Facilitation of Amygdala Kindling Development and Kindled Seizures by Metaphit

Summary: The effect of metaphit (a phencyclidine analogue with an acylating isothiocyanate) on kindling development and kindled seizures from amygdala was investigated in rats pretreated once with metaphit. Administration of a single dose of metaphit (10 or 20 mg/kg intraperitoneally i.p.) 4 h before the first electrical stimulation of the amygdala did not in itself induce seizures, but greatly facilitated development of behavioral seizures during kindling. This effect persisted throughout the whole process of electrical amygdala kindling without further dosing. In contrast, metaphit only transiently and modestly increased the growth of afterdischarge (AD) duration. In kindled rats, pretreatment with a single dose of metaphit (20 mg/kg) 8 h before the test stimulation reduced the threshold current required to elicit a stage 5 seizure and shortened the latency for bilateral forelimb clonus (BFC) without changing AD duration or BFC duration. The facilitation of kindling development and kindled seizures may be due to an excessive excitatory transmission by metaphit in the limbic seizure circuitry.     

Abnormalities in Monoamine Levels in the Central Nervous System of the Genetically Epilepsy-Prone Rat

Norepinephrine, dopamine, and 5-hydroxytryptamine concentrations were determined in the central nervous systems of genetically epilepsy-prone rats (GEPR) and in control rats. Norepinephrine concentrations were abnormal in all major areas of the central nervous system of the GEPR, with decrements existing in the telencephalon, hypothalamus-thalamus, midbrain, pons-medulla and spinal cord. An increment in the concentration of this neurotransmitter existed in the cerebellum. Dopamine concentrations were normal in all areas of the GEPR brain. Abnormalities in 5-hydroxytryptamine concentrations were also present in the GEPR. They were exclusively decrements and occurred in the telencephalon, hypothalamus-thalamus, midbrain, and pons medulla. Concentrations of this neurotransmitter were normal in the cerebellum and spinal cord. Coupled with our earlier pharmacologic data, these observations support our concept that noradrenergic and/or 5-hydroxytryptaminergic decrements are etiologically important in seizure susceptibility in the GEPR. The lack of abnormalities in brain dopamine concentrations strengthens our hypothesis that dopaminergic transmission does not regulate seizure susceptibility in this model.     

Indices of Noradrenergic Function in the Central Nervous System of Seizure-Naive Genetically Epilepsy-Prone Rats

Norepinephrine concentrations and tyrosine hydroxylase activity were determined in the brains of moderate-seizure and severe-seizure genetically epilepsy-prone rats (GEPRs) and in nonepileptic control rats. Both moderate-seizure (GEPR-3) and severe-seizure (GEPR-9) animals had widespread abnormalities in brain norepinephrine concentrations. Abnormalities in tyrosine hydroxylase activity were restricted to the midbrain. The state of abnormal seizure susceptibility, but not severity, in the GEPR may be determined by noradrenergic deficits in the hypothalamus/thalamus. Both seizure severity and susceptibility may be determined by noradrenergic deficits in the telencephalon, midbrain, and pons-medulla. Seizure severity but not susceptibility may be determined by noradrenergic abnormalities in the cerebellum.     

Effect of Midbrain and Pontine Tegmental Lesions on Audiogenic Seizures in Genetically Epilepsy-Prone Rats

A bilateral mechanical lesion of the midbrain and pontine tegmentum was found to abolish completely the tonic components of sound-induced seizures in genetically epilepsy-prone rats (GEPR) that display tonic-clonic seizures. Correlations between varied lesions placements and effects on maximal audiogenic seizures provided evidence that damage to the nucleus reticularis pontis oralis (RPO) of the midbrain and pontine reticular formation (RF) was responsible for the seizure-attenuating effects. Moreover, electrolytic lesions of the pontine RF involving the RPO nucleus were found to abolish the tonic components of the maximal audiogenic seizure. Additionally, bilateral mechanical lesions involving the RPO nucleus were found to attenuate the clonic components of sound-induced seizures in GEPR that display only running seizures and clonus. These findings are consistent with previous studies showing that pontine tegmental lesions attenuate the tonic components of maximal electroshock- and pentylenetetrazol-induced seizures, and lend further support to the hypothesis that all generalized tonic seizures share a common neural substrate. The role of the brainstem RF in tonic versus clonic convulsions is discussed in light of the present findings.     

