Ornithine decarboxylase activity in fetal and newborn rat brain: responses to hypoxic and carbon monoxide hypoxia

Temporal changes in gene expression and genotype frequency of the ornithine decarboxylase gene in native silverside Basilichthys microlepidotus: Impact of wastewater reduction due to implementation of public policies

Human activity has caused a deterioration in the health and population size of riverine species; thus, public policies have been implemented to mitigate the anthropogenic impacts of water use, watercourse transformation, and pollution. We studied the Maipo River Basin, one of the most polluted with untreated wastewater in Chile, for a period of 12 years (2007-2019). Since the implementation of new public policies, including the operation of a wastewater collector (2012), the Maipo River Basin is currently much less polluted by untreated water than before. To analyze the impact of wastewater reduction in this river basin, we studied the native silverside (Basilichthys microlepidotus), which inhabits both polluted and unpolluted areas of the river basin. Previous studies reported the overexpression of the ornithine decarboxylase (odc) gene, heterozygote deficit, and high frequency of a homozygote odc genotype in silverside populations that inhabit wastewater-polluted sites, suggesting a phenotypic change and genotypic selection in response to pollution. Here, a population affected and another population unaffected by wastewater were studied before and after implementing the wastewater collector. The physicochemical data of water samples, changes in odc expression and microsatellite variability, and odc genotype frequencies were analyzed. The results showed physicochemical changes in the affected site before and after the operation of the wastewater collector. The microsatellite loci showed no changes in either population. The odc expression in the affected site was higher before the operation of the wastewater collector. Significant changes in the genotype frequencies of the odc gene before and after the wastewater collector operation were detected only at the affected site, wherein the homozygous dominant genotype decreased from >59% to <25%. Our results suggest that public policies aimed at mitigating aquatic pollution can indirectly affect both gene expression and genotype frequencies of important functional genes.

The fetal cerebral circulation: three decades of exploration by the LLU Center for Perinatal Biology

For more than three decades, research programs in the Center of Perinatal Biology have focused on the vascular biology of the fetal cerebral circulation. In the 1980s, research in the Center demonstrated that cerebral autoregulation operated over a narrower pressure range, and was more vulnerable to insults, in fetuses than in adults. Other studies were among the first to establish that compared to adult cerebral arteries, fetal cerebral arteries were more hydrated, contained smaller smooth muscle cells and less connective tissue, and had endothelium less capable of producing NO. Work in the 1990s revealed that pregnancy depressed reactivity to NO in extra-cerebral arteries, but elevated it in cerebral arteries through effects involving changes in cGMP metabolism. Comparative studies verified that fetal lamb cerebral arteries were an excellent model for cerebral arteries from human infants. Biochemical studies demonstrated that cGMP metabolism was dramatically upregulated, but that contraction was far more dependent on calcium influx, in fetal compared to adult cerebral arteries. Further studies established that chronic hypoxia accelerates functional maturation of fetal cerebral arteries, as indicated by increased contractile responses to adrenergic agonists and perivascular adrenergic nerves. In the 2000s, studies of signal transduction established age-dependent roles for PKG, PKC, PKA, ERK, ODC, IP3, myofilament calcium sensitivity, and many other mechanisms. These diverse studies clearly demonstrated that fetal cerebral arteries were functionally quite distinct compared to adult cerebral arteries. In the current decade, research in the Center has expanded to a more molecular focus on epigenetic mechanisms and their role in fetal vascular adaptation to chronic hypoxia, maternal drug abuse, and nutrient deprivation. Overall, the past three decades have transformed thinking about, and understanding of, the fetal cerebral circulation due in no small part to the sustained research efforts by faculty and staff in the Center for Perinatal Biology.

