Remote experimentation over the Net: our first year with MALDI.
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Cooperative Behavior↗
Biomedical subjects
M V Johnston
Publications and source records attributed to M V Johnston.
MK801 decreases glutamate release and oxidative metabolism during hypoglycemic coma in piglets.
Hypoglycemic coma increases extracellular excitatory amino acids, which mediate hypoglycemic neuronal degeneration. Cerebral oxygen consumption increases during hypoglycemic coma in piglets. We tested the hypothesis that the NMDA-receptor antagonist dizocilpine (MK801) attenuates the increase in cerebral oxygen consumption during hypoglycemia. We measured EEG, cerebral blood flow (CBF), cerebral oxygen consumption (CMRO(2)) and cortical microdialysate levels of glutamate, aspartate and glycine in pentobarbital-anesthetized piglets during 60 min of insulin-induced hypoglycemic coma. NMDA-receptor distribution was measured by autoradiography. MK801 (0.75 mg/kg i.v.) was given within 5 min after onset of isoelectric EEG. Saline- and MK801-treated normoglycemic control animals were also studied. Brain temperature was maintained at 38.5+/-0.5 degrees C. MK801 prevented the 5--10-fold increase in glutamate and aspartate occurring in saline-treated hypoglycemic animals, and attenuated the increase in CMRO(2). Increases in CBF of 200--400% during hypoglycemic coma were not affected by MK801. MK801 did not alter CBF, CMRO(2) or microdialysate amino acid levels in normoglycemic control animals. Parietal cortex corresponding to microdialysis sites was highly enriched in NMDA receptors, and the density and distribution overall of NMDA receptor binding sites were comparable to that reported in other species. We conclude that NMDA receptor activation plays a central role in hypoglycemia-induced glutamate release, and contributes to increased cerebral oxygen consumption. Neuroprotective effects of MK801 during hypoglycemia in piglets may involve inhibitory effects on glutamate release and oxidative metabolism.
Animals↗
Application of the ART-2a algorithm to laser ablation aerosol mass spectrometry of particle standards.
Single-particle mass spectrometers are now commonly used to analyze atmospheric particles and generate tens of thousands of spectra from typical measurement campaigns. The ART-2a spectrum algorithm has been used to classify these spectra. In this work, we generate a range of particles that are models of those that are common in the atmosphere. A single-particle mass spectrometer is used to analyze these known particles, and the spectra are classified using ART-2a. The optimum vigilance parameter is approximately 0.5 while the optimum learning rate is approximately 0.05. The classifications elucidate limitations in generation of test particles, their analysis by single-particle techniques, and their classification by ART-2a.
Journal Article↗
Cognitive impairment in Coffin-Lowry syndrome correlates with reduced RSK2 activation.
BACKGROUND: Gene expression and protein synthesis, mediated by the transcription factor CREB (cAMP response element binding protein), play an important role in learning and memory in several species, including Drosophila, snails, and mice. Patients with the X-linked disorder Coffin-Lowry syndrome (CLS) have cognitive disabilities, distinctive features, and bony abnormalities as well as mutations in RSK2 (ribosomal S6 kinase-2), a protein kinase that activates CREB by phosphorylation at serine 133. In fibroblasts from a single patient with CLS, epidermal growth factor (EGF)-stimulated CREB phosphorylation was reduced. METHODS: The authors assessed endogenous CREB phosphorylation in a CLS fibroblast line by Western blotting and found impaired CREB phosphorylation in response to stimulation by EGF and the protein kinase C (PKC) agonist phorbol 12-myristate 13-acetate (PMA). They studied RSK2 immunoprecipitated from fibroblasts and lymphoblasts from seven patients with CLS and found a wide range in RSK2's capacity to phosphorylate the synthetic CREB-like peptide, CREBtide, after cell stimulation by PMA. RESULTS: In lymphoblasts from patients with CLS, PMA-stimulated CREBtide phosphorylation was increased 1.2- to 2.7-fold over baseline, compared to an average fourfold increase in controls. Regression analysis suggested a linear relationship between the magnitude of in vitro RSK2-mediated CREBtide phosphorylation and CLS patient intelligence level (p < 0.05). CONCLUSIONS: This report suggests a correlation between human cognitive performance and cellular capacity to activate RSK2. It provides additional evidence that the CREB kinase, RSK2, and CREB phosphorylation may play important roles in human learning and memory, as they do in lower animals.
