Experimental study on epilepsy using a "kindling preparation". Correlation between septal seizure development and psychomotor seizure]

The seizure development was investigated in seven septal kindled cats for examining a participation of septal area in psychomotor epilepsy. Daily electrical stimulation (mean: 33.5 days) of septal area could lead to the "kindled" generalized convulsion. Six stages of behavioral seizure development were distinguished: 1) attention reaction, 2) the above and immobility, 3) the above and autonomic manifestation, 4) the above and facial twitching, head nodding, 5) the above and tonic extension of contralateral forepaw, 6) the above and generalized clonic convulsions. Self-sustained after-discharge and independent interictal spike discharge appeared in the hippocampus in stage 2 or 3, in the amygdala and the globus pallidus in stage 3 or 4, and also in the ventromedial hypothalamic nucleus in stage 5. Positive transference phenomenon was confirmed in bilateral hippocampus, amygdala and globus pallidus. These findings show the progressive dissemination of secondary epileptogeneses in these secondary brain structures during the septal seizure development. Electrographic and behavioral seizure development mentioned above were completely identical to those in the hippocampal seizure that we have reported previously. It is concluded that psychomotor epilepsies may not only be triggered by the hippocampal and amygdaloid foci but by the septum and its related structuresfoei.     

Effects of Unilateral Lesion in the Midbrain Reticular Formation on Kindled Amygdaloid Convulsion in Cats

Daily stimulation of the amygdala in cats resulted in progressive development of electroclinical seizures culminating in a generalized convulsion (kindling). An electrolytic lesion in the midbrain reticular formation, ipsilateral to the stimulated amygdala, markedly elevated the generalized seizure-triggering threshold and reduced susceptibility to pentylentetrazol challenge. In contrast, globus pallidus lesions had no appreciable effect upon the generalized seizure-triggering threshold and appeared to enhance susceptibility to pentylentetrazol. The results support the hypotheses that (1) the midbrain reticular formation participates significantly in the kindled amygdaloid seizures and (2) the effects of lesions in the midbrain reticular formation do not depend upon the presence of forebrain bisection.     

A Study on Psychomotor Epilepsy with "Kindled" Cat Preparations

Seizure development was examined in amygdaloid (AM), hippocampal (HIPP) and septal (SEPT) “kindled” cats by behavioral and electrographic methods. HIPP seizure developed into motor seizure after establishing secondary epileptogenesis in AM and globus paliidus. A secondary epileptogenesis in the hippocampus was not necessary for AM seizures to develop into generalized convulsions. The SEPT seizure development was almost identical to the hippocampal seizure development. This latter finding suggests that psychomotor epilepsy may not only be triggered by the HIPP and AM focus but by the septum and its related structures. In the second experiment, the effect of various neuroactive agents on the interictal discharge frequency was studied in AM and HIPP kindled cats. Clear antagonistic action of L-Dopa against reserpine or α-MPT induced increase of IID frequency was observed. Viewed in conjunction with our previous assay study of catecholamine that showed a marked depletion of both norepi-nephrine and dopamine, in hippocampal kindled cat brain, it can be concluded that catecholamine inhibits the establishment and activation of the kindled epileptic neuro-circuits.     

Endorphin mediation of post-ictal effects of kindled seizures in rats

Brief electrical stimulation of the enkephalin-rich globus pallidus at 1-h intervals produced kindled, clonic seizures in rats as rapidly as similar stimulation of the amygdala. Massing the kindling trials at 10-min intervals inhibited the occurrence of subsequent seizures, especially following globus pallidus stimulation. Naloxone (20 mg/kg), an opiate receptor antagonist, reversed this post-ictal inhibition of seizures following massed trials, but had no effect on seizures kindled at 1-h intervals. Thus, endorphin-released during seizures do not appear to mediate the production of kindled seizures, but do appear to mediate the transient posts ictal inhibition of seizures.     

Sleep, subcortical stimulation and kindling in the cat.

