The long-lasting hyperpolarization of the neuronal membrane often de-inactivates additional excitatory currents of the low- threshold Ca 2 + spike type, which in turn will have a gre ater impact on the synchronization of the network. It has been therefore pro- posed that th e slow oscillation acts as a precursor of nocturnal SW seizures ( 14 , 16 ). Electroencephalographic correlates of the slow oscillation The synchronous nature of the sl ow oscillation has a direct impact on the electroencephalogram (EEG). Therefore the slow os cillation is detectable in the gross brain activity of the sleeping brain. First, the slow oscillation is expressed in the local \201 eld potentials re \202 ect- ing the membrane currents generated by neurons and, possibly, glial cells. Since the depolarizing phase of t he slow oscillation re \202 ects the excitation of all neurons, the corresponding extracel lu- lar \201 eld potential consists of a negative de \202 ection ( 27 ). The shape of th is negative potential has been found similar to the one of the K-complex ( 36 , 35 ). Besid es disclosing the cellular bases of the K-complex, our studies have also established that t his EEG event has a periodic and spontaneous recurrence (with the exception of occasional, sensory evoked K-complexes), and is generated in all sleep stages. Among the ions with a signi \201 cant impact on the neuronal excit- ability, K + and Ca 2 + were repeatedly investigated. The more syn- chronized the network, the higher the amplitu de of its oscillations, with more K + being expelled in the extracellular space during acti on potentials and other currents. During SW seizures, the extracellular concentration of K + increases from resting values around 3 \200\2233.5 mM to pathological levels around 9 \200\22312 mM ( 46 \200\22350 ). An increase in the extracellular K + concentration has pro ved to favor SW seizures ( 13 , 46 , 51 ). Extracellular K + is regulated by glial cells up take ( 32 , 52 , 53 ,) followed by spatial buffering through gap junctions connecting the g lial syncytium ( 54 , 55 ). The latter phenomenon evens out K + but may also contribute to the general depolarization of the neuronal membrane potential (Fig. 1. 3 ) by positively sh ifting the Nernst equilibrium potential. The hyperpolarizing phase of the slow oscillation corresponds to a round wave that has a ne gative polarity in the cortical depth ( 27 ) when measured with alternating current (AC) am pli \201 ers (i.e. after removal of direct current (DC) and very slow components). Althoug h AC recordings are the rule in routine EEG, it should be kept in mind that the procedure i s altering the real shape of \201 eld potential and EEG waves by introducing some arti \201 cial compo- nents, like the negative wave during the hyperpolarizing phase of the slow oscillation. In fact, being the result of network disfacilita- tion, the \201 eld expres sion of the hyperpolarizing phase marks a return to resting extracellular potential (see co mparison between DC and AC recordings in \201 gure 3 from reference 37). Cortical seizures developing in a circumscribed focus generate a local increase in extracel lular K + , which is then spatially buffered through the syncytium of glial cells at more d istant locations. The neuronal population of the latter would thus become the target of syn chronous synaptic bombardment from the seizure focus and would act in an environment with i ncreased K + concentration. Hence, synchronization of neuronal activity, the striking featu re of sleep activities, creates favorable premises for seizure genesis. The protective mech anism against this seems to rely on the ability of glial cells to regulate the extracellula r K + concentration through oxford textbook of epilepsy and epileptic seizures 4 A Depth-EEG area 5 V m 0 2 2 s Intra area 5 \210\22267 mV \210\22280 mV Slow oscillation Spike-wave Fast runs 0.2 s B - Wave-triggered-average Slow oscillation Beginning of seizure Middle of seizure EEG spike K-complex PDS V m 0 1 0.2 s Fig. 1.2 Spontaneously occurring seizure, developing without discontinuity from slow sleep- like oscillation. Intracellular recording from regular-spiking area 5 neuron together with depth-EEG from the vicinity in area 5 in a cat under ketamine-xylazine anesthesia. A) Smoot h transition from slow oscillation to complex seizure consisting of SW complexes at \210 2 Hz and fast runs at \210 15 Hz. The seizure lasted for \210 25 s. Epochs of slow oscilla tion preceding the seizure, SW complexes, and fast runs are indicated and expanded below. N ote postictal depression (hyperpolarization) in the intracellularly recorded neuron ( \210 6 s), associated with suppression of EEG slow oscillation (compare to left part of trace). B) Wave-triggered-average during the slow oscillation, at the beginning of seizure and duri ng the middle part of seizure. Averaged activity was