Yiqing Liu

Hypoxic-Ischemic Oligodendroglial Injury in Neonatal Rat Brain

Neonatal periventricular white matter injury is a major contributor to chronic neurologic dysfunction. In a neonatal rat stroke model, myelin basic protein (MBP) immunostaining reveals acute periventricular white matter injury. Yet, the extent to which myelin proteins can recover after neonatal hypoxic-ischemic injury is unknown. We developed a quantitative method to correlate the severity of the hypoxic-ischemic insult with the magnitude of loss of MBP immunostaining. Seven-day-old (P7) rats underwent right carotid ligation, followed by exposure to 8% oxygen for 1, 1.5, 2, or 2.5 h. On both P12 and P21, white matter integrity was evaluated by densitometric analysis of MBP immunostaining, and the amount of tissue injury was evaluated by morphometric measurements of cerebral hemisphere areas. The most severe hypoxic-ischemic insults (2.5 h) elicited marked reductions in MBP immunostaining ipsilaterally on both P12 and P21. In contrast, in mildly lesioned animals (1.5 h), MBP immunostaining was reduced ipsilaterally on P12, but 2 wk after lesioning, on P21, there was a substantial restoration of MBP immunostaining. The restoration in MBP immunostaining could reflect either functional recovery of injured oligodendroglia or proliferation and maturation of oligodendroglial precursors. Our data demonstrate that quantitative measurement of MBP immunostaining provides a sensitive indicator of acute oligodendroglial injury. Most importantly, we show that in this neonatal rodent stroke model, restoration of myelin proteins occurs after moderate, but not after more severe, cerebral hypoxia-ischemia.

Docosahexaenoic acid pretreatment confers neuroprotection in a rat model of perinatal cerebral hypoxia-ischemia

OBJECTIVE We hypothesized that pretreatment with docosahexaenoic acid (DHA), a potentially neuroprotective polyunsaturated fatty acid, would improve function and reduce brain damage in a rat model of perinatal hypoxia-ischemia. STUDY DESIGN Seven-day-old rats were divided into 3 treatment groups that received intraperitoneal injections of DHA 1, 2.5, or 5 mg/kg as DHA-albumin complex and 3 controls that received 25% albumin, saline, or no injection. Subsequently, rats underwent right carotid ligation followed by 90 minutes of 8% oxygen. Rats underwent sensorimotor testing (vibrissae-stimulated forepaw placing) and morphometric assessment of right-sided tissue loss on postnatal day 14. RESULTS DHA pretreatment improved forepaw placing response to near-normal levels (9.5 +/- 0.9 treatment vs 7.1 +/- 2.2 controls; normal = 10; P < .0001). DHA attenuated hemisphere damage compared with controls (P = .0155), with particular benefit in the hippocampus with 1 mg/kg (38% protection vs albumin controls). CONCLUSION DHA pretreatment improves functional outcome and reduces volume loss after hypoxia-ischemia in neonatal rats.

Early Appearance of Functional Deficits after Neonatal Excitotoxic and Hypoxic-Ischemic Injury: Fragile Recovery after Development and Role of the NMDA Receptor

We sought to determine whether neonatal rats that sustain unilateral cerebral hypoxic-ischemic or excitotoxic insults (1) manifest contralateral sensorimotor deficits during development or in adulthood and (2) recover from those deficits. Seven-day-old (P7) rats received a right intrastriatal injection of the glutamate analog N-methyl-D-aspartate (NMDA). Unilateral hypoxia-ischemia (HI) was induced by right carotid ligation followed by 1.5 h in 8% O2. Both procedures produce neuronal loss in the striatum and sensorimotor cortex. Nonlesioned controls were included. We scored percent forepaw placement on the edge of a horizontal surface, with lateral vibrissa stimulation, from P9 to P19, and at P33 and P50. Then, on P50, rats were treated with the NMDA antagonist MK-801 to determine whether deficits could be reinstated. NMDA- and HI-lesioned rats exhibited a deficit in contralateral vibrissa-stimulated forepaw placing that emerged during the second week of life. Yet, by P33 and P50, the lesioned groups and controls were indistinguishable. MK-801 injection on P50 resulted in transient reinstatement of the placing deficit. After unilateral neonatal excitotoxic or HI brain injury, contralateral sensorimotor deficits are detected, but in many animals, these deficits have resolved by adulthood. Thus, timing of sensorimotor tests may influence their sensitivity for detection of focal neuropathology originating in the neonatal period.

