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

We describe an animal preparation in which a semichronic or chronic limbic epileptiform syndrome can be produced reliably by unilateral microinjection of tetanus toxin in cat ventral hippocampus. Injections were given at 1-week intervals until abnormal EEG activity was observed. After two to five injections, the animals abruptly began to exhibit intermittent spikes and subclinical discharges that soon gave way to spontaneous and recurrent behavioral seizures which gradually increased in frequency, duration, and severity in the next 12-48 h. Anticonvulsant therapy (phenobarbital, PB) was required within the first 3 days of the syndrome, since life-threatening generalized tonic-clonic seizures (GTCS) and status epilepticus would develop if the animal were left untreated. If severe seizures were prevented by antiepileptic drugs (AEDs) there was complete remission of the syndrome and repeat injection was necessary to reinitiate seizures. Animals that experienced severe seizures or that were reinjected after remission developed a chronic seizure syndrome and could be maintained with AEDs for long times (greater than 1 year) without significant debilitation. Although early spikes and subclinical discharges were typically focal to ipsilateral limbic sites, initial seizures appeared explosively in the form of a high-amplitude, high-frequency discharge, which often had an apparently bilateral limbic onset. On the other hand, chronic seizures had much more gradual onset and spread, often consisting of periodic sharp waves or low-amplitude sinusoidal discharge that was more clearly focal to ipsilateral limbic sites. Throughout the syndrome, ictal behavioral manifestations were highly stereotyped and very comparable to those described by other investigators in studies of clinical and experimental limbic epilepsy. All animals exhibited signs of independent contralateral involvement during the syndrome, ranging from independent contralateral spikes to subclinical discharges with a clear contralateral onset. None of the animals exhibited structural lesions on histologic examination at the level of light microscopy.
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PMID:Chronic/semichronic limbic epilepsy produced by microinjection of tetanus toxin in cat hippocampus. 159 13

A small dose of tetanus toxin (2-5 ng; 10 mouse LD50) injected into the rat hippocampus produces a chronic epileptic syndrome in which epileptic discharges recur intermittently for 6-8 weeks. Hippocampal slices prepared during this period and maintained in vitro generate both evoked and spontaneous epileptic discharges. The present study used slices prepared 8-18 days after injection of tetanus toxin or vehicle solution into both hippocampi to test whether or not synaptic inhibition was selectively impaired in this experimental epilepsy. Intracellular recordings were made from CA3 pyramidal layer neurones within the tetanus toxin focus, which was identified by field potential recordings of synchronous bursts evoked by afferent stimulation. The intrinsic properties of these neurones did not differ from comparable cells in control-injected rats. All cells generated excitatory postsynaptic potentials (EPSPs) following stimulation of stratum radiatum in CA3. In control slices EPSPs were followed by a 'fast' inhibitory postsynaptic potential (IPSP), peaking at 25-30 ms, with a mean amplitude (+/- SEM) of -6.7 mV (+/- 0.66). In the epileptic slices these were absent, and the EPSP prolonged so that the potential at 30 ms was a depolarisation of +6.6 mV (+/- 2.75). The slow IPSP at 120 ms dropped to -0.27 mV (+/- 0.18) from -3.97 mV (+/- 1.43) (11 cells in each group). The loss of IPSPs cannot be attributed to a shift in reversal potentials in the toxin-injected group because no IPSPs were unmasked by current injection (n = 11). IPSPs also occurred spontaneously in the neurones in control slices, with a mean amplitude of -1.30 mV. Their frequency decreased by a factor of 13 in cells from the chronic focus induced by tetanus toxin (P less than 0.0001, analysis of variance), but their amplitude did not change significantly (mean of -1.22 mV). Spontaneous EPSPs were significantly more frequent and slightly smaller in the toxin-injected group (mean amplitudes 1.35 and 1.13 mV respectively). Together these studies support the hypothesis that the chronically recurring seizures induced by low doses of tetanus toxin can be attributed to a substantial, persistent and selective reduction of inhibitory neurotransmission in the hippocampus.
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PMID:Sustained and selective block of IPSPs in brain slices from rats made epileptic by intrahippocampal tetanus toxin. 161 77

