Developing Rat Brain Research Articles

Noxious Stimulation Attenuates Ketamine-induced Neuroapoptosis in the Developing Rat Brain

Ketamine induces neuroapoptosis in neonatal rodents. However, these experimental paradigms were performed without concurrent noxious stimulation, a condition that does not reflect the interaction of anesthesia and surgical stimulation. Noxious stimulation with and without concurrent analgesic drugs has been shown to have divergent patterns of neuronal activation and cell death. We hypothesized that concurrent noxious stimulation would attenuate ketamine-induced caspase-3 activation. Postnatal day 7 Sprague-Dawley rat pups were randomized to a 6-h exposure to ketamine with and without peripheral noxious stimulation by intraplantar injection of complete Freund's adjuvant. A cohort of naïve rat pups with and without complete Freund's adjuvant injections served as control subjects. Neuroapoptosis was measured by cleaved caspase-3 expression and terminal deoxynucleotidyl-transferase mediated 2'-deoxyuridine 5'-triphosphate nick end labeling staining. In order to determine if concurrent noxious simulation altered the expression of cell survival and cell cycle proteins, levels of protein kinase B and glycogen synthase kinase-3β and cyclin D1 were measured. Ketamine induced a significant increase in cleaved caspase-3 expression and terminal deoxynucleotidyl-transferase mediated 2'-deoxyuridine 5'-triphosphate nick end labeling staining with increases in cyclin D1 levels. Concurrent noxious stimulation with ketamine attenuated caspase-3 activation and maintained cyclin D1 levels. Phosphorylation of protein kinase B and glycogen synthase kinase-3β was not definitively altered under these conditions. The administration of ketamine with concurrent noxious stimulation results in the attenuation of the neuroapoptotic response. These findings suggest that concurrent surgery and procedural pain attenuates ketamine-induced neuroapoptosis.

Hypoxic ischaemic hypothermia promotes neuronal differentiation and inhibits glial differentiation from newly generated cells in the SGZ of the neonatal rat brain

Hypothermia is a potential therapy for cerebral hypoxic ischaemic injury in adults and neonates. The mechanism of the neuroprotective effects of hypothermia after hypoxia–ischaemia (HI) in the developing rat brain remains unclear. In this research, 7-day-old rats underwent left carotid artery ligation followed by the administration of 8% oxygen for 2h. These rats were divided into hypothermic (rectal temperature, 32–33°C for 24h) and normothermic (36–37°C for 24h) groups immediately after HI. All rats were given 50mg/kg/day 5-bromodeoxyuridine (BrdU) intraperitoneally at 4–6 days and sacrificed at 1 or 2 weeks after HI. We found a significant decrease in infarct volume and the neuron loss were also detected in the subgranular zone (SGZ) in the hypothermic group at 7 and 14 days after HI compared with the normothermic group. BrdU immunopositive cells were reduced greatly in the hypothermic group compared with the normothermic group. Hypothermia did not change the number of nestin-labelled cells in the ipsilateral SGZ at 1 and 2 weeks after HI. The differentiation of newly generated cells was assessed by double immunolabelling of BrdU with glial fibrillary acidic protein (GFAP), O4 or Neuronal Nuclei (NeuN). The ratio of BrdU+–GFAP+ or BrdU+–O4+ to total BrdU+ staining decreased dramatically, but the ratio of BrdU+–NeuN+ to total BrdU+ staining increased significantly in the hypothermic group compared to the normothermic group at 2 and 6 weeks after HI. These results suggest that the reduction in neuron loss observed after mild hypothermia may be associated with enhanced neuronal differentiation and decreased glial differentiation in the SGZ after HI. These observations are noteworthy for clinical hypothermia therapy following cerebral HI injury during the perinatal period.