Abnormalities, Multiple↗
Excitotoxicity in neonatal hypoxia.
Hypoxic-ischemic encephalopathy (HIE) in neonates is a disorder of excessive neuronal excitation that includes seizures, abnormal EEG activity, and delayed failure of oxidative metabolism with elevated levels of lactic acid in the brain. Evidence from experimental models and clinical investigation indicates that HIE is triggered by a profound disruption in the function of glutamate synapses so that re-uptake of glutamate from the synapse is impaired and post-synaptic membranes containing glutamate receptors are depolarized. Severe hypoxemia preferentially depolarizes neuronal membranes, while ischemia probably has greater impact on the activity of glial glutamate re-uptake. Together, severe hypoxia and ischemia trigger a delayed cascade of events that may result in cell death by necrosis and/or apoptosis. Apoptosis is far more prominent in the neonate than in the adult and activation of cysteine proteases such as caspase-3 is a very important pathway in excitotoxic neonatal injury. Understanding the complex molecular networks triggered by an excitotoxic insult in the neonate provides insight into patterns of selective neuronal vulnerability and potential therapeutic strategies.
Apoptosis↗
Delayed increase in neuronal nitric oxide synthase immunoreactivity in thalamus and other brain regions after hypoxic-ischemic injury in neonatal rats.
We examined the response of neuronal nitric oxide synthase (nNOS)-containing CNS neurons in rats exposed to a unilateral hypoxic-ischemic insult at 7 days of age. Animals were sacrificed at several time points after the injury, up to and including 7 days (Postnatal Day 14). Brain regions ipsilateral to the injury (including cerebral cortex, caudate-putamen, and thalamus) exhibited delayed, focal increases in nNOS immunoreactivity. The increase in nNOS immunoreactive fiber staining was prominent in areas adjacent to severe neuronal damage, especially in the cortex and the thalamus, regions that are also heavily and focally injured in term human neonates with hypoxic-ischemic encephalopathy. In cerebral cortex, these increases occurred despite modest declines in nNOS catalytic activity and protein levels. Proliferation of surviving nNOS immunoreactive fibers highlights regions of selective vulnerability to hypoxic-ischemic insult in the neonatal brain and may also contribute to plasticity of neuronal circuitry during recovery.
Animals↗
Developmental disorders of activity dependent neuronal plasticity.
A number of neurodevelopmental disorders are caused by defects in activity dependent neuronal plasticity, the process by which neuronal activity shapes developing neuronal circuits. These disorders are caused by genetic mutations or other factors that disrupt intracellular signaling pathways that link the cell surface with the nuclear machinery for gene expression. The signaling pathways disrupted by these disorders are involved in learning, memory and behavior as well as in the synaptic proliferation and pruning that occurs during normal development. Examples of neurodevelopmental disorders that target plasticity include X-linked disorders such as Rett, Fragile-X and Coffin-Lowry Syndromes as well as acquired disorders such as cretinism. Several other X-linked mental retardation syndromes as well as autosomal disorders including neurofibromatosis type 1 and tuberous sclerosis also involve signaling pathways involved in neuronal plasticity. Disruption of neuronal plasticity is a mechanism that may underlie a diverse group of neurodevelopmental disorders.
Brain Diseases↗
Pharmacologically induced preconditioning with diazoxide: a novel approach to brain protection.
