Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0036572 (seizures)
 80,221 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Currents evoked by applications of gamma-aminobutyric acid (GABA) to acutely dissociated thalamic neurones were analysed by voltage-clamp techniques, and the effects of the anticonvulsant succinimides ethosuximide (ES) and alpha-methyl-alpha-phenylsuccinimide (MPS) and the convulsants tetramethylsuccinimide (TMS), picrotoxin, pentylenetetrazol (PTZ), and bicuculline methiodide were assessed. 2. TMS (1 microM-10 microM) reduced responses to iontophoretically applied GABA, as did picrotoxin (0.1-100 microM), PTZ (1-100 mM) and bicuculline (1-100 microM). 3. ES, in high concentrations (1-10 mM), reduced GABA responses to a lesser extent, and also occluded the reductions in GABA-evoked currents produced by TMS, picrotoxin, and PTZ. ES did not occlude the effects of bicuculline on GABA responses. Therefore, we propose that ES acts as a partial agonist at the picrotoxin GABA-blocking receptor. 4. MPS had no effect on GABA responses (at a concentration of 1 mM), and, like ES, occluded the GABA-blocking actions of TMS, apparently acting as a full antagonist. 5. The anticonvulsant actions of ES and MPS against TMS and PTZ-induced seizures may thus involve two independent mechanisms: (1) the occlusion of TMS and PTZ GABA-blocking effects; and (2) the previously described specific effect of ES and MPS on low-threshold calcium current of thalamic neurones. The latter cellular mechanism may be more closely related to petit mal anticonvulsant activity.
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PMID:Differential effects of petit mal anticonvulsants and convulsants on thalamic neurones: GABA current blockade. 211 43

We assessed the role of gamma-aminobutyric acid (GABA) as a potential causative agent of hypoxic respiratory depression by monitoring the response of the phrenic neurogram to systemic infusion of the GABA antagonist bicuculline (0.01 mg.kg-1.min-1) under control conditions and during isocapnic brain hypoxia produced by CO inhalation in separate groups of anesthetized, glomectomized, vagotomized, paralyzed, and ventilated cats with blood pressure held constant. The maximum effect of bicuculline in subseizure doses in control cats was to increase minute phrenic activity to 151 +/- 14% of preinfusion values. Infusion was continued until seizure activity was seen in the electroencephalogram. A 53% decrease of arterial O2 content resulted in a marked reduction of both peak phrenic amplitude and phrenic firing frequency to 16 and 64% of control values, respectively. Infusion of bicuculline while the level of hypoxia was maintained constant restored both peak phrenic amplitude and phrenic firing frequency to prehypoxic levels. The maximum effect of bicuculline was to increase minute phrenic activity to 123 +/- 13% of the prehypoxic value. These results suggest that although GABA has only a modest role in determining the output of the control phrenic neurogram, a significant portion of the phrenic depression that occurs during hypoxia can be attributed to inhibition of respiratory neurons by GABA.
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PMID:GABA antagonism reverses hypoxic respiratory depression in the cat. 212 85

The anticonvulsant action of progabide, an agonist of gamma-aminobutyric acid (GABA)A and GABAB receptors, was investigated in the kindling model of epilepsy in rats. Progabide shortened afterdischarge durations and attenuated the severity of the accompanying convulsive responses in previously kindled rats from the amygdala (AM), frontal cortex (FC), ventral and dorsal hippocampus (HIPP), in a dose-dependent manner. Although progabide was less effective in the dorsal HIPP kindled seizures, the efficacy was potent in AM, FC and ventral HIPP kindled seizures. On the other hand, the anticonvulsant action of baclofen, a selective agonist of GABAB receptors, was relatively weak in terms of the measurement of the afterdischarge duration of AM and HIPP kindled seizures even at toxic doses, compared with progabide. In addition, the anticonvulsant effects of progabide were partially reversed by treatment with the antagonist of benzodiazepine receptors, Ro 15-1788, whereas Ro 15-1788 administration alone did not alter AM kindled seizures. We concluded that the action of progabide may be mediated via the GABA/benzodiazepine receptor complex. These results support the hypothesis that a failure of GABAA-mediated inhibition is one of the bases of induction and generalization of seizures.
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PMID:An analysis of anticonvulsant actions of GABA agonists (progabide and baclofen) in the kindling model of epilepsy. 215 38

