'Kindling' a sleep disorder: degree of sleep pathology predicts kindled seizure susceptibility in cats

Increased cortical excitability after selective REM sleep deprivation in healthy humans: a transcranial magnetic stimulation study

BACKGROUND

REM sleep has antiepileptogenic properties whereas, its loss is known to have a proconvulsive role. However, the mechanisms underlying the proepileptogenic effects of REM sleep deprivation are yet not fully understood. The aim of our study was to evaluate the effects of selective REM sleep deprivation (SRD) on cortical excitability in healthy subjects by means of transcranial magnetic stimulation (TMS).

METHODS

Ten normal subjects underwent three TMS sessions: (1) in baseline condition (BL), (2) after SRD by awakening them at each REM sleep onset and (3) after non-rapid eye movement sleep awakenings (NREM-A) as control for potential non-specific effects of interruptions. The TMS investigation included two protocols: (a) the evaluation of motor evoked potentials (MEPs) and silent period (SP) parameters, recorded in response to single pulse magnetic stimulation; (b) the evaluation of the time course of intracortical motor activity tested with paired-pulse TMS applied at inter-stimulus intervals of 1-10 ms.

RESULTS

After SRD the principal finding observed using single pulse TMS was a significant reduction in the duration of SP whereas, a reduction of intracortical inhibition was found, using the paired-pulse TMS. TMS parameters did not show significant changes after NREM-A with respect to BL.

CONCLUSIONS

SRD may influence cortical excitability with a reduction of inhibitory intracortical mechanisms, thus supporting the proconvulsant role of REM loss.

Single neuron burst firing in the human hippocampus during sleep

Although there are numerous non-primate studies of the single neuron correlates of sleep-related hippocampal EEG patterns, very limited hippocampal neuronal data are available for correlation with human sleep. We recorded human hippocampal single neuron activity in subjects implanted with depth electrodes required for medical diagnosis and quantitatively evaluated discharge activity from each neuron during episodes of wakefulness (Aw), combined stage 3 and 4 slow-wave sleep (SWS), and rapid eye movement (REM) sleep. The mean firing rate of the population of single neurons was significantly higher during SWS and Aw compared with REM sleep (p = 0.002; p < 0.0001). In addition, burst firing was significantly greater during SWS compared with Aw (p = 0.001) and REM sleep (p < 0.0001). The synchronized state of SWS and associated high-frequency burst discharge found in human hippocampus may subserve functions similar to those reported in non-primate hippocampus that require burst firing to induce synaptic modifications in hippocampal circuitry and in hippocampal projections to neocortical targets that participate in memory consolidation.

Gabapentin-induced modulation of interictal epileptiform activity related to different vigilance levels

OBJECTIVES

Gabapentin (GBP) is a novel antiepileptic drug (AED), currently used as add-on therapy in patients with partial seizures. Similar to other AEDs, little is known about its effects on nocturnal sleep, despite the strict relationship between sleep and epileptic discharges. The aim of our study was to evaluate the effects of chronic therapy with GBP on both nocturnal sleep and on interictal epileptiform abnormalities (IEA) in relation to the different sleep stages.

METHODS

Eighteen patients affected by partial seizures resistant to common AEDs were submitted to nocturnal polygraphic recordings under baseline conditions and after 4 months of add-on GBP treatment.

RESULTS

We observed a significant increase in unilateral/focal IEA during light NREM sleep and a significant reduction in bilateral/diffuse IEA during wakefulness after sleep onset (WASO) with respect to the baseline condition. A significant increase in REM sleep and slow wave sleep (SWS) associated with a reduction in the number of awakenings and Stage 1 was also observed after GBP chronic therapy.

CONCLUSIONS

GBP therapy improves the sleep pattern of epileptic patients and it seems to modulate the expression of IEA with different effects in relation to the various vigilance levels.

Ontogeny of feline temporal lobe epilepsy. III: Spontaneous sleep and arousal disorders in amygdala-kindled kittens

