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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The anatomy, physiology, and biochemistry of the dorsal membrane muscle (DMA) and the superficial extensor muscle accessory head (SEAcc) in the abdomen of the crayfish, Procambarus clarkii and lobster, Homarus americanus, are reported. These muscles have not been previously characterized physiologically or biochemically. The anatomy was originally described by Pilgrim and Wiersma (1963. J Morph 113:453-587). The arrangement of these muscles varies depending on the abdominal segment. The function of the dorsal membrane muscle is to retract the thin articulating membrane joining the cuticular segments so that the dorsal membrane does not evert during extension of the abdomen. Consequently, the articular membrane does not protrude, and thus potential damage to the membrane is minimized. Examination of nerve terminal morphology revealed strings of varicosities, usually only associated with tonic terminals. The electrophysiological data indicate that there are at least four tonic excitatory and one inhibitory motor neuron innervating these muscles. Facilitation indices and fatigue-resistance indicate physiologically the tonic nature of innervation. Anti-GABA antibodies demonstrate the anatomical presence of an inhibitor motor neuron. The SDS electrophoretic analysis of myofibrillar proteins and Western blots of key protein isoforms for these muscles in crayfish and lobsters also indicate that the DMA and SEAcc muscles are tonic phenotype. J. Exp. Zool. 287:353-377, 2000.
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PMID:Characterization of muscles associated with the articular membrane in the dorsal surface of the crayfish abdomen. 1098 Apr 94

Symptomatic forms of central nervous hyperexcitability (NHE) due to magnesium deficiency results from the sum of direct cellular effects and of local and systemic mediated effects inducing depolarization and NHE. Direct effects associate decreased energy and cationic gradient with disturbances in Ca distribution, decreased second messenger nucleotidic ratio and increased susceptibility to peroxidation. Local mediated effects associate increased activity of excitatory neuromediators: acetylcholine, catecholamines and ionotropic - (NMDA and non-NMDA) - receptors of excitatory aminoacids (EAA), with decreased activity of inhibitory neuromediators: GABA, taurine, glutaurine, adenosine and K receptors of opioids. Systemic mediated effects associate increased production of inflammatory mediators: neuropeptides, prostanoids, cytokines Th 1, aldehydes with decreased activity of oxidant and antialdehyde defences. Compensatory factors instrumental in the latency of NHE due to magnesium deficiency may also be direct or mediated. Increased intracellular pH, modifications of Ca and Mg binding proteins, increase in 'magnesium-like' polyamines, stimulation of cellular antioxidant system; decreased activity of EAA metabotropic receptors and of opioid mu (and delta) receptors, increased activity of inhibitory neuromediators, increased production of anti-inflammatory mediator such as cytokines Th 2, stimulation of systemic antioxidant and antialdehyde defences. A lot of diverse compounds are able to palliate symptomatic NHE due to magnesium deficiency either by pharmacodynamic effects or through physiopathological intervention. The efficiency of these treatments can be evaluated on multiple disparate parameters. The pattern of NHE due to magnesium deficiency differs according to species, strains, gender, age and intensity of magnesium deficiency. For example: hot plate test showed a hypoalgesia 'morphine-like' pattern induced by magnesium deficiency cured by magnesium acetyltaurinate in mice whilst paw pressure test showed a hyperalgic pattern caused by magnesium deficiency cured by dizolcipine in rats. Now it seems difficult to rank hierarchically the various physiopathological mechanisms of NHE due to magnesium deficiency. But the proposed general scheme of the factors controlling this NHE provides a possible explanation of both diffuse symptomatic and latent forms and stresses the complexity of the physiopathological mechanisms of central NHE due to magnesium deficiency.
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PMID:Physiopathology of symptomatic and latent forms of central nervous hyperexcitability due to magnesium deficiency: a current general scheme. 1115 99

To probe the effect of glutamine and GABA on metabolism of [U-(13)C]glutamate, cerebellar astrocytes were incubated with [U-(13)C]glutamate (0.5 mM) in the presence and absence of glutamine (2.5 mM) or GABA (0.2 mM). It could be shown that consumption of [U-(13)C]glutamate was decreased in the presence of glutamine and release of labeled aspartate and [1,2,3-(13)C]glutamate decreased as well, whereas the concentrations of these metabolites increased inside the cells. Glutamine decreased energy production from [U-(13)C]glutamate presumably by substituting for glutamate as an energy substrate. No additional effect was seen in the presence of both glutamine and GABA. When cerebellar granule neurons were incubated with [U-(13)C]glutamate (0.25 mM) and GABA (0.05 mM), less [U-(13)C]glutamate was used for energy production than in controls. Because the barbiturate thiopental did not elicit such response (Qu et al., 2000, Neurochem Int 37:207-215) it appears that GABA also has a metabolic function in the glutamatergic cerebellar granule neurons in contrast to the astrocytes.
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PMID:Effect of glutamine and GABA on [U-(13)C]glutamate metabolism in cerebellar astrocytes and granule neurons. 1174 15

