Brain Research, 535 (1990) 163-168
163
Elsevier BRES 24416
Spontaneous sleep epilepsy in amygdala-kindled kittens: a preliminary report Margaret N. Shouse, James V. Langer and Paul R. Dittes Department of Anatomy and Cell Biology, UCLA School of Medicine, Los Angeles, CA 90024 (U.S.A.) and Sleep Disturbance Research (151A3), VA Medical Center, Sepulveda, CA 91343 (U.S.A.)
(Accepted 21 August 1990) Key words: Slow-wavesleep; Rapid eye movement sleep; Slow-wavesleep-rapid eye movement sleep transition; Spontaneous seizure; Sleep
epilepsy; Noradrenaline
We describe a model of 'sleep epilepsy' after amygdala kindling in kittens. Seizure activity was evaluated at different times in the sleepwake 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 prototypie 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.
We recently described the ontogeny of feline temporal lobe epilepsy (TLE) after amygdala kindling in 24 kittens and adult cats 25,26. In so doing, we reported the first model of spontaneous epilepsy in immature animals. We now report the first model of convulsive 'sleep epilepsy' in any species. Conclusions are based upon 12 preadolescent kittens ranging in age from 2.5 to 6.5 months at initial focal afterdischarge (AD) determination. Eleven of the 12 kittens were females that reach puberty at 7-9 months11; the only male was 3.5 months at initial A D threshold. All kittens were still prepubertal at the end of kindling. Neurosurgica119'29 amygdala kindling 7,32 and follow-up procedures are described in the initial report 26. Only the salient points are summarized here. Kittens had bilateral, tripolar leads in the basolateral amygdala and jeweler's screws over the intact frontal sinus for monopolar (n = 6), bipolar (n = 5) or bilateral (n = 1) amygdala kindling. Standard implants for evaluation of sleep and waking states included jeweler's screws threaded into the b o n e over motor cortex and the orbit, plus stainless steel wires in the nuchal musculature to register cortical EEGs, eye movements (EOG) and muscle tone (EMG), respectively. Kittens of 4 months and older also had bilateral tripolar electrodes in the
lateral geniculate nucleus (LGN) to record ponto-geniculo-occipital (PGO) spikes. Kindling procedures employed daily electrical stimulation of the amygdala (1 s train of 60 Hz biphasic square waves of 0.1 ms duration) while cats were in a state of alert wakefulness. Initially, focal A D thresholds were determined by a method of limits procedure. Afterward, kittens received one stimulus per day at initial focal A D intensity until the first stage 6 seizure (a generalized tonic-clonic convulsion or GTC). Finally, GTC thresholds were established by the same method used at the beginning of kindling. Four modifications of our standard kindling protocol compensated for high focal A D thresholds (15-20 mA) in 4 young kittens. Changes involved (1) raising the ceiling on stimulus intensity from 2 m A to 40 mA, (2) reducing stimulus duration from 1 s to 0.1 s at intensities over 2 mA, (3) multiple daily stimulation to determine initial focal A D thresholds and (4) bilateral amygdala stimulation of one kitten in which focal A D could not be evoked ipsilaterally at 40 m A 26. At the conclusion of immediate post-kindling thresholds, kittens were followed from 3 days to at least one year to document the stability of evoked and spontaneous seizure susceptibility and its modulation by the sleepwake cycle. Timing of seizures in the sleep-wake cycle
Correspondence: M.N. Shouse, Sleep Disturbance Research (151A3) VA Medical Center, Sepulveda, CA 91343, U.S.A.
0006-8993/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
164 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 of 7). One kitten with spontaneous seizures died before determination of seizure patterns in the sleep-wake cycle. Evoked seizure susceptibility was indexed by GTC thresholds, using the one-day procedure described for sleep-waking state assessment of thresholds in adult cats 23'25. Initially, thresholds were established once daily during alert waking. Initial stimulus intensity was 100 p A - 3 0 0 p A below the previous day's threshold and increased by 25 p A to 100 p A increments at one-min intervals until an evoked GTC. Waking thresholds were repeated to criterion stability (3 consecutive, identical GTC thresholds). Animals then rotated through a partially counterbalanced sequence in which threshold tests were conducted in a different sleep or waking state each day. Three stable states and one transitional state were assessed: alert waking, SWS, the transition from SWS to REM sleep and R E M sleep. Stable states were defined by/> 1 min of the continuous polygraphic signs of waking, SWS or REM sleep, per Ursin and Sterman 3t. The transition from SWS into R E M was considered part of SWS and lasted < 1 min by definition; onset of the S W S - R E M transition was identified by a trend toward cortical E E G desynchronization, often accompanied by phasic events (eye movements and PGO spikes) and sometimes by progressive reduction in muscle tone. Threshold testing was disrupted by rapid postkindling onset of spontaneous epilepsy in kittens < 5 months, and the paradigm was completed only by 5 older preadolescent kittens > 5 months at initial AD. Table I contains threshold data from these 5 kittens. Thresholds were lowest, meaning seizure susceptibility was highest during SWS and the R E M transition; conversely, thresholds were highest, meaning that seizure susceptibility was lowest during stable R E M sleep. Alert waking was intermediate between seizure-prone and seizure-resistant sleep states, as previously reported for amygdala-kindled adult cats 23. Evoked seizure patterns also correspond to the timing of spontaneous convulsions in amygdalakindled kittens, as described below. Seven of the 12 kittens (58%) developed spontaneous epilepsy after kindling. Six of the 8 youngest kittens ( < 5.5 months) had spontaneous seizures 24 h to two months after initial kindling. Only one of the 4 oldest preadolescent kittens (5.5-6.5 months) developed spontaneous epilepsy; onset was delayed 4 months after kindling and coincided with the conclusion of threshold testing. Spontaneous seizures often occurred in bouts of 2-6, and 83 of 85 occurred ~< 72 h after an evoked convulsion.
