Dynamic spatio-temporal imaging of early reflow in a neonatal rat stroke model

Preventive Effects of Neuroprotective Agents in a Neonatal Rat of Photothrombotic Stroke Model

Neonatal ischemic stroke has a higher incidence than childhood stroke. Seizures are the first sign for the need for clinical assessment in neonates, but many questions remain regarding treatments and follow-up modalities. In the absence of a known pathophysiological mechanism, only supportive care is currently provided. Stroke-induced microglia activation and neuroinflammation are believed to play a central role in the pathological progression of neonatal ischemic stroke. We induced a photothrombotic infarction with Rose Bengal in neonatal rats to investigate the effects of pre- and post-treatment with Aspirin (ASA), Clopidogrel (Clop), and Coenzyme Q10 (CoQ10), which are known for their neuroprotective effects in adult stroke. Pre-stroke medication ameliorates cerebral ischemic injury and reduces infarct volume by reducing microglia activation, cellular reactive oxygen species (ROS) production, and cytokine release. Post-stroke administration of ASA, Clop, and CoQ10 increased motor function and reduced the volume of infarction, and the statistical evidence was stronger than that seen in the pre-stroke treatment. In this study, we demonstrated that ASA, Clop, and CoQ10 treatment before and after the stroke reduced the scope of stroke lesions and increased behavioral activity. It suggests that ASA, Clop, and CoQ10 medication could significantly have neuroprotective effects in the neonates who have suffered strokes.

Prostaglandin E1-Mediated Collateral Recruitment Is Delayed in a Neonatal Rat Stroke Model

While arterial reflow after a stroke represents an important challenge for better outcomes, it is also very important that sudden recanalization does not produce local oxidative and nitrogen species, deleterious for the brain and more particularly the immature brain. Our objective was to determine whether a supply in prostaglandin (Pg) E1 (Alprostadil), via its action on arterial pressure, might progressively improve cerebral reperfusion in a neonatal stroke model. Arterial blood flow was measured using ultrasonography. Rate-limiting and Pg terminal synthesizing enzymes were evaluated using reverse-transcriptase polymerase chain reaction. Our data suggests that a supply in PgE1 might delay and improve the ipsilateral reperfusion by decreasing thromboxane A synthase-1 gene, the density of reactive astrocytes and lesion volume.

A Model of Perinatal Ischemic Stroke in the Rat: 20 Years Already and What Lessons?

Neonatal hypoxia-ischemia (HI) and ischemia are a common cause of neonatal brain injury resulting in cerebral palsy with subsequent learning disabilities and epilepsy. Recent data suggest a higher incidence of focal ischemia-reperfusion located in the middle cerebral artery (MCA) territory in near-term and newborn babies. Pre-clinical studies in the field of cerebral palsy research used, and still today, the classical HI model in the P7 rat originally described by Rice et al. (1). At the end of the 90s, we designed a new model of focal ischemia in the P7 rat to explore the short and long-term pathophysiology of neonatal arterial ischemic stroke, particularly the phenomenon of reperfusion injury and its sequelae (reported in 1998). Cerebral blood-flow and cell death/damage correlates have been fully characterized. Pharmacologic manipulations have been applied to the model to test therapeutic targets. The model has proven useful for the study of seizure occurrence, a clinical hallmark for neonatal ischemia in babies. Main pre-clinical findings obtained within these 20 last years are discussed associated to clinical pattern of neonatal brain damage.

In vivo microdialysis with ultra performance liquid chromatography-mass spectrometry for analysis of tetramethylpyrazine and its interaction with borneol in rat brain and blood

Tetramethylpyrazine (TMP) has been widely used in the treatment of ischemic cerebrovascular disease. However, the mechanism of TMP and how to increase its bioavailability need to be further explored. In our study, an in vivo microdialysis sampling technique coupled with ultra-performance liquid chromatography-mass spectrometry method was developed to investigate the pharmacokinetic properties of TMP and its interaction with different doses of borneol (BO) in rats. Linearity of TMP in brain and blood dialysates exhibited good linear relationships over the concentration range of 0.991-555.14 ng/mL. The specificity, linearity, accuracy, precision, matrix effect and stability were within acceptable ranges. The results demonstrated that BO had a marked impact on the pharmacokinetic properties of TMP. After co-administration, the areas under the concentration-time curve (AUC) of TMP in brain and blood were significantly increased. Meanwhile, the peak concentration of TMP in brain was also enhanced. The AUC_Brain /AUC_Blood of TMP, increased from 44% to 56 and 60.8% after co-administration with BO (15 and 30 mg/kg). The pharmacodynamic results showed that TMP co-administration with BO enhanced the cerebral blood flow during the period of ischemia and reduced the infarct volume. Overall, it might be an effective way to treat stroke to use TMP co-administered with BO.

