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Query: UMLS:C0036572 (seizures)
 80,221 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interruption of GABA infusion in the cerebral cortex and in the hippocampus produces electrographic seizures in rats. Here, we have used the hippocampal slice preparation to induce a 'GABA withdrawal syndrome (GWS)'. With the stimulation parameters used (0.2 Hz, 200 microseconds), activation of the Schaffer afferents produced one population spike in the CA1 subfield, while multiple population spikes were observed in the slices previously incubated in GABA. Also, we recorded an increase in the amplitude of the population spike when compared to its control value. Paired pulse test showed absence of recurrent inhibition in these slices. These results suggest a dysfunction in GABAergic neurotransmission.
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PMID:Hyperexcitability of hippocampal CA1 region in brain slices after GABA withdrawal. 133 96

In sheep, administration of a combination of zolazepam and tiletamine hydrochloride resulted in a dose dependent reduction in the duration of epileptic activity induced by an electric stun applied to the head. The compound also lengthened the normal period of reflex suppression that occurs after a stun. Excitatory amino acid receptor antagonists (2-amino-7-phosphonoheptanoic and 2-amino-5-phosphonovaleric acids) also reduced the duration of epileptic activity following an electric stun. These drugs did not alter the time of pedal and ear pinch reflex suppression. Administration of bicuculline (a gamma amino-4-butyric acid [GABA] receptor antagonist) reduced the period of stun induced reflex suppression and increased seizure duration. Administration of a GABA receptor agonist, baclofen, increased the duration of reflex suppression. The results suggest that the development of epileptiform-like activity following application of an electric current to the head is dependent upon excitatory amino acid receptors. The reflex suppression that also arises following an electric stun is contributed to by the activation of GABA receptor mechanisms.
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PMID:Contribution of amino acid transmitters to epileptiform activity and reflex suppression in electrically head stunned sheep. 134 45

The abundant CNS cholesterol and its sulfate derivative serve as precursors of different neurosteroids, which bidirectionally modulate neuronal excitability, by potentiating or inhibiting function of the GABAA receptors. The regulation of GABAA receptors in the CNS by the steroids of central or peripheral origin may constitute a vital means of brain-body communication, essential for integrated whole organism responses to external stimuli or internal signals. Modulation of the brain GABA receptors by neurosteroids may form the basis of a myriad of psychophysiological phenomena, such as memory, stress, anxiety, sleep, depression, seizures and others. Therefore, the aberrant synthesis of centrally-active steroids may contribute to defects in neurotransmission, resulting in a variety of neural and affective disorders. The biosynthesis of neurosteroids may also be altered by diet and certain psychotropic drugs, thereby affecting excitation of neurons. Hereditary differences in the level of synthesis and catabolism of different neurosteroids may underlie individual variations in CNS excitability, contributing to differences in personality traits, including the inherited susceptibility to drug addition.
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PMID:Neurosteroids: endogenous bimodal modulators of the GABAA receptor. Mechanism of action and physiological significance. 134 41

Several model systems have been used to test the hypothesis that the release of FFA in the brain is regulated by depolarization of neurons. This FFA release is likely the result of the activation of phospholipase A2. The increased neuronal activity that occurs due to synchronous depolarization during seizures causes activation of phospholipase A2. Decreasing neuronal activity by administering the anxiolytic, diazepam, appears to decrease the activity of phospholipase A2. The GABA antagonist, bicuculline, which causes depolarization by negating the hyperpolarizing tone imposed on neurons by GABA, causes FFA release in synaptosomes and in neurons in tissue culture. Likewise, the glutamate agonist, kainic acid, which depolarizes neurons by opening sodium channels, increases the activity of phospholipase A2. PC-specific phospholipase C, another enzyme important in the generation of the second messenger, DG, is also activated by depolarization. Several important questions remain to be answered. The site of FFA release, in terms of the pre-vs. postsynaptic membrane, is not clear, although the experiments with synaptosomes support the hypothesis that activation of phospholipase A2 may be an important regulator of presynaptic events. This idea has also been suggested by studies on the phenomenon of long-term potentiation, where free 20:4 or its metabolites may be involved in presynaptic facilitation of neurotransmitter release (Freeman et al., 1990; Massicotte et al., 1990; Williams et al., 1989; also see Dorman, this volume). The activation of the PI cycle and subsequent stimulation of protein kinase C may be a postsynaptic event important in the integration of inputs at the dendrite and soma or a presynaptic event involved in the modulation of neurotransmitter release (Taniyama et al., 1990; El-Fakahany et al., 1990; also see Nishizuka, this volume). Therefore the stimulation of a PC-specific phospholipase C, which is capable of generating large amounts of DG over a prolonged period of time (Exton, 1990; Martinson et al., 1990; Diaz-Laviada et al., 1990), could occur at either site. Another important question is the role of FFA and DG in affecting cell-cell signaling events, particularly with regard to ion fluxes. Modulation of an acetylcholine-linked K+ channel in the heart by FFA and their oxygenation products has been reported (Kim and Clapham, 1989). The cardiac muscarinic receptor is linked to a hyperpolarizing K+ channel via a G protein.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Reciprocal regulation of fatty acid release in the brain by GABA and glutamate. 135 87