TABLE I Timing o f evoked convulsions during the sleep-wake cycle
Mean GTC thresholds + S.D. are provided for 5 kindled kittens tested at least 3 times in each sleep or waking state. Threshold is the inverse of seizure susceptibility. Susceptibilityis highest during SWS, especiallythe REM transition, and lowest during stable REM sleep. Age at initial A D
5- to 6.5-month-old kittens(n=5)
Alert waking
GTC thresholds (mA) ....................... SWS SWS to REM transition
REM sleep
0.7+0.3 0.6+0.2* 0.5_+0.2 * 0.8_+0.5*
• P < 0.05 from alert waking. The first seizure was usually observed behaviorally and followed by polygraphic or split-screen video recordings to document timing of subsequent seizures in the sleepwake cycle. Two convulsions occurred after a lengthy postictal period. One spontaneous G T C was delayed 5 months, and another occurred after a 9 month, convulsion-free period. Partial seizures were not observed and may have escaped detection because of minor clinical accompaniment. Three types of spontaneous seizures were documented, all with generalized E E G manifestations. Two were non-convulsive seizures seen infrequently in one kitten each. The third type was a convulsion (n = 85 to date), observed frequently in 6 of the 7 kittens with spontaneous seizures. Seizure types and their timing in the sleep-wake cycle are described individually and then collectively. One subconvulsive seizure type resembled a complexpartial seizure similar to a stage 3 amygdala-kindled seizure. Chewing or lipsmacking, headnodding and forelimb clonus were accompanied by generalized E E G discharges in all sleep or waking states except stable REM 2s. The other subconvulsive seizure type was unlike anything seen during routine kindling. We dubbed these 'catnip' seizures, because the kitten had continuous absence-like staring and purred continuously for up to 1.5 h at a time. Periodic dorsoflexion of the head, sometimes followed by 'jackknife' seizures, was associated with multi-spike or multi-sharp-and-wave transients resembling k-complexes over motor cortex and in the amygdala. Seizures persisted throughout waking and SWS and ceased only during rare periods of active waking and REM sleep (Fig. 1). These peculiar electroclinical events were clearly observed in the kitten kindled with bilateral amygdala stimulation. 'Catnip' seizures might represent a severe form of complex-partial epilepsy or even a facsimile of West syndrome 33.
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Fig. 1. a+b: two continuous 80-s tracings show grossly abnormal EEGs associated with spontaneous 'catnip seizures' during wakefulness (a) and sleep (b). EEGs during quiet waking and SWS are nearly indistinguishable (top of a and b) and are normalized only during rare episodes of active waking with movement and REM sleep (bottom of a and b). Quiet waking and SWS tracings show diffuse background EEG slowing with spike-wave and polyspike-wave complexes superimposed on spindles in motor cortex and the amygdala, best visualized in channels 1 and 3. Clinically, the kitten showed continuous absence-like staring with periodic dorsoflexion of head and 'jackknife' seizures. Clonic movement of the eyes, head and torso seemed to accompany the epileptiform spindles, which sometimes resembled 'epileptic k-complexes'. Cats are not supposed to have k-complexes. Nevertheless, this particular EEG anomaly occurred in the amygdala during waking and over cortex during SWS in all kindled kittens, typically in conjunctions with a discrete 'head nod' which could occur at the beginning or end of the complex. These EEG samples were obtained from a kitten kindled by bilateral amygdala stimulation at 3.5 months of age. Paper speed is 15 mm/s. By far, the most c o m m o n spontaneous seizure type o b s e r v e d was a G T C similar to a stage-6 e v o k e d seizure during kindling 32. Eighty-one % of polygraphic or splits c r e e n v i d e o r e c o r d e d G T C s occurred during SWS sleep, whereas only 19% occurred in waking. The most seizurep r o n e p e r i o d within SWS was the S W S - R E M transition, as illustrated in Fig. 2.
