Foveal thickness and its association with visual acuity in adults born preterm with very low birth weight: A two-country birth cohort study.

PURPOSE: To explore foveal and parafoveal thickness in adults born preterm with very low birth weight (VLBW) and its association with best-corrected visual acuity (BCVA) and gestational age (GA) compared to adults born at term. METHODS: In a joint study of the Helsinki Study of Very Low Birth Weight Adults (Finland) and the NTNU Low Birth Weight Life study (Norway), 106 VLBW and 143 term-born controls were examined with spectral-domain optical coherence tomography and BCVA at age 31-43 years. Thickness of retinal layers was segmented in the foveal and parafoveal areas of the macula. RESULTS: The total retinal thickness in the foveal area was thicker in VLBW adults compared with controls; mean (SD): 292.5 µm (28.2) and 272.4 µm (20.2); p < 0.001, and thinner in the parafoveal areas of the macula. These findings could be explained by a thicker inner retinal layer in the foveal area found in VLBW adults compared with controls (mean difference 20.4 µm; CI: 15.0 to 25.9), where a thicker fovea was associated with lower GA, but not BCVA. CONCLUSION: Adults born preterm with VLBW had a thicker retina in the foveal area than controls and this was associated with GA, but not with BCVA. These changes seem to be related to a thicker inner retinal layer in VLBW adults. The findings imply that signs of macular underdevelopment are still present in adulthood, but not necessarily related to reduced visual function.

Visual outcomes and their association with grey and white matter microstructure in adults born preterm with very low birth weight.

Individuals born with very low birth weight (VLBW; < 1500 g) have a higher risk of reduced visual function and brain alterations. In a longitudinal cohort study, we assessed differences in visual outcomes and diffusion metrics from diffusion tensor imaging (DTI) at 3 tesla in the visual white matter pathway and primary visual cortex at age 26 in VLBW adults versus controls and explored whether DTI metrics at 26 years was associated with visual outcomes at 32 years. Thirty-three VLBW adults and 50 term-born controls was included in the study. Visual outcomes included best corrected visual acuity, contrast sensitivity, P100 latency, and retinal nerve fibre layer thickness. Mean diffusivity, axial diffusivity, radial diffusivity, and fractional anisotropy was extracted from seven regions of interest in the visual pathway: splenium, genu, and body of corpus callosum, optic radiations, lateral geniculate nucleus, inferior-fronto occipital fasciculus, and primary visual cortex. On average the VLBW group had lower contrast sensitivity, a thicker retinal nerve fibre layer and higher axial diffusivity and radial diffusivity in genu of corpus callosum and higher radial diffusivity in optic radiations than the control group. Higher fractional anisotropy in corpus callosum areas were associated with better visual function in the VLBW group but not the control group.

Visual function in adults born preterm with very low birth weight-A two-country birth cohort study.

PURPOSE: The purpose of the study was to investigate visual function and vision-related general health in adults that were born preterm with very low birth weight (VLBW: birth weight < 1500 g) in their 30s-40s. METHODS: We recruited 137 adults born preterm with VLBW and 158 term-born controls aged 31-43 years from two birth cohorts: the Helsinki Study of Very Low Birth Weight Adults (Finland) and the NTNU Low Birth Weight in a Lifetime Perspective study (Norway). We used neonatal data and measured refraction, best-corrected visual acuity (BCVA) using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart, contrast sensitivity, visual fields, intraocular pressure (IOP), self-reported vision-targeted health status with the National Eye Institute Visual Function Questionnaire-25. RESULTS: VLBW adults had a lower BCVA ETDRS score than controls: mean (SD) better eye 86.7 (13.4) versus 90.2 (4.4), p = 0.02; mean (SD) worse eye 82.3 (14.9) versus 87.6 (4.6), p = 0.003. VLBW adults also had lower contrast sensitivity thresholds in several spatial frequencies and scored lower than controls in eight out of the 12 subscales of self-reported vision-targeted health status. Refraction, visual fields and IOP were similar between groups. Two VLBW participants were blind. None had been treated for retinopathy of prematurity. CONCLUSION: We suggest that lower visual function and vision-related health represent life-long consequences of prematurity and VLBW in the studied 31- to 43-year-old cohort. The underlying mechanisms remain to be determined.

