Pediatric de novo movement disorders and ataxia in the context of SARS-CoV-2.

OBJECTIVE: In the fourth year of the COVID-19 pandemic, mortality rates decreased, but the risk of neuropsychiatric disorders remained the same, with a prevalence of 3.8% of pediatric cases, including movement disorders (MD) and ataxia. METHODS: In this study, we report on a 10-year-old girl with hemichorea after SARS-CoV-2 infection and immunostained murine brain with patient CSF to identify intrathecal antibodies. Additionally, we conducted a scoping review of children with MD and ataxia after SARS-CoV-2 infection. RESULTS: We detected antibodies in the patient's CSF binding unknown antigens in murine basal ganglia. The child received immunosuppression and recovered completely. In a scoping review, we identified further 32 children with de novo MD or ataxia after COVID-19. While in a minority of cases, MD or ataxia were a symptom of known clinical entities (e.g. ADEM, Sydenham's chorea), in most children, the etiology was suspected to be of autoimmune origin without further assigned diagnosis. (i) Children either presented with ataxia (79%), but different from the well-known postinfectious acute cerebellar ataxia (older age, less favorable outcome, or (ii) had hypo-/hyperkinetic MD (21%), which were choreatic in most cases. Besides 14% of spontaneous recovery, immunosuppression was necessary in 79%. Approximately one third of children only partially recovered. CONCLUSIONS: Infection with SARS-CoV-2 can trigger de novo MD in children. Most patients showed COVID-19-associated-ataxia and fewer-chorea. Our data suggest that patients benefit from immunosuppression, especially steroids. Despite treatment, one third of patients recovered only partially, which makes up an increasing cohort with neurological sequelae.

Hodgkin Lymphoma Cell Lines and Tissues Express mGluR5: A Potential Link to Ophelia Syndrome and Paraneoplastic Neurological Disease.

Ophelia syndrome is characterized by the coincidence of severe neuropsychiatric symptoms, classical Hodgkin lymphoma, and the presence of antibodies to the metabotropic glutamate 5 receptor (mGluR5). Little is known about the pathogenetic link between these symptoms and the role that anti-mGluR5-antibodies play. We investigated lymphoma tissue from patients with Ophelia syndrome and with isolated classical Hodgkin lymphoma by quantitative immunocytochemistry for mGluR5-expression. Further, we studied the L-1236, L-428, L-540, SUP-HD1, KM-H2, and HDLM-2 classical Hodgkin lymphoma cell lines by FACS and Western blot for mGluR5-expression, and by transcriptome analysis. mGluR5 surface expression differed significantly in terms of receptor density, distribution pattern, and percentage of positive cells. The highest expression levels were found in the L-1236 line. RNA-sequencing revealed more than 800 genes that were higher expressed in the L-1236 line in comparison to the other classical Hodgkin lymphoma cell lines. High mGluR5-expression was associated with upregulation of PI3K/AKT and MAPK pathways and of downstream targets (e.g., EGR1) known to be involved in classical Hodgkin lymphoma progression. Finally, mGluR5 expression was increased in the classical Hodgkin lymphoma-tissue of our Ophelia syndrome patient in contrast to five classical Hodgkin lymphoma-patients without autoimmune encephalitis. Given the association of encephalitis and classical Hodgkin lymphoma in Ophelia syndrome, it is possible that mGluR5-expression in classical Hodgkin lymphoma cells not only drives tumor progression but also triggers anti-mGluR5 encephalitis even before classical Hodgkin lymphoma becomes manifest.

Real-World Experience Treating Pediatric Epilepsy Patients With Cenobamate.