triggered by the steepest part of the depolarizing component in cortical neuron (dotted lines), during the three epochs. The dept h-negative \201 eld component of the slow oscillation (associated with cell \200\231s dep olarization) is termed K-complex . During the seizure, the depolarizing component reaches t he level of a paroxysmal depolarizing shift ( PDS ), associated with an EEG spike . Modi \201 ed from ( 16 ). uptake, since impaired glial uptake of K + may cause epileptiform activity in the hippocamp us ( 56 ). K + and Ca 2 + ) and the intracortical \201 eld activity during SW seizures ( 19 , 20 , 3 7 ) have allowed us to establish a pattern of correlation between these functional entities . Thus, it appeared that glial cells also express phasic depolarizations in relation to int erictal and ictal PDSs (Fig. 1. 3 ). Variations of the glial membrane potentials during sleep SW seizures It has been well known for a long time that epileptic seizures are accompanied by signi \201 cant increases in t he extracellular K + con- centration ( 46 \200\22348 ) and persistent depolarization of gli al cells ( 8 \200\223 10 ). Simultanous intracellular recordings of pairs of neurons and gl ia, together with extracellular ionic concentrations (mainly The estimate of neuronal and glial depolarizations during the phasic events building up the SW cycles led to high correlative values ( > 84 % ) ( 28 ). Since the neuronal phasic depo larizations are made of entry of Na + and Ca 2 + and exit of chloride (Cl \210\222 ) and K + , while the glial ones mostly re \202 ect entry of K + (and possibly Ca 2 + ), the incr eased correlation between the depolarizations of the two CHAPTER 1 neurophysiology of epilepsy 5 V m 0 1 0.5 s A B 0 mV V m 0 2 Intra glia 5 s \210\22280 mV Intra neutron \210\22276 mV Fig. 1.3 Neuron \200\223glia interaction during SW seizures. Continuous recording containin g a double neuron \200\223glia impalement (A), and neuron- \201 eld recording (B) in corti cal association area 7. The two electrodes are separated by <1 mm. The transition from A to B is marked by the withdrawal of the pipette from the glia ( oblique open arrowhead ). Epo chs within the squares are expanded above the respective panels. Modi \201 ed from ( 37 ). cell types suggests that the ionic activity of Na + and Ca 2 + is propor- tional to that of K + and/or that the neuronal phasic depolarizations depend on the amount of extracellular K + . Alternatively, it could be that SW seizures are accompanied by a more active glial up take of extracellular K + . lags between the activities of pairs of neurons in parallel with the development of the sei zure might suggest increased synaptic cou- pling ( 14 , 59 ). On the other hand, numerous s tudies have demon- strated that the extracellular Ca 2 + concentrations decrease during SW seizures (Fig. 1. 5A ) ( 20 , 60 \200\22363 ). Knowing that synaptic ef \201 cacy critical ly depends on extracellular Ca 2 + levels ( 64 ), and assuming that the observed depletion is due to postsynaptic Ca 2 + entry, these data challenge the classical view of the synapti c synchronization during SW seizures. Although Ca 2 + uptake may also occur at the presynap tic level ( 65 , 66 ), several lines of evidence suggest the preponderance of the postsynap tic uptake ( 67 \200\22371 ). This phenomenon alone could pro- duce a steady decoupling of the neuronal networks during seizures. Nevertheless, ictal extracellular Ca 2 + levels disp lay phasic varia- tions in relation to rhythmic occurring PDSs (Fig. 1. 5B ) ( 20 ). A loca lly increased extracellular Ca 2 + concentration coincides with the onset of a PDS and, alt hough the overall variations have rela- tively low amplitude ( \210 0.1 mM), they might exp lain the relative increased network excitability at the onset of a PDS (see \201 gure 10 in reference 28). These data seem to con \201 rm a previous report ( 45 ) in which the abi lity of the seizure-prone neocortical network to respond to electrical stimuli with interic tal PDSs depended on the time lag between the end of the previous spontaneous PDS and the m oment at which the stimulus was presented (Fig. 1. 5C ). Measurements of membrane capacitance of both cortical glia and neurons during control sleep periods and SW seizures devel- oping from the slow sleep oscillations suggests that the gl ial cells (not the neurons) undergo swelling and/or increased communica- tion through gap j unctions during paroxysmal discharges (Fig. 1. 