Perinatal hypoxia induces a long-lasting increase in unstimulated gaba release in rat brain cortex and hippocampus. The protective effect of pyruvate

Lasting mesothalamic dopamine imbalance and altered exploratory behavior in rats after a mild neonatal hypoxic event

Introduction

Adversities during the perinatal period can decrease oxygen supply to the fetal brain, leading to various hypoxic brain injuries, which can compromise the regularity of brain development in different aspects. To examine the catecholaminergic contribution to the link between an early-life hypoxic insult and adolescent behavioral aberrations, we used a previously established rat model of perinatal hypoxia but altered the hypobaric to normobaric conditions.

Methods

Exploratory and social behavior and learning abilities were tested in 70 rats of both sexes at adolescent age. Inherent vertical locomotion, sensory-motor functions and spatial learning abilities were explored in a subset of animals to clarify the background of altered exploratory behavior. Finally, the concentrations of dopamine (DA) and noradrenaline in midbrain and pons, and the relative expression of genes for DA receptors D1 and D2, and their down-stream targets (DA- and cAMP-regulated phosphoprotein, Mr 32 kDa, the regulatory subunit of protein kinase A, and inhibitor-5 of protein phosphatase 1) in the hippocampus and thalamus were investigated in 31 rats.

Results

A lesser extent of alterations in exploratory and cognitive aspects of behavior in the present study suggests that normobaric conditions mitigate the hypoxic injury compared to the one obtained under hypobaric conditions. Increased exploratory rearing was the most prominent consequence, with impaired spatial learning in the background. In affected rats, increased midbrain/pons DA content, as well as mRNA levels for DA receptors and their down-stream elements in the thalamus, but not the hippocampus, were found.

Conclusion

We can conclude that a mild hypoxic event induced long-lasting disbalances in mesothalamic DA signaling, contributing to the observed behavioral alterations. The thalamus was thereby indicated as another structure, besides the well-established striatum, involved in mediating hypoxic effects on behavior through DA signaling.

Perinatal hypoxia and thalamus brain region: increased efficiency of antiepileptic drug levetiracetam to inhibit GABA release from nerve terminals

Levetiracetam (LV), 2S-(2-oxo-1-pyrrolidiny1) butanamide, is an antiepileptic drug. The exact mechanisms of anticonvulsant effects of LV remain unclear. In this study, rats (Wistar strain) underwent hypoxia and seizures at the age of 10–12 postnatal days (pd). [3H]GABA release was analysed in isolated from thalamus nerve terminals (synaptosomes) during development at the age of pd 17–19 and pd 24–26 (infantile stage), pd 38–40 (puberty) and pd 66–73 (young adults) in control and after perinatal hypoxia. The extracellular level of [3H]GABA in the preparation of thalamic synaptosomes increased during development at the age of pd 38–40 and pd 66–73 as compared to earlier ones. LV did not influence the extracellular level of [3H]GABA in control and after perinatal hypoxia at all studied ages. Exocytotic [3H]GABA release in control increased at the age of pd 24–26 as compared to pd 17–19. After hypoxia, exocytotic [3H]GABA release from synaptosomes also increased during development. LV elevated [3H]GABA release from thalamic synaptosomes at the age of pd 66–73 after hypoxia and during blockage of GABA uptake by NO-711 only. LV realizes its antiepileptic effects at the presynaptic site through an increase in exocytotic release of [3H]GABA in thalamic synaptosomes after perinatal hypoxia at pd 66–73. LV exhibited a more significant effect in thalamic synaptosomes after perinatal hypoxia than in control ones. The action of LV is age-dependent, and the drug was inert at the infantile stage that can be useful for an LV application strategy in child epilepsy therapy. Keywords: brain development, exocytosis, GABA, levetiracetam, perinatal hypoxia, thalamic synaptosomes

Sex and age differentially affect GABAergic neurons in the mouse prefrontal cortex and hippocampus following chronic intermittent hypoxia

