Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0085584 (encephalopathy)
 18,178 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Alzheimer type II astrocyte change is the distinctive morphologic alteration in brain of humans and experimental animals succumbing to hepatic encephalopathy (HE). Whether this change is a primary event in the pathogenesis of HE or whether it is secondary to injury of some other component(s) of the CNS has not been clarified. Studies in a rat model of HE have revealed early reactive changes in astrocytes characterized by cytoplasmic hypertrophy. During the later phases, degenerative changes ensue corresponding to the Alzheimer type II change observed by light microscopy. In view of the role of astrocytes in ammonia detoxification and the importance of ammonia in the pathogenesis of HE, we have suggested that the initial astrocytic changes are the morphological correlates of ammonia detoxification. We have speculated that the later degenerative alterations could lead to failure by astrocytes to carry out key functions (e.g., neurotransmitter uptake, ion regulation, and the like) and contribute the development of the encephalopathy. Recently, the potential involvement of astrocytes in HE has been further investigated, using primary astrocyte cultures. Exposure of cultures to ammonia at clinically relevant concentrations has shown morphologic changes closely resembling those observed in experimental HE in vivo. These deleterious effects can partly be prevented by raising cyclic AMP levels in cells. Other potential toxins (octanoic acid, phenol) have shown pathologic changes as well. Although some alterations were common to all three, they each possessed distinctive pathological effects. A synergistic interaction has also been demonstrated with these toxins. Functional studies of ammonia-treated astrocytes have shown the following: With low doses or short-term exposure, the uptakes of K+, glutamate, and GABA remained unchanged or slightly increased, whereas with higher doses or longer treatment, those activities diminished. A fall in ATP values occurred with prolonged ammonia treatment. Preliminary findings have shown no significant derangements in the beta-adrenergic receptor, except for a slight decrease in receptor affinity. However, cyclic AMP production was diminished following stimulation with isoproterenol. A slight rise in the number of benzodiazepine receptors was found. These studies indicate that profound changes occur in astrocytes following exposure to ammonia and other putative toxins. It is proposed that toxins and factors involved in the precipitation of HE do so by affecting astroglial properties. Derangements in such properties may lead to glial dysfunction (primary gliopathy), resulting in an encephalopathic state.
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PMID:The role of astrocytes in hepatic encephalopathy. 330 80

In order to determine whether disturbances in GABA homeostasis might play a role in the pathogenesis of sepsis-related encephalopathy, serum and brain tissue GABA concentrations from six areas of the brain (cortex, diencephalon, striatum, hippocampus, midbrain, and pons-medulla) were determined in a rat model of bacterial sepsis (cecal ligation and perforation). The results were compared to those obtained from sham operated control animals. All septic animals demonstrated clinical signs of encephalopathy and had elevated serum GABA levels (0.92 +/- 0.3 uM versus 0.48 +/- 0.15 in controls, p less than 0.01). GABA content in the specific subcompartments of the brain, however, were similar in the two groups. These results indicate that although serum GABA levels are elevated during sepsis, GABA is unlikely to play an important role in the pathogenesis of sepsis-related encephalopathy.
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PMID:gamma-Aminobutyric acid (GABA) and sepsis-related encephalopathy. 334 57

Bulk-isolated astrocytes from rats with early hepatogenic encephalopathy (HE) induced with thioacetamide responded to the increase of potassium in the incubation medium from 5 mM to 75 mM with a markedly enhanced release of previously taken up [14C]gamma-aminobutyric acid ([14C]GABA). The process was not affected by omission of calcium and/or addition of EGTA to the incubation medium. Only a slight stimulation of GABA release by high potassium was observed in astrocytes from control rats. In contrast, histamine and histidine were vigorously released from control astrocytes in high-potassium medium, and their release was not enhanced by HE, indicating that the observed phenomenon is specific for GABA.
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PMID:Enhanced potassium-stimulated gamma-aminobutyric acid release by astrocytes derived from rats with early hepatogenic encephalopathy. 358 44