4 ) ( 19 ). The swelling of glial cells corr oborates with previous experi- ments demonstrating shrinkage of the extracellular space dur ing periods of increased extracellular K + ( 57 ). Therefore, in both cases, ephaptic trans mission through the cortex might be favored during SW discharges, as previously observed in the hippocampus ( 58 ) and could account, at least in part, for the increased synchroniza- tion recorded during epileptic seizures ( 14 ). Correlates of paroxysmal glial activities with extracellular ionic (K + and/or Ca 2 + ) con centrations Compared with the slow sleep oscillation, SW seizures appear as hypersynchronou s phenomena. The progressive reduction of time Intraglial as well as extracellular K + recordings during SW dis- charges show, in parallel with the Ca 2 + depletion, a progressive oxford textbook of epilepsy and epileptic seizures 6 could be involved in this process. First, glial cells take up Ca 2 + through voltage-depend ent channels ( 77 ), further contributing to the extracellular depletion of this ion. The s ubsequent increase of the intraglial Ca 2 + , together with the increase resulting from the glutamate-mediated neuronal activity ( 78 ), may result in gluta- mate release from glia ( 79 \200\22381 ) and excitation of the neighboring neurons. Such an effect may be enhanced by the increased excitabil- ity of axons resulting from the extracellular Ca 2 + depletion ( 82 ). Field potential Intra glia (reconstr.) \210\22288 mV V m 0 1 It appears, therefore, that the tight homeostasis of the extracel- lular potassium plays a pivotal role in keeping the normal brain oscillations from evolving into paroxysmal ones. G lial cells nor- mally ful \201 l this function. However, once the potassium regulation is compromised, the same cells also participate in the propagation/ generalization of the icta l activities. Several studies have drawn the attention to the fact that glial dysfunction i s intimately associated with the genesis of epileptic behavior. Among others, the opening o f the blood \200\223brain barrier and the ensuing extravasation of blood proteins entrain a cascade of events beginning with astrocytic acti- vation ( 83 ), downregulation of inward- rectifying potassium (Kir 4.1) channels in astrocytes, and impaired interstitial potassium buff- ering, ultimately leading to the genesis of epileptogenic foci ( 84 ). Intra glia Cx 5 s Capacitance [pF] 35 30 25 20 15 Are nocturnal SW seizures generated in the cortex or in the thalamus? The site of genesis o f SW seizures has been hotly debated during the past decades. The hypothesis that SW seizur es are generated within thalamic networks stemmed from old studies in which, however, no se lf-sustained activity outlasted SW-like cortical responses to medial thalamic stimulation ( 85 ). This hypothesis was replaced by the more reasonable idea that sleep spindles develop into SW seizures because of an enhanced excitability of neocortical neurons ( 86 ). Marcus and Watson ( 87 ) and Steriade ( 2 ) had emphasized the leading role of the cortex. More r ecently, intracel- lular studies in our laboratory have demonstrated that the corti- cally generated slow oscillation is the seed for paroxysmal developments such as SW seizures ( 14 , 15 , 59 ). Moreover, the tha- lamus of decorticated cats was unable to trigger seizures even after systemic or local injection of bicuculline ( 88 ). In contrast, local microinjec tions of bicuculline in the cortex of athalamic cats pro- duced widespread synchronous seiz ures ( 88 ). It was thus con- cluded that the minimal substrate for the generation of such SW seizures is the neocortex, although the active participation of some thalamocortical cel ls was not precluded. 10 Fig. 1.4 Glial capacitance measurements during SW seizures elicited by electrical stimulati on. The seizure was evoked by six trains of cortical stimuli at 1 Hz (every train contains 10 stimuli at 100 Hz). The second trace ( reconstr. ) represents the glial membrane potenti al after arti \201 cially eliminating the hyperpolarizing pulses (third trace) applied in order to calculate the membrane capacitance from the charging curve of the membrane. The ca pacitance increase re \202 ects swelling and/or enhanced gap junction communication. Modi \201 ed from ( 19 ). depolarization and, respectively, an increase in extracellular K + . Ca 2 + and K + dynamic s are clearly different (Fig. 1. 5D ). The epilep- tic tissue bene \201 ts from an enhance d gap junction communication ( 19 , 72 , 73 ), thus supporting the hypothesis that large co rtical ter- ritories may be synchronized during SW seizures by means of K + waves traveling through a functional gap junction syncytium. This observation gains more weight in the pre sence of depleted extracel- lular Ca 2 + at levels that are incompatible with synaptic func tional- ity. Indeed, simultanous extracellular K + concentrations at cortical sites separat ed by more than 2 mm, together with an intracellular recording close to one of the K + elec trodes (Fig. 1. 