Ana-Maria Zagrean

Oxidative damage following cerebral ischemia depends on reperfusion ‐ a biochemical study in rat

The extent of brain injury during reperfusion appears to depend on the experimental pattern of ischemia/reperfusion. The goals of this study were: first, to identify the rate of free radicals generation and the antioxidant activity during ischemia and reperfusion by means of biochemical measurement of lipid peroxidation (LPO) and both enzymatic (superoxid dismutase ‐ SOD, catalase ‐ CAT, glutathion peroxidase ‐ GPx) and non‐enzymatic antioxidants activity (glutathione ‐ GSH); and second, to try to find out how the pattern of reperfusion may influence the balance between free radical production and clearance. Wistar male rats were subject of four‐vessel occlusion model (Pulsinelly & Brierley) cerebral blood flow being controlled by means of two atraumatic arterial microclamps placed on carotid arteries. The level of free radicals and the antioxidant activity were measured in ischemic rat brain tissue homogenate using spectrophotometrical techniques. All groups subjected to ischemia shown an increase of LPO and a reduction of the activity of enzymatic antioxidative systems (CAT, GPx, SOD) and non‐enzymatic systems (GSH). For both groups subjected to ischemia and reperfusion, results shown an important increase of LPO but less significant than the levels found in the group with ischemia only. Statistically relevant differences (p<0.01) between continuous reperfusion and fragmented reperfusion were observed concerning the LPO, CAT, SOD and GSH levels, oxidative aggresion during fragmented reperfusion being more important.

Oxytocin is neuroprotective against oxygen–glucose deprivation and reoxygenation in immature hippocampal cultures

Oxytocin triggers an excitatory-to-inhibitory switch in GABA (gamma-aminobutyric acid) actions in immature neurons and this was found to increase their resistance to anoxic episodes. In this study we examined the neuroprotective effect of oxytocin on immature hippocampal cultures subjected to oxygen-glucose deprivation (OGD) both immediately after the insult, as well as after 6h of reoxygenation. We measured metabolic activity fluorometrically using resazurin and found that cellular viability was increased in the oxytocin treated group both immediately after OGD, as well as after 6 h of reoxygenation. While the oxytocin receptor antagonist atosiban blocked the effect of oxytocin, the Na+-K+-2Cl(-) cotransporter (NKCC1) blocker bumetanide protected neurons after reoxygenation. The effects of oxytocin are dose-related. Our results suggest that oxytocin exerts a prolonged neuroprotective action on fetal neurons. Perinatal pharmacologic manipulation of oxytocin receptors may have detrimental effects by increasing susceptibility of the fetal brain to hypoxic-ischemic insults.

Multimodal Approaches for Regenerative Stroke Therapies: Combination of Granulocyte Colony-Stimulating Factor with Bone Marrow Mesenchymal Stem Cells is Not Superior to G-CSF Alone

Attractive therapeutic strategies to enhance post-stroke recovery of aged brains include methods of cellular therapy that can enhance the endogenous restorative mechanisms of the injured brain. Since stroke afflicts mostly the elderly, it is highly desirable to test the efficacy of cell therapy in the microenvironment of aged brains that is generally refractory to regeneration. In particular, stem cells from the bone marrow allow an autologous transplantation approach that can be translated in the near future to the clinical practice. Such a bone marrow-derived therapy includes the grafting of stem cells as well as the delayed induction of endogenous stem cell mobilization and homing by the stem cell mobilizer granulocyte colony-stimulating factor (G-CSF). We tested the hypothesis that grafting of bone marrow-derived pre-differentiated mesenchymal cells (BM-MSCs) in G-CSF-treated animals improves the long-term functional outcome in aged rodents. To this end, G-CSF alone (50 μg/kg) or in combination with a single dose (106 cells) of rat BM MSCs was administered intravenously to Sprague-Dawley rats at 6 h after transient occlusion (90 min) of the middle cerebral artery. Infarct volume was measured by magnetic resonance imaging at 3 and 48 days post-stroke and additionally by immunhistochemistry at day 56. Functional recovery was tested during the entire post-stroke survival period of 56 days. Daily treatment for post-stroke aged rats with G-CSF led to a robust and consistent improvement of neurological function after 28 days. The combination therapy also led to robust angiogenesis in the formerly infarct core and beyond in the “islet of regeneration.” However, G-CSF + BM MSCs may not impact at all on the spatial reference-memory task or infarct volume and therefore did not further improve the post-stroke recovery. We suggest that in a real clinical practice involving older post-stroke patients, successful regenerative therapies would have to be carried out for a much longer time.