Benzodiazepines are the most potent drugs used in the management of status epilepticus (SE). A number of presynaptic, postsynaptic, and nonsynaptic actions of benzodiazepines have been described. However, only the benzodiazepines' enhancement of gamma-aminobutyric acid (GABA)ergic inhibition and their reduction of repetitive firing occur at concentrations of unbound drug comparable to those that block absence seizures or stop clinical SE in patients. Thus, it is likely that these actions contribute to antiepileptic and anti-SE efficacy of the benzodiazepines. A predictable sequence of progressive electroencephalographic (EEG) changes during the course of generalized convulsive SE, both in humans and in experimental models, has been recently described. The homology of the sequence of EEG patterns in patients and in experimental models supports the concept that animal models should be useful in evaluating the treatment of clinical SE, and benzodiazepines are effective in stopping SE in a number of animal models. Late SE in animals, however, as in humans, is less responsive to treatment than is early SE. Forty-seven clinical studies in which clonazepam, diazepam, or lorazepam was used in the treatment of SE have been reported. Overall, lasting control of SE was achieved in 79% of the 1,346 patients in these noncontrolled studies. However, no data yet exist to differentiate the efficacy of 1 of the benzodiazepines from that of the others. Therefore, the choice of benzodiazepine is best determined by availability and by pharmacokinetic differences. Because of a much smaller volume of distribution of unbound drug, lorazepam appears to have a significantly longer effective duration of action against SE than does diazepam, which is rapidly redistributed to lipid stores in the body after intravenous administration. For this reason, we now use lorazepam in the initial treatment of patients with generalized convulsive SE.
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PMID:The role of benzodiazepines in the management of status epilepticus. 215 32

Gamma-aminobutyric acid (GABA)-mediated chloride uptake was determined in synaptoneurosomes prepared from the brains of entorhinal cortex-kindled and paired control rats. Subjects were sacrificed either 24 h or 28 days after the experimental animals had exhibited their sixth stage 5 convulsion. In the cortex and cerebellum, no difference was observed between kindled and control animals at either time period. In the brain-stem, however, a significant reduction (approximately 50%) in chloride uptake was observed in kindled subjects both 24 h and 28 days after the last seizure. These findings are consistent with the hypothesis that the 'kindled state' results from a long-lasting decrease in GABA-mediated inhibitory activity.
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PMID:Reduced GABA-mediated chloride flux in entorhinal cortex-kindled rat brains. 216 59

The hippocampus, a component of the limbic system, is a prominent subcortical structure, which not only contains high concentrations of zinc, but also exhibits regional variations in this essential element, with concentrations being highest in the hilar region and lowest in the fimbria. For example, the concentration of zinc in the mossy fiber axons has been estimated to approach 300-350 microM. Both zinc and pyridoxal phosphate (PLP) deficiency and excess have been reported to produce epileptiform seizures, which are blocked by gamma-aminobutyric acid (GABA). The proposed mechanism is that at physiological concentrations zinc stimulates the activity of the hippocampal pyridoxal kinase (50% stimulation at 1.7 x 10(-7) M), enhancing the formation of PLP, whereas in pharmacological doses zinc inhibits the activity of glutamate decarboxylase (GAD) directly (50% inhibition at 6.5 X 10(-4) M) by preventing the binding of PLP to HoloGAD. Furthermore, recent studies have shown that two forms of GAD are found in the rat brain. One form (GAD A) does not require PLP for maximal activity, while another form (GAD B) does. Furthermore, the ratio between GAD A and GAD B is nonuniform throughout brain areas, and the hippocampus contains twice as much GAD B (the PLP-requiring GAD) as GAD A. Although the hippocampus is a common target of exogenous neurotoxic agents, "free" zinc in greater than physiological concentrations should be considered an endogenous central neurotoxin. For example, iontophoretically applied zinc in the frontoparietal cortex enhances and prolongs the firing rate of neurons in urethane-anesthetized rat. In addition, zinc (50-500 microM) significantly depresses the paired-pulse potentation in the hippocampal CA3 subfield. Moreover, zinc selectively blocks the action of N-methyl-D-aspartate on cortical neurons and enhances the quisqualate receptor-mediated injury. Finally zinc competitively inhibits the calcium-dependent release of transmitter by inhibiting the entry of Ca2+ into the nerve terminals. Since zinc in a concentration of 300-350 microM could not possibly remain "unbound" in the hippocampus, we searched for and identified a metallothionein-like protein (MT) in the bovine hippocampus, which produces two isoforms on reverse-phase HPLC and lacks aromatic amino acids, but possesses metallomercaptide bonds. We believe that the hippocampal metallothionein, by donating zinc to an extensive number of zinc-activated, PLP-mediated biochemical reactions, modulates synaptic functions. Furthermore, by virtue of its inducibility, metallothionein binds additional amounts of zinc, maintains its steady-state concentration, prevents inhibition of an extensive number of sulfhydryl-containing enzymes and receptor sites, and hence averts metal-related neurotoxicity.
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PMID:Hippocampal zinc thionein and pyridoxal phosphate modulate synaptic functions. 219 11