Introduction: In one third of all patients with epilepsy, seizure freedom is not achieved through anti-seizure medication (ASM). These patients have an increased risk of earlier death, poorer cognitive development, and reduced quality of life. Cenobamate (CNB) has recently been approved as a promising novel ASM drug for the treatment of adults with focal-onset epilepsy. However, there is little experience for its application in pediatric patients. Methods: In a multicenter study we evaluated retrospectively the outcome of 16 pediatric patients treated "off label" with CNB. Results: In 16 patients with a mean age of 15.38 years, CNB was started at an age of 15.05 years due to DRE. Prior to initiation of therapy, an average of 10.56 (range 3-20) ASM were prescribed. At initiation, patients were taking 2.63 (range 1-4) ASM. CNB was increased by 0.47 ± 0.27mg/kg/d every 2 weeks with a mean maximum dosage of 3.1 mg/kg/d (range 0.89-7) and total daily dose of 182.81 mg (range 50-400 mg). Seizure freedom was achieved in 31.3% and a significant seizure reduction of >50% in 37.5%. Adverse events occurred in 10 patients with fatigue/somnolence as the most common. CNB is taken with high adherence in all but three patients with a median follow-up of 168.5 days. Conclusion: Cenobamate is an effective ASM for pediatric patients suffering from drug-resistant epilepsy. In addition to excellent seizure reduction or freedom, it is well-tolerated. Cenobamate should be considered as a novel treatment for DRE in pediatric patients.

Modified Zipper Method, a Promising Treatment Option in Severe Pediatric Immune-Mediated Neurologic Disorders.

OBJECTIVE: To introduce and evaluate a modified version of the "zipper method"-a treatment strategy alternating intravenous immunoglobulin (IVIG) and plasma exchange (PLEX) first reported for 9 pediatric cases of Guillain-Barré syndrome in 2018-for treatment of severe immune-mediated neurologic disorders in children. METHODS: The modified zipper method comprised longer intervals between PLEX-IVIG cycles (48 hours instead of 24 hours), more cycles (7-10 instead of 5), a consistent plasma volume exchange (instead of the original multistep approach), and variable infusion times for IVIGs (4-8 hours). The modified zipper method was applied as an individual treatment approach once standard therapy failed. The follow-up ranged from 6 months to 2 years. Cases were analyzed retrospectively. Disease severity was mainly quantified by the Guillain-Barré syndrome disability score. RESULTS: Four children (9-15 years) with (1) Miller-Fisher syndrome, (2) Bickerstaff brainstem encephalitis, (3) common Guillain-Barré syndrome, and (4) severe acute disseminated encephalomyelitis were treated by the modified zipper method. Results for duration of mechanical ventilation (median of 12 days, interquartile range [IQR] 8-16), hospital stay (median of 23 days, IQR 22-24), and time to unaided walking (median of 22 days, IQR 21-37) outperformed previous studies with IVIG/PLEX alone or IVIG + PLEX combinations unlike the zipper method. CONCLUSION: The modified zipper method is associated with a low mortality, a short mechanical ventilation time, a short hospital stay, and an excellent outcome in children with severe Guillain-Barré syndrome or acute disseminated encephalomyelitis. Our regimen is streamlined for applicability. Results emphasize its robust effectiveness as an option for therapy escalation in severe neuroimmunologic diseases. Now, multicenter trials are needed to evaluate this novel treatment strategy.

Neurodevelopmental outcome at 2 years after neuroendoscopic lavage in neonates with posthemorrhagic hydrocephalus.