Prenatal and Neonatal Exposure to Perfluorooctane Sulfonic Acid Results in Changes in miRNA Expression Profiles and Synapse Associated Proteins in Developing Rat Brains

We previously identified a number of perfluorooctane sulfonic acid (PFOS)-responsive transcripts in developing rat brains using microarray analysis. However, the underlying mechanisms and functional consequences remain unclear. We hypothesized that microRNAs (miRNAs), which have emerged as powerful negative regulators of mRNA and protein levels, might be responsible for PFOS-induced mRNA changes and consequent neural dysfunctions. We used eight miRNA arrays to profile the expression of brain miRNAs in neonatal rats on postnatal days (PND) 1 and 7 with maternal treatment of 0 (Control) and 3.2 mg/kg of PFOS feed from gestational day 1 to PND 7, and subsequently examined six potentially altered synapse-associated proteins to evaluate presumptive PFOS-responsive functions. Twenty-four brain miRNAs on PND 1 and 17 on PND 7 were significantly altered with PFOS exposure (P < 0.05), with miR-466b, -672, and -297, which are critical in neurodevelopment and synapse transmission, showing a more than 5-fold reduction. Levels of three synapse-involved proteins, NGFR, TrkC, and VGLUT2, were significantly decreased with no protein up-regulated on PND 1 or 7. Perfluorooctane sulfonic acid might affect calcium actions during synapse transmission in the nervous system by interfering with SYNJ1, ITPR1, and CALM1 via their targeting miRNAs. Our results indicated that miRNA had little direct regulatory effect on the expression of mRNAs and synapse-associated proteins tested in the developing rat brain exposed to PFOS, and it seems that the PFOS-induced synaptic dysfunctions and changes in transcripts resulted from a combinatory action of biological controllers and processes, rather than directed by one single factor.

PirB restricts neuronal regeneration in developing rat brain following hypoxia-ischemia

The inhibitors of axonal regeneration in the myelin sheath are considered to be major contributors to the lack of regeneration in the central nervous system (CNS) following hypoxic-ischemic (HI) brain damage. As well as the Nogo receptor (NgR), the paired-immunoglobulin-like receptor B (PirB) is a functional receptor for the myelin inhibitors of axonal regeneration. The inhibition of PirB and NgR activities may block most of the inhibitory effects of myelin inhibitors on nerve regeneration. We observed the PirB protein and mRNA expression in HI-damaged rat cortical neurons using immunohistochemistry and reverse transcription-polymerase chain reaction assays. In addition, we treated the HI-damaged rat cortical neurons using PirB antibodies to observe the regeneration of injured neurons. Moreover, the Rock II activity in HI-damaged rat cortical neurons treated with PirB antibodies was observed using western blot analysis. The mRNA and protein levels of PirB increased in newborn rat cortical neurons following HI damage. Treatment with PirB antibodies is able to improve axonal regeneration following HI damage compared with normal axonal growth. Rock II activity also increased in the HI-damaged rat brain. The inhibition of PirB is therefore a potential therapeutic method to promote the regeneration of HI-damaged axons and the inhibitory signal may be transduced through the Rho-ROCK signaling pathway.

Roles of advanced glycation end products and its receptor on the fetal brain injury in pregnant rats with gestational diabetes mellitus