Regional Forebrain Noradrenalin Release in Response to Focal and Generalized Seizures Induced by Hippocampal Kindling Stimulation

In vivo microdialysis was used to monitor noradrenalin (NA) release in the rat hippocampus, sensorimotor cortex and amygdala in response to seizures induced by electrical kindling stimulation in the hippocampus. Generalized seizures increased NA output in the hippocampus five-fold above baseline level (as assessed with 2-min sampling periods). The peak value was seen 2–4 min after onset of seizure activity and baseline was reached after another 6–8 min. In the sensorimotor cortex, there was a seven-fold increase showing a similar time-course. Focal hippocampal seizures gave rise to three-fold and 80% increases above baseline in the hippocampus and sensorimotor cortex, respectively. A unilateral knife transection of the dorsal noradrenergic bundle reduced hippocampal NA release induced by focal seizures by 53%. In animals subjected to 30 stimulus-evoked seizures with 5-min intervals ('rapid kindling'), maximal NA output was observed after the third seizure in both hippocampus (237% increase) and amygdala (122% increase). NA levels tapered off with repeated stimulation and reached baseline after nine stimulations in the hippocampus; in the amygdala, the NA output was still slightly elevated at the end of the stimulation period. These results indicate that there is a general activation of the locus coeruleus system during focal as well as generalized seizures, as evidenced by marked increases in transmitter release from noradrenergic terminals in all forebrain areas studied. NA output in areas exhibiting seizure activity is dependent on impulse flow in locus coeruleus neurons and probably also on local regulatory mechanisms active at the noradrenergic terminal level. The increase in inhibitory noradrenergic transmission in both epileptic and non-epileptic brain regions may dampen ongoing seizure activity as well as lessen its spread and generalization.     

Abnormalities in Brain Serotonin Concentration, High-Affinity Uptake, and Tryptophan Hydroxylase Activity in Severe-Seizure Genetically Epilepsy-Prone Rats

Summary: We characterized the nature of the deficit in brain serotonin (5-HT) exhibited by genetically epilepsy-prone rats (GEPR-9s) by regionally assessing three markers for 5-HT terminals/neurons (5-HT content, 5-HT uptake into the P₂synaptosomal fraction, and tryptophan hydroxylase activity) in GEPR-9s and nonepileptic control rats. As compared with controls, GEPR-9s had reduced brain 5-HT concentration, synaptosomal 5-HT uptake, and tryptophan hydroxylase activity (measured in vivo and in vitro) in most regions of the forebrain and in selected regions of brainstem. Analysis of kinetic constants for synaptosomal [³H]5-HT uptake and in vitro tryptophan hydroxylase activity showed that the decrements in these parameters exhibited by GEPR-9s resulted from reductions in V _max rather than changes in K_m . In general, the reduction in each of the presynaptic markers for 5-HT terminals/neurons was similar in both magnitude and in their regional distribution in the GEPR-9 brain. An exception to this was noted in the midbrain tegmentum of GEPR-9s, which displayed a significant reduction in tryptophan hydroxylase activity without showing alterations in 5-HT concentration or in high-affinity 5-HT uptake. The present findings support the hypothesis that there is a widespread reduction in the number of serotonergic terminals/neurons in GEPR-9 brain.     

Differences Between Two Feline Epilepsy Models in Sleep and Waking State Disorders, State Dependency of Seizures and Seizure Susceptibility: Amygdala Kindling Interferes with Systemic Penicillin Epilepsy