OBJECTIVE: A standardized guideline for treatment of posthemorrhagic hydrocephalus in premature infants is still missing. Because an early ventriculoperitoneal shunt surgery is avoided due to low body weight and fragility of the patients, the neurosurgical treatment focuses on temporary solutions for CSF diversion as a minimally invasive approach. Neuroendoscopic lavage (NEL) was additionally introduced for early elimination of intraventricular blood components to reduce possible subsequent complications such as shunt dependency, infection, and multiloculated hydrocephalus. The authors report their first experience regarding neurodevelopmental outcome after NEL in this patient cohort. METHODS: In a single-center retrospective cohort study with 45 patients undergoing NEL, the authors measured neurocognitive development at 2 years with the Bayley Scales of Infant Development, 2nd Edition, Mental Developmental Index (BSID II MDI) and graded the ability to walk with the Gross Motor Function Classification System (GMFCS). They further recorded medication with antiepileptic drugs (AEDs) and quantified ventricular and brain volumes by using 3D MRI data sets. RESULTS: Forty-four patients were alive at 2 years of age. Eight of 27 patients (30%) assessed revealed a fairly normal neurocognitive development (BSID II MDI ≥ 70), 28 of 36 patients (78%) were able to walk independently or with minimal aid (GMFCS 0-2), and 73% did not require AED treatment. Based on MR volume measurements, greater brain volume was positively correlated with BSID II MDI (rs = 0.52, 95% CI 0.08-0.79) and negatively with GMFCS (rs = -0.69, 95% CI -0.85 to -0.42). Based on Bayesian logistic regression, AED treatment, the presence of comorbidities, and also cerebellar pathology could be identified as relevant risk factors for both neurodevelopmental outcomes, increasing the odds more than 2-fold-but with limited precision in estimation. CONCLUSIONS: Neuromotor outcome assessment after NEL is comparable to previously published drainage, irrigation, and fibrinolytic therapy (DRIFT) study results. A majority of NEL-treated patients showed independent mobility. Further validation of outcome measurements is warranted in an extended setup, as intended by the prospective international multicenter registry for treatment of posthemorrhagic hydrocephalus (TROPHY).

Hamartoma of the optic nerve in a young child­case report and review of the literature.

PURPOSE: Hamartomas are well described but yet incompletely understood sporadic benign lesions that can arise in various locations. Hypothalamic hamartomas of infancy are often associated with severe developmental disturbances. We present a case of an infant boy with a hamartoma that arises from the optic nerve and lead to progressive unspecific seizure activity, behavioral problems and precautious puberty. METHODS: A 1-year-old male patient was presented with horizontal nystagmus and developmental retardation. Magnetic resonance imaging (MRI) with contrast revealed an isointense mass ventral of the chiasm consistent with a hamartoma. Soon after the MRI, the mother of the patient reported gelastic-like seizures. The patient was evaluated by an interdisciplinary team, and surgery was recommended. Intraoperatively, a firm attachment to the optic nerve was recognized and a thin remnant layer of tissue was left behind. RESULTS: After an uncomplicated near total resection, the patient improved significantly. After 6 months, the frequency of seizures reoccurred, which were again unresponsive to antiepileptic medication. In a second operation, a complete resection of the remnants was performed, and the patient showed lasting clinical improvement. CONCLUSION: We conclude that hamartomas mimicking hypothalamic symptoms can also arise from the optic pathway and that a reoperation, if feasible, of even small remnants is essential in order to achieve lasting symptom relieve.

Interstitial 12p deletion involving more than 40 genes in a patient with postnatal microcephaly, psychomotor delay, optic nerve atrophy, and facial dysmorphism.

Interstitial deletions of chromosome 12p are rare, and the phenotype spectrum is therefore still unknown. The thirteen patients reported so far suffer from developmental delay, optic nerve hypoplasia, micropenis, hypoplastic hair and skin, oligodontia, brachydactyly, and arterial hypertension. We report a de novo 12p12.2-p11.22 deletion of 9.2 Mb detected by array CGH analysis in a boy with global developmental delay, muscular hypotonia, postnatal microcephaly, facial dysmorphism including small ears, epicanthus, broad nasal bridge and hypoplastic nostrils. In addition, the patient had optic nerve atrophy, inverted nipples, micropenis, and a hemangioma. The deleted region encompasses more than 40 reference genes. We compare phenotype and deletion extent of our index patient to that of previous reports and thereby contribute to the understanding of interstitial 12p deletion phenotypes. Knowledge of the pattern of this deletion phenotype will help clinicians to diagnose this abnormality in their patients and to counsel the parents accordingly. Further descriptions may be able to contribute to the clarification.

Dose-dependent effects of erythropoietin in propofol anesthetized neonatal rats.