A longitudinal study of the effects of sleep on amygdaloid kindling showed that kindling disrupted normal sleep patterns by reducing REM sleep and increasing awake time. Few interictal spike discharges were observed during the awake stage, while a marked increase in discharge was observed during the light and deep sleep stages. No discharges were observed during REM sleep. During the immediate post-stimulation period the nonstimulated amygdala showed a much higher rate of spike discharge. On the other hand, there was an increase in spike discharge in the stimulated amygdala during natural sleep without preceding amygdaloid stimulation. Amygdaloid stimulation at the generalized seizure threshold during each sleep stage resulted in a generalized convulsion. The influence of subcortical electrical stimulation on kindled amygdaloid convulsions was investigated in a second experiment. Stimulation of the centre median and the caudate nucleus was without effect on kindled convulsions, while stimulation of the mesencephalic reticular formation at high frequency (300 Hz) reduced the latency of onset of kindled generalized convulsions. Stimulation of the nucleus ventralis lateralis of the thalamus at low frequency (10 Hz) prolonged the convulsion latency, and at high current levels blocked the induced convulsion. Stimulation in the central gray matter at low frequency (10 Hz) also blocked kindled amygdaloid convulsions.     

Hippocampal seizure and secondary epileptogenesis in the "kindled" cat preparations.

The behavioral, electrographic and transference characteristics were investigated in hippocampal kindled cats. All animals developed generalized convulsions following daily hippocampal stimulation (mean 51.8 days). A distinct sequence of behavioral events was observed prior to the seizure and classified into six stages. Motor seizure manifestations appeared along with the emergence of an entirely independent after-discharge and interictal discharge in the bilateral globus pallidus (GP) and amygdala (AM). Secondary site convulsions were triggered with initial stimulation in the GP, contralateral dorsal hippocampus and in most AM sites. This finding suggests that after the primary site was kindled, these previously unstimulated secondary structures attained a response potency equal to that of the primary site. Furthermore, the "all-or nothing" response was confirmed both in the primary and secondary site convulsions.     

Effect of pirenzepine, a muscarinic M1 receptor antagonist, on amygdala kindling in rat.

Kindling, an animal model of complex partial seizures with secondary generalization, is performed by daily application of low-intensity electrical brain stimulation. The purpose of this study was to investigate the role of muscarinic M1 receptors on amygdala kindling in the rat. Bipolar nichrome stimulation and recording electrodes were stereotaxically implanted into the right and left basolateral amygdala. Extradural recording electrodes were also placed bilaterally in the skull over the cortex. Amygdala stimulation was applied twice daily at the current intensity of afterdischarge threshold. Seizure intensity was graded by using Racine's standard five-stage scale. In the first group of experiments, saline or pirenzepine (10, 25, 50 and 100 nmol), a muscarinic M1 receptor antagonist, was injected intracerebroventricularly 1 h before the electrical stimulation. In the second group of experiments, rats were kindled to full stage 5 seizures. After a recovery period, 50 nmol of pirenzepine was administered intracerebroventricularly to kindled animals. In the first group of experiments, none of the animals pretreated with the doses of 50 and 100 nmol of pirenzepine reached a stage 5 seizure. Pirenzepine significantly retarded kindling seizure development and increased the total number of stimulations required to reach the first stage 5 seizure. Afterdischarge duration was also reduced in the pirenzepine 10 nmol group as compared with that in the saline-pretreated group. In the second group, seizure stage and afterdischarge duration were not affected by pirenzepine in fully-kindled animals. The findings of this study suggest that muscarinic M1 receptors may have a critical role in the development of kindling epileptic activity, but not in already kindled seizures.     