To study the roles of advanced glycation end products and its receptor on fetal brain injury of gestational diabetes mellitus (GDM) rats. Twenty one adult pregnant Wistar rats were administered streptozotocin (STZ) intraperitoneally to induce GDM rats model. The fourteen pregnant rats were divided into two groups according to the fasting glucose on the 3(rd) day of pregnancy:severe GDM group with the fasting glucose > 16.7 mmol/L and mild GDM group with the fasting glucose between 6.7 - 16.7 mmol/L. Another seven pregnant rats were chosen as the severe GDM and intervention with micronutrient group, receiving gavage with micronutrient during the whole pregnancy. Five control rats received the same volume of citric acid buffer. All the pregnant rats were tested fasting glucose from the tail vein and their weight on the pregnant day 3, 13 and 19. Maternal serum levels of AGE were measured by ELISA and RAGE levels in the embryonic brain tissues were tested by immunohistochemistry. (1) There was no statistically significant difference of pre-pregnancy fasting glucose level among all groups (P > 0.05). The fasting glucose levels on the 3(rd) day and the mean fasting glucouse level of pregnancy in the severe GDM group and the severe GDM and intervention with micronutrient group were higher than those of the control group (P < 0.05). And there was no significant difference between the severe GDM group and the severe GDM and intervention with micronutrient group (P > 0.05). (2) The serum AGE levels in the severe GDM group and the mild GDM group were (1037 ± 38) ng/L and (880 ± 34) ng/L respectively, with no significant difference (P > 0.05). The serum AGE levels in the control group and the severe GDM and intervention with micronutrient group were (857 ± 32) ng/L and (988 ± 37) ng/L, and the difference was statistically significant (P < 0.05). The serum AGE levels in the severe GDM and intervention with micronutrient group and in the mild GDM group had no significant difference (P > 0.05). (3) The serum AGE levels in the severe GDM group, mild GDM group and the control group were positively associated with the mean glucose level of pregnancy (r = 0.603, P < 0.05) and the grlucose on the 3(rd) day of pregnancy (r = 0.704, P < 0.05). (4) The fetal brain nerve cell number and morphology in the control group were normal. While in the mild GDM group fetal brain nerve cells decreased, the proliferation and swelling of glial cells were seen. In the severe GDM group and the severe GDM and intervention with micronutrient group, the fetal brain cells furtherly reduced, and large vacuole around the cells, deformation and debris of the cells were seen. Glial scar formation was visible in some fetal brain tissues. There was a few RAGE expression in the control fetal brain tissues. In the mild GDM group and the severe GDM group, RAGE expression increased significantly. And the RAGE expression intensity in the severe GDM and intervention with micronutrient group was between the severe and the mild GDM groups. (1) Abnormal fetal brain development of GDM rats was associated with the increase of maternal serum AGE and the enhancement of RAGE expression in fetal brain tissues, which suggested that AGE/RAGE pathway may play an important role in the fetal brain injury of GDM rats. (2) Micronutrients can reduce the brain damage of GDM fetuses.

Decreased GABABR expression and increased neuronal cell death in developing rat brain after PTZ-induced seizure

The objective of this study was to evaluate the PTZ-induced seizures effects on GABAB receptor (R) expression and to observe its neurodegenerative effect in hippocampal part of developing rat brain. In the present study, high dose of pentylenetetrazol (PTZ 40 mg/kg) was injected in developing rats of age 5 weeks having average weight of 60-65 g for 4 days. Further, baclofen (B 3 mg/kg i.p) agonist and phaclofen (P 30 μg/rat) antagonist of GABABR were injected along with PTZ. Western blot analysis was used to elucidate expression of GABABR protein upon PTZ, baclofen and phaclofen exposure in the developing rat brain. Furthermore, PTZ-induced apoptotic neurodegeneration was also observed through the release of caspase-3 antibody and propidium iodide (PI) staining using confocal microscopy. Seizure was confirmed using electroencephalography (EEG) data obtained from the Laxtha EEG-monitoring device in the EEG recording room and EEG was monitored 5-15 min after PTZ injection. The results of the present study showed that PTZ-induced seizure significantly decreased GABABR expression and induced neuronal apoptosis in cortical and hippocampal part of brain. While, baclofen reverse the effect of PTZ by increasing the expression of GABABR as compared to the PTZ- , PTZ plus B- and PTZ plus P-treated groups. Our findings indicated that PTZ-induced seizure showed not only decrease in GABABR expression but also cause neuronal apoptosis in the developing rat brain.