BACKGROUND: Ischemic preconditioning is an endogenous mechanism whereby brief periods of ischemia render neurons resistant to subsequent lethal insults. This protection appears to alter cellular apoptosis and can be induced by potassium channel openers acting on the inner membrane of the mitochondria (mitoK(ATP)). To test the hypothesis that pharmacologic preconditioning could provide neuroprotection, the mitoK(ATP) opener diazoxide was used in a canine model of brain injury induced by hypothermic circulatory arrest (HCA). METHODS: Seventeen dogs were placed on cardiopulmonary bypass (CPB) and cooled to 18 degrees C. After 2 hours of HCA, animals were rewarmed and weaned from CPB. Six dogs received intravenous diazoxide (2.5 mg/kg bolus 15 minutes prior to CPB, then 0.5 mg/min until circulatory arrest, then restarted for the first hour of rewarming). Six animals received vehicle only. Five received diazoxide and the mitoK(ATP) blocker 5-hydroxydecanoate (5-HD). Using a modified Pittsburgh Canine Neurological Scoring System (0 = normal, 500 = brain death), animals were evaluated every 24 hours for 3 days. The brains were removed and histologic sections of four regions characteristically injured in this model were scored (0 = no injury, 4 = infarction) by a neuropathologist in a blinded fashion. RESULTS: Clinical scoring showed marked improvement in the diazoxide group at 48 hours (101 +/- 10.5 vs 165 +/- 14.8, p < 0.01) and 72 hours (54 +/- 9.3 vs 137 +/- 12.1, p < 0.01). This neuroprotection was attenuated when 5-HD was concomitantly administered. Three of four brain regions typically injured in this model (cortex, hippocampus, and entorhinal cortex) had significant neuron preservation in the diazoxide group. Likewise, combined region scores were significantly improved in the treatment group (1.18 +/- 0.2 vs 2.46 +/- 0.2, p < 0.01). CONCLUSIONS: Pretreatment with diazoxide resulted in significant improvement in both clinical neurologic scores and histopathology in our model of HCA. This suggests that pharmacologic preconditioning with the mitoK(ATP) channel opener diazoxide may offer effective neuroprotection during HCA.
Animals↗
Prolonged suppression of brain nitric oxide synthase activity by 7-nitroindazole protects against cerebral hypoxic-ischemic injury in neonatal rat.
Nitric oxide mediates glutamate-induced excitotoxicity associated with cerebral hypoxia-ischemia through production in the brain by several isoforms of nitric oxide synthase (NOS). We examined the influence of the selective neuronal NOS inhibitor, 7-nitroindazole (7-NI), on brain NOS activity and its neuroprotective effects against cerebral hypoxic-ischemic injury in the postnatal day (PND) 7 rat. In the first set of experiments, 7-NI (50 mg/kg) administered intraperitoneally (i.p.) transiently inhibited NOS activity to 40% below the vehicle control level at 1 h after injection (P<0.001, analysis of variance (ANOVA)). In contrast, 7-NI (100 mg/kg, i.p.) inhibited NOS activity to 56% below the control level at 1 h with prolonged suppression of NOS activity at 3, 6, 9 and 12 h after injection. Two-factor ANOVA revealed an overall effect on NOS activity of 7-NI treatment (P<0.001) and time after injection (P<0.001). In the second set of experiments, 7-NI (50, 100 mg/kg) or an equal volume of vehicle was administered after unilateral carotid artery ligation, but 30 min before hypoxia in PND 7 rats. 7-NI (100 mg/kg) significantly protected against cerebral hypoxic-ischemic injury (100 mg/kg of 7-NI, 1.7+/-1.0% damage; control, 8.7+/-1.6%,P<0.05). 7-NI administered 15 min after cerebral hypoxia-ischemia was not neuroprotective. The data suggest that the protective effect of 7-NI is dose dependent, and is related to the duration of suppressed NOS activity.
Aging↗
Neurobiology of Rett syndrome: a genetic disorder of synapse development.
Rett syndrome is a developmental disorder that restricts brain growth beginning in the first year of life and evidence from neuropathology and neuroimaging indicates that axonodendritic connections are especially vulnerable. In a study of amino acid neurotransmitter receptors using receptor autoradiography in tissue slices of frontal cortex and the basal ganglia, we found a biphasic age-related pattern with relatively high receptor densities in young RS girls and lower densities at later time. Using microarray analysis of gene expression in frontal cortex, we found that some of the most prominent alterations occurred in gene products related to synapses, including the NMDA receptor NR1 subunit, the cytoskeletal protein MAP-2 and synaptic vesicle proteins. Using a new antibody that recognizes MeCP2, the transcription factor mutated in RS, we established that most neurons in the rodent brain express this transcription factor. We hypothesize that a major effect of mutations in the MeCP2 protein is to cause age-related disruption of synaptic proliferation and pruning in the first decade of life.
Adolescent↗
Neuroimaging studies in Rett syndrome.