It is uncertain whether a brief hypoxic exposure exerts long lasting effects on central nervous system amino acid neurotransmission. The purpose of this study was to test the hypothesis that a short period of hypoxia would affect release of excitatory and inhibitory amino acids during subsequent bicuculline-induced seizure. Utilizing in vivo microdialysis in cerebral cortex of rabbits, we observed no significant increase in extracellular fluid (ECF) concentrations of the excitatory amino acids, glutamate and aspartate, or the inhibitory amino acids, GABA and taurine, during a 30-min exposure to hypoxia (FiO2 = 0.08). In addition, there was no significant change in these amino acids during uncomplicated seizure. However, when seizure was complicated by a preceding period of hypoxia, there was a marked and progressive rise in both excitatory and inhibitory amino acids in ECF. We conclude that a short period of hypoxia, which itself does not cause changes in ECF concentrations of excitatory amino acids, may nonetheless contribute to neuronal injury by altering the levels of ECF amino acids during a subsequent insult.
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PMID:Hypoxia increases extracellular concentrations of excitatory and inhibitory neurotransmitters in subsequently induced seizure: in vivo microdialysis study in the rabbit. 135 67

Benzodiazepines (BZ) and steroid hormone derivatives can potentiate the inhibitory actions of GABA through interactions with the GABAA/BZ/chloride ionophore complex. The present study examines whether the in vivo hormone milieu of rats modulates GABA/BZ receptors and/or benzodiazepine responses. The influences of gender, estrous cycle, and the diminution of steroid levels on GABA/BZ receptors and BZ anticonvulsant responses were tested by comparing these parameters in groups of intact male, intact female, orchidectomized, and ovariectomized rats. The hormonal milieu appears to modulate the GABA recognition site and possibly GABA-related responses in rats. This is evidenced by the decrease in cortical GABAA receptor affinity seen in females compared with other hormone groups and the gender-related difference observed in susceptibility to seizures induced by the GABA antagonist bicuculline. In cycling females, high circulating levels of progesterone were correlated with heightened seizure thresholds, suggesting that progestins serve a protective role in the control of seizure activity. Although a gender-related difference in cortical BZ binding affinity was observed, BZ receptor parameters in several other brain areas and BZ anticonvulsant responses were unaffected by physiological fluctuations in gonadal hormones.
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PMID:Influences of gender, gonadectomy, and estrous cycle on GABA/BZ receptors and benzodiazepine responses in rats. 135 68

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in brain, opens chloride channels through actions on GABAA receptors. We now report base and amino acid sequences of the alpha 1, alpha 2, and alpha 3 subunits from GABAA receptors of audiogenic seizure-prone (DBA/2J) and -resistant (C57BL/6J) inbred strains of mice. Inbreeding had fixed different alleles of the alpha 1 subunit in the two strains, giving five base differences in the cDNAs. None of these affected amino acid sequence, but one did create a NsiI restriction site potentially useful in mapping genomic DNA. No base or amino acid sequence differences between the strains were detected for the other two subunits. Northern blots revealed no apparent strain differences in message levels for these three subunits in whole brains of the mice at 3 weeks of age, the peak of seizure susceptibility in DBA/2J, but did reveal distinct regional and developmental patterns of expression among the subunits in mouse brain.
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PMID:The alpha 1, alpha 2, and alpha 3 subunits of GABAA receptors: comparison in seizure-prone and -resistant mice and during development. 135 7

