%; P =.016). Incidence of death before discharge and other neonatal morbidities were similar. The multiple-course group had a reduction of 0.46 +/- 0.19 cm in head circumference at birth (P =.013) when adjusted for gestational age and preeclampsia. The 2 groups had similar birth weights. Infants born at > or =35 weeks' gestation, multiple-gestation infants, and infants who were born >7 days after the last corticosteroid dose had similar outcomes, regardless of the number of courses they received. Mothers treated with multiple courses compared with a single course had a significantly higher incidence of postpartum endometritis (P =.013), even though they had a lower incidence of prolonged rupture of membranes (24% vs 33%, P =.06) and similar cesarean delivery rates.

CONCLUSION

Exposure to multiple courses of antenatal corticosteroids compared with a single course resulted in a significant reduction in the incidence of respiratory distress syndrome in singleton preterm infants delivered within a week of the last corticosteroid dose. This was associated with a reduction in birth head circumference and an increased incidence of maternal endometritis. Whether the potential benefits of repeated therapy clearly outweigh the risks will ultimately be determined in randomized prospective controlled trials.

Antenatal glucocorticoids and programming of the developing CNS

Glucocorticoids (GCs) are essential for many aspects of normal brain development. However, there is growing evidence from a number of species that exposure of the fetal brain to excess GC, at critical stages of development, can have life-long effects on behavior and neuroendocrine function. The hypothalamo-pituitary-adrenal axis, which is central to the integration of the individual's endocrine and behavioral response to stress, appears highly sensitive to excess GC exposure during development. A number of animal studies have shown that exposure to synthetic GCs in utero results in adult offspring that exhibit hyperactivity of the hypothalamo-pituitary-adrenal axis. This will have a long-term impact on health, inasmuch as increased life-long exposure to endogenous GC has been linked to the premature onset of diseases associated with aging. The mechanisms involved in the permanent programming of hypothalamo-pituitary-adrenal function and behavior are not well understood. Synthetic GCs are used extensively to promote pulmonary maturation in fetuses at risk of being delivered before term. Therefore, it is important that we understand the potential long-term consequences of prenatal GC exposure on brain development as well as the underlying mechanisms involved. This review will explore the current state of knowledge in this rapidly expanding field.

Retinal maturation is delayed by repeated, but not single, maternal injections of betamethasone in sheep

PURPOSE

The safety and efficacy of prescribing a single maternal course of corticosteroid during pregnancy has been documented in human trials. However, the current trend is to prescribe repeated courses of corticosteroid. We investigated an aspect of the safety of this practice in an animal model.

METHODS

Date-mated ewes received saline, single or four corticosteroid injections between days 104 and 124 of gestation (term = 150). Lambs were delivered on day 125 or 145 by caesarian section after spinal anaesthesia. Eye diameters were measured and semi-thin toluidine-blue-stained transverse sections of retinae were analysed using an Optimus Image Analysis program.

RESULTS

At 125 days, retinal measures in the ventral periphery and area centralis were significantly thinner than control (p = 0.0001). At 145 days, total eye size was significantly reduced compared with control (p = 0.03), and retinal measures in the ventral periphery (p = 0.0001), but not the area centralis (p = 0.19), remained significantly different from control.

CONCLUSION

Repeated maternal administration of corticosteroid may affect retinal maturation in the fetus.

Adolescent nicotine exposure causes persistent upregulation of nicotinic cholinergic receptors in rat brain regions

Whereas numerous studies have explored the consequences of fetal or adult nicotine exposure, little or no basic research has been conducted for nicotine exposure during adolescence, the developmental period in which regular cigarette use typically begins. We administered nicotine to adolescent rats on postnatal days 30-47 via continuous infusion with implanted osmotic minipumps, using a dose rate (3-6 mg kg-1 day-1) set to achieve plasma nicotine levels found in smokers; results were compared to exposure of adult rats. During and after exposure, we assessed nicotinic cholinergic receptor binding in the midbrain, cerebral cortex, and hippocampus, using [3H]cytisine. Robust receptor upregulation was observed with both adolescent and adult nicotine exposure but there were major differences in the regional specificity and persistence of effect. In adolescents, upregulation was uniform across all regions during the infusion period, whereas in adults, there was a distinct regional hierarchy: midbrain < cerebral cortex < hippocampus; accordingly, receptors in the adolescent midbrain were upregulated far more than with adult exposure. In addition, adolescent nicotine treatment produced long-lasting effects on the receptors, with significant increases still apparent in male rats 1 month after the termination of drug exposure. We also obtained evidence for hippocampal cell damage in adolescent female rats exposed to nicotine, characterized by increases in total membrane protein concentration indicative of a decrease in overall cell size. Adolescent nicotine exposure thus elicits region- and gender-selective effects that differ substantially from those in adults, effects that may contribute to increased addictive properties and lasting deficits in behavioral performance.

Effect of exogenous corticosteroids on the developing central nervous system: a review

Corticosteroid therapy is used in a variety of developmental clinical settings. Prenatally, maternal administration of corticosteroids is used primarily in the prevention of respiratory distress syndrome. Postnatally, corticosteroids are used to treat a variety of infant diseases such as autoimmune hemolytic anemia and hypoglycemia. Treatment regimes often involve repeated administration, on a weekly basis prenatally and daily postnatally, despite an absence of safety data from randomized clinical trials. A large number of animal studies, the majority of which used rodents, have shown that both repeated prenatal or neonatal administration of exogenous corticosteroids has a wide range of detrimental effects on the structure and function of the developing central nervous system (CNS). None of these studies included long-term follow-up. Despite the reported detrimental effects on CNS development, a number of animal studies have shown that pretreatment with corticosteroids nevertheless protect the brain from hypoxia-ischemic injury; however, clinically such treatment is no longer favored. Studies using large animal models and with long-term follow-up should be undertaken to establish the relative risks and benefits of the repeated application of exogenous corticosteroids.