Recent work in the learned helplessness paradigm suggests that neuronal sensitization and fatigue processes are critical to producing the behavioral impairment that follows prolonged exposure to an unsignaled inescapable stressor such as a series of electric tail shocks. Here we discuss how an interaction between serotonin (5-HT) and corticosterone (CORT) sensitizes GABA neurons early in the pretreatment session with inescapable shock. We propose that this process eventually depletes GABA, thus removing an important form of inhibition on excitatory glutamate transmission in the amygdala, hippocampus, and frontal cortex. When rats are re-exposed to shock during shuttle-escape testing 24 hrs later, the loss of inhibition (as well as other excitatory effects) results in unregulated excitation of glutamate neurons. This state of neuronal over-excitation rapidly compromises metabolic homeostasis. Metabolic fatigue results in compensatory inhibition by the nucleoside adenosine, which regulates neuronal excitation with respect to energy availability. The exceptionally potent form of inhibition associated with adenosine receptor activation yields important neuroprotective benefits under conditions of metabolic failure, but also precludes the processing of information in fatigued neurons. The substrates of adaptive behavior are removed; performance deficits ensue.
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PMID:Stressor controllability and learned helplessness research in the United States: sensitization and fatigue processes. 1206 65

The goal of this study was to investigate the behavioral and subjective effects of a single dose of progesterone in men and women. Certain metabolites of progesterone (e.g., allopregnanolone) are potent positive allosteric modulators of GABA(A) receptors, and produce sedative-like effects in laboratory animals. This study was designed to examine the acute effects of these neurosteroids in humans. Women (n=7) in their early follicular phase and men (n=10) received intramuscular injections of progesterone (200 mg) or placebo. Dependent measures included plasma levels of progesterone and allopregnanolone, self-report measures of mood and subjective effects and behavioral measures of psychomotor performance. Plasma concentrations of progesterone and allopregnanolone increased reliably and with little intersubject variability after drug administration, and levels were similar in men and women. Administration of progesterone produced small, delayed increases in heart rate and feelings of fatigue, and it impaired smooth eye pursuit. These results suggest that, although the effects are modest and not simply related to plasma concentrations, progesterone and its metabolites can produce sedative-like effects in both men and women.
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PMID:Administration of progesterone produces mild sedative-like effects in men and women. 1464 65

This paper summarizes the current knowledge concerning the biosynthesis of neurosteroids in the human brain, the enzymes mediating these reactions, their localization, and the putative effects of neurosteroids. The presence of the steroidogenic enzymes cytochrome P450(SCC), aromatase, 5alpha-reductase, 3alpha-hydroxysteroid dehydrogenase, and 17beta-hydroxysteroid dehydrogenase in the human brain has now been firmly established by molecular biological and biochemical studies. Their presence in the cerebral cortex and in the subcortical white matter indicates that various cell types, either neurons or glial cells, are involved in the biosynthesis of neuroactive steroids in the brain. The following functions are attributed to specific neurosteroids: modulation of GABA(A), N-methyl-d-aspartate (NMDA), nicotinic, muscarinic, serotonin (5-HT(3)), kainate, glycine and sigma receptors, neuroprotection and induction of neurite outgrowth, dendritic spines, and synaptogenesis. We still do not know whether and how the steroidogenic enzymes are involved in the pathophysiology of the nervous system. The first clinical investigations in humans produced evidence for an involvement of neuroactive steroids in conditions such as fatigue during pregnancy, premenstrual syndrome, postpartum depression, catamenial epilepsy, and depressive disorders. Further and improved knowledge of the biochemical pathways of neurosteroidogenesis and their actions on the brain may enable new perspectives in the understanding of the physiology of the human brain as well as in the pharmacological treatment of its disturbances.
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PMID:Neurosteroid biosynthesis in the human brain and its clinical implications. 1499 41