Controlled arterial reflow after ischemia induces better outcomes in the juvenile rat brain

Our objective was to determine whether controlled reflow on one side and/or the other side after bilateral carotid occlusion release could reduce cell death in focal ischemic P14 rats. Arterial blood flow was measured using ultrasonography. Cell death, inflammation and nitrotyrosine were measured using immunofluorescence. When reflow was first induced in the contralateral side, we observed improved outcome markers compared with those when reflow was first induced in the ipsilateral side and/or simultaneous reflow was induced in both sides. Our data suggest that progressive rerouting of arterial flow through the circle of Willis toward the ischemic site reduced cell death.

Different response to antiepileptic drugs according to the type of epileptic events in a neonatal ischemia-reperfusion model

Perinatal arterial stroke is the most frequent form of cerebral infarction in children. Neonatal seizures are the most frequent symptom during the neonatal period. The current management of perinatal stroke is based on supportive care. It is currently unknown if treatment of the seizures modifies the outcome, and no clinical studies have focused on seizures during neonatal stroke. We studied the effect of phenobarbital and levetiracetam on an ischemic-reperfusion stroke model in P7 rats using prolonged electroencephalographic recordings and a histologic analysis of the brain (24h after injury). The following two types of epileptic events were observed: 1) bursts of high amplitude spikes during ischemia and the first hours of reperfusion and 2) organized seizures consisting in discharges of a 1-2Hz spike-and-wave. Both phenobarbital and levetiracetam decreased the total duration of the bursts of high amplitude spikes. Phenobarbital also delayed the start of seizures without changing the total duration of epileptic discharges. The markedly limited efficacy of the antiepileptic drugs studied in our neonatal stroke rat model is frequently observed in human neonatal seizures. Both drugs did not modify the stroke volume, which suggests that the modification of the quantity of bursts of high amplitude spikes does not influence the infarct size. In the absence of a reduction in seizure burden by the antiepileptic drugs, we increased the seizure burden and stroke volume by combining our neonatal stroke model with a lithium-pilocarpine-induced status epilepticus. Our data suggest that the reduction of burst of spikes did not influence the stroke volume. The presence of organized seizure with a pattern close to what is observed in human newborns seems related to the presence of the infarct. Further research is required to determine the relationship between seizure burden and infarct volume.

Ischemic postconditioning in cerebral ischemia: Differences between the immature and mature brain?

Ischemic postconditioning (postC), defined as serial mechanical interruptions of blood flow at reperfusion, effectively reduces myocardial infarct size in all species tested so far, including humans. In the brain, ischemic postC leads to controversial results regardless of variations in factors such as onset time of beginning, the duration of ischemia and/or reperfusion, and the number of cycles of occlusion/reperfusion. Thus, many major issues remain to be resolved regarding its protective effects. Future studies should aim to identify the parameters that yield the strongest protection, as well as to understand why the efficacy of ischemic postC differs between models. This review will focus on initial hemodynamic changes and their consequences, and on specific features such as NO-dependent vascular tone and/or prolonged acidosis in cerebral ischemia-reperfusion in order to better understand the dynamics of ischemic postC in the developing brain.