Epilepsy complicates severe head trauma. Development of persistent seizures appears to correlate with the extent of trauma. Although early reports suggested that prophylactic administration of antiepileptic drugs would prevent epileptogenesis, controlled studies have failed to corroborate this assumption. Head trauma initiates a sequence of responses that includes altered blood flow and vasoregulation, disruption of the blood-brain barrier, increases in intracranial pressure, focal or diffuse ischemia, hemorrhage, inflammation, necrosis, and disruption of fiber tracts. The presence of an intracranial hematoma has a robust association with the development of post-traumatic epilepsy. Extravasation of blood is followed by hemolysis and deposition of heme-containing compounds into the neuropil, initiating a sequence of univalent redox reactions and generating various free radical species, including superoxides, hydroxyl radicals, peroxides, and perferryl ions. Free radicals initiate peroxidation reactions by hydrogen abstraction from methylene groups adjacent to double bonds of fatty acids and lipids within cellular membranes. Intrinsic enzymatic mechanisms for control of free radical reactions include activation of catalase, peroxidase, and superoxide dismutase. Steroids, proteins, and tocopherol also terminate peroxidative reactions. Tocopherol and selenium are effective in preventing tissue injury initiated by ferrous chloride and heme compounds. Treatment strategies for prevention or prophylaxis of post-traumatic epilepsy must await absolute knowledge of mechanisms. Antioxidants and chelators may be useful, given the speculation that peroxidative reactions may be an important component of brain injury responses. However, potential treatment strategies involving gamma-aminobutyric acid (GABA) agonists, NMDA receptor antagonists, and barbiturates need further scientific assessment.
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PMID:Post-traumatic epilepsy: cellular mechanisms and implications for treatment. 222 73

Perinatal hypoxia is known as a risk factor for human epilepsies. Previous studies in our laboratory have shown that the rats with postnatal hypoxia show facilitation of the kindling formation and enhanced susceptibility to pentylenetetrazol (PTZ)-induced seizures even after the maturation. In the present study, the effects of postnatal hypoxia (100% N2, for approximately 5 min, at ten days of age) on monoamine and amino acid levels in the brain of adult rats (three months of age) were investigated to clarify the biochemical basis of the enhanced seizure susceptibility. In the hypoxia-treated rats, norepinephrine (NE) was significantly decreased in the pons-medulla (82% of control) and hypothalamus (85%) as compared with controls. Dopamine (DA) was decreased in the pons-medulla (83%). A decrease in DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), was also noted in the substantia nigra (71%) and hippocampus (64%), respectively. On the other hand, gamma-aminobutyric acid (GABA) was significantly increased in the striatum (121%). These findings indicate that the enhanced seizure susceptibility in these rats may be attributed to 1) impaired development of noradrenergic and dopaminergic neurons, of which these transmissions are known as inhibitory modulators of seizure discharge in some animal models of epilepsies, and 2) changes of GABAergic and dopaminergic transmissions in the striato-nigral pathway, which is a wellknown regulation system for seizure propagation.
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PMID:[Long-term effects of postnatal hypoxia on monoamine and amino acid levels in the rat brain]. 226 92

The gamma-aminobutyric acid (GABA) antagonist, bicuculline, induces generalized motor seizures when injected into a discrete site ('area tempestas') in the deep prepiriform cortex at concentrations considerably lower than those that induce convulsions from closely adjacent areas or other forebrain sites such as amygdala and hippocampus. This observation prompted the suggestion that the area tempestas is a crucial epileptogenic site involved in seizure generation. In the present study, the region functionally defined as area tempestas in rats was bilaterally destroyed by microinjection of ibotenic acid. Systemic administration of bicuculline induced generalized motor seizures in both lesioned and non-lesioned animals without any indication of differences in seizure severity or latency. This argues against the suggestion that the deep prepiriform cortex plays a crucial role in the generation of seizures following systemic administration of GABA antagonists.
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PMID:Lesions of the deep prepiriform cortex ('area tempestas') in rats do not affect the convulsant action of systemically administered bicuculline. 230 24

This study demonstrates that the central medial intralaminar nucleus (CeM) controls generalized seizure threshold and expression, and that these functions are under gamma-aminobutyric acid (GABA)ergic control, with significant differences between receptor subtypes. Injections of the GABAA-agonist piperidine-4-sulfonic acid and the GABAB-agonist (-)baclofen in the CeM markedly facilitated myoclonic and clonic seizures, but had different effects on tonic seizures. These results are best explained by the concept that the CeM is not a site of seizure origin or spread but rather regulates other structures involved in seizures.
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PMID:The central medial nucleus: thalamic site of seizure regulation. 230 21


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