Fig. 3 shows population data for spontaneous seizures. Timing in the s l e e p - w a k e cycle was determined by polygraphic and split-screen video monitoring. The graph depicts 7 non-convulsive episodes ( d e a r bars) and 31 GTCs (filled bars). There were 3 main findings. (1) Subconvulsive seizures occurred indiscriminately during wakefulness and SWS,
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Fig. 2. A continuous 3-min polygraphic tracing illustrating a spontaneous convulsion with bifocal amygdala onset during a lengthy transition from SWS to REM. The initial part of the sample shows SWS with frequent sleep spindles over motor cortex. The REM transition begins in the last third of the top tracing and is identified by cortical EEG desynchronization with continued PGO spiking. The EOG channel is out in this record, but there is a reduction in muscle tone just prior to a behavioral arousal. The behavioral arousal is clearly visible in the EMG channel and was time-locked to bifocal amygdala discharge. A few seconds later, a GTC with amygdala onset began. This is one of 17 seizures recorded in a cat kindled as a 4-month-old kitten. Paper speed is 10 mm/s.
as r e p o r t e d in human complex-partial epilepsy 1 and also West s y n d r o m e 5'18. (2) Convulsions occurred predominantly during SWS (81%), most of them during the R E M transition (55% of total). A similar propensity to spontaneous or e v o k e d convulsions occurs in h u m a n T L E 2'3° and in amygdala-kindled adult cats 22'23. (3) Neither seizure type occurred during stable R E M sleep. This
result concurs with o t h e r feline and clinical data indicating that R E M sleep is the most antiepileptic state in the s l e e p - w a k e cycle for generalized epilepsy 3'23'24. S l e e p - w a k i n g state m o d u l a t i o n of seizures in amygdala-kindled kittens parallels m a n y clinical observations. First, kindled kittens were m o r e susceptible to spontaneous and e v o k e d convulsions during sleep than waking,
167
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Fig. 3. The timing of spontaneous seizures in the sleep-wake cycle, as verified by polygraphic or split-screen video recordings. Seven episodes of non-convulsive seizures (clear bars) and 31 convulsions (dark bars) were distributed in 4 sleep or waking states after amygdala kindling in preadolescent kittens. Non-convulsiveseizures occurred randomly in waking and SWS, whereas most convulsions occurred during SWS, especially in the transition from SWS to REM sleep (*P < 0.05 from alert waking and REM sleep). No generalized seizures were recorded during stable REM,sleep.
consistent with clinical data designating TLE the prototypic pure sleep epilepsy 12'13. Nearly 60% of the patients with TLE have convulsions only during sleep. Moreover, N R E M sleep, particularly the transition into REM, is the most susceptible period for convulsions in both species 2'23'3°. Sleep-stage specificity in kindled cats was manifested by frequent spontaneous convulsions in young kittens and by reduced thresholds in older preadolescents and adults. Ontogenetic factors in amygdala kindling thus appear to influence the degree of sleepactivated TLE, reaffirming experimental and clinical evidence that epilepsy is a disease with onset in youth s, 12-14,17,34.
Another parallel to the clinical literature was established by the state-specificity of kindled convulsions versus the random occurrence of subconvulsive seizures during wakefulness and SWS. It is well known that convulsions are more entrained to the sleep-wake cycle than any other human seizure manifestation 12'24. This finding implies that seizure propagation is the most critical variable affected by sleep-state physiology. 1 Billiard, M., Epilepsies and the sleep-wake cycle. In M.B. Sterman, M.N. Shouse and E Passouant (Eds.), Sleep and Epilepsy, Academic, New York, 1982, pp. 269-286. 2 Cadhillac, J., Complex partial seizures and REM sleep. In M.B. Sterman, M.N. Shouse and E Passouant (Eds.), Sleep and Epilepsy, Academic, New York, 1982, pp. 315-324. 3 Calvo, J.M., Alvarado, R., Briones, R., Paz, C. and FernandezGuardiola, A., Amygdaloid kindling during rapid eye movement (REM) sleep in cats, Neurosci. Left., 29 (1982) 255-259.