The objective of the study was to determine whether contemporary feline models of petit mal (systemic penicillin epilepsy) or temporal lobe epilepsy (amygdala kindling) resemble human seizure disorders with respect to disturbances of sleep and waking states, the state dependency of seizures, and transference of seizure susceptibility. These variables were examined in 6-h polygraphic recordings before and during exposure to both seizure models in 24 cats; 12 cats had intramuscular (i.m.) injections of 300,000 or 400,000 IU/kg of penicillin prior to kindling, and 12 were kindled before penicillin challenge. Results were as follows. First, penicillin increased light slow wave sleep (SWS) and drowsiness, during which spike-wave (SW) activity was maximal. Generalized tonic-clonic convulsions (GTCs) occurred predominantly in drowsiness after awakening from SWS. Second, kindling produced more deep SWS than did penicillin; susceptibility to kindled GTCs peaked during deep SWS, especially in transition to rapid eye movement sleep (REM). Third, penicillin did not influence subsequent sleep disorders or seizure susceptibility during kindling; kindling interfered with penicillin-induced GTCs, SW activity, and sleep disorders. Collectively, the findings suggest distinct state disorders and state-dependent seizure profiles in the two models. These differences parallel human analogues and may have contributed to the transference results. Kindling is a chronic model with persistent sleep and seizure abnormalities that differ from and may have discouraged penicillin epilepsy. Penicillin is an acute model with transient state and seizure disorders, a fact that may account for the absence of penicillin transference to kindling.     

Short bursts of weak pulses break postictal inhibition in the neocortex of Wistar rats

PURPOSE: Postictal inhibition (PI) is a decrease in excitability that follows an epileptic seizure and decreases probability of new seizure occurrence. PI may involve both increased inhibition and persisting elevated excitation. Our experiments tested whether shorter trains of weak stimuli are able to unmask this residual increase of excitability during the PI. METHODS: Four epileptic afterdischarges (ADs) were evoked by intense electrical stimulation (20 s, 8 Hz, current intensity at 5x threshold) of the neocortex in two groups (A, B) of Wistar rats. Before the first AD and during the 10-min interictal period, 8-Hz trains of four weak pulses (half of the intensity used for the AD triggering; 4P) were applied every 20 s in group B and a single pulse with similar parameters in group A. RESULTS: The number of interictal epileptiform events evoked by 4P in the group B was significantly higher than that in the group A (evoked by single pulses) except after the second AD. Epileptic events were triggered by 4P also immediately after the AD termination. CONCLUSIONS: It is apparent that weak stimulation can trigger epileptic phenomena during PI. Our results indicate that it is no longer possible to perceive PI only as persisting extreme and active inhibition. An appropriate stimulation can reveal more subtle (but important) excitatory events contributing to the functional status during the postictal period.     

Role of Brainstem Structures in Seizures Initiated from the Deep Prepiriform Cortex of Rats

Summary: Previous studies showed that brainstem sei zures can still be evoked after transections that separate forebrain from brainstem. We sought to determine wheth er forebrain-evoked electrographic seizures require brain stem connections for initiation and generalization. Male Sprague-Dawley rats weighing 295–320 g implanted with epidural electrodes had brain transections placed at the pre-, mid-, or postcollicular level. In experiment 1, the transections were limited to severing the brainstem, spar ing the telencephalon laterally; these are referred to as “core” transections. In experiment 2, the transections severed the brainstem and also cut through the lateral telencephalon. These “extended” transections were ei ther (a) bilateral, (b) unilateral (i.e., a hemitransection confined to one hemisphere), or (c) partial (sparing path ways ventral to the pretectal nuclei). All transections were performed under ether anesthesia, and seizures were initiated 3 h later by focal infusion of bicuculline (BIC) into the area tempestas (AT) through a previously implanted guide cannula. In experiment 1, bilateral fore brain electrographic seizures occurred in the complete absence of connections between forebrain and brainstem, showing that the brainstem is not required for forebrain evoked seizures. In experiment 2, forebrain seizures evoked by BIC in AT were suppressed by bilateral ex tended transections which interrupted connections be tween AT and the caudal lateral telencephalon. Under these circumstances, application of carbachol with BIC reinstated the forebrain seizure response. These results indicate that carbachol application served to compensate for loss of an excitatory influence on AT resulting from the severing of connections with the caudal telencepha lon. The demonstration of direct projections from ento rhinal cortex to AT using Fluoro-Gold tracing together with the finding that extended brain transections caudal to the telencephalon do not suppress focally evoked fore brain seizures provided further support for the notion that AT afferents from the caudal telencephalon regulate the sensitivity of AT to BIC. The present findings provide further evidence that seizure substrates in the forebrain and brainstem are separable and independent.     