Extracellular field excitatory postsynaptic potentials (fEPSPs) were recorded in area CA1 of rat hippocampal slices in vitro. The responses evoked by spontaneously released glutamate and GABA were recorded from area CA1 pyramidal neurons in rat hippocampal slices in whole-cell mode. The glutamate and GABA receptor-associated ligand-gated currents were obtained from dissociated single hippocampal pyramidal cells. The results showed that 4-aminopyridine (4-AP) had obvious effects on both presynaptic and postsynaptic events. Applications of 4-AP in micromolar concentration resulted in persistent enhancement of the initial slope of fEPSPs with the half-maximal enhancement concentration (EC(50)) of 46.7+/-2.68 microM. At the concentration of 200 microM, 4-AP increased the initial slopes of the total fEPSPs, NMDA- and AMPA-mediated fEPSPs components to 225.6+/-23.8%, 177.4+/-20.1% and 142.3+/-18.9%, respectively, but had no effect on the fiber volley. The half-maximal stimulus intensity to induce responses was reduced from 5.14+/-0.27 to 3.58+/-0.23 V. The frequencies of mEPSCs and mIPSCs were increased to 324.2+/-25.4% and 287.3+/-36.3% by 200 microM 4-AP. The amplitude histograms of mEPSCs and mIPSCs were fitted with Gaussian distributions. After 200 microM 4-AP application, the first and second peaks in Gaussian distributions of mEPSCs were shifted from 8.73+/-0.94 and 17.78+/-2.13pA to 10.48+/-0.82 and 21.14+/-2.45 pA, while those of mIPSCs were shifted from 13.65+/-0.96 and 25.51+/-2.95 pA to 11.21+/-1.04 and 23.08+/-2.37 pA. At 200 microM, 4-AP reduced paired-pulse facilitation and accelerated synaptic fatigue induced by stimulation at 10 Hz (for 1 s) and the ratio of fEPSPs(10)/fEPSPs(1) was decreased from 1.62+/-0.16 to 0.61+/-0.15. At 200 microM, 4-AP inhibited postsynaptic GABA currents induced by 5 microM GABA to 68.2+/-15.5%: by countering the effect of enhanced release of GABA from presynaptic terminals, this could depress the inhibitory pathway. Also at 200 microM, 4-AP increased NMDA currents to 155.3+/-17.8%, but had no significant effect on AMPA currents (94.2+/-15.6%). Our experimental results thus show that 4-AP-induced changes of synaptic transmission in area CA1 of rat hippocampus may be attributed to 4-AP's effects on both presynaptic terminals and postsynaptic receptors.
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PMID:Effect of 4-aminopyridine on synaptic transmission in rat hippocampal slices. 1505 26

Mood-modulating profiles of antiepileptic drugs (AEDs) have been classified by Ketter, Post, and Theodore [Neurology 1999; 53 (5, Suppl. 2) S53-76] into two classes: the first class is assumed to have deactivating effects related to GABA potentiation, and the second class is assumed to have activating effects that are associated with glutamate attenuation. We tested this hypothesis by reviewing the multiple mechanisms of action of topiramate (TPM) and levetiracetam (LEV) together with clinical behavioral side effects of patients who had been treated with TPM and LEV in a tertiary referral center for epilepsy. We found LEV to manifest activating and deactivating side effects equally and TPM to act as a deactivating AED, with tiredness/sleepiness side effects being predominant. TPM, in comparison to LEV, was found to be associated with a high incidence of side effects. Testing the hypothesis of Ketter et al. (1999) the deactivating effects of TPM may be coupled to a predominance of potentiation of GABA, but the oversimplified basis of the model needs to be acknowledged.
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PMID:Ketter's hypothesis of the mood effects of antiepileptic drugs coupled to the mechanism of action of topiramate and levetiracetam. 1582 Mar 45

ASTA Medica is developing retigabine, a carbamic acid ethyl ester and a selective potassium channel opener, for the treatment of complex partial seizures. Phase II trials have commenced [249117], and a multicenter placebo-controlled dosage-finding study has begun in Europe and Australia [392702]. Retigabine is also undergoing phase II testing in Germany, Switzerland, Russia and the US for the potential treatment of epilepsy [323383]. Phase II trials have shown >50% reduction in seizure frequency in 12 of 35 patients with refractory epilepsy [373379]. Phase I clinical trials for epilepsy were successfully completed in Germany in 1995 [180371]. Single and multiple dose trials demonstrated the tolerability and favorable pharmacokinetic behavior of the compound [264306]. The compound showed good compatibility and exhibits an antisense anticonvulsive effect in various preclinical epilepsy models [250565,299344]. Side effects of mild to moderate tiredness, fatigue and nausea were observed [276123]. The spectrum of activity of retigabine resembles that of valproate, but its potency is greater and toxicity is reduced [373379]. The mechanism of action of retigabine is probably multifactorial. Research has shown that retigabine acts as a selective K+ channel opener in neuronal cells and this can be expected to contribute to its anticonvulsant effect [273670]. In addition it demonstrates potentiation of GABA transmission and possibly also weak modulation of sodium and calcium channels [299344]. Retigabine also has neuroprotective activity with potential for the treatment of stroke and neurodegenerative diseases, such as Alzheimer's disease, Huntington's disease and multiple sclerosis [249381]. In February 2000, Lehman Brothers predicted product launch could be as early as 2002 for epilepsy in the US [357788]. In February 1999, Lehman Brothers predicted that the first major launch date of the drug would be 2003, and the year of peak sales to be 2011 [319225].
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PMID:Retigabine (ASTA Medica). 1603 7