The basis for propagated T L E during the R E M transition is unknown. However, forebrain is innervated by the brainstem regions implicated in the R E M transition 2s and in seizure generalization 4'16. Of these, locus ceruleus seems a logical choice because adrenergic cells in its vicinity discharge at progressively reduced rates during the transition into R E M 9A°'2°'21. Declining NE release at this time could promote seizure propagation from temporal lobe, as the proconvulsant effects of reduced NE levels are well established 4'16. Effects could be mediated directly or indirectly, but locus cells are thought to project to the amygdala and hippocampus in cats 15. For these reasons, reduced NE secretion might disinhibit epileptic neurons in the temporal lobe, thereby promoting secondary seizure generalization during the R E M transition. Results in kindled kittens also pertain to the expression of seizure pathology in stable sleep and waking states, excluding the R E M transition. Convulsive seizure activity still peaked during stable SWS, was intermediate during alert wakefulness and plummeted during stable R E M sleep. The neurophysiological basis for seizureprone and seizure-resistant properties of stable states is poorly elaborated. However, some evidence suggests that synchronous modes of cell discharge during SWS provide a natural mechanism for epileptic E E G potentials, whereas the asynchronous patterns generating waking and R E M sleep E E G desynchronization do not 6. Finally, profound lower motor neuron inhibition seems to impede motor seizure manifestations independently and could reinforce the anticonvulsant actions of R E M sleep 27. In conclusion, the development of spontaneous sleep convulsions in kindled kittens validates amygdala kindling as a model of developmental TLE 17 and of sleep epilepsy. Findings are consistent with the modulation of local seizure propagation by different sleep and waking states and point to ascending influences from locus ceruleus as a secondary generalization mechanism during the R E M transition. Specifically, decreased NE release during the R E M transition might encourage seizure propagation by disinhibiting epileptic discharge at the kindled TLE focus. This work was supported by the Veterans Administration and by PHS Grant NS25629. 4 Corcoran, B.W. and Mason, S.T., Role of forebrain catecholamines in amygdaioid kindling, Brain Research, 190 (1980) 473-484. 5 Fukuyama, Y., Shionaga, A. and Iida, Y., Polygraphic study during whole night sleep in infantile spasms, Eur. Neurol., 18 (1979) 302-311. 6 Gloor, E, Generalized epilepsy with spike-wave discharge: a re-interpretation of its electrographic and clinical manifestations, Epilepsia, 20 (1977) 571-588.
168 7 Goddard, G.V., Mclntyre, D.C. and Leech, C.K., A permanent change in brain function resulting from daily electrical stimulation, Exp. Neurol., 25 (1969) 295-330. 8 Hauser, W.A. and Kurland, L.T., The epidemiology of epilepsy in Rochester, Minnesota, 1935 through 1967, Epilepsia, 16 (1975) 1-66. 9 Hobson, J.A., McCarley, R.W. and Wyzinski, P.W., Sleep cycle oscillation: reciprocal discharge by two brain stem neuronal groups, Science, 289 (1975) 55-58. 10 Hobson, J.A., Lydic, R. and Baghdoyan, H.A., Evolving concept of sleep cycle generation: from brain centers to neuronal populations, Behav. Brain Sci., 9 (1986) 371-448~ 11 Inglis, J.K., Introduction to Laboratory Animal Science and Technology, Pergamon, New York, 1980. 12 Janz, D., The grand real epilepsies and the sleeping waking cycle, Epilepsia, 3 (1962) 69-109. 13 Janz, D., Epilepsy and the sleeping-waking cycle. In P.J. Vincken and G.W. Bryn (Eds.), Handbook of Clinical Neurology, Vol. 15, The Epilepsies, Elsevier, Amsterdam, 1974, pp. 457-490. 14 Kriegstein, A.R., Suppes, T. and Prince, D.A., Cellular and synaptic physiology and epileptogenesis of the developing rat neocortical neurons in vitro, Dev. Brain Res., 34 (1987) 161-171. 15 McBride, R.I. and Sutin, J., Projections of the locus coeruleus and adjacent pontine tegmentum in the cat, J. Comp. Neurol., 165 (1976) 265-284. 16 Mclntyre, D.C., Saari, M. and Pappas, B.A., Potentiation of amygdala in adult or infant rats by injection of 6-hydroxydopamine, Exp. Neurol., 63 (1979) 527-544. 17 Moshe, S.L., Sperber, E.F. and Albala, B.J., Kindling as a model of epilepsy in developing animals. In E Morrell (Ed.), Kindling and Synaptic Plasticity, Dirkauser, Boston, in press. 18 Ohtahara, S., Yamatoy and Ohtsuka, Y., Prognosis of Lennox syndrome. Long-term clinical and electroencephalographic follow-up study, with special reference to West syndrome, Folia Psychiatr. Neurol. Jpn., 30 (1976) 275-287. 19 Rose, G,H. and Goodfellow, E.F., A Stereotaxic Atlas of the Kitten Brain: Coordinates of 104 Selected Structures, Brain Information Service/Brain Research Institute, University of California, Los Angeles, 1973. 20 Sakai, K., Anatomical and physiological basis of paradoxical sleep. In D.J. McGinty et al. (Ed.), Brain Mechanisms of Sleep, Raven Press, New York, 1985, pp. 111-137. 21 Sakai, K., Executive mechanisms of paradoxical sleep, Arch.