Exposure to Gamma-aminobutyric-acid (GABA)(A)-receptor agonists and N-Methyl-D-Aspartate (NMDA)-antagonists has been demonstrated to induce neurodegeneration in newborn rats. Exogenous erythropoietin (EPO) protects against NMDA antagonist-mediated neuronal death. In this study we evaluated whether EPO is also effective in limiting neurodegeneration of the GABA(A)-mimetic agent propofol in newborn rats. 6 day old rats were randomized to one of four groups and treated with intraperitoneal applications of 3 x 30 mg/kg propofol at 0, 90 and 180 min, propofol in combination with 5000 IU/kg rEPO, propofol in combination with 20,000 IU/kg rEPO or sham injections of PAD II solution as controls. After 24h, brains of the animals were histopathologically examined and a summation score of degenerated cells was calculated for every brain. Propofol increased neuronal degeneration scores from 16,090+/-4336 to 28,860+/-6569 (p<0.01). This effect was completely abolished by low-dose rEPO (14,270+/-4542, p<0.001 versus propofol only; p>0.05 versus controls). In contrast, high-dose rEPO was not protective (23 930+/-8896, p>0.05 versus propofol only). Propofol may cause neuronal death in newborn rat brains, which is prevented by low-dose rEPO but not high-dose rEPO.

Neurodegeneration in newborn rats following propofol and sevoflurane anesthesia.

Propofol and sevoflurane are commonly used drugs in pediatric anesthesia. Exposure of newborn rats to a variety of anesthetics has been shown to induce apoptotic neurodegeneration in the developing brain. Newborn Wistar rats were treated with repeated intraperitoneal injections of propofol or sevoflurane inhalation and compared to controls. Brains were examined histopathologically using the De Olmos cupric silver staining. Additionally, a summation score of the density of apoptotic cells was calculated for every brain. Spatial memory learning was assessed by the Morris Water Maze (MWM) test and the hole board test, performed in 7 weeks old animals who underwent the same anesthetic procedure. Brains of propofol-treated animals showed a significant higher neurodegenerative summation score (24,345) when compared to controls (15,872) and to sevoflurane-treated animals (18,870). Treated animals also demonstrated persistent learning deficits in the hole board test, whereas the MWM test revealed no differences between both groups. Among other substances acting via GABAA agonism and/or NMDA antagonism propofol induced neurodegeneration in newborn rat brains whereas a sevoflurane based anesthesia did not. The significance of these results for clinical anesthesia has not been completely elucidated. Future studies have to focus on the detection of safe anesthetic strategies for the developing brain.

Cannabinoids enhance susceptibility of immature brain to ethanol neurotoxicity.

OBJECTIVE: Marijuana and alcohol are most widely abused drugs among women of reproductive age. Neurocognitive deficits have been reported in children whose mothers used marijuana during pregnancy. Maternal consumption of ethanol is known to cause serious developmental deficits METHODS: Infant rats and mice received systemic injections of Delta(9)-tetrahydrocannabinol (THC; 1-10mg/kg) or the synthetic cannabinoid WIN 55,212-2 (1-10mg/kg), alone or in combination with subtoxic and toxic ethanol doses, and apoptotic neurodegeneration was studied in the brains RESULTS: Acute administration of THC (1-10mg/kg), the principal psychoactive cannabinoid of marijuana, markedly enhanced proapoptotic properties of ethanol in the neonatal rat brain. THC did not induce neurodegeneration when administered alone. Neuronal degeneration became disseminated and severe when THC was combined with a mildly intoxicating ethanol dose (3gm/kg), with the effect of this drug combination resembling the massive apoptotic death observed when administering ethanol alone at much higher doses. The detrimental effect of THC was mimicked by the synthetic cannabinoid WIN 55,212-2 (1-10mg/kg) and counteracted by the CB(1) receptor antagonist SR141716A (0.4mg/kg). THC enhanced the proapoptotic effect of the GABA(A) agonist phenobarbital and the N-methyl-D-aspartate receptor antagonist dizocilpine. Interestingly, infant CB(1) receptor knock-out mice were less susceptible to the neurotoxic effect of ethanol. Furthermore, the CB(1) receptor antagonist SR141716A ameliorated neurotoxicity of ethanol INTERPRETATION: These observations indicate that CB(1) receptor activation modulates GABAergic and glutamatergic neurotransmission and primes the developing brain to suffer apoptotic neuronal death.