Treatment with docosahexaenoic acid after hypoxia-ischemia improves forepaw placing in a rat model of perinatal hypoxia-ischemia.

OBJECTIVE Docosahexaenoic acid (DHA) is a dietary fatty acid with neuroprotective properties. We hypothesized that DHA treatment after hypoxia-ischemia would improve function and reduce brain volume loss in a perinatal rat model. STUDY DESIGN Seven-day-old Wistar rat pups from 7 litters (n = 84) underwent right carotid ligation, followed by 8% O(2) for 90 minutes. Fifteen minutes after hypoxia-ischemia, pups were divided into 3 treatment groups (intraperitoneal injections of DHA 1, 2.5, or 5 mg/kg) and 2 control groups (25% albumin or saline). At 14 days, rats underwent vibrissae-stimulated forepaw placing testing, and bilateral regional volumes were calculated for cortex, striatum, hippocampus, and hemisphere. RESULTS Posthypoxia-ischemia treatment with DHA acid significantly improved vibrissae forepaw placing (complete responses: 8.5 ± 2 treatment vs 7.4 ± 2 controls; normal = 10; P = .032, t test). Postinjury DHA treatment did not attenuate brain volume loss in any region. CONCLUSION Posthypoxia-ischemia DHA treatment significantly improves functional outcome.

Docosahexaenoic Acid augments hypothermic neuroprotection in a neonatal rat asphyxia model

Background: In neonatal rats, early post-hypoxia-ischemia (HI) administration of the omega-3 fatty acid docosahexaenoic acid (DHA) improves sensorimotor function, but does not attenuate brain damage. Objective: To determine if DHA administration in addition to hypothermia, now standard care for neonatal asphyxial brain injury, attenuates post-HI damage and sensorimotor deficits. Methods: Seven-day-old (P7) rats underwent right carotid ligation followed by 90 min of 8% O2 exposure. Fifteen minutes later, pups received injections of DHA 2.5 mg/kg (complexed to 25% albumin) or equal volumes of albumin. After a 1-hour recovery, pups were cooled (3 h, 30°C). Sensorimotor and pathology outcomes were initially evaluated on P14. In subsequent experiments, sensorimotor function was evaluated on P14, P21, and P28; histopathology was assessed on P28. Results: At P14, left forepaw function scores (normal: 20/20) were near normal in DHA + hypothermia-treated animals (mean ± SD 19.7 ± 0.7 DHA + hypothermia vs. 12.7 ± 3.5 albumin + hypothermia, p < 0.0001) and brain damage was reduced (mean ± SD right hemisphere damage 38 ± 17% with DHA + hypothermia vs. 56 ± 15% with albumin + hypothermia, p = 0.003). Substantial improvements on three sensorimotor function measures and reduced brain damage were evident up to P28. Conclusion: Unlike post-HI treatment with DHA alone, treatment with DHA + hypothermia produced both sustained functional improvement and reduced brain damage after neonatal HI.

Maternal high-fat diet influences outcomes after neonatal hypoxic-ischemic brain injury in rodents

The typical US diet has >30% calories from fat; yet, typical laboratory diets contain 17% calories from fat. This disparity could confound the clinical relevance of findings in cerebral ischemia models. We compared outcomes after neonatal brain injury in offspring of rat dams fed standard low-fat chow (17% fat calories) or a higher fat diet (34% fat calories) from day 7 of pregnancy. On postnatal day 7, hypoxic-ischemic injury was induced by right carotid ligation, followed by 60, 75 or 90 min 8% oxygen exposure. Sensorimotor function, brain damage, and serum and brain fatty acid content were compared 1 to 4 weeks later. All lesioned animals developed left forepaw placing deficits; scores were worse in the high-fat groups (p < 0.0001, ANOVA). Similarly, reductions in left forepaw grip strength were more pronounced in the high-fat groups. Severity of right hemisphere damage increased with hypoxia-ischemia duration but did not differ between diet groups. Serum and brain docosahexaenoic acid fatty acid fractions were lower in high-fat progeny (p < 0.05, ANOVA). We speculate that the high-fat diet disrupted docosahexaenoic acid-dependent recovery mechanisms. These findings have significant implications both for refinement of neonatal brain injury models and for understanding the impact of maternal diet on neonatal neuroplasticity.