Retinal structure and visual pathway function at school age in children born extremely preterm: a population-based study.

BACKGROUND: Children born extremely preterm (gestational age < 28 weeks) show reduced visual function even without any cerebral or ophthalmological neonatal diagnosis. In this study, we aimed to assess the retinal structure with optical coherence tomography (OCT) and visual function with pattern-reversal visual evoked potentials (PR-VEPs) in a geographically defined population-based cohort of school-aged children born extremely preterm. Moreover, we aimed to explore the association between measures of retinal structure and visual pathway function in this cohort. METHODS: All children born extremely preterm from 2006-2011 (n = 65) in Central Norway were invited to participate. Thirty-six children (55%) with a median age of 13 years (range = 10-16) were examined with OCT, OCT-angiography (OCT-A), and PR-VEPs. The foveal avascular zone (FAZ) and circularity, central macular vascular density, and flow were measured on OCT-A images. Central retinal thickness, circumpapillary retinal nerve fibre layer (RNFL) and inner plexiform ganglion cell layer (IPGCL) thickness were measured on OCT images. The N70-P100 peak-to-peak amplitude and N70 and P100 latencies were assessed from PR-VEPs. RESULTS: Participants displayed abnormal retinal structure and P100 latencies (≥ 2 SD) compared to reference populations. Moreover, there was a negative correlation between P100 latency in large checks and RNFL (r = -.54, p = .003) and IPGCL (r = -.41, p = .003) thickness. The FAZ was smaller (p = .003), macular vascular density (p = .006) and flow were higher (p = .004), and RNFL (p = .006) and IPGCL (p = .014) were thinner in participants with ROP (n = 7). CONCLUSION: Children born extremely preterm without preterm brain injury sequelae have signs of persistent immaturity of retinal vasculature and neuroretinal layers. Thinner neuroretinal layers are associated with delayed P100 latency, prompting further exploration of the visual pathway development in preterms.

Cost consequences of task-shifting intravitreal injections from physicians to nurses in a tertiary hospital in Norway.

BACKGROUND: Anti-vascular endothelial growth factor is a medicine administered intravitreally by an injection to maintain visual acuity in patients with a variety of retinal diseases. The demand for this treatment has grown considerably in the westernized world the last two decades and will continue to increase due to an aging population. Because of the high volume, injections seize enormous resources and represent high costs for both hospitals and society. Task-shifting of injections from physicians to nurses may be a means to reduce such costs, however the magnitude of possible savings has been poorly investigated. To this end we investigated changes in the hospital costs per injection, six-year cost projections of physician- versus nurse-administered injections for a Norwegian tertiary hospital and we compared the societal costs per patient per year. METHODS: Patients (n = 318) were randomized to either physician- or nurse administered injections, and data were prospectively collected. Hospital costs per injection were calculated as the sum of training costs, personnel time and running expenses. The number of injections for the years 2014 - 21 from a Norwegian tertiary hospital was combined with age group specific injection prevalence and population projections to calculate cost projections for 2022 - 27. Societal costs per patient were calculated as the sum of hospital costs, transport costs for patients, caregivers' use of time, costs of ophthalmology consultations and community-based homecare. RESULTS: The hospital costs per injection were 5.5 € higher for physicians compared to nurses (281.6 € versus 276.1 €). Cost projections estimated an annual hospital saving of task-shifting of 48 921 € for 2022 - 27. Societal costs per patient did not differ significantly between the two groups (mean 4988 € vs 5418 €, p = 0.398). CONCLUSION: Task-shifting of injections from physicians to nurses can reduce hospital costs and increase the flexibility of physician resources. The annual savings are modest, but increased demand for injections might increase future cost savings. To achieve future savings for society, organizing ophthalmology consultations and injections on the same day to reduce the number of visits might be a solution. TRIAL REGISTRATION: ClinicalTrials.gov NCT02359149 (09/02/2015).