Obstructive sleep apnea (OSA), a chronic sleep disorder characterized by repetitive reduction or cessation of airflow during sleep, is widely prevalent and is associated with adverse neurocognitive sequelae including increased risk of Alzheimer's disease (AD). In humans, OSA is more common in elderly males. OSA is characterized by sleep fragmentation and chronic intermittent hypoxia (CIH), and recent epidemiological studies point to CIH as the best predictor of neurocognitive sequelae associated with OSA. The sex- and age- specific effects of OSA-associated CIH on specific cell populations such as γ-aminobutyric acid (GABA)-ergic neurons in the hippocampus and the medial prefrontal cortex (mPFC), regions important for cognitive function, remain largely unknown. The present study examined the effect of 35 days of either moderate (10% oxygen) or severe (5% oxygen) CIH on GABAergic neurons in the mPFC and hippocampus of young and aged male and female mice as well as post-accelerated ovarian failure (AOF) female mice. In the mPFC and hippocampus, the number of GABA-labeled neurons increased in aged and young severe CIH males compared to controls but not in young moderate CIH males. This change was not representative of the individual GABAergic cell subpopulations, as the number of parvalbumin-labeled neurons decreased while the number of somatostatin-labeled neurons increased in the hippocampus of severe CIH young males only. In all female groups, the number of GABA-labeled cells was not different between CIH and controls. However, in the mPFC, CIH increased the number of parvalbumin-labeled neurons in young females and the number of somatostatin-labeled cells in AOF females but decreased the number of somatostatin-labeled cells in aged females. In the hippocampus, CIH decreased the number of somatostatin-labeled neurons in young females. CIH decreased the density of vesicular GABA transporter in the mPFC of AOF females only. These findings suggest sex-specific changes in GABAergic neurons in the hippocampus and mPFC with males showing an increase of this cell population as compared to their female counterparts following CIH. Age at exposure and severity of CIH also differentially affect the GABAergic cell population in mice.

Age-Dependency of Levetiracetam Effects on Exocytotic GABA Release from Nerve Terminals in the Hippocampus and Cortex in Norm and After Perinatal Hypoxia

Perinatal hypoxia can lead to multiple chronic neurological deficits, e.g., mental retardation, behavioral abnormalities, and epilepsy. Levetiracetam (LEV), 2S-(2-oxo-1-pyrrolidiny1) butanamide, is an anticonvulsant drug with proven efficiency in treating patients with focal and generalized seizures. Rats were underwent hypoxia and seizures at the age of 10-12 postnatal days (pd). The ambient level and depolarization-induced exocytotic release of [³H]GABA (γ-aminobutyric acid) were analyzed in nerve terminals in the hippocampus and cortex during development at the age of pd 17-19 and pd 24-26 (infantile stage), pd 38-40 (puberty) and pd 66-73 (young adults) in norm and after perinatal hypoxia. LEV had no effects on the ambient [³H]GABA level. The latter increased during development and was further elevated after perinatal hypoxia in nerve terminals in the hippocampus during the whole period and in the cortex in young adults. Exocytotic [³H]GABA release from nerve terminals increased after perinatal hypoxia during development in the hippocampus and cortex, however this effect was preserved at all ages during blockage of GABA transporters by NO-711 in the hippocampus only. LEV realized its anticonvulsant effects at the presynaptic site through an increase in exocytotic release of GABA. LEV exerted more significant effect after perinatal hypoxia than in norm. Action of LEV was strongly age-dependent and can be registered in puberty and young adults, but the drug was inert at the infantile stage.

Expression and functions of glutamate and γ‑aminobutyric acid transporters in ischemic models