The effects of melatonin on endoplasmic reticulum stress during brain development in rat

Endoplasmic reticulum (ER) stress is induced in various physiological or pathological conditions. During embryonic development, ER stress occurs in order to organize neuronal architecture. Melatonin, pineal hormone, has roles for neuronal protection as well as cell death inhibition. The purpose of this study was to confirm the effect of melatonin treatment (10 mg/kg/day) into the Sprague Dawley rats under conditioned photoperiod (L/D, LL, and DD) on ER stress during brain development. As a result, maternal body weight was lower in the melatonin‐treated rats (MT) than control rats (Con) in LL as well as DD group at embryonic day 20 (P&lt;0.05). Body weight of pups was higher in MT than Con group under LD and DD condition, whereas lowest in MT group under LL condition (P&lt;.05). mRNA expression of eIF2a, PERK and XBP‐1 were significantly decreased in MT compared to Con group at embryonic day 20 (P&lt;.05) Interestingly, expression of LC3 mRNA was significantly decreased in MT group of LL and DD condition at the same time point (P&lt;0.05). Taken together, endogenous and/or exogenous melatonin reduced autophagy activation as well as ER stress during embryonic development suggesting that melatonin is beneficial to formation of nervous system.

Biochemical Changes in Rat Brain Exposed to Low Intensity 9.9 GHz Microwave Radiation

Present study concerns with various biochemical changes in the developing rat brain exposed to 9.9GHz (square wave modulated, 1kHz) at power density 0.125mW/cm(2) (specific absorption rate 1.0W/kg) for 2h/day for 35days. Thirty days old male wistar rats were used for this present study. Each group consists of eight animals. After the exposure, biochemical assays such as calcium ion efflux, calcium-dependent protein kinase (PKC), and ornithine decarboxylase (ODC) were performed on the brain tissue. Results of this study reveal that chronic exposure of rat to microwave radiation alter the activity of certain enzymes. There was a significant increase in calcium ion efflux and the activity of ODC. On the other hand, there is a significant decrease in PKC activity. Since these enzymes are related to growth, any alteration may lead to affect functioning of the brain and its development.

Developmental Regulation and Spatiotemporal Redistribution of the Sumoylation Machinery in the Rat Central Nervous System

BackgroundSmall Ubiquitin-like MOdifier protein (SUMO) is a key regulator of nuclear functions but little is known regarding the role of the post-translational modification sumoylation outside of the nucleus, particularly in the Central Nervous System (CNS).Methodology/Principal FindingsHere, we report that the expression levels of SUMO-modified substrates as well as the components of the sumoylation machinery are temporally and spatially regulated in the developing rat brain. Interestingly, while the overall sumoylation is decreasing during brain development, there are progressively more SUMO substrates localized at synapses. This increase is correlated with a differential redistribution of the sumoylation machinery into dendritic spines during neuronal maturation.Conclusions/SignificanceOverall, our data clearly demonstrate that the sumoylation process is developmentally regulated in the brain with high levels of nuclear sumoylation early in the development suggesting a role for this post-translational modification during the synaptogenesis period and a redistribution of the SUMO system towards dendritic spines at a later developmental stage to modulate synaptic protein function.

Sex differences in microglial colonization of the developing rat brain

Microglia are the resident immune cells within the brain and their production of immune molecules such as cytokines and chemokines is critical for the processes of normal brain development including neurogenesis, axonal migration, synapse formation, and programmed cell death. Notably, sex differences exist in many of these processes throughout brain development; however, it is unknown whether a sex difference concurrently exists in the colonization, number, or morphology of microglia within the developing brain. We demonstrate for the first time that the number and morphology of microglia throughout development is dependent upon the sex and age of the individual, as well as the brain region of interest. Males have overall more microglia early in postnatal development [postnatal day (P) 4], whereas females have more microglia with an activated/amoeboid morphology later in development, as juveniles and adults (P30-60). Finally, gene expression of a large number of cytokines, chemokines and their receptors shifts dramatically over development, and is highly dependent upon sex. Taken together, these data warrant further research into the role that sex-dependent mechanisms may play in microglial colonization, number, and function, and their potential contribution to neural development, function, or potential dysfunction.

