 |
 Previous Article | Next Article 
The Journal of Neuroscience, June 1, 1998, 18(11):4285-4294
Seizure-Induced Neuronal Injury: Vulnerability to Febrile
Seizures in an Immature Rat Model
Zsolt
Toth1,
Xiao-Xin
Yan1, 2,
Suzie
Haftoglou1,
Charles E.
Ribak1, and
Tallie Z.
Baram1, 2
Departments of 1 Anatomy and Neurobiology and
2 Pediatrics, University of California, Irvine, Irvine,
California 92697-4475
 |
ABSTRACT |
Febrile seizures are the most common seizure type in young
children. Whether they induce death of hippocampal and amygdala neurons
and consequent limbic (temporal lobe) epilepsy has remained controversial, with conflicting data from prospective and retrospective studies. Using an appropriate-age rat model of febrile seizures, we
investigated the acute and chronic effects of hyperthermic seizures on
neuronal integrity and survival in the hippocampus and amygdala via
molecular and neuroanatomical methods. Hyperthermic seizures-but not
hyperthermia alone-resulted in numerous argyrophilic neurons in
discrete regions of the limbic system; within 24 hr of seizures, a
significant proportion of neurons in the central nucleus of the
amygdala and in the hippocampal CA3 and CA1 pyramidal cell layer were
affected. These physicochemical alterations of hippocampal and amygdala
neurons persisted for at least 2 weeks but were not accompanied by
significant DNA fragmentation, as determined by in situ
end labeling. By 4 weeks after the seizures, no significant neuronal
dropout in these regions was evident. In conclusion, in the immature
rat model, hyperthermic seizures lead to profound, yet primarily
transient alterations in neuronal structure.
Key words:
seizures; animal model; febrile seizures; epilepsy; neuronal death; excitotoxicity; apoptosis; in situ end
labeling
| |
INTRODUCTION |
Febrile seizures are the most common
seizure type in the human infant and young child (Verity et al., 1985 ;
Shinnar, 1990; Hauser, 1994). Prospective epidemiological studies have
indicated that febrile seizures do not progress to temporal lobe
epilepsy (TLE) (Nelson and Ellenberg, 1976; Shinnar, 1990; Knudsen,
1996). However, retrospective analyses of adults with TLE document a high prevalence (30-50%) of a history of febrile seizures during early childhood, suggesting an etiological role for these seizures in
the development of TLE (Gloor, 1991; Cendes et al., 1993). A role for
neuronal damage induced by febrile seizures in the pathogenesis of
mesial temporal sclerosis, the pathological hallmark of TLE, has been
postulated (Falconer et al., 1964; Sagar and Oxbury, 1987; Gloor,
1992). An alternative mechanism for the correlation of febrile seizures
and TLE involves pre-existing neuronal injury that triggers both the
febrile seizures and the subsequent TLE.
In general, both electrophysiological and behavioral manifestations of
seizures in the immature human and in developing experimental animals
are more severe than are those resulting from equivalent proconvulsant
drugs or insults in the mature brain (Sperber et al., 1992). For
example, during the second postnatal week in the rat, kainic acid leads
to status epilepticus with dramatic mortality at doses that cause only
mild seizures in the adult (Albala et al., 1984; Holmes and Thompson,
1988; Chang and Baram, 1994). Seizure induction by a hypoxic insult is
also age-dependent, peaking on the 10th postnatal day (Jensen et al.,
1991; Owens et al., 1997). In addition, seizures induced by
hyperthermia and fever in the rat and human, respectively, are almost
exclusive to the developmental period (Berg et al., 1992; Baram et al.,
1997).
Despite the severity of seizures in a number of experimental paradigms,
neuronal death, i.e., cell loss as a result of these seizures, does not
appear to occur during the first 2 postnatal weeks in the rat (Nitecka
et al., 1984; Sperber et al., 1992; Holmes, 1997). Studies using DNA
fragmentation or silver-staining methods have failed to reveal acute
cell death after severe seizures induced by convulsants such as kainic
acid (Sperber et al., 1991), pilocarpine, or hypoxia (Owens et al.,
1997), even though all three treatments cause widespread acute cell
death in older animals (Ben-Ari et al., 1981; Clifford et al., 1987).
Furthermore, long-term studies of kainic acid-induced seizures have
revealed neither a decrease in neuronal number in limbic areas that are
vulnerable in the adult nor a sprouting response that is observed in
adult animals after loss of "target" postsynaptic neurons (Sperber
et al., 1992; Baram and Ribak, 1995).