Glutamate and γ-aminobutyric acid (GABA) transporters serve central roles in normal neuronal activity and are associated with numerous pathological brain conditions, including ischemia and epilepsy. However, the interplay between these transporters in ischemia remains unclear. In the present study, the expression levels of the excitatory amino acid carrier 1 (EAAC1) and GABA transporter 1 (GAT1) were analyzed in vivo and in vitro within ischemic models by immunofluorescence, western blot and RT-qPCR. Cell survival rates were analyzed following altered expression of these transporters within neuronal cells by flow cytometry. Expression levels of EAAC1 were reduced within the cerebrum of focal cerebral ischemic middle cerebral artery occlusion rat models as well as in primary neurons cultured under hypoxia. However, GAT1 expression levels were slightly elevated under ischemic conditions. The altered expression levels of EAAC1 and GAT1 were combined within neuron cells and the effects were investigated. Apoptotic analysis revealed that EAAC1 suppression and overexpression of GAT1 increased neuronal cell apoptosis under hypoxic conditions; however, EAAC1 overexpression combined with GAT1 knockdown reduced neuronal cell apoptosis under hypoxic conditions. The present study detected the expression levels of the glutamate and GABA transporters under hypoxia, in association with ischemia. The results indicated that, increased expression of EAAC1 combined with GAT1 suppression may provide protective effects in the treatment of epilepsy and ischemia.

Effects of new fluorinated analogues of GABA, pregabalin bioisosters, on the ambient level and exocytotic release of [3H]GABA from rat brain nerve terminals

Recently, we have shown that new fluorinated analogues of γ-aminobutyric acid (GABA), bioisosters of pregabalin (β-i-Bu-GABA), i.e. β-polyfluoroalkyl-GABAs (FGABAs), with substituents: β-CF₃-β-OH (1), β-CF₃ (2); β-CF₂CF₂H (3), are able to increase the initial rate of [³H]GABA uptake by isolated rat brain nerve terminals (synaptosomes), and this effect is higher than that of pregabalin. So, synthesized FGABAs are structural but not functional analogues of GABA. Herein, we assessed the effects of synthesized FGABAs (100μM) on the ambient level and exocytotic release of [³H]GABA in nerve terminals and compared with those of pregabalin (100μM). It was shown that FGABAs 1-3 did not influence the ambient level of [³H]GABA in the synaptosomal preparations, and this parameter was also not altered by pregabalin. During blockage of GABA transporters GAT1 by specific inhibitor NO-711, FGABAs and pregabalin also did not change ambient [³H]GABA in synaptosomal preparations. Exocytotic release of [³H]GABA from synaptosomes decreased in the presence of FGABAs 1-3 and pregabalin, and the effects of FGABAs 1 &3 were more significant than those of FGABAs 2 and pregabalin. FGABAs 1-3/pregabalin-induced decrease in exocytotic release of [³H]GABA from synaptosomes was not a result of changes in the potential of the plasma membrane. Therefore, new synthesized FGABAs 1 &3 were able to decrease exocytotic release of [³H]GABA from nerve terminals more effectively in comparison to pregabalin. Absence of unspecific side effects of FGABAs 1 &3 on the membrane potential makes these compounds perspective for medical application.

Synthesis of new fluorinated analogs of GABA, Pregabalin bioisosteres, and their effects on [(3)H]GABA uptake by rat brain nerve terminals

Fluorinated analogs of natural substances take an essential place in the design of new biologically active compounds. New fluorinated analogs of γ-aminobutyric acid, that is, β-polyfluoroalkyl-GABAs (FGABAs), were synthesized with substituents: β-CF3-β-OH (1), β-CF3 (2); β-CF2CF2H (3). FGABAs are bioisosteres of Pregabalin (Lyrica®, Pfizer's blockbuster drug, β-i-Bu-GABA), and have lipophilicity close to this medicine. The effects of synthesized FGABAs on [(3)H]GABA uptake by isolated rat brain nerve terminals (synaptosomes) were assessed and compared with those of Pregabalin. FGABAs 1-3 (100μM) did not influence the initial velocity of [(3)H]GABA uptake when applied acutely, whereas an increase in this parameter was found after preliminary incubation of FGABAs with synaptosomes. Pregabalin after preliminary incubation with synaptosomes caused unidirectional changes in the initial velocity of [(3)H]GABA uptake. Using specific inhibitors of GAT1 and GAT3, NO-711 and SNAP5114, respectively, the ability of FGABAs 1-3 to influence non-GAT1 and non-GAT3 uptake activity of nerve terminals was analyzed, but no specificity was found. Therefore, new synthesized FGABAs are structural but not functional analogs of GABA (because they did not inhibit synaptosomal [(3)H]GABA uptake). Moreover, FGABAs are able to increase the initial velocity of [(3)H]GABA uptake by synaptosomes, and this effect is higher than that of Pregabalin.