Maternal prenatal omega-3 fatty acid supplementation attenuates hyperoxia-induced apoptosis in the developing rat brain

Supraphysiologic amounts of oxygen negatively influences brain maturation and development. The aim of the present study was to evaluate whether maternal ω-3 long-chain polyunsaturated fatty acid (ω-3 FA) supplementation during pregnancy protects the developing brain against hyperoxic injury. Thirty-six rat pups from six different dams were divided into six groups according to the diet modifications and hyperoxia exposure. The groups were: a control group (standard diet+room air), a hyperoxia group (standard diet+80% O2 exposure), a hyperoxia+high-dose ω-3 FA-supplemented group, a hyperoxia+low-dose ω-3 FA-supplemented group, a room air+low-dose ω-3 FA-supplemented+group, and a room air+high dose ω-3 FA-supplemented group. The ω-3 FA's were supplemented as a mixture of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) from the second day of pregnancy until birth. Rat pups in the hyperoxic groups were exposed to 80% oxygen from birth until postnatal day 5 (P5). At P5, all animals were sacrificed. Neuronal cell death and apoptosis were evaluated by cell count, TUNEL, and active Caspase-3 immunohistochemistry. Histopathological examination showed that maternally ω-3 FA deficient diet and postnatal hyperoxia exposure were associated with significantly lower neuronal counts and significantly higher apoptotic cell death in the selected brain regions. Ω-3 FA treatment significantly diminished apoptosis, in the selected brain regions, in a dose dependent manner. Our results suggest that the maternal ω-3 FA supply may protect the developing brain against hyperoxic injury.

Myo9b and RICS Modulate Dendritic Morphology of Cortical Neurons

Regulated growth and branching of dendritic processes is critical for the establishment of neuronal circuitry and normal brain functions. Rho family GTPases, including RhoA, Rac1, and Cdc42, play a prominent role in dendritic development. RhoA inhibits dendritic branching and growth, whereas Rac1/Cdc42 does the opposite. It has been suggested that the activity of RhoA must be kept low to allow dendritic growth. However, how neurons restrict the activation of RhoA for proper dendritic development is not clear. In the present study, we undertook a comprehensive loss-of-function analysis of putative RhoA GTPase-activating proteins (RhoA GAPs) in the cortical neurons. The expression of 16 RhoA GAPs was detected in the developing rat brain, and RNA interference experiments suggest that 2 of them, Myo9b and RICS, are critical regulators of dendritic morphogenesis. Knockdown of either Myo9b or RICS in cultured cortical neurons or developing cortex resulted in decreased dendrite length and number. Inhibition of RhoA/ROCK signaling restores the defects of dendritic morphology induced by knockdown of Myo9b or RICS. These data demonstrate that Myo9b and RICS repress RhoA/Rock signaling and modulate dendritic morphogenesis in cortical neurons, providing evidence for critical physiological function of RhoA GAPs in regulation of dendritic development.

Gestational Restraint Stress and the Developing Dopaminergic System: An Overview

Prenatal stress exerts a strong impact on fetal brain development in rats impairing adaptation to stressful conditions, subsequent vulnerability to anxiety, altered sexual function, and enhanced propensity to self-administer drugs. Most of these alterations have been attributed to changes in the neurotransmitter dopamine (DA). In humans; dysfunction of dopaminergic system is associated with development of several neurological disorders, such as Parkinson disease, schizophrenia, attention-deficit hyperactivity disorder, and depression. Evidences provided by animal research, as well as retrospective studies in humans, pointed out that exposure to adverse events in early life can alter adult behaviors and neurochemical indicators of midbrain DA activity, suggesting that the development of the DA system is sensitive to disruption by exposure to early stressors. The purpose of this article is to provide a general overview of published studies and our own study related to the effect of prenatal insults on the development of DA metabolism and biology, focusing mainly in articles involving prenatal-restraint stress protocols in rats. We will also attempt to make a correlation between theses alterations and DA-related pathological processes in humans.