The involvement of synaptosomal neurotransmitter amino-acids in seizure susceptibility and seizure severity was explored. The amino-acid contents of brain synaptosomes were determined in three sublines of Rb mice differing in their response to an acoustic stimulus: Rb1, clonic-tonic seizure-prone, Rb2, clonic seizure-prone, and Rb3, seizure-resistant. Synaptosomes were prepared from 6 brain areas considered to be involved in seizure activity: olfactory bulbs, amygdala, inferior colliculus, hippocampus, cerebellum, pons-medulla. The steady-state levels of GABA and glycine (Gly), inhibitory amino-acids, of taurine (Tau), an inhibitory neurotransmitter of neuromodulator, of aspartate (Asp) and glutamate (Glu), excitatory amino-acids, as well as of serine (Ser) and glutamine (Gln), two precursors of neurotransmitter amino-acids, were determined by HPLC. Low levels of Tau, GABA, and Ser in hippocampus, Gly in amygdala, Glu in hippocampus, inferior colliculus and pons, Gln and Asp in inferior colliculus appeared to correlate with seizure-susceptibility. GABA and Asp in olfactory bulb, Gln in amygdala, hippocampus and pons, ser in olfactory bulb and pons, appeared to be associated either with seizure-severity or -diversity. A strong involvement of hippocampus (Tau, GABA, Ser, Glu, and Gln) and inferior colliculus (Asp, Glu, Gln) in audiogenic seizure-susceptibility, and of olfactory bulb (GABA, Asp) in seizure-severity and/or -diversity is suggested.
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PMID:Involvement of synaptosomal neurotransmitter amino acids in audiogenic seizure-susceptibility and -severity of Rb mice. 135 66

The influence of sustained epileptic seizures evoked by intraperitoneal injection of kainic acid on the gene expression of the neuropeptides somatostatin and neuropeptide Y and on the damage of neurons containing these peptides was studied in the rat brain. Injection of kainic acid induced an extensive loss of somatostatin and, though less pronounced, of neuropeptide Y neurons in the inner part of the hilus of the dentate gyrus. Neuropeptide Y-immunoreactive neurons located in the subgranular layer of the hilus, presumably pyramidal-shaped basket cells, were spared by the treatment. Although neuropeptide Y messenger RNA was not detected in granule cells of control rats, it was found there after kainic acid seizures at all time intervals investigated (12 h to 90 days after injection of kainic acid). High concentrations of neuropeptide Y messenger RNA were especially observed 24 h after injection of kainic acid. At this time neuropeptide Y messenger RNA was also transiently observed in CA1 pyramidal cells. Neuropeptide Y synthesis in granule cells in turn gave rise to an intense immunoreactivity of the peptide in the terminal field of mossy fibers which persisted for the entire time period (90 days) investigated. In addition, neuropeptide Y messenger RNA concentrations were also drastically elevated in presumptive basket cells located at the inner surface of the granule cell layer, especially at the "late" time intervals investigated (30-90 days after kainic acid). These data support the concept that extensive activation of granule cells by limbic seizures contributes to the observed neuronal cell death in CA3 pyramidal neurons and interneurons of the hilus. Consecutively, basket cells containing neuropeptide Y and presumably GABA might be activated and participate in recurrent inhibition of granule cells. Neuropeptide Y-immunoreactive fibers observed in the inner molecular layer at "late" time intervals after kainic acid may result either from collateral sprouting of mossy fibers or from basket cells extensively expressing the peptide. It is speculated that neuropeptide Y synthesized and released at a high rate from granule cells and basket cells may exert a protective action against seizures.
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PMID:Functional changes in neuropeptide Y- and somatostatin-containing neurons induced by limbic seizures in the rat. 136 Jan 55

Limbic seizure-activity was induced by injecting kainic acid into the amygdala of rats. Extracellular levels of amino acids were monitored by microdialysis in the hippocampus. No changes were detected in the levels of glutamate and aspartate. The level of glycine also remained unchanged, whereas GABA showed an increase of approximately 35%. The level of glutamine decreased by approximately 30%, and that of serine by approximately 20%. The results indicate that increased turnover may exist in the glutamate transmitter pool. In addition, impairment of GABA-release seems not to be a pathogenetic factor in seizure-induced hippocampal neuron loss. It is concluded that even during sustained seizure-activity, the extracellular level of glutamate, is maintained within narrow limits. A proposed index for excitatory neurodegeneration, glutamate x glycine/GABA, was found to be decreased in this seizure model. We therefore suggest that seizure-induced neuron death is not reflected by alterations in the extracellular levels of glutamate and aspartate, thought to act as direct neurotoxins.
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PMID:Limbic seizure-induced changes in extracellular amino acid levels in the hippocampal formation: a microdialysis study of freely moving rats. 136 14


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