Limbic projection from the amygdala to the basal forebrain and the neostriatum was studied physiologically during development of amygdaloid kindling in cats. Stimulation of the basolateral amygdaloid nucleus (BL) produced the negative field potential monosynaptically in the nucleus accumbens (Acb), while in the caudate nucleus (Cd) it produced a slight negative deflection with a longer latency. The latter is produced disynaptically as it showed marked facilitation in its amplitude when two stimuli were applied at short intervals. After a single period of tetanic stimulation of the BL with a 2-s train of 50-Hz pulses, there was a long-term potentiation (LTP) of both Acb and Cd responses in amplitude to test pulses to the same electrode. These responses increased up to 140% of the pre-tetanus control for 1 h following tetanic stimulation and declined gradually back to the baseline thereafter. However, a slight or moderate increase in the response was observed even 24 h later. Therefore, trains of stimuli presented once per day had a cumulative effect on the negative field potentials evoked in the Acb and the Cd in the early stage of kindling development. In particular, the disynaptic response in the Cd increased markedly to over 10 times as the prekindled control. These findings suggest that LTP in amygdalo-striatal synaptic transmission following tetanic stimulation represents an example of plastic changes in a neuronal chain within the neostriatum, which would underlie the pathophysiological mechanism for developing motor seizures of amygdaloid kindling.
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PMID:Long-term potentiation of the amygdalo-striatal synaptic transmission in the course of development of amygdaloid kindling in cats. 166 Sep 86

Electroconvulsive shock-induced seizures elevate seizure thresholds in humans and interfere with kindling in animals; opioids may mediate the anticonvulsant mechanism. In a potential model of acute electroconvulsive shock in hippocampal slices, a high-intensity tetanus via the mossy fibers substantially delayed subsequent in vitro kindling through the Schaffer collaterals. Naloxone blocked this effect, implicating the opioid system in the antiepileptogenic properties of this model.
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PMID:Naloxone blocks antiepileptogenic properties of an in vitro electroconvulsive shock model. 168 76

The tetanus toxin model of epilepsy, involving direct microinjection of toxin into the mammalian brain, has a number of advantages relative to other chronic models. However, chronic seizure foci have been confined primarily to the hippocampus. In the present study, 5 cats received total doses of 7.5-22.5 ng of tetanus toxin applied to the left primary motor cortex through an epidural cannula. After 2-18 days, all 5 cats exhibited similar persistent epileptiform syndromes. Three distinct types of spontaneous seizures were noted: focal motor seizures of variable complexity, focal motor seizures with secondary generalization, and epilepsia partialis continua. All cats required anticonvulsant therapy. Simple focal motor seizures, which predominated, were electrographically characterized by 3-5 Hz spike-sharp wave activity, originating in the left motor cortex, associated with contralateral shoulder and forepaw clonus and jacksonian spread. Electrographic activity quickly spread to ipsilateral neocortical structures, and in longer episodes to the cingulate gyri. Seizure foci were still active as long as 37 days after toxin injection. Light microscopic damage attributable to the toxin was absent. These experiments further generalized the tetanus toxin model and confirmed its advantages.
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PMID:Chronic focal epilepsy induced by microinjection of tetanus toxin into the cat motor cortex. 169 99

The chronic epileptic syndrome induced by injecting tetanus toxin into rat hippocampus causes functional changes that essentially are permanent, outlasting the period of active seizures by at least 1 year. These long-term changes have been characterized by an impaired performance on a range of behavioral tasks, which in turn have been associated with a physiologic depression of hippocampal evoked responses but not with any discernible histopathology. In the present study, we examined the hippocampi of rats in the postseizure phase of the tetanus toxin model and observed no significant changes in the concentration of neurochemical markers for six neurotransmitters. Therefore, the long-term reduction in hippocampal excitability cannot be attributed to any major loss of afferents or hippocampal neurons using aspartate, acetylcholine, gamma-aminobutyric acid (GABA), glutamate, norepinephrine (NE), or serotonin as their transmitters.
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PMID:Lack of change in neurochemical markers during the postepileptic phase of intrahippocampal tetanus toxin syndrome in rats. 170 Sep 50