Inhalation Anesthesia-Induced Neuronal Damage and Gene Expression Changes in Developing Rat Brain.

Nitrous Oxide (N2O), an N-methyl-D-aspartate (NMDA) receptor antagonist, and isoflurane (ISO), which acts on multiple receptors including postsynaptic gamma-aminobutyric acid (GABA) receptors, are frequently used inhalation anesthetics, alone or as a part of a balanced anesthetic regimen administered to pregnant women and to human neonates and infants requiring surgery. The current study investigated histological features and gene expression profiles in response to prolonged exposure to N2O or ISO alone, and their combination in developing rat brains. Postnatal day 7 rats were exposed to clinically-relevant concentrations of N2O (70%), ISO (1.0%) or N2O plus ISO (N2O + ISO) for 6 hours. The neurotoxic effects were evaluated and the brain tissues were harvested for RNA extraction 6hours after anesthetic administration. The prolonged exposure to N2O + ISO produced elevated neuronal cell death as indicated by an increased number of TUNEL-positive cells in frontal cortical levels compared with control. No significant neurotoxic effects were observed in animals exposed to N2O or ISO alone. DNA microarray analysis revealed gene expression changes after N2O, ISO or N2O + ISO exposure. Differentially expressed genes (DEGs) from the N2O + ISO group were significantly associated with 45 pathways directly related to brain functions. Although the gene expression profiles from animals exposed to N2O or ISO alone were remarkably different from those of the control group, the pathways of these genes involved were not closely associated with neurons. These findings provide novel insights into the mechanisms by which N2O + ISO cause neurotoxicity in the developing brain, suggesting multiple factors are involved in the neuronal cell death-inducing effects (cascades) of N2O + ISO.

Expression of Ext1, Ext2, and heparanase genes in brain of senescence-accelerated OXYS rats in early ontogenesis and during development of neurodegenerative changes

Heparan sulfate (HS) and heparan sulfate proteoglycans (HSPG) play a significant role in brain development, and their structural and quantitative changes are revealed during aging and in neurodegenerative disorders. The mechanism of these changes is not clear, but is likely to be associated with alteration in the expression and/or activity of enzymes responsible for HSPG biosynthesis and degradation. The contents of mRNAs of the genes Ext1 and Ext2 encoding polymerization enzymes and of gene Hpse of heparanase degrading HS were determined in the brain of prematurely aging OXYS rats during early postnatal development and during appearance of signs of brain accelerated aging (at age of 1, 7, 14, 30, 60, and 420 days). Wistar rats of the same age were used as controls. Expression levels of the genes Ext1, Ext2, and Hpse in the brain of rats of both strains were maximal during the two first weeks of life, and the contents of mRNAs of all genes in the brain of newborn and 7-day-old OXYS rats were significantly higher than in Wistar rats. By the 14th day of life the differences leveled, but at the age of 30 days on the background of a decrease in the contents of mRNAs of Ext1, Ext2, and Hpse in OXYS rats they became more pronounced (three-, four-, and twofold, respectively). Differences between the strains were absent at the age of 60 days and 14 months, and expression of all the genes was significantly lower than in the newborn animals. A strong positive correlation was found between contents of mRNAs of all the studied genes, and this suggested that heparanase should be involved in HSPG metabolism together with Ext1 and Ext2. Based on these and earlier findings, we conclude that development of the OXYS rat brain occurs on the background of significant alterations in HSPG metabolism that precede the development of neurodegenerative manifestations recently detected by magnetic resonance imaging.

