The reverse transcription polymerase chain reaction (RT-PCR) is the most sensitive method for the detection of low-abundance mRNA, often obtained from limited tissue samples. However, it is a complex technique, there are substantial problems associated with its true sensitivity, reproducibility and specificity and, as a quantitative method, it suffers from the problems inherent in PCR. The recent introduction of fluorescence-based kinetic RT-PCR procedures significantly simplifies the process of producing reproducible quantification of mRNAs and promises to overcome these limitations. Nevertheless, their successful application depends on a clear understanding of the practical problems, and careful experimental design, application and validation remain essential for accurate quantitative measurements of transcription. This review discusses the technical aspects involved, contrasts conventional and kinetic RT-PCR methods for quantitating gene expression and compares the different kinetic RT-PCR systems. It illustrates the usefulness of these assays by demonstrating the significantly different levels of transcription between individuals of the housekeeping gene family, glyceraldehyde-3-phosphate-dehydrogenase (GAPDH).

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Absolute quantification of mRNA using real-time reverse transcription polymerase chain reaction assays.

Real-time RT-PCR has become a common technique, no longer limited to specialist core facilities. It is in many cases the only method for measuring mRNA levels of vivo low copy number targets of interest for which alternative assays either do not exist or lack the required sensitivity. Benefits of this procedure over conventional methods for measuring RNA include its sensitivity, large dynamic range, the potential for high throughout as well as accurate quantification. To achieve this, however, appropriate normalisation strategies are required to control for experimental error introduced during the multistage process required to extract and process the RNA. There are many strategies that can be chosen; these include normalisation to sample size, total RNA and the popular practice of measuring an internal reference or housekeeping gene. However, these methods are frequently applied without appropriate validation. In this review we discuss the relative merits of different normalisation strategies and suggest a method of validation that will enable the measurement of biologically meaningful results.

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Real-time RT-PCR normalisation; strategies and considerations

The knowledge of the pathophysiology after traumatic head injury is necessary for adequate and patient-oriented treatment. As the primary insult, which represents the direct mechanical damage, cannot be therapeutically influenced, target of the treatment is the limitation of the secondary damage (delayed non-mechanical damage). It is influenced by changes in cerebral blood flow (hypo- and hyperperfusion), impairment of cerebrovascular autoregulation, cerebral metabolic dysfunction and inadequate cerebral oxygenation. Furthermore, excitotoxic cell damage and inflammation may lead to apoptotic and necrotic cell death. Understanding the multidimensional cascade of secondary brain injury offers differentiated therapeutic options.

Pathophysiology of traumatic brain injury

Diabetes increases the risk for disorders that predispose individuals to hospitalization, including coronary artery, cerebrovascular and peripheral vascular disease, nephropathy, infection, and lower-extremity amputations. The management of diabetes in the hospital is generally considered secondary in importance compared with the condition that prompted admission. Recent studies (1,2) have focused attention to the possibility that hyperglycemia in the hospital is not necessarily a benign condition and that aggressive treatment of diabetes and hyperglycemia results in reduced mortality and morbidity. The purpose of this technical review is to evaluate the evidence relating to the management of hyperglycemia in hospitals, with particular focus on the issue of glycemic control and its possible impact on hospital outcomes. The scope of this review encompasses adult nonpregnant patients who do not have diabetic ketoacidosis or hyperglycemic crises.

For the purposes of this review, the following terms are defined (adapted from the American Diabetes Association [ADA] Expert Committee on the Diagnosis and Classification of Diabetes Mellitus) (3): 

The prevalence of diabetes in hospitalized adult patients is not known. In the year 2000, 12.4% of hospital discharges in the U.S. listed diabetes as a diagnosis. The average length of stay was 5.4 days (4). Diabetes was the principal diagnosis in only 8% of these hospitalizations. The accuracy of using hospital discharge diagnosis codes for identifying patients with …

https://care.diabetesjournals.org/content/diacare/27/2/553.full.pdf

Management of diabetes and hyperglycemia in hospitals.

Rapid removal of glutamate from the extracellular space is required for the survival and normal function of neurons. Although glutamate transporters are expressed by all CNS cell types, astrocytes are the cell type primarily responsible for glutamate uptake. Astrocyte glutamate uptake also plays a role in regulating the activity of glutamatergic synapses. Lastly, release of glutamate from astrocytes, via transporter reversal and other routes, can contribute to glutamate receptor activation. This review examines the mechanisms of astrocyte glutamate uptake and release, with particular focus on high-affinity Na+-dependent transporters. Transporter regulation, energetics, and physiological roles are discussed. GLIA 32:1–14, 2000. Published 2000 Wiley-Liss, Inc.