State disorders and state-dependent seizures in amygdala-kindled cats

This study replicated and extended previous work indicating a reciprocal relationship between persistent sleep disorders and seizure susceptibility in amygdala-kindled cats. Eight kindled cats (experimental group) and six nonkindled cats (control group) were assessed for several sleep and waking state parameters. Seizure susceptibility, indexed by thresholds to generalized afterdischarge and tonic-clonic convulsions, was also evaluated in experimental subjects during each of the following states: alert but quiet wakefulness, slow-wave sleep, transitions from slow-wave to REM sleep, and REM sleep. There were two primary findings: (i) slow-wave sleep and transitions from it to REM sleep were disrupted in amygdala-kindled cats whereas REM sleep was normal when an effective transition had been made; and (ii) disturbed states were also more susceptible to generalized seizures than were stable REM sleep and waking episodes, suggesting that abnormal rather than normal sleep created a predisposition for seizures.     

Anatomical correlates of electrical and behavioral events related to amygdaloid kindling

Anatomical structures demonstrating increased glucose uptake during the various stages of amygdaloid kindling in rats were identified by the ¹⁴C-2-deoxyglucose (DG) autoradiographic technique. Partial (stages 1 and 2) seizures were correlated with increased DG uptake in the ipsilateral amygdala and its direct projection fields. The appearance of generalized motor (stages 3, 4, and 5) seizures was accompanied by less limbic involvement and recruitment of a bilateral system including substantia nigra, specific and nonspecific thalamic nuclei, globus pallidus, and neocortex. Increased hippocampal DG uptake was correlated with prolonged amygdaloid afterdischarge duration but not with the behavioral seizure stage. This study does not reveal which of these structures are responsible for the observed behavioral and electrical events and which are activated by them. It does suggest, however, that three discrete anatomical systems underlie the generation of partial seizures, generalized motor seizures, and local afterdischarge.     

Spontaneous sleep epilepsy in amygdala-kindled kittens: a preliminary report

We describe a model of 'sleep epilepsy' after amygdala kindling in kittens. Seizure activity was evaluated at different times in the sleep-wake cycle. Susceptibility was documented by thresholds for evoked convulsions in kittens without spontaneous seizures (n = 5) and by polygraphic or split-screen video recordings in kittens with spontaneous seizures (n = 6). There were 3 main findings: (1) subconvulsive seizures occurred randomly in waking and slow-wave-sleep (SWS); (2) convulsive seizure activity peaked during SWS, especially during the transition from SWS into rapid-eye-movement (REM) sleep; (3) generalized seizure activity was suppressed during stable REM sleep. Seizure patterns thus resemble clinical data designating convulsive temporal lobe epilepsy (TLE) the prototypic pure sleep epilepsy, whereas complex-partial TLE can occur at any time. Prominent secondary TLE generalization during the REM transition suggested involvement of brainstem regions which generate REM onset and innervate the temporal lobe. Adrenergic cells of the locus ceruleus discharge at progressively reduced rates during the transition into REM. Decreased norepinephrine release at this time might disinhibit epileptic neurons in the kindled focus, thus encouraging seizure propagation during the REM transition.     

A study of psychomotor epilepsy with "kindled" cat preparations.

Seizure development was examined in amygdaloid (AM), hippocampal (HIPP) and septal (SEPT) "KINDLED" CATS BY BEHAVIORAL AND Electrographic methods. hipp seizure developed into motor seizure after establishing secondary epileptogenesis in AM and globys paliidus. A secondary epileptogenesis in the hippocampus was not necessary for AM seizures to develop into generalized conculsions. The SEPT seizure development was almost identical to the hippocampal seizure development. This latter finding suggests that psychomotor epilepsy may not only ne triggered by the HIPP and AM focus but by the septum and its related structures. In the second experiment, the effect of various neuroactive agents on the interictal dischage frequency was studied in AM and HIPP kindled cats. Clear antagonistic action of L-Dopa against reserpine or alpha-MPT induced increase of IID frequency was observed. Viewed in conjunction with our previous assay study of catecholamine that showed a marked depletion of both norepinephrine and dopamine, in hippocampal kindled cat brain, it can be concluded that catecholamine inhibits the establishment and activation of the kindled epileptic neurocircuits.     