Hypoxic regulation of the fetal cerebral circulation

Fetal cerebrovascular responses to acute hypoxia are fundamentally different from those observed in the adult cerebral circulation. The magnitude of hypoxic vasodilatation in the fetal brain increases with postnatal age although fetal cerebrovascular responses to acute hypoxia can be complicated by age-dependent depressions of blood pressure and ventilation. Acute hypoxia promotes adenosine release, which depresses fetal cerebral oxygen consumption through action of adenosine on neuronal A1 receptors and vasodilatation through activation of A2 receptors on cerebral arteries. The vascular effect of adenosine can account for approximately half the vasodilatation observed in response to hypoxia. Hypoxia-induced release of nitric oxide and opioids can account for much of the adenosine-independent cerebral vasodilatation observed in response to hypoxia in the fetus. Direct effects of hypoxia on cerebral arteries account for the remaining fraction, although the vascular endothelium contributes relatively little to hypoxic vasodilatation in the immature cerebral circulation. In contrast to acute hypoxia, fetal cerebral blood flow tends to normalize during acclimatization to chronic hypoxia even though cardiac output is depressed. However, uncompensated chronic hypoxia in the fetus can produce significant changes in brain structure and function, alteration of respiratory drive and fluid balance, and increased incidence of intracranial hemorrhage and periventricular leukomalacia. At the level of the fetal cerebral arteries, chronic hypoxia increases protein content and depresses norepinephrine release, contractility, and receptor densities associated with contraction but also attenuates endothelial vasodilator capacity and decreases the ability of ATP-sensitive and calcium-sensitive potassium channels to promote vasorelaxation. Overall, fetal cerebrovascular adaptations to chronic hypoxia appear prioritized to conserve energy while preserving basic contractility. Many gaps remain in our understanding of how the effects of acute and chronic hypoxia are mediated in fetal cerebral arteries, but studies of adult cerebral arteries have produced many powerful pharmacological and molecular tools that are simply awaiting application in studies of fetal cerebral artery responses to hypoxia.

Beneficial effects of melatonin on morphological changes in postnatal cerebellar tissue owing to epileptiform activity during pregnancy in rats: light and immunohistochemical study

Although it has been demonstrated that maternal epilepsy has some harmful effects on newborn individuals, current data concerning the effects of epileptic phenomena in pregnant mothers on newborn pups are still limited. This study was undertaken to investigate the changes in the cerebellum of newborns of pinealectomized rats subjected to experimental epilepsy during pregnancy. In our study, the rats were randomly divided into six groups: intact control group, anesthesia control group, epilepsy group, melatonin-treated epileptic group, surgical pinealectomy group, and group of melatonin treatment following pinealectomy procedure. At 1 month after pinealectomy, an acute grand mal epileptic seizure was induced by 400 IU penicillin-G administration into their intrahippocampal CA3 region during the 13th day of their pregnancy in all animals except intact control group. On the neonatal first day, pups were perfused transcardially and the cerebellums removed were processed for light microscopic and immunohistochemical studies. Normal migration and maturation were determined in the postnatal rat cerebellum in both intact control and anesthesia (ketamine-xylazine) control groups, but the morphological structure of cerebellum in the epilepsy control group corresponded to the early embryonal period. It was found that experimental epilepsy or pinealectomy procedure enhanced nestin immunoreactivity, but exogenous melatonin treatment (30 microg/100 g body weight, i.p.) following pinealectomy inhibited increased nestin expression induced by melatonin deprival in vermis region of newborn rat cerebellum (P < 0.001). Our results confirm that epileptic seizures during pregnancy may impair neurogenesis and neuronal maturation in newborns, which are more dramatic in the presence of melatonin deficiency during pregnancy, explaining more harmful effects of epileptic seizures to embryos of aged mothers. To the best of our knowledge, this is the first study reporting the effects of maternal epilepsy during pregnancy in pinealectomized rats on nestin immunoexpression in the newborn rat cerebellum.

Influence of penicillin-induced epileptic activity during pregnancy on postnatal hippocampal nestin expression in rats: light and electron microscopic observations

OBJECTS

Current data concerning the effects of maternal epileptic phenomena on newborns are limited. In clinical practice, therefore, it is difficult to suggest proper guidelines on this issue. This study was carried out to investigate the morphological changes in the hippocampus of newborn pups of rats subjected to experimental epilepsy during pregnancy.