Manganese and Epilepsy: Brain Glutamine Synthetase and Liver Arginase Activities in Genetically Epilepsy Prone and Chronically Seizured Rats

Summary: Low blood manganese (Mn²⁺) concentration is associated with epilepsy in humans and rats. The low Mn²⁺ concentration is attributed by some investigators to the seizure activity associated with the epilepsy, whereas others propose that the low Mn²⁺ concentration may be secondary to genetic mechanisms underlying the epilepsy. To begin to differentiate between these possibilities, Mn²⁺-binding enzymes of liver and brain (i.e., arginase and glutamine synthetase, respectively) were assayed in rats exposed to chronically induced seizures and in genetically epilepsy-prone rats (GEPRs). Chronic seizures caused a decrease in whole blood Mn²⁺ levels but did not affect brain Mn²⁺ concentrations. Arginase activity was increased in livers of rats with chronic seizure as compared with controls, but this difference was eliminated when Mn²⁺ was added to the assay. Brain glutamine synthetase activity was unaffected by chronic seizures, but the activity of this enzyme was significantly lower in GEPR brain than in control brain. Liver arginase activity tended to be lower in GEPRs, although the difference was not statistically significant. These data indicate that seizures affect liver arginase activity through changes in liver Mn²⁺ concentration, but GEPRs show abnormalities in Mn²⁺ -dependent enzymes apparently independent of seizure activity.     

Precipitous induction of audiogenic kindling by activation of adenylyl cyclase in the amygdala

Purpose: Kindling of audiogenic seizure (AGS) involves ≥14 AGS over 1–2 weeks in genetically epilepsy‐prone rats (GEPR‐9s) and induces gradual seizure duration increases, epileptiform electroencephalography (EEG), and emergence of post tonic clonus (PTC), which are long‐lasting. N‐methyl‐d ‐aspartate (NMDA)–receptor activation in lateral amygdala (LA) is implicated in AGS kindling initiation. However, the persistence of AGS kindling appears to be dependent on molecular mechanisms initiated by NMDA‐receptor activation, which may involve adenylyl cyclase (AC). This study attempted to mimic AGS kindling persistently in nonkindled GEPR‐9s by one‐time activation of AC in LA. Methods: The effects of a single focal bilateral microinjection into LA of an AC activator, MPB forskolin {7‐Deacetyl‐7‐[O‐(N‐methylpiperazino)‐γ‐butyryl]‐forskolin dihydrochloride} (25–100 pmol/side), on seizure behavior in GEPR‐9s were evaluated. Results: One‐time bilateral microinjection of MPB forskolin in GEPR‐9s precipitously induced an AGS kindling–like effect, which involved significant increases in seizure duration and long‐lasting susceptibility to AGS that culminates in PTC. This effect occurred at 24 h after MPB forskolin microinjection and lasted ≥5 weeks. The effect was seen when AGS was initiated at 1 and 12 h after microinjection, but not if AGS was induced only at 24 h, indicating the importance of the temporal proximity of AGS induction to the MPB forskolin microinjection. Discussion: These findings indicate that one‐time activation of AC within the NMDA receptor–mediated molecular cascade results in precipitous induction of AGS kindling. These data further suggest that AC activation in the LA may be an important epileptogenic mechanism that subserves the long‐lasting persistence of AGS kindling.     

Kindling of the Interpeduncular Nucleus and Its Influence on Subsequent Amygdala Kindling in Rats

Summary We examined the effect of interpeduncular nucleus (IPN) kindling on subsequent amygdala (AM) kindling in rats (n = 9). Eleven to 15 daily IPN stimulations at an afterdischarge (AD)-inducing threshold (40CL1000 PA, biphasic sine waves, 1–3 s) produced progressive AD growth (9 of 9 rats) and recruitment of behavioral seizures (7 of 9 rats). The final form of the latter was generalized tonic-clonic seizures with or without a limbic seizure component. The latter was associated with ictal involvement of AM and sensorimotor cortex. Subsequent AM kindling resulted not only in more rapid kindling, but also in tonic seizure associated with a protracted loss of postural control (5–20 s) not observed in animals undergoing AM kindling without previous IPN kindling (n = 5).These findings indicate that the IPN can be kindled and that subsequent AM kindling utilizes the proconvulsant neuroplastic changes that have been already established by IPN kindling.     

Bradycardia and asystole with the use of vagus nerve stimulation for the treatment of epilepsy: a rare complication of intraoperative device testing.