The GABA level, and the glutamic acid decarboxylase (GAD) and GABA-aminotransferase (GABA-T) activities were measured in the cortex and striatum of rats in which the early stages of hepatogenic encephalopathy (HE) had been induced by few intraperitoneal administrations of thioacetamide (TAA). Besides, the GABA binding to synaptic plasma membranes (SPM) isolated from whole brain hemispheres was examined. The first part of the study revealed significant changes both in the neurotransmitter level and in the enzyme activities; no correlation was observed, however, between the accumulation of GABA and the progression of the disease. In contrast, subsequent stages of HE in the TAA model were found to be characterized by a gradual decrease of both Bmax and KD values for GABA binding, which may reflect a gradual decrease in the number of binding sites, accompanied by sensitization of the remaining receptors. The results are discussed in view of the possible involvement of this inhibitory neurotransmitter in the pathogenesis of HE.
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PMID:Changes in the metabolism and binding of GABA in the rat brain in thioacetamide-induced hepatogenic encephalopathy. 370 58

Chronic thiamine deprivation in the rat leads to selective neuropathological damage to pontine structures. Onset of neurological symptoms of thiamine deprivation (ataxia, loss of righting reflex) was accompanied by selective decreases (of the order of 30%) in the activity of alpha-ketoglutarate dehydrogenase (alpha KGDH) in lateral vestibular nucleus and hypothalamus. Enzyme activities were decreased to a lesser extent in medulla oblongata, striatum and hippocampus and were unchanged in other brain structures. No changes in alpha KGDH occurred prior to the onset of neurological signs of thiamine deprivation. Administration of the central thiamine antagonist, pyrithiamine, results within 3 weeks in loss of righting reflex and convulsions and in more widespread neuropathological changes than those observed following thiamine deprivation. alpha KGDH activities were found to be substantially diminished in all brain regions studied following pyrithiamine treatment with most severe changes occurring in brain regions found to be vulnerable to pyrithiamine (lateral vestibular nucleus, hypothalamus, midbrain, medulla-pons). In some cases, alpha KGDH changes preceded the appearance of neurological symptoms of pyrithiamine treatment. Such decreases in alpha KGDH may explain previous findings of region-selective changes in energy metabolism and of decreased synthesis of glucose-derived neurotransmitters (acetylcholine, GABA, glutamate) in pyrithiamine-treated rat brain. Thiamine administration to symptomatic pyrithiamine treated rats resulted in reversal of neurological signs of encephalopathy and in normalisation of defective alpha KGDH activity in all brain regions. These findings suggest that the reversible neurological symptoms associated with Wernicke's Encephalopathy in man likely result from region-selective impairment of alpha KGDH.
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PMID:Activities of thiamine-dependent enzymes in two experimental models of thiamine-deficiency encephalopathy. 2. alpha-Ketoglutarate dehydrogenase. 372 63

Evidence has been recently produced that neurological changes which characterize hepatic encephalopathy due to fulminant hepatic failure in rats are linked with a pathology of GABA receptors. In the search for the peripheral toxins responsible for the CNS impairment present in hepatic encephalopathy it has been shown that the administration of ammonia and mercaptans and octanoic acid in normal rats reproduced behavioural and electrophysiological changes similar to those seen in galactosamine induced encephalopathy. The present report shows that a subacute administration of the above toxins induced a marked alteration of the GABA receptor complex which may account for the CNS derangement of hepatic encephalopathy.
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PMID:Toxins in hepatic encephalopathy: the role of the synergistic effect of ammonia, mercaptans and short chain fatty acids. 609 1

Dopamine receptors were studied in striatal synaptosomes prepared from rat brain with hepatic encephalopathy induced by galactosamine-HCl and documented by visual evoked potential recordings. In order to further characterize the model, plasma amino acid levels and striatal catecholamines and octopamine levels were assayed. In agreement with previous reports in animal and in man, plasma amino acids were increased both in mild and severe stage of this pathology. Striatal levels of norepinephrine and dopamine fell during the development of coma while octopamine rose. Dopamine binding studies showed a decrease in the affinity during the mild stage and a reduction of receptor numbers in the severe stage of encephalopathy. The overall results, in the light of previous reports on GABA receptor studies, seem to indicate the presence in the development of encephalopathy of an imbalance between the dopaminergic and the GABAergic system leading to a prevalence of GABAergic inhibitory system.
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PMID:Down regulation of striatal dopamine receptors in experimental hepatic encephalopathy. 640 89