Visual function correlates with neurodevelopment in a population cohort of school-aged children born extremely preterm.

AIM: To investigate visual function and neurodevelopment in a geographically defined population cohort of school-aged children born extremely preterm. METHODS: All children born extremely preterm in Central Norway between 2006 and 2011 (n=65) were identified, and 36 (median age, min/max: 13, 10/16) were included. Best-corrected visual acuity (BCVA), contrast sensitivity (four spatial frequencies), parent-reported challenges and neuropsychological testing in learning, executive functions, motor skills, perception, reaction time, working and visual memory, processing speed, and pattern separation were measured. Brain MRI (3T) was acquired and read by a neuroradiologist. RESULTS: Median (min/max) BCVA letter score was 85 (35/91) in the better and 82 (13/89) in the worse eye. ROP participants (n=7) had lower contrast sensitivity in the two highest spatial frequencies (p = 0.024 and p = 0.004). Parent-reported challenges correlated negatively with BCVA (learning: p = 0.014; executive functions: p = 0.002; motor skills: p = 0.000; and perception: p = 0.001), while motor skills correlated negatively with one (p = 0.010) and perception with two (p = 0.003 and p = 0.009) of four spatial frequencies. Neuropsychological tests were reduced relative to norms. None had MRI-verified preterm brain injury. CONCLUSION: Visual function was subnormal and correlated with parent-reported challenges in a small cohort of extremely preterm school-aged children, indicating that visual function may be a marker of neurodevelopmental outcomes.

Patient satisfaction following a switch from treat-and-extend to observe-and-plan regimen in age-related macular degeneration.

OBJECTIVE: Standard treatment of neovascular age-related macular degeneration (nAMD) is intravitreal injections (IVI) of antivascular endothelial growth factor (anti-VEGF) according to treat-and-extend (TnE). Observe-and-plan (OnP), a new regimen based on each individual's relapse interval lead to fewer clinical visits and has so far shown to be safe in treatment-naïve patients. In this study, we explore patient satisfaction and safety in nAMD when switching from TnE to OnP. METHODS AND ANALYSIS: 38 participants treated acording to TnE for ≥12 months were included and switched from TnE to OnP with their last stable interval. Main outcome was patient satisfaction (Leeds Satisfaction Questionnaire). Secondary outcomes were best-corrected visual acuity (BCVA), central retinal thickness (CRT) before and 12 months after switch and number of monitoring visits and injections of anti-VEGF 12 months prior to and following switch. RESULTS: Mean patient satisfaction was higher (3.7±0.5 SD) at 12 months after switch from TnE to OnP than before (3.6±0.5 SD, p=0.009, response rate 76%). BCVA and CRT were unchanged. Number of monitoring visits and injections were lower in the 12 months following than prior to switch (p<0.001). CONCLUSION: A switch from TnE to OnP in a non-treatment-naïve population resulted in higher patient satisfaction, while maintaining stable BCVA. This indicates that OnP may be applicable in the large group of nAMD patients that have received IVI for several years. OnP may alleviate the treatment burden on both individual and society of frequent clinical visits while increasing patient satisfaction.

Visuopathy of prematurity: is retinopathy just the tip of the iceberg?

Research on retinopathy of prematurity (ROP) focuses mainly on the abnormal vascularization patterns that are directly visible for ophthalmologists. However, recent findings indicate that children born prematurely also exhibit changes in the retinal cellular architecture and along the dorsal visual stream, such as structural changes between and within cortical areas. Moreover, perinatal sustained systemic inflammation (SSI) is associated with an increased risk for ROP and the visual deficits that follow. In this paper, we propose that ROP might just be the tip of an iceberg we call visuopathy of prematurity (VOP). The VOP paradigm comprises abnormal vascularization of the retina, alterations in retinal cellular architecture, choroidal degeneration, and abnormalities in the visual pathway, including cortical areas. Furthermore, VOP itself might influence the developmental trajectories of cerebral structures and functions deemed responsible for visual processing, thereby explaining visual deficits among children born preterm.