We report the ontogeny and persistence of sleep and arousal disorders in amygdala-kindled kittens. We also identify procedural differences that may explain discrepancies in the literature on postkindling sleep disorders. The study population consisted of 12 preadolescent kittens kindled between 2.5 and 6.5 months of age, 8 of which were followed to adulthood (> or = 1 year), and 8 unkindled implanted control animals. Sleep and seizure patterns were monitored on 12-24-h polygraphic or split-screen video recordings of EEG and behavioral activity. Kindled kittens displayed spontaneous seizure and interictal sleep anomalies that persisted to adulthood, as follows. As compared with neurosurgical controls, kindled kittens exhibited slow-wave sleep (SWS) and REM sleep insomnia at least 1 year after kindling and 1-5 months after convulsions, regardless of postictal recording delay. Sleep and arousal defects in kindled kittens were similar to but more pronounced than those in kindled adult cats, possibly because kittens spontaneously became epileptic. Detection of postkindling SWS insomnia could be masked by brief scoring epochs (less than the preferred 1-min epoch for cats); recurrent behavioral arousals after kindling frequently aborted 1-min SWS epochs but often did not interrupt 30-s SWS epochs (based on 1-min vs. 30-s minimum duration scoring criteria). Detection of postkindling REM sleep insomnia could be masked in kittens with alternating patterns of REM loss and REM rebound; all these kittens showed periodic bouts of REM onset from waking after kindling. Different data collection and analysis procedures influence detection of sleep and arousal disorders in amygdala-kindled cats when replication of findings is attempted. We conclude that these differences explain some controversies regarding the nature and prevalence of sleep disturbances in the kindling literature in temporal lobe epilepsy (TLE).

Transitory and short-duration changes of sleep organization provoked by amygdaloid kindling in the cat: a daily 23-hour sleep recording study

The effect of amygdaloid kindling on sleep organization was tested in chronically implanted cats on a 12:12 light-dark cycle. Electrical kindling stimuli were delivered to the amygdala every 2 h during the light period. Total sleep time and percentage, mean duration, and mean number, as well as the hourly accumulation of waking (W) and sleep (slow wave sleep I and II, and paradoxical sleep) episodes were assessed from daily 23-h sleep recordings, consisting of baseline control recordings, control recordings where cats were briefly alerted at 2-h intervals to mimic the kindling trials manipulation, and recordings on each kindling day. The kindling process was completed within six days achieving three to five consecutive fully kindled seizures. Analysis of total recording time showed that the kindling process enhanced W stage and diminished total sleep time only on the second kindling day. Analysis of light and dark periods demonstrated compensatory W and sleep changes during the dark periods. Hourly sleep stage time accumulation was slowed during kindling trials, but compensated while stimuli were suspended. All of these changes returned to baseline values at the end of kindling. No significant differences between changes induced by kindling and those produced by alerting trials were found. We conclude that sleep alterations can not be exclusively attributed to kindling development, and that sleep is able to become adapted to the focal and generalized seizures effect.

Effects of seizures, kindling, and carbamazepine on sleep organization in cats

We studied the relationships between epilepsy, sleep, and anticonvulsant drugs in kindled cats. No sleep alteration was present at midkindling. When the animals became fully kindled, a reduction in REM sleep percentage and the number of entries into REM sleep were observed compared to baseline. In addition, with further seizures, an increase in the percentage of wakefulness appeared, accompanied by a further reduction in the number of entries into REM sleep. It therefore seems that there is a progressive disruption of sleep, dependent on the increasing number of tonic-clonic generalized seizures. After a seizure-free interval, REM sleep and wakefulness returned to baseline values. A reduction in the percentage of stage II compared to baseline was found and remained as a long-term effect of the kindling process. Acute administration of carbamazepine (CBZ) reduced the REM sleep percentage. This effect, paralleled by a reduction in the number of entries into REM sleep, was evident both at baseline and when the animals were fully kindled. After a large number of seizures, however, CBZ administration did not cause a further reduction in the already low percentage of REM sleep. Results are discussed with reference to previous literature. We propose a hypothesis of competition between seizure and REM sleep in the elimination of epileptogenic and hypnogenic factors.

Kindling and its consequences on learning in rats

To study the learning performance of pentylenetetrazol- and amygdala-kindled Wistar rats we used the following learning tests: short-term memory was tested in the response-to-change model, brightness discrimination was tested in a Y-chamber, and two-way active avoidance learning was tested in a shuttle-box. Short-term memory was not impaired by both kindling procedures. Considering two-way active avoidance learning the performance of pentylenetetrazol (PTZ)-kindled rats was significantly diminished. This effect persists over a period of 4 weeks. However, amygdala (AMY)-kindled rats acquired this task like the controls. In brightness discrimination reaction (BDR) the learning performance of PTZ-kindled animals was not influenced. Although the acquisition of BDR was nearly identical, the 24-h retention was remarkably diminished in AMY-kindled rats. It was hypothesized that the different kindling procedures interfere in different ways and extent with neuronal circuits resulting in different functional impairments.