METHODS

Eighteen Swiss Albino rats were randomly divided into three groups (n=6): experimental group, saline-injected sham surgery group, and intact control group. In the experimental group of rats, an acute grand mal epileptic seizure was induced by 400 IU penicillin-G administration into their intra-hippocampal CA3 region with a stereotaxic device during the 13th day of their pregnancy. On the first neonatal day, pups were perfused with intracardiac fixative solution under anesthesia, and newborn hippocampi were dissected surgically for light and electron microscopic examinations. In an immunohistochemical study using Rat-401 mono-clonal antibody and peroxidase, nestin expression was analyzed in the developing hippocampal tissue.

RESULTS

Histologically, normal migration and hippocampal maturation were determined in the newborn rat hippocampus in the control and the sham-operated groups. It was observed that the morphological structure of hippocampus in the experimental group corresponded to the early embryonal period. Most importantly, it was found that nestin (+)cell density was increased in the experimental epilepsy group in contrast to the control and sham groups.

CONCLUSION

It has been concluded that epileptic seizures during embryonic life may cause impaired hippocampal neurogenesis and maturation,explaining the potentially harmful effects of epileptic seizures on the embryo at the early stage of neuronal differentiation. This is the first report regarding the alterations in nestin expression in newborn rat hippocampus. In the light of such findings, it will also be necessary to evaluate the functional consequences of a va-riety of epileptic seizures on learning and memory in neonates.

Risks and benefits of nicotine to aid smoking cessation in pregnancy

Cigarette smoking during pregnancy is the single largest modifiable risk for pregnancy-related morbidity and mortality in the US. Addiction to nicotine prevents many pregnant women who wish to quit smoking from doing so. The safety and efficacy of nicotine replacement therapy (NRT) for smoking cessation during pregnancy have not been well studied. Nicotine is classified by the US Food and Drug Administration as a Pregnancy Category D drug. Animal studies indicate that nicotine adversely affects the developing fetal CNS, and nicotine effects on the brain may be involved in the pathophysiology of sudden infant death syndrome (SIDS). It has been assumed that the cardiovascular effects of nicotine resulting in reduced blood flow to the placenta (uteroplacental insufficiency) is the predominant mechanism of the reproductive toxicity of cigarette smoking during pregnancy. Short term high doses of nicotine in pregnant animals do adversely affect the maternal and fetal cardiovascular systems. However, studies of the acute effects of NRT in pregnant humans indicate that nicotine alone has minimal effects upon the maternal and fetal cardiovascular systems. Cigarette smoking delivers thousands of chemicals, some of which are well documented reproductive toxins (e.g. carbon monoxide and lead). A myriad of cellular and molecular biological abnormalities have been documented in placentas, fetuses, and newborns of pregnant women who smoke. The cumulative abnormalities produced by the various toxins in cigarette smoke are probably responsible for the numerous adverse reproductive outcomes associated with smoking. It is doubtful that the reproductive toxicity of cigarette smoking is primarily related to nicotine. We recommend the following. Efficacy trials of NRT as adjunctive therapy for smoking cessation during pregnancy should be conducted. The initial dose of nicotine in NRT should be similar to the dose of nicotine that the pregnant woman received from smoking. Intermittent-use formulations of NRT (gum, spray, inhaler) are preferred because the total dose of nicotine delivered to the fetus will be less than with continuous-use formulations (transdermal patch). A national registry for NRT use during pregnancy should be created to prospectively collect obstetrical outcome data from NRT efficacy trials and from individual use. The goal of this registry would be to determine the safety of NRT use during pregnancy, especially with respect to uncommon outcomes such as placental abruption. Finally, our review of the data indicate that minimal amounts of nicotine are excreted into breast milk and that NRT can be safely used by breast-feeding mothers.

