Bulent Goren

Neuronal protective effects of focal ischemic pre- and/or postconditioning on the model of transient focal cerebral ischemia in rats.

We investigated the neuroprotective effects of pre- and postconditioning on infarct volume in the transient middle cerebral artery occlusion (MCAo) model in rats. Thirty-two male rats were divided into occlusion, preconditioning, postconditioning and both pre- and postconditioning groups. MCAo (120 minutes) was monitored with continuous cerebral tissue oxygen (O2) pressure (PtiO2). Pre-conditioning comprised 10 minutes of MCAo, 24 hours prior to the 120 minute MCAo. The postconditioning algorithm was 30 seconds of reperfusion followed by 30 seconds of MCAo. This cycle was repeated 3 times at the onset of reperfusion. Comparison of infarct volumes showed a significant difference between the conditioned groups and occlusion group. Although there was better protection in the preconditioning group compared with the other two conditioned groups, the results did not reach statistically significant levels. The results suggest that preconditioning, postconditioning and pre/post conditioning have protective effects on cerebral ischemia.

The effects of sevoflurane and isoflurane on intracranial pressure and cerebral perfusion pressure after diffuse brain injury in rats.

Twenty-four adult male Wistar rats, weighing 220 to 290 g, were anesthetized with 30 mg/kg intraperitoneal sodium thiopental, then underwent a tracheostomy. After diffuse impact–acceleration brain injury (BI) was induced, each rat was paralyzed and mechanically ventilated with 30% O2 in nitrous oxide (N2O). The rats were assigned randomly to two groups, each of which received one of the two volatile anesthetic agents, sevoflurane or isoflurane. The anesthetics were administered at 0.5, 0.75, 1.0, and 1.25 minimal alveolar concentration (MAC) for 30 minutes each, respectively, and anesthesia was maintained at 0.75 MAC during the last hour of the study period. Intracranial pressure (ICP), mean arterial pressure (MAP), rectal and intrahemispheric temperatures, and end-tidal volatile anesthetic concentrations were monitored continuously throughout the 3 hours, with measurements recorded every 15 minutes. At baseline, there were no significant differences between the two groups regarding the monitored physiologic values. In the sevoflurane group, MAP fell significantly after 45 minutes, and a similar change was observed in the isoflurane group after 30 minutes (P < .05, P < .01, and P < .001, respectively). Intracranial pressure increased significantly at 45 minutes in the sevoflurane group (P < .01) and remained elevated from 60 minutes until the end of the study period (P < .01, P < .001). Although ICP increased in the isoflurane group, the change was not significant. Cerebral perfusion pressure (CPP) decreased in parallel with MAP, with the reduction in the sevoflurane group being more pronounced than that in the isoflurane group. The results demonstrated that, under the conditions of diffuse BI, animals that were anesthetized with sevoflurane had higher ICP and lower CPP levels than those anesthetized with isoflurane.

Neuroprotective effects of melatonin administered alone or in combination with topiramate in neonatal hypoxic-ischemic rat model.

PURPOSE The objective of this study was to compare the effects of two neuroprotective agents; melatonin, a free radical scavenger and topiramate, AMPA/kainate receptor antagonist, administered alone or in combination in neonatal hypoxic-ischemic model. METHODS After being anesthetized, 7-day-old pups underwent ischemia followed by exposure to hypoxia. The pups were divided into 4 groups in order to receive the vehicle, melatonin, topiramate and combination of topiramate and melatonin. These were administered intraperitoneally for three times; the first before ischemia, the second after hypoxia and the third 24 hours after the second dose. After sacrification, infarct volume and apoptosis were evaluated. RESULTS Percent infarcted brain volume was significantly reduced in rats which received drugs compared with those which received the vehicle. The number of TUNEL positive cells per unit area in hippocampus and cortex were markedly reduced in drug treated groups compared with control group. No significant differences were found regarding percent infarcted brain volume and number of TUNEL positive cells among drug-treated groups. CONCLUSIONS Melatonin and topiramate, administered either alone or in combination significantly reduced the percent infarcted brain volume and number of TUNEL positive cells suggesting that these agents may confer benefit in treatment of infants with hypoxic-ischemic encephalopathy.