6A ) have shown that, at some distance from a presumed epileptic focus, the esti- mated intracellular K + concentration increases faster than the K + concentration of its extracellular environment ( 20 ). These data suggest that the propagation of the epile ptic activity in the cortex may use spatial buffering through the glial syncytium rather th an the simple diffusion through the extracellular space. The minor role played by the thalamus in the genesis of such SW seizures is in agreement wi th recordings from a majority (at least 60 % ) of thalamic neurons in intact animals showin g a tonic hyperpolarization, superimposed by phasic IPSPs, during seizures (Fig. 1. 7 ) ( 1 5 , 89 ). The behavior of such thalamocortical cells further precludes their active implica tion in reinforcing the oscillations during seizures. It was suggested that the tonic hyper - polarization was induced by the corticofugal projections of GABAergic thalamic reticular neurons that faithfully follow corti- cal PDSs. A minority of thalamocortical cells was, ho wever, dis- charging spike-bursts or spike-trains at 2 \200\2234 Hz, in phase with the depo larizing components of the cortical seizure. Therefore, during paroxysmal attacks the thala mic activity undergoes the antagonist in \202 uence of the steady excitatory cortex and in hibitory thalamic reticular neurons. This balance may evolve during the seizure itself, This hypothesis gains corroborative support from the fact that iso \202 urane and other vo latile anesthetics, known to block gap junctions communication ( 74 ), are widely used to p revent status epilepticus ( 75 , 76 ). Thus, in the absence of an ef \201 cient synaptic p athway to synchronize networks of neurons, the alternative path- way using the spatial buff ering of K + appears as a compensatory mechanism contributing to the spreading of the seizu res and to the synchronization of large cortical territories (Fig. 1. 6B ). Two ions CHAPTER 1 neurophysiology of epilepsy 7 A B - WTA Field potential (DC) 0 mV V m 5 \210\2229 mV V m 2 V m 0 2 0.2 s Intra neuron \210\22260 mV V m 5 5 s \210\22260 mV Ca2+ M m 5 0 0 out 0.7 mM 1 mM M m 2 0 . . C D Intra neuron Field potential (DC) 0 mV \210\22280 mV V m 5 5 s V m 5 Intra glia a b c a b c \210\22273 mV Ca2+ out 1 mM V m 0 2 M m 2 0 . 50 ms Fig. 1.5 A) Decrease of extracellular Ca 2 + concentrations ((Ca 2 + ) out ) during SW seiz ures. Simultanous intracellular recording of a neuron in the suprasylvian gyrus and of neig hboring DC \201 eld potentials and (Ca 2 + ) out . SW seizures are accompanied by a persi stent drop of \210 0.6 mM of the extracellular Ca 2 + concentration and by phasic oscillat ions of the (Ca 2 + ) out during the SW complexes B) The wave-triggered averages (n = 40) w ere aligned with the maximum slope of the neuronal depolarization ( vertical dotted line ), and depict the relationship between the neuronal paroxysmal depolarization, the \201 eld potential and the Ca 2 + concentration. Extracellular Ca 2 + increases during the hyperpol arizing phase foregoing the onset of the ictal discharge, and decreases during the subseque nt neuronal depolarization. C) Relative refractoriness of cortically-elicited PDSs. Intrace llular recording of a neuron in area 7. Three PDSs elicited by cortical stimuli to area 5 w ere superimposed and aligned; see stimuli artifacts from top to bottom. The amplitude and d uration of cortically-evoked PDS depended on their \200\230time-distance \200\231 from the preceding (spontaneously occurring) PDSs: PDSs decreased both in duration and amplitude as the stimulus was closer to the spontaneous PDS. D) Relationship between (Ca 2 + ) out and glial activities during recurrent SW seizures. Intraglial, DC \201 eld potentials, and Ca 2 + concentrations were measured at short distance (<1 mm) in the suprasylvian gyrus. Duri ng seizures, the glial steady depolarization and presumably the (K + ) out , had a differen t time course from the (Ca 2 + ) out : the onset of the seizure was simultanous in glia and \201 eld potential (black arrowheads oriented downward) and before the Ca 2 + started to decrease (empty arrowhead downward). The end of the seizure was marked \201 rst by a rap id return of Ca 2 + to normal values (empty arrowhead upward), followed by a much slower re turn of the glia and \201 eld potential to control potentials (black arrowhead upward). M odi \201 ed from: (A), (B), and (D) ( 20 ), and (C) ( 45 ). as suggested by the progression of the overall synchronization in corticothalamic networks, which becomes stronger as the seizure develops and more territories are recruited ( 59 ). traf \201 c of ions, have an active role in modulating the neuronal behavior. In the absen ce of reliable neuron-to-neuron synaptic transmission, alternative pathways may be used by the extraneuro- nal partners. Further investigation of the blood \200\223brain barrier and the implication of its transporters may bring new insights as to their contribution to paro xysmal discharges. From this perspec- tive, intractability may well be the reflection of ou r limited knowledge of the ensemble of mechanisms underlying epileptic