Limbic seizures, but not kindling, reversibly impair place learning in the Morris water maze

We investigated the effects of kindling and kindled seizures in different limbic structures on place and cue learning in the Morris water maze. The triggering of seizures by stimulation of the perforant path, septum, or amygdala prior to daily training impaired place learning, but had little effect on visible platform training or swim speed. Seizures triggered by stimulation of the medial perforant path after daily training also impaired place learning. Conversely, place learning proceeded normally in rats tested 24 h after kindling triggered by stimulation of the perforant path, septum, or amygdala, indicating that kindling per se does not affect place learning. Each group was able to learn the location of a reversed platform when pretraining seizures were discontinued; and perforant path and septal kindled rats, but not amygdaloid kindled rats, were impaired at learning the location of a reversed platform when seizures were triggered before training. The results confirm previous reports that limbic seizures produce amnesia, but they contradict the finding that hippocampal kindling impairs learning on tasks sensitive to hippocampal lesions.     

Thalamic kindling: electrical stimulation of the lateral geniculate nucleus produces photosensitive grand mal seizures

Kindling is traditionally viewed as a chronic, focal epilepsy model which consistently induces complex partial seizures from limbic structures in animals. This study revealed that primary or exceedingly rapid secondary generalized seizures could also be kindled when stimulation was applied to the lateral geniculate nucleus, a thalamic region involved in sleep regulation and possibly also photosensitive epilepsy. Two experiments were conducted in cats. Experiment 1 compared the development of generalized tonic-clonic convulsions and associated sleep disorders following electrical stimulation of the lateral geniculate nucleus (N = 4) and the amygdala (N = 4). Experiment 2 described the effects of intermittent light stimulation on seizure thresholds in both groups. Three primary findings distinguished the epileptogenic process in those two brain regions. First, generalized electroencephalographic and clinical seizures accompanied the first afterdischarge obtained with thalamic stimulation. In contrast, focal seizures with secondary generalization appeared during a 3- to 4-week period of afterdischarge elicitations from the amygdala. Second, amygdala-kindled cats showed fewer sleep spindles during slow-wave sleep whereas cats kindled in the lateral geniculate nucleus had abnormal sleep spindles approaching spike wave-like activity. Third, only the latter cats showed reduced seizure thresholds in response to photic stimulation. Based on the anatomic substrates involved, the clinical and electrographic profiles observed during kindling and the type of sleep disturbance shown, we concluded that lateral geniculate nucleus kindling may represent primary generalized epilepsy, possibly of a photosensitive nature; alternatively, the rapid propagation of abnormal discharge was also consistent with the important role of the thalamus in secondary seizure generalization.     

Effect of transient hippocampal inhibition on amygdaloid kindled seizures and amygdaloid kindling rate

In this study the effect of transient inhibition of the CA1 region of the dorsal hippocampus by lidocaine on amygdala kindling rate and amygdaloid kindled seizures was investigated. In experiment 1, rats were divided into four groups. In group 1, animals were implanted only with a tripolar electrode into the amygdala but in groups 2-4, two guide cannulae were also implanted into the CA1 regions of the dorsal hippocampi. Animals were stimulated daily to be kindled. In groups 3 and 4, saline or 2% lidocaine (1 microl/2 min) was also injected respectively into the hippocampus, 5 min before each stimulation. Results obtained showed that amygdala kindling rate and the number of stimulations to receive from stage 4 to stage 5 seizure were significantly increased in group 4. In experiment 2, lidocaine (1% and 2%) was infused (1 microl/2 min) into the hippocampus of amygdala kindled rats bilaterally and animals were stimulated at 5, 15 and 30 min after drug injection. Twenty four h before lidocaine injection, saline was also infused (1 microl/2 min) into the hippocampus as control. Obtained results showed that afterdischarge duration was reduced 5 min after lidocaine (1% and 2%) injection. Stage 5 seizure duration was also decreased 5 and 15 min after 2% lidocaine. Thus, it may be suggested that in amygdala kindling, activation of the hippocampal CA1 region has a role in seizure acquisition and seizure severity so that inhibition of this region results in decreasing of seizure severity and retards amygdala kindling rate.     