Neuroimaging is a key instrument for determining structural and in vivo functional status of the brain, non-invasively. Multiple approaches can now determine aspects of anatomic and neurochemical changes in brain, and have been utilized effectively in Rett Syndrome patients to understand the biological basis of this neurodevelopmental disorder. Studies performed at our institute include volumetric analyses of MRI, magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), cerebral blood flow measurements with MRI, and positron emission tomography scans (PET). These studies have provided considerable insight into mechanisms underlying the clinical features of this disease. Volumetric analyses suggest that decreased brain volume in RS results from global reductions in both gray and white matter of the brain. A selective vulnerability of the frontal lobes is evidenced by the preferential reduction of blood flow, increased choline and reduced n-acetyl aspartate (NAA) by MRS, and increased glucose uptake in these same regions as shown by ((18)F)-fluorodeoxyglucose (FDG) PET scans. We hypothesize that the increased glucose uptake relates to increased glutamate cycling in synapses. The resulting neuroexcitotoxic injury to the developing brain contributes to the seizures, behavioral disturbance and respiratory irregularities commonly seen in phases 1 and 2 of this disorder.
Adolescent↗
Age-dependent effects of trihexyphenidyl in extrapyramidal cerebral palsy.
Trihexyphenidyl (Artane) is a centrally active muscarinic antagonist commonly used to treat patients with generalized dystonia. In a retrospective survey of 22 consecutive children with extrapyramidal cerebral palsy, we evaluated trihexyphenidyl on upper extremity and lower extremity function, expressive language, and drooling. Functional changes were assessed using a parental questionnaire (rating scale 1-5: from 1 = little or no change to 5 = tremendous change, with scores in either a positive or negative direction). Improvements of +4 or +5 were reported in eight children for upper extremity function, in eight children for verbal expressive language, in five for drooling, and in none for lower extremity function. Using bivariate linear regression modeling to investigate variables associated with treatment effects, there was a significant inverse relationship between age at initiation of medication and therapeutic response. Furthermore, beneficial responses were specific to upper-extremity function and expressive language. These results suggest that younger children are more likely to respond to trihexyphenidyl and that primary functional benefits include improved fine motor abilities and expressive language. A prospective masked study with a standardized clinical instrument is needed to confirm these findings.
Age Factors↗
Mental practice combined with physical practice for upper-limb motor deficit in subacute stroke.
BACKGROUND AND PURPOSE: This case report describes a patient with upper-limb hemiparesis (ULH) who received a program combining physical therapy for the affected side with mental practice. CASE DESCRIPTION: The patient was a 56-year-old man with stable motor deficits, including ULH, on his dominant side resulting from a right parietal infarct that occurred 5 months previously. He received physical therapy for an hour 3 times a week for 6 weeks. In addition, 2 times a week the patient listened to an audiotape instructing him to imagine himself functionally using the affected limb. The patient also listened to the audiotape at home 2 times a week. Pretreatment and posttreatment measures were the upper-extremity scale of the Fugl-Meyer Assessment of Sensorimotor Impairment (Fugl-Meyer Scale), the Action Research Arm Test (ARA), and the Stroke Rehabilitation Assessment of Movement (STREAM). OUTCOMES: The patient exhibited reduction in impairment (Fugl-Meyer Scale) and improvement in arm function, as measured by the ARA and STREAM. DISCUSSION: Mental practice may complement physical therapy to improve motor function after stroke.
Activities of Daily Living↗
Coordinated and adequately funded state streams for rehabilitation of newly injured persons with tbi.
Traumatic brain injury (TBI) rates are highest among families with the lowest income levels. A paucity of appropriate funding streams for low-income, recently injured TBI patients is reported to cause delays in provision of early postacute rehabilitation or to cause patients to be discharged without receiving rehabilitation. There are also reports of patients remaining in hospitals with minimal care or being returned home, both because of a lack of a discharge site. The purposes of this exploratory study were to: (1) identify model aspects of existing publicly supported and administered programs for postacute individuals with TBI; (2) present results of a survey measuring to what extent state Medicaid programs fund postacute rehabilitation services for recently injured patients with TBI; (3) present results of interviews with trauma center social workers affiliated with the National Institute on Disability and Rehabilitation Research (NIDRR) TBI Model Systems projects to determine whether and how delays in receiving Medicaid coverage occur; and (4) make recommendations for improved systems of care for postacute individuals with TBI.
Brain Injuries↗
A randomized efficacy and feasibility study of imagery in acute stroke.