Amygdaloid kindling during wakefulness and paradoxical sleep in the cat. 2. Sleep organization changes produced by kindling development

The effect of daily electrical amygdaloid stimulation (kindling, K) during waking (W-K) and paradoxical sleep (PS-K) on sleep organization was tested in 2 groups of chronically implanted adult male cats. Animals were stimulated 3 h after the 8-h sleep recordings were begun. Percentage, total time, and mean duration and number of episodes of W, slow wave sleep I and II, and PS stages were determined. Also, the mean interval of occurrence and hourly accumulation of PS were assessed. Recordings were performed before, throughout, and immediately after kindling and 2 months after the last recorded kindled seizures. Analysis of total recording time demonstrated that in both W-K and PS-K animals the kindling process provoked only transitory changes which returned to baseline values during kindling and immediately after. Analysis of pre- and post-stimulation periods demonstrated compensatory changes in W and PS percentage during the late stages of kindling. We conclude that rather than sleep diminution, kindling provokes a circadian shift of W and PS stages.

Feline amygdaloid kindling and the sleep-waking pattern: observations on daily 22-hour polygraphic recording

For 22 h daily, polygraphic examination was made of sleep organization in four cats, both before and after amygdaloid (AM) kindling. After the completion of AM kindling and repetitive induction of kindled convulsion, the percentage of time spent in rapid eye movement sleep (REMS) significantly decreased, while the total sleep time (TST) remained unchanged. REMS suppression was most profound during the immediate postictal hours and continued through the 22-h period without a rebound increase. Slow wave sleep (SWS) was also suppressed during the postictal hours; however, this suppression was exceeded by that of REMS and was followed by a rebound increase. These changes in sleep organization were transient. During a rest interval of 2 months without kindled convulsions, they gradually disappeared and there was a complete recovery to the prekindling baseline. However, when the AM-kindled convulsion was reintroduced, there was an abrupt REMS suppression without TST change. We conclude that changes in sleep organization after AM kindling are (a) characterized by suppression of REMS and a compensatory increase in SWS, and (b) a direct but transient correlate of convulsion rather than of an acquired seizure susceptibility.

Feline amygdaloid kindling and sleep

Six hourly polygraphic examinations of sleep organization were made before and after amygdaloid (AM) kindling in 7 cats. After completion of AM kindling and the repetitive induction of kindled convulsion, the percentage of time spent in rapid eye movement sleep (REMS) significantly decreased, although the animals began to spend significantly more time in sleep. This altered sleep pattern persisted during an extended 22.5 h recording in 2 cats. The decreased waking (W) and REMS, as well as the increased slow wave sleep (SWS), appeared to be due to changes in mean duration but not in the total number of periods. Suppression of REMS but not SWS was also manifested as a delayed onset of REMS following sleep onset, the latency of which remained constant upon placement of animals in the recording chamber. These changes in sleep organization were transient, however, as they returned completely to the baseline pre-kindling level after a rest interval of 3-4 weeks without kindling stimulation. It is concluded that sleep organization changes, particularly those characterized by the suppression of REMS, are independent of the acquisition of AM-kindled seizure susceptibility; rather they are the direct correlates of generalized convulsion itself.

Amygdala kindling effects on sleep and memory in rats

Sleep disturbances accompany the development of amygdaloid-kindled seizures in cats. Some of these sleep deficits resemble those seen in aged rats; these latter changes in sleep patterns are correlated with memory impairments in the aged animals. In the present study, we examined the hypothesis that sleep deficits after kindling may be related to memory impairments. Rats were kindled for 4 weeks (2-2.5 weeks after stage 5 seizures) and were then allowed a one week recovery period. Sleep patterns were assessed through-out the kindling and recovery periods. The animals were then trained on an inhibitory avoidance apparatus and tested for retention 24 h later. Only transient sleep changes occurred during the development of kindling (to stage 5 seizures). However, continued kindling resulted in significant reductions in several sleep measures which remained depressed for at least one week after the termination of the kindling trials. As a group, kindled rats were impaired in retention of the inhibitory avoidance learned response. In kindled animals, retention performance was significantly correlated with total paradoxical sleep, the ratio of paradoxical/total sleep, and paradoxical sleep, the ratio of paradoxical/total sleep, and paradoxical sleep bout duration. These correlations are consistent with the view that deficits in paradoxical sleep may be related to deficits in some forms of memory.

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.