Hexachlorophene and Cuprizone Induce the Spongy Change of the Developing Rat Brain by Different Mechanisms: The Role of 2’, 3’-Cyclic Nucleotide 3’-Phosphodiesterase (CNPase)

The goal of this research was to identify mechanisms responsible for the spongy change induced in rats after repeated hexachlorophene (HCP) or cuprizone (CPZ) dosing. Rats were dosed with 35 mg/kg HCP for 5 days followed by drug withdrawal for 7 days suffered spongy changes to the white matter of the cerebrum, cerebellum, medulla oblongata, and spinal cord that were accompanied by degeneration of oligodendroglia. The severity of both lesions increased prominently on day 5; however, the spongy change decreased and degeneration of oligodendroglia reversed on day 12 (7 days after dosing ceased). On day 12, cerebral cortex oligodendroglia were stained strongly by anti-CNPase. Other rats were fed for 8 days with powdered chow containing 1% (w/w) CPZ, which was then withdrawn for 16 days. The rats exhibited the spongy change in the white matter of the cerebrum and cerebellum as well as oligodendroglial cell death from day 3. The severity of both lesions increased prominently on day 8. Cerebral cortex oligodendroglia were stained strongly by anti-CNPase on days 3 to 8 and decreased to the control levels by day 24 (16 days after dosing ceased). Electron microscopy revealed that oligodendroglia frequently displayed apoptotic morphology. These findings suggest that CNPase expression was induced in the course of restoration following HCP-induced insults to oligodendroglia and the myelin sheath, and in the course of demyelination by CPZ-induced damage to oligodendroglia. However, the role of CNPase on both courses is unclear.

Hypoxia inducible factor‐1α is involved in the neurodegeneration induced by isoflurane in the brain of neonatal rats

More and more data show isoflurane, a commonly used volatile anesthetic has dual effects on neuron fate. However, the underlying mechanisms that can explain the apparent paradox are poorly understood. Hypoxia inducible factor (HIF)-1α, a transcription factor, has been found regulating both prosurvival and prodeath pathways in the CNS. Previously, we found that isoflurane can activate HIF-1α under normoxic conditions in vitro and HIF-1α has been found to be involved in the pre-conditioning effect of isoflurane in various organs. Here, we investigated whether HIF-1α is a contributing factor in the neurodegenration in rodent primary cultured neurons and in developing rat brain. Isoflurane dose-dependently induced apoptotic neurodegeneration in neonatal rats as assessed by S100β, cleaved caspase 3 and poly-(ADP-ribose) polymerase (PARP), respectively. Notably, isoflurane up-regulates HIF-1α protein levels in vivo and in vitro during induction of neurodegeneration. Likewise, isoflurane resulted in a significant elevation of cytosonic calcium levels in neuron cultures. Furthermore, knockdown of HIF-1α expression in cultured neurons attenuated isoflurane-induced neurotoxicity. Finally, Morris water maze (MWM) test showed neonatal exposure to isoflurane impaired juvenile learning and memory ability in rats. These findings indicate that HIF-1α is involved in the neurodegeneration induced by isoflurane in the brain of neonatal rats, suggesting HIF-1α may be a candidate for the dual effects of isoflurane on neuron fate.

The abolishment of anesthesia-induced cognitive impairment by timely protection of mitochondria in the developing rat brain: The importance of free oxygen radicals and mitochondrial integrity

Early exposure to general anesthesia (GA) causes developmental neuroapoptosis in the mammalian brain and long-term cognitive impairment. Recent evidence suggests that GA also causes functional and morphological impairment of the immature neuronal mitochondria. Injured mitochondria could be a significant source of reactive oxygen species (ROS), which, if not scavenged in timely fashion, may cause excessive lipid peroxidation and damage of cellular membranes. We examined whether early exposure to GA results in ROS upregulation and whether mitochondrial protection and ROS scavenging prevent GA-induced pathomorphological and behavioral impairments. We exposed 7-day-old rats to GA with or without either EUK-134, a synthetic ROS scavenger, or R(+) pramipexole (PPX), a synthetic aminobenzothiazol derivative that restores mitochondrial integrity. We found that GA causes extensive ROS upregulation and lipid peroxidation, as well as mitochondrial injury and neuronal loss in the subiculum. As compared to rats given only GA, those also given PPX or EUK-134 had significantly downregulated lipid peroxidation, preserved mitochondrial integrity, and significantly less neuronal loss. The subiculum is highly intertwined with the hippocampal CA1 region, anterior thalamic nuclei, and both entorhinal and cingulate cortices; hence, it is important in cognitive development. We found that PPX or EUK-134 co-treatment completely prevented GA-induced cognitive impairment. Because mitochondria are vulnerable to GA-induced developmental neurotoxicity, they could be an important therapeutic target for adjuvant therapy aimed at improving the safety of commonly used GAs.