Task shifting of intraocular injections from physicians to nurses: a randomized single-masked noninferiority study.

PURPOSE: To test if task shifting of intraocular injections to nurses in a real-world setting can result in similar visual function outcome with equal safety profile. METHOD: All patients with either age-related macular degeneration, retinal vein occlusion or diabetic macular oedema remitted to intraocular injections at a tertiary ophthalmology department in Norway between March 2015 and May 2017, were asked to participate. The participants were randomized to either nurse- or physician-administered intraocular injections of anti-vascular endothelial growth factor. The primary outcome measure was change in best-corrected visual acuity from baseline to 1-year follow-up. The mean difference in the primary outcome between the groups was analysed by a noninferiority test with a margin of three letters in disfavour of the nurse group. Adverse events were recorded. RESULTS: Three hundred and forty-two patients entered the study. Two hundred and fifty-nine completed the 1-year follow-up and were included in the study sample for the analysis of the primary outcome. Nurse-administered intraocular injections were noninferior to physician-administered injections with 0.7 and 1.6 letters gained, respectively (95% CI of the mean difference, -2.9 to 1.0; p = 0.019, one-sided t-test). Two thousand and seventy-seven injections and three ocular adverse events were recorded. CONCLUSION: Task shifting of intraocular injections to nurses can be performed without increased risk to visual function. Such a task shift can alleviate the burden of performing intraocular injections in ophthalmology departments. To our knowledge, this is the first RCT on task shifting of a surgical procedure from physicians to nurses in a high-income country.

Transient effect of melatonin treatment after neonatal hypoxic-ischemic brain injury in rats.

Melatonin has potential neuroprotective capabilities after neonatal hypoxia-ischemia (HI), but long-term effects have not been investigated. We hypothesized that melatonin treatment directly after HI could protect against early and delayed brain injury. Unilateral HI brain injury was induced in postnatal day 7 rats. An intraperitoneal injection of either melatonin or vehicle was given at 0, 6 and 25 hours after hypoxia. In-vivo MRI was performed 1, 7, 20 and 43 days after HI, followed by histological analysis. Forelimb asymmetry and memory were assessed at 12-15 and at 36-43 days after HI. More melatonin treated than vehicle treated animals (54.5% vs 15.8%) developed a mild injury characterized by diffusion tensor values, brain volumes, histological scores and behavioral parameters closer to sham. However, on average, melatonin treatment resulted only in a tendency towards milder injury on T2-weighted MRI and apparent diffusion coefficient maps day 1 after HI, and not improved long-term outcome. These results indicate that the melatonin treatment regimen of 3 injections of 10 mg/kg within the first 25 hours only gave a transient and subtle neuroprotective effect, and may not have been sufficient to mitigate long-term brain injury development following HI.

Retinopathy of prematurity, visual and neurodevelopmental outcome, and imaging of the central nervous system.

Recent findings indicate that retinopathy of prematurity (ROP), presently classified by clinical examinations of retinal vascular tissue, is associated with structural alterations of the central nervous system. Such alterations may be the correlate of the association between ROP and impaired long-term neurocognitive and visual development. The advent of imaging techniques such as structural and diffusion tensor magnetic resonance imaging of the brain, and optical coherence tomography of the retina, will allow the complete visual system to be characterized in greater detail. It has been suggested that ROP may be not only a vascular, but a neurovascular disease, being part of a spectrum that includes pathological development in both the retinal and cerebral neurovascular interphase. We review the present knowledge in the field and point to future directions for research to tackle these questions.

Early metabolite changes after melatonin treatment in neonatal rats with hypoxic-ischemic brain injury studied by in-vivo1H MR spectroscopy.