ltal. Biol., 126 (1988) 239-257. 22 Sato, M. and Nakeshima, T., Kindling: secondary epileptogenesis, sleep and catecholamines, Can. J. Neurol. Sci., 3 (1975) 439-446. 23 Shouse, M.N., State disorders and state dependent seizures in amygdala-kindled cats, Exp. Neurol., 91 (1986) 601-608. 24 Shouse, M.N., Seizures and epilepsy during sleep. In M.H. Kryger, T. Roth and W.C. Dement (Eds.), Principles and Practice of Sleep Medicine, Saunders, Philadelphia, 1989, pp. 104-120. 25 Shouse, J., King, A., Langer, J., Wellesley, K., Vreeken, T., King, K., Siegel, J. and Szymusiak, R., Basic mechanisms underlying seizure prone and seizure resistant sleep and awakening states in feline kindled and penicillin epilepsy. In J.A. Wada (Ed.), Kindling, Vol. 4 Plenum, New York, t990, pp. 313-327. 26 Shouse, M.N., King, A., Langer, J., Vreeken, T., King, K. and Richkind, M., The ontogeny of feline temporal lobe epilepsy: kindling a spontaneous seizure disorder in kittens, Brain Research, 515 (1990) 215-224. 27 Shouse, M.N., Siegel, J.M., Wu, M.F., Szymusiak, R. and Morrisson, A.R., Mechanisms of seizure suppression during rapid eye movement (REM) sleep in cats, Brain Research, 505 (1989) 271-282. 28 Siegel, J.M., Brainstem mechanisms generating REM sleep. In M.H. Kryger, T. Roth and W~C. Dement (Eds.), Principles and Practice of Sleep Medicine, Saunders, Philadelphia, 1989, pp. 104-120. 29 Snider, R.S. and Niemer, W.T., A Stereotaxic Atlas of the Cat Brain, Univ. Chicago Press, Chicago, 1961. 30 Stevens, J.R., Lonsbury, B.L. and Goel, S.L., Seizure occurrence and interspike interval, Arch. Neurol., 26 (1972) 409-419. 31 Ursin, R. and Sterman, M.B., A Manual for Standardized Scoring of Sleep and Waking States in the Adult Cat, Brain Information Service/Brain Research Institute, 1981. 32 Wada, J.A. and Sato, M., Generalized convulsive seizures induced by daily stimulation of the amygdala in kindled cats, Neurology, 24 (1974) 565-574. 33 West, W.J., On a peculiar form of infantile convulsion, Lancet, 1 (1840-1841) 724-725. 34 Woodbury, L.A., Incidence and prevalence of seizure disorders including the epilepsies in the U.S.A.. A review and analysis of the literature. In Plan for the Nationwide Action of Epilepsy, Vol. IV, DHEW Publication No. (NIH) 78-276, 1977, pp. 24-77.
163
Elsevier BRES 24416
Spontaneous sleep epilepsy in amygdala-kindled kittens: a preliminary report Margaret N. Shouse, James V. Langer and Paul R. Dittes Department of Anatomy and Cell Biology, UCLA School of Medicine, Los Angeles, CA 90024 (U.S.A.) and Sleep Disturbance Research (151A3), VA Medical Center, Sepulveda, CA 91343 (U.S.A.)
(Accepted 21 August 1990) Key words: Slow-wavesleep; Rapid eye movement sleep; Slow-wavesleep-rapid eye movement sleep transition; Spontaneous seizure; Sleep
epilepsy; Noradrenaline
We describe a model of 'sleep epilepsy' after amygdala kindling in kittens. Seizure activity was evaluated at different times in the sleepwake 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 prototypie 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.
We recently described the ontogeny of feline temporal lobe epilepsy (TLE) after amygdala kindling in 24 kittens and adult cats 25,26. In so doing, we reported the first model of spontaneous epilepsy in immature animals. We now report the first model of convulsive 'sleep epilepsy' in any species. Conclusions are based upon 12 preadolescent kittens ranging in age from 2.5 to 6.5 months at initial focal afterdischarge (AD) determination. Eleven of the 12 kittens were females that reach puberty at 7-9 months11; the only male was 3.5 months at initial A D threshold. All kittens were still prepubertal at the end of kindling. Neurosurgica119'29 amygdala kindling 7,32 and follow-up procedures are described in the initial report 26. Only the salient points are summarized here. Kittens had bilateral, tripolar leads in the basolateral amygdala and jeweler's screws over the intact frontal sinus for monopolar (n = 6), bipolar (n = 5) or bilateral (n = 1) amygdala kindling. Standard implants for evaluation of sleep and waking states included jeweler's screws threaded into the b o n e over motor cortex and the orbit, plus stainless steel wires in the nuchal musculature to register cortical EEGs, eye movements (EOG) and muscle tone (EMG), respectively. Kittens of 4 months and older also had bilateral tripolar electrodes in the
lateral geniculate nucleus (LGN) to record ponto-geniculo-occipital (PGO) spikes. Kindling procedures employed daily electrical stimulation of the amygdala (1 s train of 60 Hz biphasic square waves of 0.1 ms duration) while cats were in a state of alert wakefulness. Initially, focal A D thresholds were determined by a method of limits procedure. Afterward, kittens received one stimulus per day at initial focal A D intensity until the first stage 6 seizure (a generalized tonic-clonic convulsion or GTC). Finally, GTC thresholds were established by the same method used at the beginning of kindling. Four modifications of our standard kindling protocol compensated for high focal A D thresholds (15-20 mA) in 4 young kittens. Changes involved (1) raising the ceiling on stimulus intensity from 2 m A to 40 mA, (2) reducing stimulus duration from 1 s to 0.1 s at intensities over 2 mA, (3) multiple daily stimulation to determine initial focal A D thresholds and (4) bilateral amygdala stimulation of one kitten in which focal A D could not be evoked ipsilaterally at 40 m A 26. At the conclusion of immediate post-kindling thresholds, kittens were followed from 3 days to at least one year to document the stability of evoked and spontaneous seizure susceptibility and its modulation by the sleepwake cycle. Timing of seizures in the sleep-wake cycle
Correspondence: M.N. Shouse, Sleep Disturbance Research (151A3) VA Medical Center, Sepulveda, CA 91343, U.S.A.