OBJECTIVE: To compare the feasibility and efficacy of a programme combining imagery and occupational therapy with a programme of therapy only. DESIGN: Randomized, controlled case series. SETTING: Subacute outpatient clinic. SUBJECTS: Thirteen consecutively admitted patients between four weeks and one year post stroke exhibiting stable motor deficits in their affected upper limbs. INTERVENTION: All patients received an hour of therapy three times a week for six weeks administered by the same physical and occupational therapists. During the same period, eight patients participated in 10-minute guided imagery sessions after each therapy session, as well as practising imagery at home twice each week. Five patients participated in a control intervention consisting of exposure to stroke information. MAIN OUTCOME MEASURES: The Fugl-Meyer Assessment of Motor Recovery (Fugl-Meyer) and Action Research Arm Test (ARA). RESULTS: After intervention, Fugl-Meyer and ARA scores of patients in the therapy only group remained virtually the same; therapy plus imagery group scores improved by 13.8 and 16.4 points, respectively, on the Fugl-Meyer and ARA. CONCLUSIONS: Imagery is a clinically feasible, cost-effective complement to therapy that may improve outcomes more than participation in therapy only.
Aged↗
Neurobiology of hypoxic-ischemic injury in the developing brain.
Hypoxic ischemia is a common cause of damage to the fetal and neonatal brain. Although systemic and cerebrovascular physiologic factors play an important role in the initial phases of hypoxic-ischemic injuries, the intrinsic vulnerability of specific cell types and systems in the developing brain may be more important in determining the final pattern of damage and functional disability. Excitotoxicity, a term applied to the death of neurons and certain other cells caused by overstimulation of excitatory, mainly glutamate, neurotransmitter receptors, plays a critical role in these processes. Selected neuronal circuits as well as certain populations of glia such as immature periventricular oligodendroglia may die from excitotoxicity triggered by hypoxic ischemia. These patterns of neuropathologic vulnerability are associated with clinical syndromes of neurologic disability such as the extrapyramidal and spastic diplegia forms of cerebral palsy. The cascade of biochemical and histopathologic events triggered by hypoxic ischemia can extend for days to weeks after the insult is triggered, creating the potential for therapeutic interventions.
Animals↗
Sculpting the developing brain.
The developing brain experiences major construction during fetal life and for at least the first decade of childhood. Many more neurons and synoptic connections are produced than are needed for later function, and the mature brain is what remains after these excess building materials are "sculpted" away. This process is thought to be the basis for the developing brain's plasticity, or the capacity to adapt its behavior and circuitry to stimulation from the external environment. Plastic reorganization of the brain is now being studied in children and adults with new noninvasive tools such as functional brain magnetic resonance imaging. This exploratory tool and other new clinical methods demonstrate how the brain's functional "maps" undergo major reorganization in response to early environmental changes. The neurobiology of brain reorganization during development is also being studied with use of new insights into the molecular mechanisms for activity-dependent neuronal plasticity. Clinical disorders such as lead poisoning, metabolic and epileptic encephalopathies, and psychosocial deprivation may arise from disrupted brain plasticity. Several mental retardation syndromes and cognitive disorders recently recognized as being secondary to genetic disruption of intracellular signaling cascades may also disrupt this process. Understanding how the brain's circuitry is sculpted during development provides an important perspective for thinking about neurodevelopmental disorders.
Brain↗
Prevalence and identification of problems in daily functioning in a primary medicine clinic.
PURPOSE: This pilot study compares scores on a health status/functional assessment measure to clinician identification of problems in functioning and referrals for these problems, based on examination of information in the patient's medical chart. METHOD: A sample of 194 participants at a primary medicine clinic in an urban general hospital completed a measure of health status and functioning, the Medical Outcomes Trust Short Form 36 (SF-36). Chart reviews were conducted to assess whether problems in functioning were addressed by the primary care clinician. RESULTS: Overall, levels of functioning on the scales of the SF-36 were well below norms for the general US population from the Medical Outcomes Study. Older adults showed lower physical functioning and higher emotional functioning than younger adults. Participants with 1, 2, or 3 chronic conditions showed increasingly lower levels of physical functioning. For participants with functional assessment scale scores in the lowest quartile, problems in functioning noted in the chart ranged from 13%-28%. Only 6% 20% of participants with marked problems in functioning were referred for further assessment or treatment. CONCLUSIONS: Functional problems are frequently important indicators of risk of development of secondary complications and need for referral. Questionnaire screening may increase identification and referral for problems in functioning in primary care settings.
Activities of Daily Living↗