Melatonin is a promising neuroprotective agent after perinatal hypoxic-ischemic (HI) brain injury. We used in-vivo 1H magnetic resonance spectroscopy to investigate effects of melatonin treatment on brain metabolism after HI. Postnatal day 7 Sprague-Dawley rats with unilateral HI brain injury were treated with either melatonin 10 mg/kg dissolved in phosphate-buffered saline (PBS) with 5% dimethyl sulfoxide (DMSO) or vehicle (5% DMSO and/or PBS) directly and at 6 hours after HI. 1H MR spectra from the thalamus in the ipsilateral and contralateral hemisphere were acquired 1 day after HI. Our results showed that injured animals had a distinct metabolic profile in the ipsilateral thalamus compared to sham with low concentrations of total creatine, choline, N-acetyl aspartate (NAA), and high concentrations of lipids. A majority of the melatonin-treated animals had a metabolic profile characterized by higher total creatine, choline, NAA and lower lipid levels than other HI animals. When comparing absolute concentrations, melatonin treatment resulted in higher glutamine levels and lower lipid concentrations compared to DMSO treatment as well as higher macromolecule levels compared to PBS treatment day 1 after HI. DMSO treated animals had lower concentrations of glucose, creatine, phosphocholine and macromolecules compared to sham animals. In conclusion, the neuroprotective effects of melatonin were reflected in a more favorable metabolic profile including reduced lipid levels that likely represents reduced cell injury. Neuroprotective effects may also be related to the influence of melatonin on glutamate/glutamine metabolism. The modulatory effects of the solvent DMSO on cerebral energy metabolism might have masked additional beneficial effects of melatonin.

Retinopathy of prematurity: inflammation, choroidal degeneration, and novel promising therapeutic strategies.

Retinopathy of prematurity (ROP) is an important cause of childhood blindness globally, and the incidence is rising. The disease is characterized by initial arrested retinal vascularization followed by neovascularization and ensuing retinal detachment causing permanent visual loss. Although neovascularization can be effectively treated via retinal laser ablation, it is unknown which children are at risk of entering this vision-threatening phase of the disease. Laser ablation may itself induce visual field deficits, and there is therefore a need to identify targets for novel and less destructive treatments of ROP. Inflammation is considered a key contributor to the pathogenesis of ROP. A large proportion of preterm infants with ROP will have residual visual loss linked to loss of photoreceptor (PR) and the integrity of the retinal pigment epithelium (RPE) in the macular region. Recent studies using animal models of ROP suggest that choroidal degeneration may be associated with a loss of integrity of the outer retina, a phenomenon so far largely undescribed in ROP pathogenesis. In this review, we highlight inflammatory and neuron-derived factors related to ROP progression, as well, potential targets for new treatment strategies. We also introduce choroidal degeneration as a significant cause of residual visual loss following ROP. We propose that ROP should no longer be considered an inner retinal vasculopathy only, but also a disease of choroidal degeneration affecting both retinal pigment epithelium and photoreceptor integrity.

Glucose and Intermediary Metabolism and Astrocyte-Neuron Interactions Following Neonatal Hypoxia-Ischemia in Rat.

Neonatal hypoxia-ischemia (HI) and the delayed injury cascade that follows involve excitotoxicity, oxidative stress and mitochondrial failure. The susceptibility to excitotoxicity of the neonatal brain may be related to the capacity of astrocytes for glutamate uptake. Furthermore, the neonatal brain is vulnerable to oxidative stress, and the pentose phosphate pathway (PPP) may be of particular importance for limiting this kind of injury. Also, in the neonatal brain, neurons depend upon de novo synthesis of neurotransmitters via pyruvate carboxylase in astrocytes to increase neurotransmitter pools during normal brain development. Several recent publications describing intermediary brain metabolism following neonatal HI have yielded interesting results: (1) Following HI there is a prolonged depression of mitochondrial metabolism in agreement with emerging evidence of mitochondria as vulnerable targets in the delayed injury cascade. (2) Astrocytes, like neurons, are metabolically impaired following HI, and the degree of astrocytic malfunction may be an indicator of the outcome following hypoxic and hypoxic-ischemic brain injury. (3) Glutamate transfer from neurons to astrocytes is not increased following neonatal HI, which may imply that astrocytes fail to upregulate glutamate uptake in response to the massive glutamate release during HI, thus contributing to excitotoxicity. (4) In the neonatal brain, the activity of the PPP is reduced following HI, which may add to the susceptibility of the neonatal brain to oxidative stress. The present review aims to discuss the metabolic temporal alterations observed in the neonatal brain following HI.