NMDA antagonist inhibits the extracellular signal-regulated kinase pathway and suppresses cancer growth.

Glutamate antagonists limit the growth of human cancers in vitro. The mechanism of anticancer action of NMDA antagonists is not known, however. In this article, we report that the NMDA antagonist dizocilpine inhibits the extracellular signal-regulated kinase 1/2 pathway, an intracellular signaling cascade that is activated by growth factors and controls the proliferation of cancer cells. Dizocilpine reduces the phosphorylation of cAMP-responsive element binding protein, suppresses the expression of cyclin D1, up-regulates the cell cycle regulators and tumor suppressor proteins p21 and p53, and increases the number of lung adenocarcinoma cells in the G(2) and S phases of the cell cycle. Silencing of the tumor suppressor protein p21 abolishes antiproliferative action of dizocilpine. Consistent with inhibition of the extracellular signal-regulated kinase 1/2-signaling cascade, dizocilpine reverses the stimulation of proliferation induced by epidermal, insulin, and basic fibroblast growth factors in lung adenocarcinoma cells. Furthermore, dizocilpine prolongs the survival of mice with metastatic lung adenocarcinoma and slows the growth of neuroblastoma and rhabdomyosarcoma in mice. These findings reveal the mechanism of antiproliferative action of dizocilpine and indicate that it may be useful in the therapy of human cancers.

Protection with estradiol in developmental models of apoptotic neurodegeneration.

Medical measures that bear no known danger for the adult brain may trigger active neuronal death in the developing brain. Pharmacological blockade of N-methyl-D-aspartate or activation of GABA(A) receptors, blockade of voltage-dependent sodium channels, and oxygen induce widespread apoptotic neurodegeneration during the period of rapid brain growth in rodents. Because such measures are often necessary in critically ill infants and toddlers, search for adjunctive neuroprotective strategies is warranted. We report that 17beta-estradiol ameliorates neurotoxicity of drugs that block N-methyl-D-aspartate receptors, activate GABA(A) receptors, or block voltage-gated sodium channels and reduces neurotoxicity of oxygen in the infant rat brain. This neuroprotective effect is reversed by tamoxifen and cannot be reproduced by 17alpha-estradiol. 17Beta-estradiol did not affect GABA(A) or N-methyl-D-aspartate currents in hippocampal neuronal cultures, indicating that direct modulation of neurotransmitter receptor/channel properties by this compound cannot explain neuroprotective effect. 17beta-Estradiol did, however, increase levels of phosphorylated extracellular signal-regulated kinase 1/2 and AKT, suggesting that activation of these prosurvival proteins may represent one mechanism for its neuroprotective action. 17Beta-estradiol and related compounds may be neuroprotective agents suitable for use in critically ill infants and toddlers. Its supplementation may particularly help to improve neurocognitive outcome in preterm infants who are prematurely deprived of maternal estrogen.

Sulthiame but not levetiracetam exerts neurotoxic effect in the developing rat brain.

Antiepileptic drugs (AEDs) used to treat seizures in pregnant women, infants, and young children can cause cognitive impairment. One mechanism implicated in the development of neurocognitive deficits is a pathologic enhancement of physiologically occurring apoptotic neuronal death in the developing brain. We investigated whether the newer antiepileptic drug levetiracetam (LEV) and the older antiepileptic drug sulthiame (SUL) have neurotoxic properties in the developing rat brain. SUL significantly enhanced neuronal death in the brains of rat pups ages 0 to 7 days at doses of 100 mg/kg and above, whereas LEV did not show this neurotoxic effect. Dosages of both drugs used in the context of this study comply with an effective anticonvulsant dose range applied in rodent seizure models. Thus, LEV is an AED which lacks neurotoxicity in the developing rat brain and should be considered in the treatment of epilepsy in pregnant women, infants, and toddlers once general safety issues have been properly addressed.