The first pyrethroid pesticide, allethrin, was identified in 1949. Allethrin and other pyrethroids with a basic cyclopropane carboxylic ester structure are type I pyrethroids. The insecticidal activity of these synthetic pyrethroids was enhanced further by the addition of a cyano group to give alpha-cyano (type II) pyrethroids, such as cypermethrin. The finding of insecticidal activity in a group of phenylacetic 3-phenoxybenzyl esters, which lacked the cyclopropane ring but contained the alpha-cyano group (and hence were type II pyrethroids) led to the development of fenvalerate and related compounds. All pyrethroids can exist as at least four stereoisomers, each with different biological activities. They are marketed as racemic mixtures or as single isomers. In commercial formulations, the activity of pyrethroids is usually enhanced by the addition of a synergist such as piperonyl butoxide, which inhibits metabolic degradation of the active ingredient. Pyrethroids are used widely as insecticides both in the home and commercially, and in medicine for the topical treatment of scabies and headlice. In tropical countries mosquito nets are commonly soaked in solutions of deltamethrin as part of antimalarial strategies. Pyrethroids are some 2250 times more toxic to insects than mammals because insects have increased sodium channel sensitivity, smaller body size and lower body temperature. In addition, mammals are protected by poor dermal absorption and rapid metabolism to non-toxic metabolites. The mechanisms by which pyrethroids alone are toxic are complex and become more complicated when they are co-formulated with either piperonyl butoxide or an organophosphorus insecticide, or both, as these compounds inhibit pyrethroid metabolism. The main effects of pyrethroids are on sodium and chloride channels. Pyrethroids modify the gating characteristics of voltage-sensitive sodium channels to delay their closure. A protracted sodium influx (referred to as a sodium 'tail current') ensues which, if it is sufficiently large and/or long, lowers the action potential threshold and causes repetitive firing; this may be the mechanism causing paraesthesiae. At high pyrethroid concentrations, the sodium tail current may be sufficiently great to prevent further action potential generation and 'conduction block' ensues. Only low pyrethroid concentrations are necessary to modify sensory neurone function. Type II pyrethroids also decrease chloride currents through voltage-dependent chloride channels and this action probably contributes the most to the features of poisoning with type II pyrethroids. At relatively high concentrations, pyrethroids can also act on GABA-gated chloride channels, which may be responsible for the seizures seen with severe type II poisoning. Despite their extensive world-wide use, there are relatively few reports of human pyrethroid poisoning. Less than ten deaths have been reported from ingestion or following occupational exposure. Occupationally, the main route of pyrethroid absorption is through the skin. Inhalation is much less important but increases when pyrethroids are used in confined spaces. The main adverse effect of dermal exposure is paraesthesiae, presumably due to hyperactivity of cutaneous sensory nerve fibres. The face is affected most commonly and the paraesthesiae are exacerbated by sensory stimulation such as heat, sunlight, scratching, sweating or the application of water. Pyrethroid ingestion gives rise within minutes to a sore throat, nausea, vomiting and abdominal pain. There may be mouth ulceration, increased secretions and/or dysphagia. Systemic effects occur 4-48 hours after exposure. Dizziness, headache and fatigue are common, and palpitations, chest tightness and blurred vision less frequent. Coma and convulsions are the principal life-threatening features. Most patients recover within 6 days, although there were seven fatalities among 573 cases in one series and one among 48 cases in another. Management is supportive. As paraesthesiae usually resolve in 12-24 hours, specific treatment is not generally required, although topical application of dl-alpha tocopherol acetate (vitamin E) may reduce their severity.
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PMID:Poisoning due to pyrethroids. 1618 Sep 29


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