Sleep disorders in kindled cats differ according to the timing of polygraphic recordings and of seizures in the sleep-wake cycle

Sleep disorders in amygdala-kindled cats differ according to the sleep or waking state in which seizures occur and the time lapse between seizures and polygraphic recordings. Twelve-hour polygraphic recordings were initiated at the following times: (i) before kindling (N = 8 cats); (ii) just after kindled convulsions during waking, slow-wave sleep (SWS), rapid-eye-movement sleep (REMS), or in transition from SWS to REMS (N = 8 cats per state), and (iii) 24 h after state-specific seizures (N = 8 cats per state). Rapid onset SWS and delayed REMS occurred in records started immediately after seizures in waking, SWS, or REMS; in contrast, seizures during transitions from SWS to REMS produced early onset REMS and SWS. Finally, records begun 24 h after seizures always revealed prolonged sleep onset and generalized sleep suppression regardless of the state in which seizures occurred. The timing of seizures and of polygraphic recordings may explain discrepancies in the literature on the type of sleep disorders seen in secondary generalized temporal lobe epilepsy.

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.

Sleep disruption with basal forebrain lesions decreases latency to amygdala kindling in cats

Sleep deprivation enhances seizure susceptibility in experimental and human epilepsies. Because sleep abnormalities are also common in these populations, a possible explanation for this close association is that sleep deprivation activates seizures by enhancing existing sleep disturbances. The present experiment examined this hypothesis by comparing sleep-waking state percentages and the number of after-discharge-eliciting stimulations required to induce generalized tonic-clonic convulsions with the amygdala kindling model of epilepsy in 3 groups of cats (n = 5 each). One group consisted of experimental subjects who received bilateral lesions of the basal forebrain, a preoptic area long implicated in the generation of normal sleep state characteristics. A second group sustained unilateral lesions of the basal forebrain area. Since only bilateral destruction of this region produces sleep-waking cycle abnormalities, this group provided a lesion control. Finally, a third group had no lesion and provided a control which allowed normative assessment of sleep state patterns and seizure susceptibility in otherwise unmanipulated cats. The results were: cats without lesions showed a parallel development of seizure and sleep disorders, the latter indexed by progressive SWS and REM sleep deficits; cats with unilateral lesions showed identical trends in the development of sleep and seizure anomalies; and cats with bilateral lesions of basal forebrain displayed similar but more severe sleep disturbances than those evidenced by control subjects and also required fewer after-discharge stimulations to establish kindled convulsions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of protein synthesis inhibitors on sleep and amygdala-kindled seizure thresholds in cats

This study examined the effects of protein synthesis inhibitors on sleep and seizure susceptibility in amygdala-kindled cats. Six cats with stable seizure thresholds were treated with 150 mg/kg of chloramphenicol or its cogener, thiamphenicol, at 12-h intervals over a 30-h period. State pattern variables were monitored continuously during the first 18 h. At 30 h, kindled seizure thresholds were measured in terms of minimum stimulus intensities (microA) required to elicit generalized tonic clonic convulsions. All cats were exposed to both drugs, with a 1-week intertrial interval and the order of drug treatment counterbalanced. Rapid eye movement (REM) sleep was significantly attenuated after chloramphenicol but was unaffected by thiamphenicol, as previously shown. Seizure thresholds were unaltered regardless of changes in sleep state physiology. The results extend previous work showing that protein synthesis inhibitors which suppress REM sleep increase seizure susceptibility only in animals that are either highly predisposed to seizures or that display REM sleep disruption as the sole sleep deficit associated with their seizure condition.

Relationships between triggered seizures, spontaneous seizures, and interictal spiking in the kindling model of epilepsy

Cats were kindled in the amygdala. After completion of kindling, their EEG was monitored almost continuously by a computer system which allowed the detection of spontaneous seizures and the quantification of interictal spikes. The relationships between seizures triggered by stimulation, spontaneous seizures, and interictal spikes in kindled and contralateral amygdalas were examined. Very few spontaneous seizures were observed; their occurrence appeared facilitated by a few triggered seizures after a long seizure-free interval. Stimulation-triggered seizures were followed first by a decrease in spiking activity during a few hours and then by an increase which could take 3 to 8 days to return to baseline. Spontaneous seizures were also, but less systematically, followed by such a sequence. Spontaneous seizures could occur when the interictal spiking rate was high as well as when it was low. It is concluded that, in the fully kindled cat, interictal spiking appears to be mainly regulated by the occurrence of seizures; the rate of spiking appears to have no bearing on the probability of occurrence of spontaneous seizures. Hence, seizures and interictal spiking could be generated by separate pathophysiologic mechanisms, the seizure-generating mechanism influencing the spike-generating mechanism but not the reverse.