Caspase-1-processed interleukins in hyperoxia-induced cell death in the developing brain.

Infants born prematurely may develop neurocognitive deficits without an obvious cause. Oxygen, which is widely used in neonatal medicine, constitutes one possible contributing neurotoxic factor, because it can trigger neuronal apoptosis in the developing brain of rodents. We hypothesized that two caspase-1-processed cytokines, interleukin (IL)-1beta and IL-18, are involved in oxygen-induced neuronal cell death. Six-day-old Wistar rats or C57/BL6 mice were exposed to 80% oxygen for various time periods (2, 6, 12, 24, and 48 hours). Neuronal cell death in the brain, as assessed by Fluoro-Jade B and silver staining, peaked at 12 to 24 hours and was preceded by a marked increase in mRNA and protein levels of caspase 1, IL-1beta, IL-18, and IL-18 receptor alpha (IL-18Ralpha). Intraperitoneal injection of recombinant human IL-18-binding protein, a specific inhibitor of IL-18, attenuated hyperoxic brain injury. Mice deficient in IL-1 receptor-associated kinase 4 (IRAK-4), which is pivotal for both IL-1beta and IL-18 signal transduction, were protected against oxygen-mediated neurotoxicity. These findings causally link IL-1beta and IL-18 to hyperoxia-induced cell death in the immature brain. These cytokines might serve as useful targets for therapeutic approaches aimed at preserving neuronal function in the immature brain, which is exquisitely sensitive to a variety of iatrogenic measures including oxygen.

Apoptotic neurodegeneration in the context of traumatic injury to the developing brain.

Head trauma is the leading cause of death and disability in the pediatric population. Some recent studies on neuropathological and biochemical features of traumatic injury to the developing brain revealed interesting aspects and potential targets for future research. Trauma triggers both excitotoxic and apoptotic neurodegeneration in the developing rat brain. Apoptotic neurodegeneration occurs in a delayed fashion over several days and contributes in an age-dependent fashion to neuropathologic outcome following head trauma, with the immature brain being exceedingly sensitive. Biochemical studies indicate that both the extrinsic and the intrinsic apoptotic pathways are involved in pathogenesis of apoptotic cell death following trauma in the developing brain and that caspase inhibition ameliorates apoptotic neurodegeneration in an infant head trauma model. Given the major contribution of apoptotic neurodegeneration to neuropathologic outcome following trauma to the developing brain, interference with apoptotic pathways may comprise a potential therapeutic target in pediatric traumatic brain injury.

Oxygen causes cell death in the developing brain.

Substantial neurologic morbidity occurs in survivors of premature birth. Premature infants are exposed to partial oxygen pressures that are fourfold higher compared to intrauterine conditions, even if no supplemental oxygen is administered. Here we report that short exposures to nonphysiologic oxygen levels can trigger apoptotic neurodegeneration in the brains of infant rodents. Vulnerability to oxygen neurotoxicity is confined to the first 2 weeks of life, a period characterized by rapid growth, which in humans expands from the sixth month of pregnancy to the third year of life. Oxygen caused oxidative stress, decreased expression of neurotrophins, and inactivation of survival signaling proteins Ras, extracellular signal-regulated kinase (ERK 1/2), and protein kinase B (Akt). The synRas-transgenic mice overexpressing constitutively activated Ras and phosphorylated kinases ERK1/2 in the brain were protected against oxygen neurotoxicity. Our findings reveal a mechanism that could potentially damage the developing brain of human premature neonates.

Anticancer agents are potent neurotoxins in vitro and in vivo.