Development of amygdaloid kindling in histidine decarboxylase-deficient and histamine H1 receptor-deficient mice

PURPOSE: This study attempted to clarify the role of histamine or histamine H1 receptors in the development of amygdaloid kindling by using histidine decarboxylase (HDC)-deficient and histamine H1 receptor (H1R)-deficient mice. METHODS: Under pentobarbital anesthesia, mice were fixed to a stereotaxic apparatus, and bipolar electrodes were implanted into the right amygdala. Electrodes were connected to a miniature receptacle, which was embedded in the skull with dental cement. A bipolar electroencephalogram was recorded; bipolar stimulation of the amygdala was applied every day with a constant-current stimulator and continued until a generalized convulsion was obtained. RESULTS: The development of amygdaloid kindling in HDC-deficient and H1R-deficient mice was significantly accelerated compared with that in their respective wild-type mice. In addition, the afterdischarge (AD) duration and generalized seizure duration in HDC-deficient and H1R-deficient mice were prolonged. Intraperitoneal injection of histidine resulted in an inhibition of amygdaloid kindled seizures in wild-type mice at doses that caused an increase in the histamine contents of the brain. However, no significant effect was observed with histidine in H1R-deficient mice at the same dose. CONCLUSIONS: These findings suggest that histaminergic mechanisms through H1 receptors play a crucial role not only in amygdaloid kindled seizures but also in the development of amygdaloid kindling.     

Role of the Claustrum in Convulsive Evolution of Visual Afferent and Partial Nonconvulsive Seizure in Primates

: Purpose: We tested cross-species validity of the role of the claustrum in the convulsive evolution of the visual afferent and amygdaloid seizure and the specificity of the claustral lesioning effect. Methods: In 7 Senegalese baboons, we examined the effect of unilateral claustral lesioning on generalized convulsive seizures either kindled from the amygdaloid nucleus (AM) and cingulate cortex (CG) or induced by intermittent photic stimulation (IPS) after systemic administration of D,L-allylglycine (AG). Results: A lesioned area common to all animals was the anterior half of the left claustrum. Postoperative restimulation of the kindled left AM or CG evoked only nonconvulsive seizures. When few convulsive seizures emerged in 1 CG-kindled animal, they were mirror image of the kindled seizure and arose from the nonlesioned right hemisphere. Restimulation of the kindled right AM or CG reactivated kindled seizures. An IPS-induced generalized convulsive seizure was transformed into a secondarily generalized seizure arising from the nonlesioned right hemisphere. Conclusions: The primate claustrum regulates the convulsive evolution of partial seizures originating from nonmotor structures such as the AM and CG and also regulates the convulsive development that follows IPS. Our findings suggest that predisposed susceptibility expressed at the claustrum may be involved in the clinical variation with respect to convulsive evolution of nonmotor partial seizures and convulsive susceptibility to IPS in human primates.     

Development of Kindled Amygdaloid Seizures After Section of the Forebrain Commissures in Rats

Repeated application of electrical stimulation to amygdala results in the progressive development and elaboration of clinical and electrographic seizures (kindling). The rate of kindling was compared in control rats and rats with various amounts of damage to the forebrain commissures. Partial or total tran-section of corpus callosum, hippocampal commissure, and anterior commissure did not retard the rate of kindled seizure development. In the few cases in which a retarded rate of kindling was observed, there was always evidence of unintended damage to rostral thalamic nuclei; no such damage was seen in forebrain-bisected rats that kindled at control rates. These results indicate that the forebrain commissures do not play an essential role in amygdaloid kindling, and they suggest that nuclei in the rostral thala-mus may participate in this phenomenon.     