Combination of mild hypothermia with neuroprotectants has greater neuroprotective effects during oxygen-glucose deprivation and reoxygenation-mediated neuronal injury

Co-treatment of neuroprotective reagents may improve the therapeutic efficacy of hypothermia in protecting neurons during ischemic stroke. This study aimed to find promising drugs that enhance the neuroprotective effect of mild hypothermia (MH). 26 candidate drugs were selected based on different targets. Primary cultured cortical neurons were exposed to oxygen-glucose deprivation and reoxygenation (OGD/R) to induce neuronal damage, followed by either single treatment (a drug or MH) or a combination of a drug and MH. Results showed that, compared with single treatment, combination of MH with brain derived neurotrophic factor, glibenclamide, dizocilpine, human urinary kallidinogenase or neuroglobin displayed higher proportion of neuronal cell viability. The latter three drugs also caused less apoptosis rate in combined treatment. Furthermore, co-treatment of those three drugs and MH decreased the level of reactive oxygen species (ROS) and intracellular calcium accumulation, as well as stabilized mitochondrial membrane potential (MMP), indicating the combined neuroprotective effects are probably via inhibiting mitochondrial apoptosis pathway. Taken together, the study suggests that combined treatment with hypothermia and certain neuroprotective reagents provide a better protection against OGD/R-induced neuronal injury.

Perinatal hypoxia: different effects of the inhibitors of GABA transporters GAT1 and GAT3 on the initial velocity of [3H]GABA uptake by cortical, hippocampal, and thalamic nerve terminals

AIM. To analyze the effects of highly selective blocker GAT1, NO-711, and substrate inhibitor GAT3, β-alanine, on the initial velocity of [(3)H]GABA uptake by cortical, hippocampal, and thalamic nerve terminals (synaptosomes) after perinatal hypoxia. METHODS. Animals were divided into two groups: control (n=17) and hypoxia (n=12). Rats in the hypoxia group underwent hypoxia and seizures (airtight chamber, 4% O2 and 96% N2) at the age of 10-12 postnatal days and were used in the experiments 8-9 weeks after hypoxia. RESULTS. In cortical synaptosomes, the effects of NO-711 (30 μΜ) and β-alanine (100 μΜ) on [(3)H]GABA uptake were similar in control and hypoxia groups. In hippocampal synaptosomes, NO-711 inhibited 84.3% of the initial velocity of [(3)H]GABA uptake in normal conditions and 80.1% after hypoxia, whereas the effect of β-alanine was increased after hypoxia from 14.4% to 22.1%. In thalamic synaptosomes, the effect of NO-711 was decreased by 79.6% in controls and by 70.9% in hypoxia group, whereas the effect of β-alanine was increased after hypoxia from 20.2% to 30.2%. CONCLUSIONS. The effectiveness of β-alanine to influence GABA uptake was increased in hippocampal and thalamic nerve terminals as a result of perinatal hypoxia and the effectiveness of NO-711 in thalamic nerve terminals was decreased. These results may indicate changes in the ratio of active GAT1/GAT3 expressed in the plasma membrane of nerve terminals after perinatal hypoxia. We showed a possibility to modulate non-GAT1 GABA transporter activity in different brain regions by exogenous and endogenous β-alanine.

Urinary neurotransmitters are selectively altered in children with obstructive sleep apnea and predict cognitive morbidity

BACKGROUND

Pediatric obstructive sleep apnea (OSA) is associated with cognitive dysfunction, suggesting altered neurotransmitter function. We explored overnight changes in neurotransmitters in the urine of children with and without OSA.

METHODS

Urine samples were collected from children with OSA and from control subjects before and after sleep studies. A neurocognitive battery assessing general cognitive ability (GCA) was administered to a subset of children with OSA. Samples were subjected to multiple enzyme-linked immunosorbent assays for 12 neurotransmitters, and adjusted for creatinine concentrations.