Anaplerosis for Glutamate Synthesis in the Neonate and in Adulthood.

A central task of the tricarboxylic acid (TCA, Krebs, citric acid) cycle in brain is to provide precursors for biosynthesis of glutamate, GABA, aspartate and glutamine. Three of these amino acids are the partners in the intricate interaction between astrocytes and neurons and form the so-called glutamine-glutamate (GABA) cycle. The ketoacids α-ketoglutarate and oxaloacetate are removed from the cycle for this process. When something is removed from the TCA cycle it must be replaced to permit the continued function of this essential pathway, a process termed anaplerosis. This anaplerotic process in the brain is mainly carried out by pyruvate carboxylation performed by pyruvate carboxylase. The present book chapter gives an introduction and overview into this carboxylation and additionally anaplerosis mediated by propionyl-CoA carboxylase under physiological conditions in the adult and in the developing rodent brain. Furthermore, examples are given about pathological conditions in which anaplerosis is disturbed.

Nurse-administered intravitreal injections of anti-VEGF: study protocol for noninferiority randomized controlled trial of safety, cost and patient satisfaction.

BACKGROUND: Intravitreal injections (IVI) of anti-vascular endothelial growth factor (anti-VEGF) now improve or stabilize visual acuity in a number of previously untreatable eye diseases, of which the main are age-related macular degeneration, retinal vein occlusion and diabetic macular edema. Most patients require multiple injections over lengthy periods of time and the prevalence of treatable conditions is increasing. Anti-VEGF IVI normally administered by physicians, therefore represent a considerable workload on ophthalmologic clinics and will continue to do so in the near future. Nurse-administered IVI may relieve this workload, but the safety, cost and patient satisfaction of such an extended role for nurses in ophthalmologic clinics has not earlier been investigated. To investigate these outcomes following independent anti-VEGF IVI by trained nurses, a noninferiority randomized controlled trial is being conducted. METHODS/DESIGN: Patients eligible for anti-VEGF treatment, minimum 304, are recruited and randomized to IVI administration by either trained nurses or physicians. The primary outcome is safety, measured by difference in mean change in visual acuity between the two groups during an observation period of 12 months. Secondary outcomes are incidence of ocular adverse events, cost per patient and patient satisfaction. DISCUSSION: This study protocol describes the design of the first randomized controlled trial of nurse-administered IVI of anti-VEGF. The study is designed to examine safety, cost and patient satisfaction during 12 months follow-up. TRIAL REGISTRATION: ClinicalTrials.gov NCT02359149 . Registered February 4, 2015.

No improvement of neuronal metabolism in the reperfusion phase with melatonin treatment after hypoxic-ischemic brain injury in the neonatal rat.

Mitochondrial impairment is a key feature underlying neonatal hypoxic-ischemic (HI) brain injury and melatonin is potentially neuroprotective through its effects on mitochondria. In this study, we have used (1) H and (13) C NMR spectroscopy after injection of [1-(13) C]glucose and [1,2-(13) C]acetate to examine neuronal and astrocytic metabolism in the early reperfusion phase after unilateral HI brain injury in 7-day-old rat pups, exploring the effects of HI on mitochondrial function and the potential protective effects of melatonin on brain metabolism. One hour after hypoxia-ischemia, astrocytic metabolism was recovered and glycolysis was normalized, whereas mitochondrial metabolism in neurons was clearly impaired. Pyruvate carboxylation was also lower in both hemispheres after HI. The transfer of glutamate from neurons to astrocytes was higher whereas the transfer of glutamine from astrocytes to neurons was lower 1 h after HI in the contralateral hemisphere. Neuronal metabolism was equally affected in pups treated with melatonin (10 mg/kg) immediately after HI as in vehicle treated pups indicating that the given dose of melatonin was not capable of protecting the neuronal mitochondria in this early phase after HI brain injury. However, any beneficial effects of melatonin might have been masked by modulatory effects of the solvent dimethyl sulfoxide on cerebral metabolism. Neuronal and astrocytic metabolism was examined by (13) C and (1) H NMR spectroscopy in the early reperfusion phase after unilateral hypoxic-ischemic brain injury and melatonin treatment in neonatal rats. One hour after hypoxia-ischemia astrocytic mitochondrial metabolism had recovered and glycolysis was normalized, whereas mitochondrial metabolism in neurons was impaired. Melatonin treatment did not show a protective effect on neuronal metabolism.