PURPOSES: A 56-year-old man with mild mental retardation, right congenital hemiparesis, and refractory partial seizures was referred for vagus nerve stimulation (VNS). METHODS: Routine lead diagnostic testing during the surgical procedure (1.0 mA, 20 Hz, and 500 micros, for approximately 17 s) resulted, during the initial two stimulations, in a bradycardia of approximately 30 beats/min. A third attempt led to transient asystole that required atropine and brief cardiopulmonary resuscitation. RESULTS: The procedure was immediately terminated, the device removed, and the patient recovered completely. A postoperative cardiologic evaluation, including an ECG, 24-h Holter monitor, echocardiogram, and a tilt-table test, was normal. CONCLUSIONS: Possible mechanisms for the bradycardia/asystole include stimulation of cervical cardiac branches of the vagus nerve either by collateral current spread or directly by inadvertent placement of the electrodes on one of these branches; improper plugging of the electrodes into the pulse generator, resulting in erratic varying intensity of stimulation; reverse polarity; and idiosyncratic-type reaction in a hypersusceptible individual. The manufacturer reports the occurrence rate in approximately 3,500 implants for this intraoperative event to be approximately one in 875 cases or 0.1%.     

Electrical Stimulation of the Centromedian Thalamic Nucleus in Control of Seizures: Long-Term Studies

Summary: Five patients with chronic incapacitating seizures averaging 15–5,000/month were selected for study. All patients had more than one seizure type and had received maximal doses of antiepileptic drugs (AEDs). The centromedian thalamic nucleus (CM) was stimulated electrically through bilateral multicontact platinum electrodes stereotaxically placed in CM and connected to internalized pulse generators. Electrophysiologic confirmation of electrode position included thalamically elicited recruiting responses and EEG desynchronization recorded at the scalp. Stimulation parameters were adjusted individually in the range of 450–800-μA intensity, 65 pps, 0.09 ms, in 1-min trains, alternating right and left side stimulation and with 4-min intervals delivered for 2 h/day. Quantitative evaluation included frequency of seizures/month, number of maximal interictal paroxysmal discharges, and frequency of background activities counted in selected scalp EEG samples, taken throughout the observation period (7–33 months). Significance of changes was evaluated by parametric Student's t test. Generalized tonic-clonic seizures (GTC) decreased dramatically, almost disappearing in all cases (p < 0.001), with a significant reduction in interictal paroxysmal discharges (p < 0.01) and a tendency toward an increase in EEG back-ground frequency. Other generalized seizures (atypical absences) decreased significantly, but there was no change in the number of complex partial seizures (CPS). CM stimulation is useful in control of GTC, but its beneficial effect on other seizure types has not been established.     

癫痫大鼠海马中神经肽Y表达的动态观察及其作用探讨

目的　探讨癫痫大鼠海马中神经肽 Y( NPY)表达的动态变化及其作用 ,以及外源性 NPY对癫痫的影响。方法　将 SD大鼠随机分为 4组 ,采用匹鲁卡品 ( PILO)癫痫动物模型及外源性 NPY侧脑室注入干预法 ,并以免疫组织化学染色观察 NPY的表达。结果　癫痫模型组 PILO注射后 ,门区、CA3区、CA1 区的 NPY阳性细胞数表达增多 ,1 2 h达高峰 ,以后逐渐下降 ,60 d又达一高峰 ;海马颗粒细胞层有 NPY异位表达 ,3 d时最明显 ;NPY干预组门区 NPY阳性细胞数较其对照组表达少。结论　 ( 1 )癫痫发作后急性期海马 NPY表达增多及颗粒细胞层出现异位表达 ,与癫痫发作有关 ;( 2 )外源性 NPY有抗癫痫作用。     

Localization of the Origin of Self-Sustained Afterdischarges (SSADs) in the Rat

The genesis of the thalamocortical self-sustained afterdischarge (SSAD) composed of spike-and-wave (S + W) rhythm was studied in adult male albino rats. Under control conditions, rhythmic electrical stimulation of the specific somatosensory nucleus of the thalamus always elicited type S + W SSAD. An electrolytic lesion of the nonspecific thalamic nuclei did not prevent generation of type S + W SSAD, while stimulation of the ventrobasal complex evoked both type S + W SSAD and another type of SSAD composed of large waves with superimposed fast activity. Elimination of the cortex (by suction or spreading depression) ipsilateral to the stimulated thalamus completely suppressed any possibility of the formation of type S + W SSAD; elimination of the contralateral cortex did not affect it. Our results suggest that the cortex is the decisive factor in the genesis of S + W rhythm, while the thalamus markedly influences the conditions of its formation.     