syndromes. Conclusions The developing of SW seizures is far from exclusively being a neu- ronal phenom enon. From the data presented here, we believe that glial cells and the extracellular envir onment, mainly through the oxford textbook of epilepsy and epileptic seizures 8 A V m 5 V m 1 Glia 2 Glia 1 \210\22280 mV [K+] 5 % in ) i ( ) o ( [K+] out M m 0 2 M m 2 3 mM (o) 60 mM (i) B Seizure focus K+ Glia Gap junctions Neuron Fig. 1.6 Propagation of K + waves during SW seizures. A) Dual intraglial recording together with the (K + ) out . The disposition of the recording electrodes in the suprasylvian gyru s is shown in the inset. The traces represent the average of 20 normalized seizure envelope s. The upper superimposition contains the intracellular seizures in the pair of glial cells expanded at their maximum amplitude (see different voltage calibrations \200\224 continuo us line for cell 1 and dotted line for cell 2 , also corresponding to the envelope traces). From the higher amplitude of the signal, it may be inferred that cell 1 is closer to a pre sumed seizure focus. The lower panel displays the intra- and extracellular K + concentratio ns superimposed and expanded at their maximum amplitude. The (K + ) in was calculated from the Nernst equilibrium potential in relation with the (K + ) out and the intracellular trac e that was recorded closely to the K + microelectrode ( 2 ). Toward the beginning of the se izure, the estimated (K + ) in rose faster than the (K + ) out ( gray area between the two traces). B) Schematic functioning of the spatial buffering during SW seizures. Important in creases in the (K + ) out may not be buffered at short distances, in which case the interna lized K + may travel through the glial syncytium and is externalized at a location with low er (K + ) out values, where it would modulate the activity of nearby neurons. Modi \201 ed from ( 20 ). A \210\227 \210\227 Depth EEG area 4 V m 0 2 Fig. 1.7 Hyperpolarization of a thalamocortical neuron during cortical SW seizures. Cat und er ketamine- xylazine anesthesia. Intracellular recording from a thalamocortical neuron in the ventrolateral (VL) nucleus, together with depth-EEG from cortical area 4. Development f rom embryonic SW activity (A, between asterisks) to longer-lasting seizures with SW complex es at about 2.5 Hz (B, between asterisks). Modi \201 ed from ( 15 ). Intra-cell VL \210\22258 mV B \210\227 \210\227 2 s CHAPTER 1 neurophysiology of epilepsy 9 References 22. Contreras D , Timofeev I , Steriade M . Mechanisms of long-lasting hyperpolarizations u nderlying slow sleep oscillations in cat corticothalamic networks . J Physiol 1996 ; 494 : 251 \200\223 64 . 1. Sato S , Dreifuss FE , Penry JK . The effect of sleep on spike-wave discharges in absenc e seizures . Neurology 1973 : 23 : 1335 \200\223 45 . 23. Steriade M , Nu ez A , Amzica F . Intracellular analysis of relations between the slow (<1 Hz) neocortical oscillation and other sleep rhythms of the electroencephalogram . J Ne urosci 1993 ; 13 : 3266 \200\223 83 . 24. Timofeev I , Steriade M . Low-frequency rhythms in the thalamus of 2. Steriade M . Interneuronal epileptic discharges related to spike-and- wave cortical seiz ures in behaving monkeys . Electroencephalogr Clin Neurophysiol 1974 ; 37 : 247 \200\223 6 3 . 3. Kellaway P . Sleep and epilepsy . Epilepsia 1985 ; 26(Suppl 1 ): S15 \200\223S 30 . 4. Gastaut H , Roger J , Soulayrol R , Saint-Jean M , Tassinari CA , Regis H , et al . Epilept ic encephalopathy of children with diffuse slow spikes and waves (alias \200\230petit mal variant \200\231) or Lennox syndrome . Ann Pediatr (Paris) 1966 ; 13 : 489 \200\223 99 . intact-cortex and decorticated cats . J Neurophysiol 1996 ; 76 : 4152 \200\223 68 . 25. St eriade M , Contreras D , Curr Dossi R , Nu ez A . The slow (<1 Hz) oscillation in reticular thalamic and thalamocortical neurons: scenario of sleep rhythm gen eration in interacting thalamic and neocortical networks . J Neurosci 1993 ; 13 : 3284 \200\223 99 . 5. Niedermeyer E . Abnormal EEG patterns (epileptic and paroxysmal) . In: Niedermeyer E , L opes da Silva F (eds) Abnormal EEG patterns (epileptic and paroxysmal) , pp. 235 \200\223 60 . Baltimore, MD : Williams & Wilkins , 1999 . 26. Sanchez-Vives MV , McCormick DA . Cellular and network mechanisms of rhythmic recurrent activity in neocortex . Nature Neurosci 2000 ; 3 : 1027 \200\223 34 . 27. Contreras D , Steriade M . Cellular basis of EEG slow rhythms: a study of dynamic corti cothalamic relationships . J Neurosci 1995 ; 15 : 604 \200\223 22 . 28. Amzica F , Massimi ni M . Glial and neuronal interactions during slow wave and paroxysmal activities in the ne ocortex . Cereb Cortex 2002 ; 12 : 1101 \200\223 13 . 6. Velasco M , Diaz-de-Leon AE , Brito F , Velasco AL , Velasco F . Sleep-epilepsy interactions in patients with intractable generalized tonic seizures and dep th electrodes in the centro median thalamic nucleus . Arch Med Res 1995 ; 26(Spec No ): S11 7 \200\223 25 . 