Astrocyte glutamate transport: Review of properties, regulation, and physiological functions †

Excitotoxic mechanisms and the role of astrocytic glutamate transporters in traumatic brain injury

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs in both acute and chronic liver failure. Although the precise pathophysiologic mechanisms responsible for HE are not completely understood, a deficit in neurotransmission rather than a primary deficit in cerebral energy metabolism appears to be involved. The neural cell most vulnerable to liver failure is the astrocyte. In acute liver failure, the astrocyte undergoes swelling resulting in increased intracranial pressure; in chronic liver failure, the astrocyte undergoes characteristic changes known as Alzheimer type II astrocytosis. In portal-systemic encephalopathy resulting from chronic liver failure, astrocytes manifest altered expression of several key proteins and enzymes including monoamine oxidase B, glutamine synthetase, and the so-called peripheral-type benzodiazepine receptors. In addition, expression of some neuronal proteins such as monoamine oxidase A and neuronal nitric oxide synthase are modified. In acute liver failure, expression of the astrocytic glutamate transporter GLT-1 is reduced, leading to increased extracellular concentrations of glutamate. Many of these changes have been attributed to a toxic effect of ammonia and/or manganese, two substances that are normally removed by the hepatobiliary route and that in liver failure accumulate in the brain. Manganese deposition in the globus pallidus in chronic liver failure results in signal hyperintensity on T1-weighted Magnetic Resonance Imaging and may be responsible for the extrapyramidal symptoms characteristic of portal-systemic encephalopathy. Other neurotransmitter systems implicated in the pathogenesis of hepatic encephalopathy include the serotonin system, where a synaptic deficit has been suggested, as well as the catecholaminergic and opioid systems. Further elucidation of the precise nature of these alterations could result in the design of novel pharmacotherapies for the prevention and treatment of hepatic encephalopathy.

Hepatic encephalopathy: An update of pathophysiologic mechanisms.

Excitotoxic mechanisms in stroke: an update of concepts and treatment strategies.

The central nervous system, and the basal ganglia in particular, is an important target in manganese neurotoxicity, a disorder producing neurological symptoms similar to that of Parkinson's disease Increasing evidence suggests that astrocytes are a site of early dysfunction and damage; chronic exposure to manganese leads to selective dopaminergic dysfunction, neuronal loss, and gliosis in basal ganglia structures together with characteristic astrocytic changes known as Alzheimer type II astrocytosis Astrocytes possess a high affinity, high capacity, specific transport system for manganese facilitating its uptake, and sequestration in mitochondria, leading to a disruption of oxidative phosphorylation In addition, manganese causes a number of other functional changes in astrocytes including an impairment of glutamate transport, alterations of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase, production of nitric oxide, and increased densities of binding sites for the "peripheral-type" benzodiazepine receptor (a class of receptor predominantly localized to mitochondria of astrocytes and involved in oxidative metabolism, mitochondrial proliferation, and neurosteroid synthesis) Such effects can lead to compromised energy metabolism, resulting in altered cellular morphology, production of reactive oxygen species, and increased extracellular glutamate concentration These consequences may result in impaired astrocytic-neuronal interactions and play a major role in the pathophysiology of manganese neurotoxicity

Manganese neurotoxicity: an update of pathophysiologic mechanisms.

Thiamine deficiency (TD) is a well-established model of Wernicke's encephalopathy. Although the neurologic dysfunction and brain damage resulting from the biochemical consequences of TD is well characterized, the mechanism(s) that lead to the selective histological lesions characteristic of this disorder remain a mystery. Over the course of many years, various structural and functional changes have been identified that could lead to cell death in this disorder. However, despite a concerted effort to explain the consequences of TD in terms of these changes, our understanding of the pathophysiology of this disorder remains unclear. This review will focus on three of these processes, i.e. oxidative stress, glutamate-mediated excitotoxicity and inflammation and their role in selective vulnerability in TD. Since TD inhibits oxidative metabolism, a feature of many neurodegenerative disease states, it represents a model system with which to explore pathological mechanisms inherent in such maladies, with the potential to yield new insights into their possible treatment and prevention.

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Alan S. Hazell

Papers

Excitotoxic mechanisms and the role of astrocytic glutamate transporters in traumatic brain injury

Hepatic encephalopathy: An update of pathophysiologic mechanisms.

Excitotoxic mechanisms in stroke: an update of concepts and treatment strategies.

Manganese neurotoxicity: an update of pathophysiologic mechanisms.

Update of Cell Damage Mechanisms in Thiamine Deficiency: Focus on Oxidative Stress, Excitotoxicity and Inflammation