Glucocorticoid administration alters nuclear transcription factors in fetal rat brain: implications for the use of antenatal steroids

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.

Indicators of delayed maturation of rat heart treated prenatally with dexamethasone

We investigated the effects of prenatal dexamethasone treatment on indicators of cardiac maturation: heart weight/body weight ratios, myosin heavy chain (MHC) expression, cell proliferation, and extracellular matrix. We administered dexamethasone, a synthetic glucocorticoid (approximately 48 microg/d, 3-wk slow release pellets), to pregnant rats (n = 8) beginning at 17 d postconception. Control dams were unmanipulated (n = 8). After approximately 4-5 d of dexamethasone exposure, hearts were collected from neonatal rats (12-24 h after birth). The prenatal dexamethasone treatment produced smaller pups with larger heart/body weight ratios, accompanied by a higher proliferative index and a reduction in extracellular matrix in the ventricles (with lowest values in the septal region) compared with control pups. We also report that, although there were no sex differences in body mass or heart and heart/body weight ratios, females had a greater proportion of cells synthesizing DNA in the heart. In addition, ventricles of male pups treated with dexamethasone contained lower levels of alpha-MHC mRNA, as reflected in a sex by treatment interaction. The changes in each parameter are consistent with delayed maturation. Our findings suggest that exposure to excess glucocorticoids in utero can affect cardiac development in potentially detrimental ways and that assessment of cardiac function should be closely monitored when such circumstances arise.

Chlorpyrifos interferes with cell development in rat brain regions

Chlorpyrifos, one of the most widely used pesticides, exhibits greater toxicity during development than in adulthood. We administered chlorpyrifos to neonatal rats in doses spanning the threshold for systemic toxicity and examined developing brain regions (brainstem, forebrain, cerebellum) for signs of interference with cell development using markers for cell packing density and cell number (DNA concentration and content) and cell size (protein/DNA ratio). Neonatal rats given 5 mg/kg of chlorpyrifos on postnatal days 1-4 showed significant mortality and the survivors exhibited severe cell loss in the brainstem; brainstem growth was maintained by enlargement of the remaining cells. This effect was not seen at 1 mg/kg, a dose that did not compromise survival or growth, nor was there any adverse effect at either dose in the forebrain, despite the fact that both brainstem and forebrain possess comparable cholinergic projections. When chlorpyrifos was administered later, on days 11-14, the major target for cell loss shifted from the brainstem to the forebrain and in this case, effects were seen at doses that did not compromise survival or growth. The loss of forebrain cell number occurred between 15 and 20 days of age rather than during the chlorpyrifos treatment. The cerebellum differed from the other regions in that it showed short-term elevations of DNA after chlorpyrifos exposure in either early or late postnatal periods; nevertheless, values then regressed to subnormal in parallel with the loss of cells in other regions. Thus, chlorpyrifos likely causes delayed cell death. Although regions rich in cholinergic projections, such as brainstem and forebrain, may be more affected than noncholinergic regions (cerebellum), the maturational timetable of each region (brainstem earliest, forebrain intermediate, cerebellum last) appears to be more important in setting the window of vulnerability. These results indicate that, even when growth or survival are unaffected, chlorpyrifos produces cellular deficits in the developing brain that could contribute to behavioral abnormalities.

Programming of brainstem serotonin transporter development by prenatal glucocorticoids

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.

Pulse dexamethasone does not impair growth and body composition of very low birth weight infants

OBJECTIVE

Evaluation of repeated pulses of dexamethasone (PDEX), given to improve cardiopulmonary outcome, on growth of very low birth weight (VLBW, < 1500 g) infants.

METHODS

In this prospective, double-blind, randomized clinical trial, VLBW infants mechanically ventilated at 1 week of age received intravenous PDEX or saline placebo (P) for 3 days, every 10 days, until no supplemental oxygen or ventilation was required or 36 weeks postmenstrual age (PMA). Weight gain, fluid intake, caloric intake, and serum glucose were monitored throughout the study. Nutritional assessment at 36 weeks PMA consisted of weight, length, head circumference, skinfold thickness measures, body composition by total body electrical conductance, and bone mineral content (BMC) by single beam photon absorptiometry.

RESULTS

37 PDEX and 31 P infants survived at least 36 days and completed the protocol. Average daily weight gain, fluid intake and caloric intake were not different between groups. The pattern of weight gain (g/kg/day, mean +/- SD) was different: PDEX infants showed significant growth delay during (3.0 +/- 11.4) and immediately after (7.8 +/- 8.7) each pulse, with subsequent growth acceleration (18.3 +/- 8.2) until the next steroid pulse. In contrast, growth rate of P infants was constant (12.6 +/- 3.7) (p = 0.04). Hyperglycemia requiring insulin therapy occurred only in the PDEX group (10/37). The catch-up growth noted between pulses in the PDEX group was explained only in part by insulin therapy. At 36 weeks PMA, there were no differences between groups in body size, composition, or BMC.

CONCLUSION

PDEX negatively affected glucose metabolism and growth patterns during and immediately after drug exposure. However, assessment near term gestational age showed similar body composition and size in both groups.

Fetal dexamethasone exposure interferes with establishment of cardiac noradrenergic innervation and sympathetic activity

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.

Glucocorticoids regulate the development of intracellular signaling: enhanced forebrain adenylate cyclase catalytic subunit activity after fetal dexamethasone exposure

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.