7. Halasz P . Runs of rapid spikes in sleep: a characteristic EEG expression of generalized malignant epileptic encephalopathies. A conceptual review with new pharmacological data . Epilepsy Res Suppl 1991 ; 2 : 49 \200\223 71 . 29. Amzica F , Steriade M . Short- and long-range neuronal synchronization of the slow (< 1 Hz) cortical oscillation . J Neurophysiol 1995 ; 73 : 20 \200\223 38 . 30. Amzica F , Ste riade M . Disconnection of intracortical synaptic linkages disrupts synchronization of a slow oscillation . J Neurosci 1995 ; 15 : 4658 \200\223 77 . 8. Dichter MA , Herman CJ , Selzer M . Silent cells during interictal discharges and seizures in hippocampal penicillin foci. Evidence for the role of extracellu lar K + in the transition from the interictal state to seizures . Brain Res 1972 ; 48 : 173 \200\223 83 . 31. Orkand RK , Nicholls JG , Kuf \202 er SW . Effect of nerve impulses on the membrane po tential of glial cells in the central nervous system of amphibia . J Neurophysiol 1966 ; 29 : 788 \200\223 806 . 9. Grossman RG , Hampton T . Depolarization of cortical glial cells during 32. Walz W . Role of glial cells in the regulation of the brain ion microenvironment . Prog Neurobiol 1989 ; 33 : 309 \200\223 33 . electrocortical activity . Brain Res 1968 ; 11 : 316 \200\223 24 . 10. Sypert GW , Ward AA , Jr . Unidenti \201 ed neuroglia potentials during propagated sei zures in neocortex . Exp Neurol 1971 ; 33 : 239 \200\223 55 . 33. Newman EA . Glial cell regulation of extracellular potassium . In: Kettenmann H , Ransom BR (eds) Glial cell regulation of extracellular potassium , pp. 717 \200\223 31 . New York : Oxford University Press , 1995 . 34. Araque A , Li N , Doyle RT , Haydon PG . SNARE protein-dependent glutamate release from astrocytes . J Neurosci 2000 ; 2 0 : 666 \200\223 73 . 11. Somjen GG . In \202 uence of potassium and neuroglia in the generation of seizures and their treatment . Adv Neurol 1980 ; 27: 155 \200\223 67 . 12. Scheffer IE, Bh atia KP , Lopes-Cendes I , Fish DR , Marsden CD , Andermann F , et al . Autosomal dominant frontal epilepsy misdiagnosed as sleep disorder . Lancet 1994 ; 343 : 515 \200\223 17 . 35. Amzica F , Steriade M . Cellular substrates and laminar pro \201 le of sleep K-complex . Neuroscience 1998 ; 82 : 671 \200\223 86 . 13. Zuckermann EC , Glaser GH . Hippocampal epileptic activity induced by localized ventric ular perfusion with high-potassium cerebrospinal \202 uid . Exp Neurol 1968 ; 20 : 87 \200\223 110 . 36. Amzica F , Steriade M . The K-complex: its slow (<1 Hz) rhythmicity and relation to delta waves . Neurology 1997 ; 49 : 952 \200\223 9 . 37. Amzica F , Steriade M . Neuronal and glial membrane potentials during sleep and paroxys mal oscillations in the neocortex . J Neurosci 2000 ; 20 : 6648 \200\223 65 . 14. Steriade M , Amzica F . Dynamic coupling among neocortical neurons during evoked and spontaneous spike-wave seizure activity . J Neurophysiol 1994 ; 72 : 2051 \200\223 69 . 38. Matsumoto H , Ajmone-Marsan C . Cortical cellular phenomena in experimental epilepsy: i nterictal manifestations . Exp Neurol 1964 ; 9 : 286 \200\223 304 . 15. Steriade M , Contreras D . Relations between cortical and thalamic cellular events duri ng transition from sleep patterns to paroxysmal activity . J Neurosci 1995 ; 15 : 623 \200 \223 42 . 39. Matsumoto H , Ajmone-Marsan C . Cortical cellular phenomena in 16. Steriade M , Amzica F , Neckelmann D , Timofeev I . Spike-wave experimental epilepsy: ictal manifestations . Exp Neurol 1964 ; 9 : 305 \200\223 26 . 40. Ayala GF , Dichter M , Gumnit RJ , Matsumoto H , Spencer WA . Genesis of epileptic interict al spikes. New knowledge of cortical feedback systems suggests a neurophysiological explana tion of brief paroxysms . Brain Res 1973 ; 52 : 1 \200\223 17 . complexes and fast components of cortically generated seizures. II. Extra- and intracellula r patterns . J Neurophysiol 1998 ; 80 : 1456 \200\223 79 . 17. Krieger J . Respiratory phy siology: breathing in normal subjects . In: Kryger MH , Roth T , Dement W (eds) Respiratory physiology: breathing in normal subjects , pp. 229 \200\223 41 . Philadelphia, PA : Saund ers , 2000 . 41. Johnston D , Brown TH . Giant synaptic potential hypothesis for epileptiform activity . Science 1981 ; 211 : 294 \200\223 7 . 18. Steriade M , Nunez A , Amzica F . A novel slow (< 1 Hz) oscillation of neocortical neur ons in vivo: depolarizing and hyperpolarizing components . J Neurosci 1993 ; 13 : 3252 \200\223 65 . 42. Steriade M , Timofeev I , Grenier F . Inhibitory components of cortical spike-wave seizures in vivo . Soc Neurosci Abstr 1998 ; 24 : 2143 . 43. Amzica F , Steriade M . Spontaneous and arti \201 cial activation of 19. Amzica F , Neckelmann D . Membrane capacitance of cortical neurons neocortical seizures . J Neurophysiol 1999 ; 82 : 3123 \200\223 38 . 