Measurements of the activities of the two key enzymes in cerebral GABA metabolism--glutamate decarboxylase (GAD) and GABA-transaminase (GABA-T)--were performed in normal rabbits and in rabbits with hepatic encephalopathy due to galactosamine-induced liver failure. Furthermore the uptake of GABA by synaptosomes was studied. Hepatic encephalopathy was associated with a marked decrease in the activity of GABA-T. This decrease in activity was already apparent in galactosamine-treated rabbits before the onset of hepatic encephalopathy. Sera and serum ultrafiltrates of rabbits with hepatic encephalopathy but not of normal rabbits or of rabbits with uremic encephalopathy were shown to inhibit GABA-T activity in vitro. Cerebral GAD activity and synaptosomal GABA uptake in rabbits with hepatic encephalopathy and in untreated animals were not different. These later findings indicate that hepatic encephalopathy is not associated with alterations of presynaptic GABA nerve terminals in the central nervous system. The demonstration of a decrease in cortical GABA-T activity provides indirect evidence for decreased GABA turnover in the brains of rabbits with hepatic encephalopathy and thus is compatible with augmented GABA-ergic inhibitory neurotransmission contributing to the neural inhibition of hepatic encephalopathy.
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PMID:Enzymes of cerebral GABA metabolism and synaptosomal GABA uptake in acute liver failure in the rabbit: evidence for decreased cerebral GABA-transaminase activity. 670 48

The aim of the present study was 2-fold: (1) to determine the ratio between the amount of GAD67 and GAD65 (two isoforms of the GABA synthetizing enzyme glutamic acid decarboxylase) in nerve endings in the mature rat cerebral cortex damaged by hypoxia-ischemia during early postnatal life; and (2) to compare two different computer-assisted procedures developed for quantitative analysis of immunofluorescence images obtained with a confocal laser scanning microscope (CLSM). One procedure was based on a program present in the standard Leica CLSM software packet for full-field analysis, the other on a specially written program for object-oriented analysis run on a Kontron IBAS-KAT image analysis system. To this end, rat pups were unilaterally exposed to hypoxic-ischemic conditions and, after a survival period of 6.5 months, sacrificed by perfusion fixation. After dissection of the brain and vibratome sectioning, three animals with substantial damage on one cortical side were selected. Sections of these animals were double-stained with primary antibodies against GAD67 and GAD65 and fluorophore-conjugated secondary antibodies and subsequently sampled with a CLSM. Analysis of the CLSM images with both computer-assisted procedures showed for all three animals a clear tendency to higher GAD67/GAD65 ratios in cortical GABAergic nerve endings on the hypoxia-damaged side than in matched areas on the contralateral side. This outcome led to the following conclusions. (1) The correspondence between the outcome of both analysis procedures indicates that both procedures are valid for quantification of immunofluorescence images of nerve endings obtained with a CLSM. (2) The outcome lends further support to our view that hypoxic-ischemic encephalopathy, sustained during early postnatal life, may result in an unstable cortical network generating abnormal synchronizations and oscillations which can be amplified and propagated as true epileptic discharges. In such a network both excitatory and inhibitory processes are tonically enhanced, the latter probably as a homeostatic reaction tending to keep abnormal excitation within physiological limits.
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PMID:Quantitative immunofluorescence data suggest a permanently enhanced GAD67/GAD65 ratio in nerve endings in rat cerebral cortex damaged by early postnatal hypoxia-ischemia: a comparison between two computer-assisted procedures for quantification of confocal laser scanning microscopic immunofluorescence images. 782 Jun 25

We report two patients with hepatic encephalopathy who developed periodic alternating gaze deviation (PAGD). Neither patient had an evident structural lesion, and the PAGD subsided after treatment of the encephalopathy. We postulate that a GABA-mediated disturbance affecting the cerebellar nodulus and uvula was responsible for the PAGD in these patients.
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PMID:Reversible periodic alternating gaze deviation in hepatic encephalopathy. 782 17


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