Disrupted pro- and antioxidative balance as a mechanism of neurotoxicity induced by perinatal exposure to lead

The aim of this paper was to examine if pre- and neonatal exposure that results in lead (Pb) concentration below ‘safe level’ (10μg/dL) in offspring blood may cause disruption of the pro/antioxidant balance in the developing rat brain. We studied oxidative stress intensity (malondialdehyde (MDA) concentration) as well as mRNA, protein expression and the activity of copper/zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), glutathione peroxidase (GPx), phospholipid hydroperoxide glutathione peroxidase (GPx4), catalase (CAT), glutathione reductase (GSR). We also measured glutathione (GSH) concentrations in selected structures of the rat brain (forebrain cortex, FC, cerebellum, C, and hippocampus, H) and showed cellular localization of GPx4, SOD1 and SOD2 expressions in the hippocampus by immunohistochemical examinations. Despite low Pb level in blood we observed decrease of the activity of some antioxidant enzymes as well as mRNA and protein expression downregulation associated with an increase of MDA level and CAT expression upregulation, especially in the hippocampus region. At the subcellular level, downregulation of SOD2 expression and decreased enzyme activity as well as mitochondrial pool of GSH suggest also that mitochondrial mechanisms might account for Pb neurotoxicity mechanism. For some enzymes, we found differences in the effects of Pb on the level of expression and activity. The activity of CAT decreased despite an increase in mRNA and protein expression; and likewise the activities SOD1, GPx1 GPx4 decreased, despite substantially unchanged level of expression. These effects may be the result of impairment of catalytic function of the enzyme protein caused by Pb interaction or of reduction in the availability of cofactors. We conclude that antioxidant system of the hippocampus of immature rat brain is highly vulnerable to perinatal Pb exposure. Therefore, oxidative stress may be one of the possible mechanisms disturbing cellular metabolism in this structure. Disruption of pro- and antioxidant balance should be considered as a potential mechanism of the observed Pb adverse effects, leading to the impaired learning ability caused by Pb exposure in children.

Consequences of nicotine exposure during different phases of rat brain development

Nicotine is a psychoactive drug whose intensity of the addiction is so tremendous that it is now the fastest growing public health hazard in the world. The present study was designed to study the toxic effects of nicotine during different phases of rat brain development. The study is extended through adult brain designated as group A, that received nicotine at the dosage of 5mg/kg of b.wt. for 21days and were sacrificed following 21days of recovery. In the second group P, pups in different gestational phases (P2–P4) were given maternal nicotine exposures for only a period of 7days followed by recovery till they had achieved the age of 40days. A significant decrease in long term memory was observed in adult rats which correlated well with a significant decrease in the acetylcholine esterase activity. Simultaneously a significant decrease in the total glutathione, GSH content and catalase activity was observed which could account for the increase in peroxidation of lipids as evaluated by malondialdehyde (MDA) content in the nicotine exposed adult rats. The consequences of maternal nicotine exposure were different during different exposures regimes the alterations were least during the early gestation period, i.e. P2 (2–9days of their gestation period) as compared to P3 (7–14days of their gestation period) and P4 (21days of their weanling period). The study indicates that the consequences of nicotine exposure are varied during different stages of brain development.