Neuroprotective effects of uridine in a rat model of neonatal hypoxic-ischemic encephalopathy.

Neonatal hypoxic-ischemic encephalopathy (HIE) is a major cause of neurological disability requiring newer therapeutic strategies. Uridine is the principal circulating pyrimidine in humans and a substrate for nucleotides and membrane phospholipids. The objective of this study was to investigate the effects of uridine in a neonatal rat model of HIE. Rat pups subjected to hypoxic-ischemic insult on postnatal day 7 were injected intraperitoneally with either saline or uridine (100, 300 or 500mg/kg) for three consecutive days and brains were collected for evaluation of brain infarct volume and apoptosis. Compared with Control group, uridine at 300 and 500mg/kg doses significantly reduced percent infarct volume, TUNEL(+) cell ratio and active Caspase-3 immunoreactivity in the cortex, as well as in CA1 and CA3 regions of the hippocampus. Uridine (300 and 500mg/kg) also decreased active Caspase-3 expression in the ipsilateral hemisphere. These data indicate that uridine dose-dependently reduces brain injury in a rat model of neonatal HIE by decreasing apoptosis.

Uridine protects against hypoxic-ischemic brain injury by reducing histone deacetylase activity in neonatal rats

PURPOSE A significant cause of neurological disability in newborns is hypoxic-ischemic encephalopathy (HIE), a disorder which involves an enhancement in histone deacetylase (HDAC) activity among underlying pathological mechanisms. We showed recently that exogenous administration of uridine to newborn rats with HIE reduced brain injury in a dose-dependent manner. The present study was performed to investigate whether uridine modulates histone acetylation/deacetylation balance in a neonatal rat model of HIE. METHODS Newborn rats that were subjected to hypoxic-ischemic (HI) insult on postnatal day 7 (P7) were injected intraperitoneally with either saline or uridine (500 mg/kg) for three consecutive days. One day after completion of treatment, brains of pups were collected for evaluation of brain infarct volume, apoptosis, HDAC activity and acetylated-Histone H3 (Ac-H3) and H4 (Ac-H4) protein levels. RESULTS Results revealed that uridine administration reduced infarct volume, active Caspase-3 levels and HDAC activity while increasing the expressions of Ac-H3 and Ac-H4 proteins. CONCLUSIONS We conclude that one mechanism by which uridine provides neuroprotection in neonatal rat HIE model involves reduction in HDAC activity.

Long-term cognitive effects of uridine treatment in a neonatal rat model of hypoxic-ischemic encephalopathy.

Hypoxic-ischemic encephalopathy (HIE), is the most common brain disorder in neonates during the perinatal period, which, to date, can only be managed to some extent by hypothermia. Uridine is the principal circulating pyrimidine in humans which is utilized as a precursor for membrane phospholipid biosynthesis. Uridine has recently been shown to provide clinical benefit in treatment of Alzheimers disease due to its involvement in increasing number of brain synapses along with other phospholipid precursors. We previously showed that uridine treatment ameliorated brain damage by reducing apoptosis in a rat model of neonatal HIE. The aim of the present study was to investigate the effects of uridine administration on cognitive functions during periadolescent period in rats subjected to hypoxic-ischemic (HI) brain damage in neonatal period. Male newborn rats were subjected to HI insult on postnatal day 7 (P7) and were injected intraperitoneally with either saline or uridine (500mg/kg) for three consecutive days. Part of pups in each group were sacrificed on P10 to collect brain samples for active Caspase-3 analyses and the remaining pups were raised through P40 to evaluate early reflexes, sensorimotor coordination and learning and memory functions by Negative Geotaxis (NG), Beam Walking (BW) and Morris Water Maze (MWM) tasks, respectively. Confirming our previous findings, we showed that uridine administration reduced apoptotic cell damage on P10. No significant difference was observed between uridine and saline groups in early reflexes or sensorimotor coordination. On the other hand, rats receiving uridine displayed improved learning and memory in MWM during periadolescent period. We conclude that uridine treatment improves learning and memory in the long term by, probably, reducing apoptotic cell death in early newborn period. This is the first study to show beneficial cognitive effects of uridine in rats with brain damage.