0006-8993/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
164 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 of 7). One kitten with spontaneous seizures died before determination of seizure patterns in the sleep-wake cycle. Evoked seizure susceptibility was indexed by GTC thresholds, using the one-day procedure described for sleep-waking state assessment of thresholds in adult cats 23'25. Initially, thresholds were established once daily during alert waking. Initial stimulus intensity was 100 p A - 3 0 0 p A below the previous day's threshold and increased by 25 p A to 100 p A increments at one-min intervals until an evoked GTC. Waking thresholds were repeated to criterion stability (3 consecutive, identical GTC thresholds). Animals then rotated through a partially counterbalanced sequence in which threshold tests were conducted in a different sleep or waking state each day. Three stable states and one transitional state were assessed: alert waking, SWS, the transition from SWS to REM sleep and R E M sleep. Stable states were defined by/> 1 min of the continuous polygraphic signs of waking, SWS or REM sleep, per Ursin and Sterman 3t. The transition from SWS into R E M was considered part of SWS and lasted < 1 min by definition; onset of the S W S - R E M transition was identified by a trend toward cortical E E G desynchronization, often accompanied by phasic events (eye movements and PGO spikes) and sometimes by progressive reduction in muscle tone. Threshold testing was disrupted by rapid postkindling onset of spontaneous epilepsy in kittens < 5 months, and the paradigm was completed only by 5 older preadolescent kittens > 5 months at initial AD. Table I contains threshold data from these 5 kittens. Thresholds were lowest, meaning seizure susceptibility was highest during SWS and the R E M transition; conversely, thresholds were highest, meaning that seizure susceptibility was lowest during stable R E M sleep. Alert waking was intermediate between seizure-prone and seizure-resistant sleep states, as previously reported for amygdala-kindled adult cats 23. Evoked seizure patterns also correspond to the timing of spontaneous convulsions in amygdalakindled kittens, as described below. Seven of the 12 kittens (58%) developed spontaneous epilepsy after kindling. Six of the 8 youngest kittens ( < 5.5 months) had spontaneous seizures 24 h to two months after initial kindling. Only one of the 4 oldest preadolescent kittens (5.5-6.5 months) developed spontaneous epilepsy; onset was delayed 4 months after kindling and coincided with the conclusion of threshold testing. Spontaneous seizures often occurred in bouts of 2-6, and 83 of 85 occurred ~< 72 h after an evoked convulsion.
TABLE I Timing o f evoked convulsions during the sleep-wake cycle
Mean GTC thresholds + S.D. are provided for 5 kindled kittens tested at least 3 times in each sleep or waking state. Threshold is the inverse of seizure susceptibility. Susceptibilityis highest during SWS, especiallythe REM transition, and lowest during stable REM sleep. Age at initial A D
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REM sleep
0.7+0.3 0.6+0.2* 0.5_+0.2 * 0.8_+0.5*
• P < 0.05 from alert waking. The first seizure was usually observed behaviorally and followed by polygraphic or split-screen video recordings to document timing of subsequent seizures in the sleepwake cycle. Two convulsions occurred after a lengthy postictal period. One spontaneous G T C was delayed 5 months, and another occurred after a 9 month, convulsion-free period. Partial seizures were not observed and may have escaped detection because of minor clinical accompaniment. Three types of spontaneous seizures were documented, all with generalized E E G manifestations. Two were non-convulsive seizures seen infrequently in one kitten each. The third type was a convulsion (n = 85 to date), observed frequently in 6 of the 7 kittens with spontaneous seizures. Seizure types and their timing in the sleep-wake cycle are described individually and then collectively. One subconvulsive seizure type resembled a complexpartial seizure similar to a stage 3 amygdala-kindled seizure. Chewing or lipsmacking, headnodding and forelimb clonus were accompanied by generalized E E G discharges in all sleep or waking states except stable REM 2s. The other subconvulsive seizure type was unlike anything seen during routine kindling. We dubbed these 'catnip' seizures, because the kitten had continuous absence-like staring and purred continuously for up to 1.5 h at a time. Periodic dorsoflexion of the head, sometimes followed by 'jackknife' seizures, was associated with multi-spike or multi-sharp-and-wave transients resembling k-complexes over motor cortex and in the amygdala. Seizures persisted throughout waking and SWS and ceased only during rare periods of active waking and REM sleep (Fig. 1). These peculiar electroclinical events were clearly observed in the kitten kindled with bilateral amygdala stimulation. 'Catnip' seizures might represent a severe form of complex-partial epilepsy or even a facsimile of West syndrome 33.