Separation and identification of glycoforms by capillary electrophoresis with electrospray ionization mass spectrometric detection.

Capillary electrophoresis (CE) is a resourceful and versatile separation method for the analysis of complex carbohydrate mixtures. In combination with electrospray ionization (ESI) mass spectrometry (MS), CE enables fast, sensitive, and efficient separations for the accurate identification of a large variety of glycoform mixture types. In this chapter several reliable off- and on-line CE-based methods for the analysis of glycoforms with ESI MS/MS are presented. The first part of this chapter is dedicated to the application of off-line CE/ESI MS to complex mixtures of O-glycopeptides and mixtures of proteoglycan-derived O-glycans, i.e., glycosaminoglycans such as depolymerized hybrid chains of chondroitin sulfate (CS) and dermatan sulfate (DS). Procedures for off-line fractionation of these heterogeneous mixtures followed by ESI MS screening and sequencing of single glycoforms by collision-induced dissociation (CID) at low energies are also described. Ample sections are further devoted to on-line CE/ESI MS technique and its application to separation and identification of O-glycopeptides and CS/DS oligosaccharides. The concept and construction principles of two different sheathless CE/ESI MS interfaces together with the protocols to be applied for successful on-line analysis of O-glycopeptides and CS/DS oligosaccharides are presented in details in the last part of the chapter.

Endogenous adenosine A1 receptor activation underlies the transient post-ischemic rhythmic delta EEG activity

OBJECTIVE Emergence of slow EEG rhythms within the delta frequency band following an ischemic insult of the brain has long been considered a marker of irreversible anatomical damage. Here we investigated whether ischemic adenosine release and subsequent functional inhibition via the adenosine A(1) receptor (A(1)R) contributes to post-ischemic delta activity. METHODS Rats were subjected to episodes of non-injuring transient global cerebral ischemia (GCI) under chloral hydrate anesthesia. RESULTS We found that a GCI lasting only 10s was enough to induce a brief discharge of rhythmic delta activity (RDA) with a peak frequency just below 1 Hz quantified as an increase by twofold of the 0.5-1.5 Hz spectral power. This post-ischemic RDA did not occur following administration of the A(1)R antagonist 8-cyclopentyl-1,3-dipropylxanthine. Nevertheless, a similar RDA could be induced in rats not subjected to GCI, by systemic administration of the A(1)R agonist N(6)-cyclopentyladenosine. CONCLUSIONS Our data suggest that A(1)R activation at levels that occur following cerebral ischemia underlies the transient post-ischemic RDA. SIGNIFICANCE It is likely that the functional, thus potentially reversible, synaptic disconnection by A(1)R activation promotes slow oscillations in the cortical networks. This should be accounted for in the interpretation of early post-ischemic EEG delta activity.

Electro‐cortical signs of early neuronal damage following transient global cerebral ischemia in rat

During recovery after a transient global cerebral ischemia (TGCI), rat electrocorticogram (ECoG) shows epochs of synchronized activity (SA) alternating with epochs of low amplitude background activity (BA). The aim of this study was to compare the changes in these electrical activities during a 30‐min recovery period that followed either a noninjuring (3 minutes, N=10) or an injuring (10 minutes, N=10) TGCI. During TGCI there was a 3 fold reduction in amplitudes of both SA and BA but no changes in frequency. During reperfusion following a 3 minutes TGCI, the amplitudes of both SA and BA recovered to about 70%. During the reperfusion that followed a 10 minutes TGCI, BA showed no recovery, whereas SA recovered to about 40%. During the 30 min reperfusion, there was a timedependent decrease in the frequency of SA, but independent on the duration of TGCI. In contrast, the frequency of the BA did not change during reperfusion. Our data indicate that following cerebral ischemia the recovery of SA can take place independently of BA. The lack of recovery in BA may indicate early subcortical neuronal damage.