Effects of Interrupted and Uninterrupted Occlusion of the Basilar Artery on Cerebral Blood Flow, and on Neurological and Histological Outcome in Rats with Subarachnoid Hemorrhage

Most neurosurgeons consider temporary vessel occlusion for aneurysmal clipping an effective technique that facilitates dissection between the aneurysm and the parent vessel. It is generally believed that repeated short periods of cerebral ischemia are safer for the brain than a single long episode. The aim of this study was to identify whether interrupted and uninterrupted vessel occlusion differs with regard to changes in brain tissue and cerebral hemodynamics after subarachnoid hemorrhage (SAH). Fifty Spraque Dawley rats (300–350 g) were placed under general anaesthesia and ventilated. The basilar artery was exposed through a transclival approach. Baseline local cerebral blood flow (LCBF) values was measured, and then the basilar artery was punctured, causing subarachnoid hemorrhage (SAH). Group I (n = 24) was subjected to 60 min of interrupted basilar artery occlusion, defined as 5 min of reperfusion after every 10 min of occlusion, group II (n = 26) 60 min of uninterrupted artery occlusion. Three days after completion of the experiment, each rat was neurologically evaluated and decapitated. Coronal brain slices were obtained and stained to assess infarct volume. Immediately after SAH, LCBF fell by 58% in group I, and by 52% in group II. In group I, each ischemic insult brought a similar reduction in LCBF, and after each release of the occlusion there was a rapid rise in flow. In group II, the LCBF values dropped initially and remained at low levels until the end of the study. The 2, 3, 5 triphenyltetrazolium chloride stained sections showed similar volumes of brainstem infarction in both groups (38.3 ± 9.2 mm 3 vs. 34.3 ± 8.7 mm 3, respectively; p > 0.05). The results suggest that there is no neuroprotective advantage to either interrupted or uninterrupted temporary blockage of blood flow during neurovascular procedures after SAH in the basilar artery region.

Uridine treatment protects against neonatal brain damage and long-term cognitive deficits caused by hyperoxia

Exposure to excessive oxygen in survivors of preterm birth is one of the factors that underlie the adverse neurological outcome in later life. Various pathological changes including enhanced apoptotic activity, oxidative stress and inflammation as well as decreased neuronal survival has been demonstrated in animal models of neonatal hyperoxia. The aim of the present study was to investigate the effect of administering uridine, an anti-apoptotic agent, on cellular, molecular and behavioral consequences of hyperoxia-induced brain damage in a neonatal rat model. For five days from birth, rat pups were either subjected continuously to room air (21% oxygen) or hyperoxia (80% oxygen) and received daily intraperitoneal (i.p.) injections of saline (0.9% NaCl) or uridine (500mg/kg). Two-thirds of all pups were sacrificed on postnatal day 5 (P5) in order to investigate apoptotic cell death, myelination and number of surviving neurons. One-thirds of pups were raised through P40 in order to evaluate early reflexes, sensorimotor coordination and cognitive functions followed by investigation of neuron count and myelination. We show that uridine treatment reduces apoptotic cell death and hypomyelination while increasing the number of surviving neurons in hyperoxic pups on P5. In addition, uridine enhances learning and memory performances in periadolescent rats on P40. These data suggest that uridine administered during the course of hyperoxic insult enhances cognitive functions at periadolescent period probably by reducing apoptotic cell death and preventing hypomyelination during the neonatal period in a rat model of hyperoxia-induced brain injury.