The role of the forebrain commissures and the septal area in the interhemispheric transfer of hippocampal afterdischarges (ADs) was investigated in the rat under halothane anesthesia. Electrical seizures were elicited from the dorsal hippocampus before and after commissurotomy. The degree of relatedness between EEG signals recorded from homologous sites of both hippocampi was quantified using two approaches: (i) a time domain analysis considering an AD as a succession of discrete bursts; the onset times of such bursts were measured and used to estimate interhemispheric onset delays; (ii) using signal analysis the linear (r2) and non-linear (h2) regression coefficients between pairs of EEG signals were computed as a function of time shift between the two signals. In this way the values of association (linear and non-linear) and the corresponding time delays were measured. In general a tetanus applied unilaterally to the dorsal CA3 field resulted in bilaterally synchronous ADs. The estimated interhemispheric time delay was in most cases zero. This bilateral synchrony disappeared after section of a specific part of the ventral hippocampal commissure (VHC), the dorso-caudal third, but was not affected by section of other commissural fibers or by a lesion of the septal area. This study also allowed evaluation of different methods of quantification of the association between EEG signals, namely the linear (r2) and the non-linear (h2) regression coefficients. The latter was shown to be a more robust measure than the former and to yield values of association even in cases in which r2 was at noise level. The experimental findings allow the conclusion that ADs elicited from an epileptogenic focus spread to homologous sites in the contralateral hemisphere following commissural systems that may be strong enough to ensure the forming of one bilateral oscillating system.
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PMID:The role of hippocampal commissures in the interhemispheric transfer of epileptiform afterdischarges in the rat: a study using linear and non-linear regression analysis. 170 Nov 20

The behavioural effects of tetanus toxin, injected into the rostral hippocampus, have been studied in rats. A single dose (1000 mouse minimum lethal doses; n = 10) of the toxin produced tail rigidity, hunched back and sound- and touch-evoked stimuli, 48 hr after the injection in all rats treated and these culminated in generalized convulsions 5-7 days later. Seizures were also observed 4 days after the injection of 2000 MLDs (n = 10), whereas a dose of 500 MLDs (n = 10) was ineffective. Similarly, dose- and time-dependent lethal effects were observed. In comparison to the contralateral (untreated) hippocampus, tetanus toxin (1000 MLDs; n = 3) produced a statistically significantly reduction in the number of cells in the CA1 pyramidal cell layer of the injected side, 7 and 10 days after the injection. No changes were observed in other sectors (CA2 and CA3 areas) of the hippocampus. In conclusion, the present experiments have shown that the focal injection of tetanus toxin into the hippocampus produced dose- and time-dependent behavioural stimulation and lethal effects in rats.
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PMID:Behavioural and neuropathological effects produced by tetanus toxin injected into the hippocampus of rats. 227 11

116 immunizations were given to 61 children with febrile convulsion or epilepsy who had not had a seizure for 1 year since the last attack. In 92 of the 116 immunizations the electroencephalogram (EEG) was examined before and after immunization. No adverse effects on the EEG were observed in 19 immunizations with Japanese encephalitis, measles, mumps or rubella vaccines. Epileptic spikes reappeared after 10 immunizations and epileptic spikes increased after 10 immunizations among 73 given for diphtheria, acellular pertussis and tetanus (DPT), diphtheria and tetanus (DT), or Bacillus Calmette-Guerin (BCG). A convulsion was observed once in one child 7 days after immunization with BCG. A follow-up EEG examination is necessary after children with convulsive disorders are immunized.
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PMID:Adverse effects on EEG and clinical condition after immunizing children with convulsive disorders. 228 15

Tetanus toxin (about 20 mouse LD50) injected into the ventral hippocampus of rats leads to brief seizures occurring intermittently over a period of weeks. Toxin injection leads to the appearance of activated microglia (detected with OX42 immunohistochemistry) in the hippocampus. After 7-14 days, many activated microglia are visible in CA1 area of dorsal hippocampus aligned with the pyramidal cell dendrites and having the morphology characteristic of 'rod cells'. Extensive cell loss is found in dorsal CA1, but not at the injection site, in about one third of injected rats.
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PMID:Tetanus toxin-induced seizures cause microglial activation in rat hippocampus. 229 95


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