Minimal behavioral effects from developmental cerebellar stunting in young rats induced by postnatal treatment with alpha-difluoromethylornithine

Postnatal treatment with alpha-difluoromethylornithine (DFMO), a potent inhibitor of ornithine decarboxylase, reduces polyamine levels in rats. Because polyamines are critically involved in growth and development, body and/or brain weights are often decreased by DFMO treatment. Here, rats were injected subcutaneously with 0, 250, 500, or 750 mg/kg of DFMO on postnatal days (PNDs) 5-10. Behavioral assessments included righting reflex, negative geotaxis, forelimb hanging, open field activity, and rotarod performance. Additionally, day of eye opening was recorded and on PND 28, whole and regional brain weights were measured. Cerebellar/whole-brain ratio was decreased in a dose-dependent manner whereas frontal cortex/whole-brain ratio was increased. Eye opening was delayed to a similar extent in all treated groups whereas body weight was unaffected. alpha-difluoromethylornithine treatment had no significant effects on the assessed behaviors. These results indicate that 6 days of DFMO treatment can substantially impact cerebellar development, but this appears to have few effects on these early assessed behaviors. However, potential behavioral alterations may not be apparent until adulthood. Published by Elsevier Science Inc.

Retinol-induced elevation of ornithine decarboxylase activity in cultured rat Sertoli cells is attenuated by free radical scavenger and by iron chelator

We investigated retinol effects in ornithine decarboxylase activity in Sertoli cells. We also tested the hypothesis that free radical scavengers and iron chelators may attenuate the effect of retinol. Sertoli cells isolated from 15-day-old Wistar rats were previously cultured for 48 h and then treated with retinol by 24 h with or without mannitol (1 mM) or 1,10 phenanthroline (100 microM). We measured ornithine decarboxylase and catalase activities and malondialdehyde concentrations in response to retinol treatment. In response to 7 microM retinol treatment ornithine decarboxylase activity increased 30%. Retinol-induced ornithine decarboxylase activity was significantly decreased by addition of free radical scavenger (mannitol) or iron chelator (1,10 phenanthroline). In addition the same effect was observed in catalase increased activity and in malondialdehyde concentrations. These results suggest that retinol treatment induced ornithine decarboxylase and catalase activity and increased malondialdehyde concentration. These effects appear to be mediate by ROS.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

GABA and histogenesis in fetal and neonatal mouse brain lacking both the isoforms of glutamic acid decarboxylase

Recent in vitro investigations have suggested that GABA is involved in the development of the mammalian central nervous system. To evaluate the roles of GABA in neurogenesis in vivo, we generated mice lacking both the isoforms of glutamic acid decarboxylase (GAD), GAD65 and GAD67, by mating GAD65- and GAD67-mutant mice generated by homologous recombination in this laboratory. Similar to GAD67-deficient mice, the GAD65/67-deficient mice did not survive after birth because of cleft palate. We thus analyzed these mice at the fetal and newborn stages. GABA was scarcely detectable in the GAD65/67-deficient brains, indicating that the GAD-independent GABA synthetic pathway was not active. The activity of ornithine decarboxylase, which is possibly involved in such a pathway, did not increase with the GAD deficiency. Histological and immunohistochemical studies of the GAD65/67-deficient brain did not reveal any discernible disorders of histogenesis. The discrepancy between the results of previous in vitro investigations, performed mostly on rat tissue, and those of the present analysis on mutant mice may be attributed to the different species used or to the possibility that other mediators can compensate for GABA functions in vivo.

Neuronal degeneration and microglial reaction in the fetal and postnatal rat brain after transient maternal hypoxia

This study examined the neuropathological changes in different areas of the brain of fetal and postnatal rats after transient maternal hypoxia. At different time intervals following hypoxia, reactive microglia as determined immunohistochemically with the antibody OX-42 that recognizes complement type three (CR3) receptors, responded vigorously to the hypoxic stress. Microglial activation was particularly evident in the cingulate cortex and the corpus callosum between 3 h and 14 days after hypoxia. Massive cell degeneration as determined ultrastructurally and significant neuronal loss as evaluated by cell counts were observed in the cingulate cortex at 1 and 3 days after hypoxic insults; thereafter, however, the neuronal density was restored to normal levels. Present results suggest that the cingulate cortex is most vulnerable to the hypoxic injury probably due to a redistribution of cerebral blood flow and/or metabolic changes. Besides being involved in the phagocytosis of cellular debris, it is suggested that the reactive microglial cells may have both neurotoxic and neurotrophic functions.