Hypothermia modulates cytokine responses after neonatal rat hypoxic-ischemic injury and reduces brain damage

While hypothermia (HT) is the standard-of-care for neonates with hypoxic ischemic injury (HII), the mechanisms underlying its neuroprotective effect are poorly understood. We examined ischemic core/penumbra and cytokine/chemokine evolution in a 10-day-old rat pup model of HII. Pups were treated for 24 hr after HII with HT (32℃; n = 18) or normothermia (NT, 35℃; n = 15). Outcomes included magnetic resonance imaging (MRI), neurobehavioral testing, and brain cytokine/chemokine profiling (0, 24, 48, and 72 hr post-HII). Lesion volumes (24 hr) were reduced in HT pups (total 74%, p < .05; penumbra 68%, p < .05; core 85%, p = .19). Lesion volumes rebounded at 72 hr (48 hr post-HT) with no significant differences between NT and HT pups. HT reduced interleukin-1β (IL-1β) at all time points (p < .05); monocyte chemoattractant protein-1 (MCP-1) trended toward being decreased in HT pups (p = .09). The stem cell signaling molecule, stromal cell-derived factor-1 (SDF-1) was not altered by HT. Our data demonstrate that HT reduces total and penumbral lesion volumes (at 24 and 48 hr), potentially by decreasing IL-1β without affecting SDF-1. Disassociation between the increasing trend in HII volumes from 48 to 72 hr post-HII when IL-1β levels remained low suggests that after rewarming, mechanisms unrelated to IL-1β expression are likely to contribute to this delayed increase in injury. Additional studies should be considered to determine what these mechanisms might be and also to explore whether extending the duration or degree of HT might ameliorate this delayed increase in injury.

Effects of dexmedetomidine on microregional O2 balance during reperfusion after focal cerebral ischemia

BACKGROUND

This study was performed to determine whether there is an association between microregional O2 balance and neuronal survival in cerebral ischemia-reperfusion using dexmedetomidine, an α2-adrenoreceptor agonist and a sedative.

METHODS

Rats were subjected to 1 hour middle cerebral artery occlusion and a 2-hour reperfusion. During reperfusion, normal saline (n = 14) or dexmedetomidine 1 μg/kg/minute (n = 14) was infused intravenously. At 2 hours of reperfusion, regional cerebral blood flow using (14)C-iodoantipyrine autoradiography, microregional arterial and venous (20-60 μm in diameter) O2 saturation (SvO2) using cryomicrospectrophotometry, and the size of cortical infarction were determined.

RESULTS

Ischemia-reperfusion decreased microregional SvO2 (52.9 ± 3.7% vs. 61.1 ± .6%, P < .005) with increased variation or heterogeneity (P < .0001) with similar regional cerebral blood flow and O2 consumption. Dexmedetomidine during reperfusion decreased the heterogeneity of SvO2 that was analyzed with an analysis of variance (P < .01) and reported as coefficient of variation (100 × standard deviation/Mean) (11.8 vs. 16.4). The number of veins with O2 saturation less than 50% decreased with dexmedetomidine (13/80 vs. 27/81, P < .01). The percentage of cortical infarct in total cortex was smaller with dexmedetomidine (8.3 ± 2.2% vs. 12.6 ± 1.5%, P < .005).

CONCLUSIONS

In the cerebral ischemic reperfused cortex, dexmedetomidine decreased the heterogeneity of SvO2 and the number of small veins with low O2 saturation suggesting improved microregional O2 supply/consumption balance. The improvement was accompanied by the reduced size of cortical infarction.

Reparative effects of neural stem cells in neonatal rats with hypoxic-ischemic injury are not influenced by host sex

BACKGROUND

Gender is increasingly recognized as an important influence on brain development, disease susceptibility, and response to pharmacologic/rehabilitative treatments. In regenerative medicine, it remains entirely unknown whether there is an interaction between transplanted stem cells and host gender that might bias efficacy and safety in some patients but not others.

METHODS

We examined the role of recipient gender in a neonatal rat hypoxic-ischemic injury (HII) model, treated with female human neuronal stem cells (hNSCs), labeled with superparamagnetic iron oxide particles implanted into the contralateral cerebral ventricle. We monitored HII evolution (by magnetic resonance imaging, histopathology, behavioral testing) and hNSC fate (migration, replication, viability).

RESULTS

Recipient gender after implantation did not influence the volume or location of ischemic injury (1, 30, or 90 d) or behavior (90 d). Superparamagnetic iron oxide labeling did not influence HII evolution. Implantation had its greatest benefit on mild/moderate injuries, which remained stable rather than increasing as in severe HII as is the natural history for such lesions.

CONCLUSION

Our results suggest that hNSC treatment (including using hNSCs that are prelabeled with iron to allow tracking in real time by magnetic resonance imaging) would be equally safe and effective for male and female human newborns with mild-to-moderate HII.