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Fig. 3 shows population data for spontaneous seizures. Timing in the s l e e p - w a k e cycle was determined by polygraphic and split-screen video monitoring. The graph depicts 7 non-convulsive episodes ( d e a r bars) and 31 GTCs (filled bars). There were 3 main findings. (1) Subconvulsive seizures occurred indiscriminately during wakefulness and SWS,
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Fig. 2. A continuous 3-min polygraphic tracing illustrating a spontaneous convulsion with bifocal amygdala onset during a lengthy transition from SWS to REM. The initial part of the sample shows SWS with frequent sleep spindles over motor cortex. The REM transition begins in the last third of the top tracing and is identified by cortical EEG desynchronization with continued PGO spiking. The EOG channel is out in this record, but there is a reduction in muscle tone just prior to a behavioral arousal. The behavioral arousal is clearly visible in the EMG channel and was time-locked to bifocal amygdala discharge. A few seconds later, a GTC with amygdala onset began. This is one of 17 seizures recorded in a cat kindled as a 4-month-old kitten. Paper speed is 10 mm/s.
as r e p o r t e d in human complex-partial epilepsy 1 and also West s y n d r o m e 5'18. (2) Convulsions occurred predominantly during SWS (81%), most of them during the R E M transition (55% of total). A similar propensity to spontaneous or e v o k e d convulsions occurs in h u m a n T L E 2'3° and in amygdala-kindled adult cats 22'23. (3) Neither seizure type occurred during stable R E M sleep. This
result concurs with o t h e r feline and clinical data indicating that R E M sleep is the most antiepileptic state in the s l e e p - w a k e cycle for generalized epilepsy 3'23'24. S l e e p - w a k i n g state m o d u l a t i o n of seizures in amygdala-kindled kittens parallels m a n y clinical observations. First, kindled kittens were m o r e susceptible to spontaneous and e v o k e d convulsions during sleep than waking,
167
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Fig. 3. The timing of spontaneous seizures in the sleep-wake cycle, as verified by polygraphic or split-screen video recordings. Seven episodes of non-convulsive seizures (clear bars) and 31 convulsions (dark bars) were distributed in 4 sleep or waking states after amygdala kindling in preadolescent kittens. Non-convulsiveseizures occurred randomly in waking and SWS, whereas most convulsions occurred during SWS, especially in the transition from SWS to REM sleep (*P < 0.05 from alert waking and REM sleep). No generalized seizures were recorded during stable REM,sleep.
consistent with clinical data designating TLE the prototypic pure sleep epilepsy 12'13. Nearly 60% of the patients with TLE have convulsions only during sleep. Moreover, N R E M sleep, particularly the transition into REM, is the most susceptible period for convulsions in both species 2'23'3°. Sleep-stage specificity in kindled cats was manifested by frequent spontaneous convulsions in young kittens and by reduced thresholds in older preadolescents and adults. Ontogenetic factors in amygdala kindling thus appear to influence the degree of sleepactivated TLE, reaffirming experimental and clinical evidence that epilepsy is a disease with onset in youth s, 12-14,17,34.
Another parallel to the clinical literature was established by the state-specificity of kindled convulsions versus the random occurrence of subconvulsive seizures during wakefulness and SWS. It is well known that convulsions are more entrained to the sleep-wake cycle than any other human seizure manifestation 12'24. This finding implies that seizure propagation is the most critical variable affected by sleep-state physiology. 1 Billiard, M., Epilepsies and the sleep-wake cycle. In M.B. Sterman, M.N. Shouse and E Passouant (Eds.), Sleep and Epilepsy, Academic, New York, 1982, pp. 269-286. 2 Cadhillac, J., Complex partial seizures and REM sleep. In M.B. Sterman, M.N. Shouse and E Passouant (Eds.), Sleep and Epilepsy, Academic, New York, 1982, pp. 315-324. 3 Calvo, J.M., Alvarado, R., Briones, R., Paz, C. and FernandezGuardiola, A., Amygdaloid kindling during rapid eye movement (REM) sleep in cats, Neurosci. Left., 29 (1982) 255-259.