Free radical-induced elevation of ornithine decarboxylase activity in developing rat brain slices

OBJECTIVE

In developing brain, we have previously shown both in vivo [L.D. Longo, S. Packianathan, J.A. McQueary, R.B. Stagg, C.V. Byus and C.D. Cain, Acute hypoxia increases ornithine decarboxylase activity and polyamine concentrations in fetal rat brain, Proc. Natl. Acad. Sci. USA, Vol. 90 (1993) 692-696] and in vitro [S. Packianathan, C.D. Cain, B.H. Liwnicz and L.D. Longo, Ornithine decarboxylase activity in vitro in response to acute hypoxia: a novel use of newborn rat brain slices, Brain Res., Vol. 688 (1995) 61-71] that acute hypoxia is associated with a significant increase in ornithine decarboxylase (ODC) activity and polyamine concentrations. We tested the hypothesis that oxygen free radicals induce an increase in ODC activity similar to that of hypoxia and that both this and the hypoxia-induced response are inhibited by free radical scavengers.

MATERIALS AND METHODS

Slices of cerebrum, 300-500 microm thick, were made from P3 newborn Sprague-Dawley rat pups and equilibrated for 1 h in artificial cerebrospinal fluid continuously bubbled with 95% O2/5% CO2. Free radical-induced ODC activity response was measured beginning after a 1-h recovery period. Experiments were performed on slices treated with 5 X 10(-7) M xanthine (X) + 10 mU/ml xanthine oxidase (XO), with or without the free radical scavengers superoxide dismutase (SOD; 100 U/ml), catalase (CAT; 700 U/ml) or glutathione peroxidase (GPX; 3 U/ml). We also quantified slice malonaldehyde concentrations in response to hypoxia (21% O2/5% CO2/74% N2).

RESULTS

Under control conditions, ODC activity was stable during the 2-h post-recovery period. In response to X/XO treatment, ODC activity increased 2.3-fold at 1.5 h post-recovery. In examining ODC activity as a function of xanthine dose, we noted that ODC activity increased in response to 2.5 X 10(-7) M xanthine; however, it decreased in response to 7.5 X 10(-7) M or higher concentrations. Free radical-induced ODC activity was significantly decreased by addition of the free radical scavengers, SOD, CAT or GPX. In addition, the hypoxic-induced increases in ODC activity and malonaldehyde concentration was also eliminated by the addition of SOD with CAT.

CONCLUSIONS

(1) Oxygen free radicals, particularly hydroxyl radical (OH.), appear to trigger an induction of ODC activity in newborn rat cerebrum slices. (2) Oxygen free radicals also appear to mediate the hypoxic-induced increase in ODC activity. (3) Any consequent increase in polyamine synthesis may have profound effects on neurogenesis and neurodifferentiation in the developing brain.

Transgenic animals as models in the study of the neurobiological role of polyamines

Natural polyamines, putrescine, spermidine and spermine, exhibit a number of neurophysiological and metabolic effects in brain preparations. In the in vitro studies, several specific sites of action have been identified such as ion channels, transmitter release and Ca2+ homeostasis. Polyamines have been linked to the development of neuronal degeneration caused by, for instance, epileptic seizures and stroke. The role of endogenous polyamines in the functioning brain is not clear, however. We review the work carried out using state-of-the-art transgenic animal models for polyamine research. A number of transgenic mouse lines carrying human ornithine decarboxylase, spermidine synthase and S-adenosylmethionine decarboxylase gene have been generated. Of these animals those with ornithine decarboxylase transgene show an extensive and constitutive expression of the enzyme in the brain with an exceedingly high putrescine concentration, a phenotype that is not encountered under physiological conditions. In this article we review the neurometabolic, behavioural and histological data that has been obtained from these transgenic mice.