Trans-resveratrol enriched maternal diet protects the immature hippocampus from perinatal asphyxia in rats

Trans-resveratrol (tRESV), a polyphenol with antioxidant properties, is common in many food sources, hence easily accessible for study as a maternal dietary supplement in perinatal asphyxia (PA). Hypoxic-ischemic encephalopathy secondary to PA affects especially vulnerable brain areas such as hippocampus and is a leading cause of neonatal morbidity. The purpose of this study is to identify new epigenetic mechanisms of brain inflammation and injury related to PA and to explore the benefit of tRESV enriched maternal diet. The hippocampal interleukin 1 beta (IL-1b), tumour necrosis factor alpha (TNFα) and S-100B protein, at 24-48h after 90min of asphyxia were assessed in postnatal day 6 rats whose mothers received either standard or tRESV enriched diet. The expression of non-coding microRNAs miR124, miR132, miR134, miR146 and miR15a as epigenetic markers of hippocampus response to PA was determined 24h post-asphyxia. Our results indicate that neural response to PA could be epigenetically controlled and that tRESV reduces asphyxia-related neuroinflammation and neural injury. Moreover, tRESV could increase, through epigenetic mechanisms, the tolerance to asphyxia, with possible impact on the neuronal maturation. Our data support the neuroprotective quality of tRESV when used as a supplement in the maternal diet on the offsprings outcome in PA.

Maternal High-Fat Diet Modifies the Immature Hippocampus Vulnerability to Perinatal Asphyxia in Rats

Background: High-fat diet (HFD) is a detrimental habit with harmful systemic consequences, including low-grade, long-lasting inflammation. During pregnancy, HFD can induce developmental changes. Moreover, HFD-related maternal obesity might enhance the risk of peripartum complications including hypoxic-ischemic encephalopathy secondary to perinatal asphyxia (PA). Objectives: Following our previous results showing that PA increases neuroinflammation and neuronal injury in the immature hippocampus and modifies hippocampal epigenetic programming, we further aimed to establish the impact of maternal HFD on offspring hippocampus response to PA. Methods: We assessed hippocampal tumor necrosis factor alpha (TNFα), interleukin 1 beta (IL-1b) and S-100B protein (S-100B), 24–48 h after PA exposure in postnatal day 6 Wistar rats, whose mothers received either the standard diet or HFD. The expression of small non-coding microRNA species miR124, miR132, miR134, miR146, and miR15a, as epigenetic markers for the maternal dietary influence on immature hippocampus response after PA, was determined 24 h after asphyxia exposure. Metabolic activity was measured using resazurin test in hippocampal cell suspension obtained 24 h after PA. Results: Our results indicate that maternal HFD additionally increases hippocampal TNFα, IL-1b, and S-100B after PA. Also, PA associated with maternal HFD induces miR124 upregulation and miR132 downregulation relative to PA only. Metabolic activity was increased in hippocampal cells from pups whose mothers received HFD. Conclusion: HFD increases the PA-induced neuroinflammation and neuronal injury, and epigenetically influences homeostatic synaptic plasticity and neuronal tolerance to asphyxia, processes associated with a higher hippocampal cellular metabolism.

Chemogenetic Recruitment of Specific Interneurons Suppresses Seizure Activity

Current anti-epileptic medications that boost synaptic inhibition are effective in reducing several types of epileptic seizure activity. Nevertheless, these drugs can generate significant side-effects and even paradoxical responses due to the broad nature of their action. Recently developed chemogenetic techniques provide the opportunity to pharmacologically recruit endogenous inhibitory mechanisms in a selective and circuit-specific manner. Here, we use chemogenetics to assess the potential of suppressing epileptiform activity by enhancing the synaptic output from three major interneuron populations in the rodent hippocampus: parvalbumin (PV), somatostatin (SST), and vasoactive intestinal peptide (VIP) expressing interneurons. To target different neuronal populations, promoter-specific cre-recombinase mice were combined with viral-mediated delivery of chemogenetic constructs. Targeted electrophysiological recordings were then conducted in an in vitro model of chronic, drug-resistant epilepsy. In addition, behavioral video-scoring was performed in an in vivo model of acutely triggered seizure activity. Pre-synaptic and post-synaptic whole cell recordings in brain slices revealed that each of the three interneuron types increase their firing rate and synaptic output following chemogenetic activation. However, the interneuron populations exhibited different effects on epileptiform discharges. Recruiting VIP interneurons did not change the total duration of epileptiform discharges. In contrast, recruiting SST or PV interneurons produced robust suppression of epileptiform synchronization. PV interneurons exhibited the strongest effect per cell, eliciting at least a fivefold greater reduction in epileptiform activity than the other cell types. Consistent with this, we found that in vivo chemogenetic recruitment of PV interneurons suppressed convulsive behaviors by more than 80%. Our findings support the idea that selective chemogenetic enhancement of inhibitory synaptic pathways offers potential as an anti-seizure strategy.