Myoclonus inducing and seizure modifying effect of cysteamine on cortical and amygdaloid kindled rats

The effect of the somatostatin depleting substance, cysteamine (100 mg/kg, i.p.), on cortical and amygdaloid kindled seizures was investigated. Cysteamine was tested after the establishment of amygdaloid kindling (AM group) and at two different developmental stages of cortical kindling, namely ‘focal-cortical’ (FC group) and ‘cortico-generalized’ seizures (CG group). In control, non-kindled, sham operated animals, cysteamine did not induce any spike activity or myoclonus. However, in all kindled groups clustered spike bursting appeared in the cortex within 5–15 min of the injection. The kindled rats exhibited myoclonic jerks at 10 to 30 min after cysteamine injection, which coincided with the cortical spikes, and continued for about 40 min. In contrast, relatively small amounts of spiking were observed in the amygdala and this did not correlate with the myoclonus. At 4 h after cysteamine injection, the motor seizure and afterdischarge durations of the kindled seizure were prolonged in all kindled groups compared with preinjection levels. However, 24 h later the motor seizure duration and the afterdischarge duration were markedly reduced from the preinjection level in the AM and the CG groups and the tonic seizure components was suppressed in the FC group. This inhibitory effect on seizure activity lasted several days and gradually disappeared. These modifying effects of cysteamine were more marked in cortical kindled, than in amygdaloid kindled animals. The results suggest that the cortex is more sensitive to the effect of cysteamine than the amygdala, and that the effect of cysteamine on kindled seizures involves two phases. The first of these phases is excitatory and the second is inhibitory, presumably reflecting an early release-inducing and a later synthesis-inhibiting effect of cysteamine on brain somatostatin.     

Effects of Intraamygdaloid Injection of Taurine and Valyltaurine on Amygdaloid Kindled Seizure in Rats

Abstract: Antiepileptic effects of intracerebral injections of taurine and valyltaurine were examined in amygdaloid kindled rats. The effects were assessed whether the animals can evoke generalized seizures by a 10,μA higher stimulation intensity than triggering thresholds. In all fully-kindled animals that have received intraamygdaloid injection of 500 nmol taurine, the kindled seizure was completely abolished. Such a significant seizure suppression (p < 0.05) was observed 12–24 h after the taurine injection. Valyltaurine (500 nmol) also suppressed the seizure in 60% of animals tested, but the effect was not statistically significant. The results indicate that taurine may effectively suppress epileptic seizures when it acts directly at the stimulation site amygdala.     

Involvement of central histamine in amygdaloid kindled seizures in rats.

The involvement of central histamine in amygdaloid kindled seizures in rats was investigated using histamine-related compounds. Histamine contents in the amygdala of electrical stimulation site was significantly decreased after development of amygdaloid kindling. Intracerebroventricular (i.c.v.) injection of histamine resulted in inhibition of amygdaloid kindled seizures. The H(1)-agonists 2-methylhistamine and 2-thiazolylethylamine also inhibited amygdaloid kindled seizures. In addition, intraperitoneal (i.p.) injection of histidine and metoprine inhibited amygdaloid kindled seizures at doses that caused increases in histamine contents of the brain. H(1)-antagonists (diphenhydramine and chlorpheniramine) attenuated histamine (i.c.v.)-induced inhibition of amygdaloid kindled seizures, however, no significant antagonism was observed with H(2)-antagonists (cimetidine, ranitidine or zolantidine). Intracerebroventricular injection of H(3)-antagonists (thioperamide and AQ 0145) resulted in a dose-related inhibition of amygdaloid kindled seizures. The same findings were observed when thioperamide and clobenpropit were injected i.p. The effects of thioperamide (i.p.) and AQ 0145 (i.p.) were inhibited by an H(3)-agonist [(R)-alpha-methylhistamine] and H(1)-antagonists (diphenhydramine and chlorpheniramine). On the other hand, H(2)-antagonists (cimetidine and ranitidine) showed no antagonistic effects. These findings suggested that a histaminergic mechanism plays an important role in suppressing amygdaloid kindled seizures through histamine H(1)-receptors.