Ornithine decarboxylase activity in vitro in response to acute hypoxia: a novel use of newborn rat brain slices

In fetal as well as newborn rats, acute hypoxic exposure results in significantly elevated brain ornithine decarboxylase (ODC) activity, polyamine concentrations, and ODC mRNA. The interpretations of these in vivo hypoxic-induced changes, however, are complicated by maternal confounding effects. To test the hypothesis that acute hypoxia will also increase ODC activity in vitro, we developed a brain slice preparation which eliminates such maternal effects. Sections of whole cerebrum, approximately 300-500 microns thick, were made from 3- to 4-day old Sprague-Dawley rat pups. The slices were equilibrated for 1 h in artificial cerebrospinal fluid (ACSF) continuously bubbled with 95% O2/5% CO2, prior to induction of hypoxia. We induced hypoxia by changing the oxygen concentration to 40%, 30%, 21%, 15%, 10%, or 0% O2, all with 5% CO2 and balance N2. In the normoxic control brain slices, low but stable basal ODC activity persisted for up to 5 h post-sacrifice. Slices in ACSF treated with bovine serum albumin (BSA), or both BSA and fetal bovine serum (FBS), however, showed stable ODC activity values 2- to 3-fold higher than slices in ACSF alone, for up to 5 h. In response to acute hypoxia (i.e., 15, 21, and 30% O2), ODC activity was elevated 1.5- to 2-fold above control values between 1 and 2 h after initiation of hypoxia. Qualitative light and electron microscopic examination of the neonatal brain slices following 2 h hypoxic exposure suggested that the great majority of cells did not show severe hypoxic damage or necrosis. It was concluded that: (1) in neonatal rat brain slices in vitro, stable ODC activity values approximating the whole brain ODC activity seen at sacrifice, can be maintained for several hours; (2) the in vivo hypoxic-induced increase in ODC activity can be approximated in vitro; (3) the neonatal rat brain slice preparation may be an alternative to other methods for studying hypoxic-induced ODC enzyme kinetics, or other brain enzymes, without maternal confounding effects; and (4) ODC activity may be an indicator of active metabolism within the newborn brain slice both in normoxia and hypoxia.

Ornithine decarboxylase activity and polyamine concentrations in fetal rat brain: response to chronic hypoxic-hypoxia and/or carbon monoxide-hypoxia

Ornithine decarboxylase activity (ODC; E.C. 4.1.1.17), is significantly elevated in fetal and newborn rat brain in response to acute hypoxia. Because relatively little is known about ODC activities and polyamine metabolism in hypoxia and also because ODC and the polyamines are essential for normal growth and development, we examined the effect of chronic maternal hypoxic-hypoxia (16-10.5% O2), carbon monoxide-hypoxia (100-200 ppm CO) and their combination, on fetal weight, fetal brain ODC activity and polyamine concentrations. Time-dated pregnant Sprague-Dawley rats were chronically exposed to hypoxia from gestational day (E-15), to gestational day 21 (E-21), in individual chambers. Pair-fed controls were given an amount equivalent to that eaten by a hypoxic dam over the previous 24 h. We measured fetal weight, as well as brain ODC activity and polyamine concentrations on both E-19 and E-21. Pair-feeding had no effect on fetal weight, ODC activity or polyamine concentrations. On both E-19 and E-21, however, fetal weights were significantly reduced with higher levels of hypoxic-hypoxia (e.g., 10.5% O2). At 100 or 200 ppm, carbon monoxide alone appeared not to affect fetal weight; however, combined with even mild hypoxia (16% O2), fetal weights were reduced almost 20%, suggesting that together, CO- and hypoxic-hypoxia exert a synergistic effect of fetal weight decrements. (1) There was no consistent pattern of ODC activity changes which correlated to the fetal weight losses or levels of hypoxia. These results suggest that ODC activity may not be a good marker for chronic, as opposed to acute hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)