Glucose metabolism and astrocyte-neuron interactions in the neonatal brain.

Glucose is essentially the sole fuel for the adult brain and the mapping of its metabolism has been extensive in the adult but not in the neonatal brain, which is believed to rely mainly on ketone bodies for energy supply. However, glucose is absolutely indispensable for normal development and recent studies have shed light on glycolysis, the pentose phosphate pathway and metabolic interactions between astrocytes and neurons in the 7-day-old rat brain. Appropriately (13)C labeled glucose was used to distinguish between glycolysis and the pentose phosphate pathway during development. Experiments using (13)C labeled acetate provided insight into the GABA-glutamate-glutamine cycle between astrocytes and neurons. It could be shown that in the neonatal brain the part of this cycle that transfers glutamine from astrocytes to neurons is operating efficiently while, in contrast, little glutamate is shuttled from neurons to astrocytes. This lack of glutamate for glutamine synthesis is compensated for by anaplerosis via increased pyruvate carboxylation relative to that in the adult brain. Furthermore, compared to adults, relatively more glucose is prioritized to the pentose phosphate pathway than glycolysis and pyruvate dehydrogenase activity. The reported developmental differences in glucose metabolism and neurotransmitter synthesis may determine the ability of the brain at various ages to resist excitotoxic insults such as hypoxia-ischemia.

Altered astrocyte-neuronal interactions after hypoxia-ischemia in the neonatal brain in female and male rats.

BACKGROUND AND PURPOSE: Increased susceptibility to excitotoxicity of the neonatal brain after hypoxia-ischemia (HI) may be caused by limited capacity of astrocytes for glutamate uptake, and mitochondrial failure probably plays a key role in the delayed injury cascade. Male infants have poorer outcome than females after HI, possibly linked to differential intermediary metabolism. METHODS: [1-(13)C]glucose and [1,2-(13)C]acetate were injected at zero, 6, and 48 hours after unilateral HI in 7-day-old rats. Intermediary metabolism was analyzed with magnetic resonance spectroscopy. RESULTS: Mitochondrial metabolism was generally reduced in the ipsilateral hemisphere for ≤6 hours after HI, whereas contralaterally, it was reduced in neurons but not in astrocytes. Transfer of glutamate from neurons to astrocytes was increased in the contralateral, but not in the ipsilateral hemisphere at 0 hour, and reduced bilaterally at 6 hours after HI. The transfer of glutamine from astrocytes to glutamatergic neurons was unaltered in both hemispheres, whereas the transfer of glutamine to GABAergic neurons was increased ipsilaterally at 0 hour. Anaplerosis (astrocytes) was decreased, whereas partial pyruvate recycling (astrocytes) was increased directly after HI. Male pups had lower astrocytic mitochondrial metabolism than females immediately after HI, whereas that of females was reduced longer and encompassed both neurons and astrocytes. CONCLUSIONS: The prolonged depression in mitochondrial metabolism indicates that mitochondria are vulnerable targets in the delayed injury after neonatal HI. The degree of astrocytic malfunction may be a valid indicator of outcome after hypoxic/HI brain injury and may be linked to the differential outcome in males and females.