RESULTS

The study comprised 50 children with OSA and 20 control subjects. Of the children with OSA, 20 had normal GCA score (mean ± SD) (101.2 ± 14.5) and 16 had a reduced GCA score (87.3 ± 13.9; P < .001). Overnight increases in epinephrine, norepinephrine, and γ-aminobutyric acid (GABA) levels emerged in children with OSA; taurine levels decreased. Using combinatorial approaches and cutoff values for overnight changes of these four neurotransmitters enabled prediction of OSA (area under the curve [AUC]: 0.923; P < .0001). Furthermore, GABA and taurine alterations, as well as overnight reductions in phenylethylamine, were more prominent in children with OSA and low GCA than in children with OSA and normal GCA (P < .001), and they reliably discriminated GCA status (AUC: 0.977; P < .0001).

CONCLUSIONS

Pediatric OSA is associated with overnight increases in urinary concentrations of catecholamines indicative of heightened sympathetic outflow. Increases in GABA levels and decreases in taurine levels could underlie mechanisms of neuronal excitotoxicity and dysfunction. Combinatorial approaches using defined cutoffs in overnight changes in concentrations of selected neurotransmitters in urine may not only predict OSA but also the presence of cognitive deficits. Larger cohort studies appear warranted to confirm these findings.

The dynamics of changes in hippocampal GABAergic system in rats exposed to early-life hypoxia-induced seizures

Hypoxia-evoked seizures (H/S) early in life lead to multiple chronic neurological deficits. Here, we present the results of studying GABA release and uptake in hippocampal axon terminals of rats exposed to H/S at 10-12 days of age. We characterized (i) exocytotic release of GABA; (ii) the initial rate of GABA uptake; (iii) the regulation of GABA release by presynaptic GABA(B) receptors. Rats were used for experiments 2, 4 and 8 weeks after H/S. We found that exocytotic [(3)H]GABA release was higher in rats exposed to H/S, and a maximal difference in the release was observed between the control and experimental rats tested 2 weeks after H/S. In contrast, the initial rate of GABA uptake decreased with age, and this tendency was more pronounced in rats exposed to H/S. Using (±)-baclofen and SKF 97541 as agonists of GABA(B) receptor, we revealed that a significant difference in the auto-inhibition of exocytotic [(3)H]GABA release was detected only between the control and experimental adult rats (8 weeks after hypoxia). The inhibitory effect dropped dramatically in the control adults, but only slightly decreased in adult rats exposed to H/S, thus becoming threefold more potent after hypoxic injury. Together, the results show that H/S affects the dynamics of age-dependent changes in the GABAergic system, and that the enhanced GABA(B) receptor-mediated auto-inhibition can be an important factor in weakening the postsynaptic inhibition and in the development of hyperexcitability in rats exposed to H/S.

Energy depletion in seizures: anaplerosis as a strategy for future therapies

Seizure activity can lead to energy failure and neuronal injury, resulting in neurological and cognitive sequelae. Moreover, mutations affecting genes encoding for proteins that maintain energy homeostasis within the cell often result in an epileptic phenotype, implying that energy failure can contribute to epileptogenesis. Indeed, there is evidence to indicate that the efficacy of the ketogenic diet, a treatment for refractory epilepsy, can be partly explained by its effect on increasing energetic substrates. The ATP level, reflecting the energy level of a cell, is maintained by the potential gradient across the mitochondrial membrane. This potential gradient is maintained by NADH/H(+) equivalents, produced by reactions within the tricarboxylic acid cycle (TCA-cycle). Anaplerosis, the replenishment of TCA-cycle substrates, therefore represents an appealing strategy to address energy failure such as occurs in seizures. There is accumulating evidence that pyruvate, a classical anaplerotic substrate, has seizure suppressive effects and protects against seizure induced cell death. This review summarizes the evidence for the contribution of TCA cycle deficits in generating seizures. We highlight the role for TCA substrate supplementation in protecting against seizures and seizure induced cell death, and propose that these are important targets for future translational research addressing energy depletion in seizures. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.