Neurotoxicity of anticancer agents complicates treatment of children with cancer. We investigated neurotoxic effects of common cytotoxic drugs in neuronal cultures and in the developing rat brain. When neurons were exposed to cisplatin (5-100 microM), cyclophosphamide (5-100 microM), methotrexate (5-100 microM), vinblastin (0.1-1 microM), or thiotepa (5-100 microM), a concentration-dependent neurotoxic effect was observed. Neurotoxicity was potentiated by nontoxic glutamate concentrations. The N-methyl-D-aspartate receptor antagonist MK 801 (10 microM), the AMPA receptor antagonists GYKI 52466 (10 microM) and NBQX (10 microM), and the pancaspase inhibitor Ac-DEVD-CHO (1 nM) ameliorated neurotoxicity of cytotoxic drugs. To investigate neurotoxicity in vivo, we administered to 7-day-old rats the following: cisplatin (5-15 mg/kg i.p.), cyclophosphamide (200-600 mg/kg i.p.), thiotepa (15-45 mg/kg), or ifosfamide (100-500 mg/kg) and their brains were analyzed at 4 to 24 hours. Cytotoxic drugs produced widespread lesions within cortex, thalamus, hippocampal dentate gyrus, and caudate nucleus in a dose-dependent fashion. Early histological analysis demonstrated dendritic swelling and relative preservation of axonal terminals, which are morphological features indicating excitotoxicity. After longer survival periods, degenerating neurons displayed morphological features consistent with active cell death. These results demonstrate that anticancer drugs are potent neurotoxins in vitro and in vivo; they activate excitotoxic mechanisms but also trigger active neuronal death.

Entorhinal cortex lesion in the mouse induces transsynaptic death of perforant path target neurons.

Entorhinal cortex lesion (ECL) is a well described model of anterograde axonal degeneration, subsequent sprouting and reactive synaptogenesis in the hippocampus. Here, we show that such lesions induce transsynaptic degeneration of the target cells of the lesions pathway in the dentate gyrus. Peaking between 24 and 36 hours post-lesion, dying neurons were labeled with DeOlmos silver-staining and antisera against activated caspase 3 (CCP32), a downstream inductor of programmed cell death. Within caspase 3-positive neurons, fragmented nuclei were co-localized using Hoechst 33342 staining. Chromatin condensation and nuclear fragmentation were also evident in semithin sections and at the ultrastructural level, where virtually all caspase 3-positive neurons showed these hallmarks of apoptosis. There is a well-described upregulation of the apoptosis-inducing CD95/L system within the CNS after trauma, yet a comparison of caspase 3-staining patterns between CD95 (Ipr)- and CD95L (gld)-deficient with non-deficient mice (C57/bl6) provided no evidence for CD95L-mediated neuronal cell death in this setting. However, inhibition of NMDA receptors with MK-801 completely suppressed caspase 3 activation, pointing to glutamate neurotoxicity as the upstream inducer of the observed cell death. Thus, these data show that axonal injury in the CNS does not only damage the axotomized neurons themselves, but can also lethally affect their target cells, apparently by activating glutamate-mediated intracellular pathways of programmed cell death.

Mechanisms leading to disseminated apoptosis following NMDA receptor blockade in the developing rat brain.

The developing rodent brain is vulnerable to pharmacological blockade of N-methyl-d-aspartate (NMDA) receptors which can lead to severe and disseminated apoptotic neurodegeneration. Here, we show that systemic administration of the NMDA receptor antagonist MK801 to 7-day-old rats leads to impaired activity of extracellular signal-regulated kinase 1/2 (ERK1/2) and reduces levels of phosphorylated cAMP-responsive element binding protein (CREB) in brain regions which display severe apoptotic neurodegeneration. Impaired ERK1/2 and CREB activity were temporally paralleled by sustained depletion of neurotrophin expression, particularly brain-derived neurotrophic factor (BDNF). BDNF supplementation fully prevented MK801-induced neurotoxicity in immature neuronal cultures and transgenic constitutive activation of Ras was associated with marked protection against MK801-induced apoptotic neuronal death. These data indicate that uncoupling of NMDA receptors from the ERK1/2-CREB signaling pathway in vivo results in massive apoptotic deletion of neurons in the developing rodent brain.