44. Neckelmann D , Am zica F , Steriade M . Changes in neuronal and glia during sleep oscillations and spike-wave seizures . J Neurophysiol 1999 ; 82 : 273 1 \200\223 46 . conductance during different components of cortically generated spike-wave seizures . Neuro science 2000 ; 96 : 475 \200\223 85 . 20. Amzica F , Massimini M , Manfridi A . Spatial buffering during slow and paroxysmal slee p oscillations in cortical networks of glial cells in vivo . J Neurosci 2002 ; 22 : 1042 \200\223 53 . 45. Steriade M , Amzica F . An intracellular study of excitability in the seizure-prone neo cortex in vivo . J Neurophysiol 1999 ; 82 : 3108 \200\223 22 . 46. Fertziger AP , Ranck JB , Jr . Potassium accumulation in interstitial 21. Massimini M , Amzica F . Extracellular calcium \202 uctuations and intracellular potentials in the cortex during the slow sleep oscillation . J Neurophysiol 2 001 ; 85 : 1346 \200\223 50 . space during epileptiform seizures . Exp Neurol 1970 ; 26 : 571 \200\223 85 . oxford textbook of epilepsy and epileptic seizures 10 69. Borst JG , Sakmann B . Depletion of calcium in the synaptic cleft of a calyx-type synap se in the rat brainstem . J Physiol (Lond) 1999 ; 521 : 123 \200\223 33 . 47. Futamachi KJ , Mutani R , Prince DA . Potassium activity in rabbit cortex . Brain Res 1974 ; 75 : 5 \200\223 25 . 48. Moody WJ , Futamachi KJ , Prince DA . Extracellular potassium activity 70. Rusakov DA , Kullmann DM , Stewart MG . Hippocampal synapses: during epileptogenesis . Exp Neurol 1974 ; 42 : 248 \200\223 63 . do they talk to their neighbors? Trends Neurosci 1999 ; 22 : 382 \200\223 8 . 71. King RD , Wiest MC , Montague PR , Eagleman DM . Do extracellular 49. Sypert GW , Ward AA Jr . Changes in extracellular potassium activity during neocortical propagated seizures . Exp Neurol 1974 ; 45: 19 \200\223 41 . Ca 2 + signals carry information through neural tissue? Trends Neurosci 2000 ; 23 : 12 \200\223 13 . 50. Somjen GG . Extracellular potassium in the mammalian central nervous system . Prog Biophys Mol Biol 1979 ; 42 : 135 \200\223 90 . 72. Lee SH , Magge S , Spencer DD , Sontheimer H , Cornell-Bell AH . 51. McBain CJ , Traynelis SF , Dingledine R . High potassium induced Human epileptic astrocytes exhibit increased gap junction coupling . Glia 1995 ; 15 : 195 \200\223 202 . synchronous bursts and electrographic seizures . In: Schwartzkroin PA (ed) Epilepsy: Models , Mechanisms and Concepts , pp. 437 \200\223 61 . Cambridge: Cambridge University Press , 1993 . 73. Bordey A , Lyons SA , Hablitz JJ , Sontheimer H . Electrophysiological characteristics of reactive astrocytes in experimental cortical dysplasia . J Neurophysiol 2001 ; 85 : 1719 \200\223 31 . 52. Ballanyi K , Grafe P , Ten Bruggencate G . Ion activities and potassium uptake mechanis ms of glial cells in guinea-pig olfactory cortex slices . J Physiol (Lond) 1987 ; 382 : 159 \200\223 74 . 74. Mantz J , Cordier J , Giaume C . Effects of general anesthetics on 53. Kettenmann H . K + and Cl - uptake by cultured oligodendrocytes . intercellular communications mediated by gap junctions between astrocytes in primary cultur e . Anesthesiology 1993 ; 78 : 892 \200\223 901 . 75. Kofke WA , Snider MT , Young RS , Ra mer JC . Prolonged low \202 ow Can J Physiol Pharmacol 1987 ; 65 : 1033 \200\223 7 . 54. Kettenmann H , Ransom BR . Electrical coupling between astrocytes and between oligodend rocytes studied in mammalian cell cultures . Glia 1988 ; 1 : 64 \200\223 73 . iso \202 urane anesthesia for status epilepticus . Anesthesiology 1985 ; 62 : 653 \200 \223 6 . 76. Kofke WA , Young RS , Davis P , Woelfel SK , Gray L , Johnson D , et al . 55. Nicholson C . Extracellular space as the pathway for neuron-glial cell Iso \202 urane for refractory status epilepticus: a clinical series . Anesthesiology 1989 ; 71 : 653 \200\223 9 . interaction . In: Kettenmann H , Ransom BR (eds) Neuroglia , pp. 387 \200\223 97 . New Yor k : Oxford University Press , 1995 . 77. MacVicar BA . Voltage-dependent calcium channels in glial cells . 56. Janigro D , Gasparini S , D \200\231Ambrosio R , McKhann G II , DiFrancesco D . Reduction of K + uptake in glia prevents long-term depression maintenance and causes epilep tiform activity . J Neurosci 1997 ; 17 : 2813 \200\223 24 . Science 1984 ; 226 : 1345 \200\223 7 . 78. Cornell-Bell AH , Finkbeiner SM , Cooper MS , Smith SJ . Glutamate induces calcium wave s in cultured astrocytes: long-range glial signaling . Science 1990 ; 247 : 470 \200\223 3 . 57. Dietzel I , Heinemann U , Hofmeier G , Lux HD . Transient changes in the size of the ex tracellular space in the sensorimotor cortex of cats in relation to stimulus-induced change s in potassium concentration . Exp Brain Res 1980 ; 40 : 432 \200\223 9 . 79. Parpura V , Basarsky TA , Liu F , Jeftinija K , Jeftinija S , Haydon PG . Glutamate-med iated astrocyte-neuron signaling . Nature 1994 ; 369 : 744 \200\223 7 . 