Efficacy and Safety of Vagus Nerve Stimulation in Patients With Complex Partial Seizures

Summary: A clinical trial of chronic intermittent vagal stimulation in five patients suggests that the procedure may be safe and effective as adjunctive treatment of medically intractable seizures of partial onset. Patients tolerated well the implantation of the neurocybernetic prosthesis and the vagal stimulation without serious physiological or lifestyle changes. Stimulation of the vagus nerve either reduced the seizure frequency or decreased the duration or intensity of seizures. Adverse side effects were limited to a tingling sensation in the throat and hoarseness during stimulation. A major complication was mechanical interruption of the wire-electrode circuitry, with consequent cessation of stimulation. The small number of patients and the relatively short follow-up period make this a pilot study, but the results are promising.     

Seizures produced by pilocarpine: Neuropathological sequelae and activity of glutamate decarboxylase in the rat forebrain

Morphological analysis of brains from rats receiving a convulsant dose of the muscarinic cholinergic agonist, pilocarpine hydrochloride (380 mg/kg), revealed a widespread damage to the forebrain as assessed by light microscopy 5–7 days after seizures. The substantia nigra, olfactory cortex, amygdala, hippocampus, septum, temporal cortex and thalamus underwent prominent morphological injury and cell loss. A concurrent assessment of the activity of -glutamate decarboxylase (GAD), the γ-aminobutryrate (GABA) synthesizing enzyme, demonstrated marked deficits in GAD activity in the brain regions undergoing morphological insult. Diazepam, 10 mg/kg, and scopolamine hydrochloride, 10 mg/kg, administered 30 min prior to the injection of pilocarpine, 380 mg/kg, prevented acute behavioral and electrographic, and long-term morphological and biochemical sequelae of seizures. These findings suggest that the muscarinic antagonist, scopolamine, and the anticonvulsant benzodiazepine, diazepam, may aid in preventing extensive brain damage related to pathological muscarinic cholinergic overactivity. The similarity of the topography of the damage and deficits in the GAD activity in brains of rats treated with pilocarpine indicates that GABAergic neurons are lost in the subregions of the brain preferentially sensitive to the convulsant action of pilocarpine.     

Effects of Taurine on Kindled Amygdaloid Seizures in Rats, Cats, and Photosensitive Baboons

Acute administration of taurine produced a transient loss of susceptibility to photically induced seizures in photosensitive baboons, but failed to affect kindled amygdaloid convulsions in baboons, rats, and cats. In addition, it was totally ineffective in changing the course of spontaneous status epilepticus in kindled cats. These results suggest that a taurine-deficiency model of epilepsy applies only to certain types of seizure-generating conditions, apparently excluding kindled amygdaloid convulsions.     

Electrical stimulation of the contralateral mesial temporal structure induces an ipsilateral seizure pattern in mesial temporal lobe epilepsy

PURPOSE: We examined the mode of seizure development induced by electrical stimulation in patients with mesial temporal lobe epilepsy. METHODS: Of 25 patients undergoing intracranial EEG evaluation and electrical stimulation ipsilateral to the presumed site of habitual seizure origin, 17 patients had additional stimulation studies on the contralateral temporal lobe. RESULTS: Fourteen of the 25 patients had seizures induced with ipsilateral stimulation, and two of the 17 patients had seizures with contralateral stimulation. Seizures induced by ipsilateral stimulation started in the ipsilateral temporal lobe, whereas those induced by contralateral stimulation originated from the ipsilateral temporal lobe structure and were identical to the habitual seizures. CONCLUSIONS: Electrical stimulation of the temporal lobe structure opposite the site of habitual seizure origin is said to induce a seizure rarely. However, according to our preliminary results, if contralateral stimulation elicits a habitual seizure in the ipsilateral temporal lobe, it might be considered additional confirmatory evidence of seizure lateralization.