The basis for propagated T L E during the R E M transition is unknown. However, forebrain is innervated by the brainstem regions implicated in the R E M transition 2s and in seizure generalization 4'16. Of these, locus ceruleus seems a logical choice because adrenergic cells in its vicinity discharge at progressively reduced rates during the transition into R E M 9A°'2°'21. Declining NE release at this time could promote seizure propagation from temporal lobe, as the proconvulsant effects of reduced NE levels are well established 4'16. Effects could be mediated directly or indirectly, but locus cells are thought to project to the amygdala and hippocampus in cats 15. For these reasons, reduced NE secretion might disinhibit epileptic neurons in the temporal lobe, thereby promoting secondary seizure generalization during the R E M transition. Results in kindled kittens also pertain to the expression of seizure pathology in stable sleep and waking states, excluding the R E M transition. Convulsive seizure activity still peaked during stable SWS, was intermediate during alert wakefulness and plummeted during stable R E M sleep. The neurophysiological basis for seizureprone and seizure-resistant properties of stable states is poorly elaborated. However, some evidence suggests that synchronous modes of cell discharge during SWS provide a natural mechanism for epileptic E E G potentials, whereas the asynchronous patterns generating waking and R E M sleep E E G desynchronization do not 6. Finally, profound lower motor neuron inhibition seems to impede motor seizure manifestations independently and could reinforce the anticonvulsant actions of R E M sleep 27. In conclusion, the development of spontaneous sleep convulsions in kindled kittens validates amygdala kindling as a model of developmental TLE 17 and of sleep epilepsy. Findings are consistent with the modulation of local seizure propagation by different sleep and waking states and point to ascending influences from locus ceruleus as a secondary generalization mechanism during the R E M transition. Specifically, decreased NE release during the R E M transition might encourage seizure propagation by disinhibiting epileptic discharge at the kindled TLE focus. This work was supported by the Veterans Administration and by PHS Grant NS25629. 4 Corcoran, B.W. and Mason, S.T., Role of forebrain catecholamines in amygdaioid kindling, Brain Research, 190 (1980) 473-484. 5 Fukuyama, Y., Shionaga, A. and Iida, Y., Polygraphic study during whole night sleep in infantile spasms, Eur. Neurol., 18 (1979) 302-311. 6 Gloor, E, Generalized epilepsy with spike-wave discharge: a re-interpretation of its electrographic and clinical manifestations, Epilepsia, 20 (1977) 571-588.
168 7 Goddard, G.V., Mclntyre, D.C. and Leech, C.K., A permanent change in brain function resulting from daily electrical stimulation, Exp. Neurol., 25 (1969) 295-330. 8 Hauser, W.A. and Kurland, L.T., The epidemiology of epilepsy in Rochester, Minnesota, 1935 through 1967, Epilepsia, 16 (1975) 1-66. 9 Hobson, J.A., McCarley, R.W. and Wyzinski, P.W., Sleep cycle oscillation: reciprocal discharge by two brain stem neuronal groups, Science, 289 (1975) 55-58. 10 Hobson, J.A., Lydic, R. and Baghdoyan, H.A., Evolving concept of sleep cycle generation: from brain centers to neuronal populations, Behav. Brain Sci., 9 (1986) 371-448~ 11 Inglis, J.K., Introduction to Laboratory Animal Science and Technology, Pergamon, New York, 1980. 12 Janz, D., The grand real epilepsies and the sleeping waking cycle, Epilepsia, 3 (1962) 69-109. 13 Janz, D., Epilepsy and the sleeping-waking cycle. In P.J. Vincken and G.W. Bryn (Eds.), Handbook of Clinical Neurology, Vol. 15, The Epilepsies, Elsevier, Amsterdam, 1974, pp. 457-490. 14 Kriegstein, A.R., Suppes, T. and Prince, D.A., Cellular and synaptic physiology and epileptogenesis of the developing rat neocortical neurons in vitro, Dev. Brain Res., 34 (1987) 161-171. 15 McBride, R.I. and Sutin, J., Projections of the locus coeruleus and adjacent pontine tegmentum in the cat, J. Comp. Neurol., 165 (1976) 265-284. 16 Mclntyre, D.C., Saari, M. and Pappas, B.A., Potentiation of amygdala in adult or infant rats by injection of 6-hydroxydopamine, Exp. Neurol., 63 (1979) 527-544. 17 Moshe, S.L., Sperber, E.F. and Albala, B.J., Kindling as a model of epilepsy in developing animals. In E Morrell (Ed.), Kindling and Synaptic Plasticity, Dirkauser, Boston, in press. 18 Ohtahara, S., Yamatoy and Ohtsuka, Y., Prognosis of Lennox syndrome. Long-term clinical and electroencephalographic follow-up study, with special reference to West syndrome, Folia Psychiatr. Neurol. Jpn., 30 (1976) 275-287. 19 Rose, G,H. and Goodfellow, E.F., A Stereotaxic Atlas of the Kitten Brain: Coordinates of 104 Selected Structures, Brain Information Service/Brain Research Institute, University of California, Los Angeles, 1973. 20 Sakai, K., Anatomical and physiological basis of paradoxical sleep. In D.J. McGinty et al. (Ed.), Brain Mechanisms of Sleep, Raven Press, New York, 1985, pp. 111-137. 21 Sakai, K., Executive mechanisms of paradoxical sleep, Arch.
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