80. Pasti L , Volterra A , Pozzan T , Carmignoto G . Intracellular calcium oscillations in astrocytes: a highly plastic, bidirectional form of communication between neurons and astro cytes in situ . J Neurosci 1997 ; 17 : 7817 \200\223 30 . 58. Taylor CP , Dudek FE . Synchronization without active chemical synapses during hippocampal afterdischarges . J Neurophysiol 1984 ; 52 : 143 \200\223 55 . 59. Neckelmann D , Amzica F , Steriade M . Spike-wave complexes and fast components of cort ically generated seizures. III. Synchronizing mechanisms . J Neurophysiol 1998 ; 80 : 1480 \200\223 94 . 81. Bezzi P, Carmignoto G , Pasti L , Vesce S , Rossi D , Rizzini BL , et al . Prostaglandi ns stimulate calcium-dependent glutamate release in astrocytes . Nature 1998 ; 391 : 281 \200\223 5 . 60. Heinemann U , Lux HD , Gutnick MJ . Extracellular free calcium and 82. Hille B . Ion Channels of Excitable Membranes . Sunderland, MA : potassium during paroxysmal activity in the cerebral cortex of the cat . Exp Brain Res 1977 ; 27 : 237 \200\223 43 . Sinauer , 1991 . 83. Seiffert E , Dreier JP , Ivens S , Bechmann I , Tomkins O , Heinemann U , et al . Lasti ng blood-brain barrier disruption induces epileptic focus in the rat somatosensory cortex . J Neurosci 2004 ; 24 : 7829 \200\223 36 . 84. Ivens S , Kaufer D , Flores LP , Bechmann I , Zumsteg D , Tomkins O , et al . TGF-beta receptor-mediated albumin uptake into astrocyte s is involved in neocortical epileptogenesis . Brain 2007 ; 130 : 535 \200\223 47 . 85. Ja sper HH , Droogleever-Fortuyn J . Experimental studies on the functional anatomy of petit-m al epilepsy . Res Publ Assoc Nerv Ment Dis 1949 ; 26 : 272 \200\223 98 . 61. Somjen GG . Stimulus-evoked and seizure-related responses of extracellular calcium activity in spinal cord compared to those in cerebral cortex . J Neur ophysiol 1980 ; 44 : 617 \200\223 32 . 62. Pumain R , Kurcewicz I , Louvel J . Fast extracellular calcium transients: involvement in epileptic processes . Science 1983 ; 222 : 177 \200\223 9 . 63. Hablitz JJ , Heinemann U . Extracellular K + and Ca 2 + changes during epileptiform dis charges in the immature rat neocortex . Brain Res 1987 ; 433 : 299 \200\223 303 . 64. King RD , Wiest MC , Montague PR . Extracellular calcium depletion 86. Gloor P , Fariello RG . Generalized epilepsy: some of its cellular as a mechanism of short-term synaptic depression . J Neurophysiol 2001 ; 85 : 1952 \200 \223 9 . mechanisms differ from those of focal epilepsy . Trends Neurosci 1988 ; 11 : 63 \200\223 8 . 65. Alici K , Heinemann U . Effects of low glucose levels on changes in (Ca 2 + ) o induced by stimulation of Schaffer collaterals under conditions of blocked chemical synaptic trans mission in rat hippocampal slices . Neurosci Lett 1995 ; 185 : 5 \200\223 8 . 87. Marcus EM , Watson CW . Symmetrical epileptogenic foci in monkey cerebral cortex . Arch Neurol 1968 ; 19 : 99 \200\223 116 . 88. Steriade M , Contreras D . Spike-wave complexes and fast components of cortically gener ated seizures. I. Role of neocortex and thalamus . J Neurophysiol 1998 ; 80 : 1439 \200 \223 55 . 66. Igelmund P , Zhao YQ , Heinemann U . Effects of T-type, L-type, N-type, P-type, and Q-type calcium channel blockers on stimulus- induced pre- and postsynap tic calcium \202 uxes in rat hippocampal slices . Exp Brain Res 1996 ; 109 : 22 \200\223 32 . 89. Pinault D , Leresche N , Charpier S , Deniau JM , Marescaux C , Vergnes M , et al . Intracellular recordings in thalamic neurones during spontaneous spike and wave discharges in rats with absence epilepsy . J Physiol (Lond) 1998 ; 509 : 449 \200\223 56 . 67. Heinemann U , Pumain R . Effects of tetrodotoxin on changes in extracellular free calcium induced by repetitive electrical stimulation and iontophoretic a pplication of excitatory amino acids in the sensorimotor cortex of cats . Neurosci Lett 198 1 ; 21 : 87 \200\223 91 . 90. Mintz IM , Sabatini BL , Regehr WG . Calcium control of transmitter release at a cerebellar synapse . Neuron 1995 ; 15 : 675 \200\223 88 . 68. Bollmann JH , Helmchen F , Borst JG , Sakmann B . Postsynaptic Ca 2 + 91. Qian J , Colmers WF , Saggau P . Inhibition of synaptic transmission by neuropeptide Y in rat hippocampal area CA1: modulation of presynaptic Ca 2 + entry . J Neurosci 1997 ; 17 : 8169 \200\223 77 . in \202 ux mediated by three different pathways during synaptic transmission at a calyx-ty pe synapse . J Neurosci 1998 ; 18 : 10409 \200\223 19 . CHAPTER 2 Neurogenetics of Epilepsy Renzo Guerrini and Elena Parrini molecular diagnosis is now available for different forms of epilepsy. However, ethical prob lems may arise especially in asymptomatic mutation carriers or in individuals and families in which although mutations of speci \201 c genes have been identi \201 ed, severity of t he associated phenotype is unpredictable.