A model of febrile seizures in the immature rat has recently been
characterized (Baram et al., 1997). This paradigm relies on rat pups
during a brain-development age equivalent to that of the human infant
and young child (Dobbing and Sands, 1973). Furthermore, the model is
associated with little immediate morbidity, permitting prospective
long-term analyses of the effects of hyperthermic seizures on neuronal
integrity and survival. The goals of the current study were to (1)
investigate potential acute injury induced by hyperthermic seizures,
(2) define the topographical distribution of vulnerable neurons, and
(3) determine whether acute neuronal injury after hyperthermic seizures
produces significant neuronal loss.
| |
MATERIALS AND METHODS |
Hyperthermic seizures experimental design
Animals. Rat pups were offspring of time-pregnant
Sprague Dawley-derived rats obtained from Zivic-Miller (Zelienople,
PA). Mothers were kept on a 12 hr light/dark schedule and given lab chow and water ad libitum (Yi and Baram, 1994; Baram et al.,
1997). The time of birth of pups was determined every 12 hr, and the day of birth was considered day 0. Litters were culled to 12 pups on
the first postnatal day and kept in quiet, uncrowded American Association for Accreditation of Laboratory Animal Care-approved facilities at a room temperature of 21-22°C. Overall, 89 rat pups participated in the study and were divided into experimental groups as
described below.
Hyperthermia induction paradigm. The hyperthermic seizure
paradigm has been described previously in detail (Baram et al., 1997).
Briefly, on postnatal day 10, the core temperature of pups was raised
using a regulated stream of moderately heated air. Pups were placed on
the floor of a 3 l glass container, and the air stream was
directed ~50 cm above them. Rectal temperatures were measured at
baseline, at 2 min intervals, and at the onset of hyperthermic
seizures, which occur in >93% of rats (Baram et al., 1997).
Hyperthermia was maintained for 30 min, aiming for a core temperature
of 41-42°C, and the presence and duration of seizures for each pup
were noted at 2 min intervals. After the hyperthermia period, rats were
placed on a cool surface, monitored for 15 min, and then returned to
home cages for rehydration by the mothers. Pups who were sedated
because of diazepam or pentobarbital pretreatment were hydrated orally
and returned to their cages when their behavior normalized (typically
<1 hr). The behavioral seizures in this paradigm are stereotyped and
easily monitored and have been shown to correlate with EEG rhythmic
epileptiform discharges from the hippocampus and amygdala (Baram et
al., 1997). These seizures consist of complete arrest of the
heat-induced hyperkinesis, unilateral body flexion, and biting of an
extremity, occasionally followed by clonic or "swimming"
motions.
Experimental groups. The overall strategy was to compare the
presence of neuronal injury in three experimental groups. (1) Controls
(n = 24) were maintained normothermic for age (rectal temperature, 33-34°C) throughout the experiments. (2) Hyperthermia controls (n = 14) were rendered hyperthermic, but
seizures were prevented by pretreatment with intraperitoneal diazepam
(5 mg/kg) or the short-acting barbiturate pentobarbital (30 mg/kg)
before hyperthermia induction. (3) The third group experienced
hyperthermic seizures (n = 51).
For determination of DNA fragmentation, groups (n = 3-4 per group) of animals subjected to hyperthermic seizures were
killed at the following time points after the seizures: 1, 4, 8.5, 20, and 48 hr. An additional group (n = 4) was subjected to
hyperthermia twice, leading to a total seizure duration of 60 ± 2 min, and was killed 20 hr after the second seizure episode.
Normothermic animals (n = 7) and pups in whom
hyperthermia-induced seizures were prevented with pentobarbital (see
above) were used as controls. For analysis of neuronal injury using the
Gallyas "dark"-neuron stain, animals were killed 24 hr, 1 week, or
2 weeks after seizure induction. For cell counting, animals
(n = 12; 4 per experimental group) were killed 4 weeks
after the hyperthermic seizures.
In situ end labeling
In situ end labeling (ISEL) provides a positive label
of dying cells, leading to increased sensitivity over methods relying on the "dropout" of neurons. ISEL was modified from Sakhi et al. (1994). Briefly, frozen 20 µm sections were thawed, dried, and fixed
in 4% buffered paraformaldehyde, followed by ethanol dehydration. After rehydration and preincubation in a Tris buffer, 50 µl of reaction mix [966 µl of buffer, 4 µl of nucleotide mix (Sakhi et
al., 1994), 10 µl of DNA polymerase I (10 U/µl; Promega, Madison, WI), and 20 µl of dUTP-biotin (Sigma, St. Louis, MO) per 1000 µl]
were applied for 1 hr. UTP-biotin-tagged cleaved DNA ends were
visualized using a commercial avidin-biotin kit (VECTASTAIN; Vector
Laboratories, Burlingame, CA). Sections were counterstained with acid
fuchsin (Chang and Baram, 1994), and the number of labeled neurons with
clumped chromatin in the central nucleus of the amygdala and the
hippocampus was determined. Sections from adult rats subjected to
kainic acid-induced status epilepticus and allowed a 20 hr survival
time were run in parallel as "positive controls" to confirm the
validity of the ISEL method at this time point.
Histological methods
For all histological methods, control and experimental groups
were processed together, without knowledge of treatment group. Animals
were killed and perfused as described elsewhere (Baram and Ribak, 1995;
Ribak and Baram, 1996). Briefly, under deep anesthesia, rats were
perfused transcardially with saline followed by a 4% paraformaldehyde-2.5% glutaraldehyde-0.1 M phosphate
buffer solution. Brains were left in situ overnight and then
post-fixed for a week in the same fixative. Brains were sectioned
coronally with a vibratome at 100 µm for silver staining and at 20 µm for Nissl staining for neuronal counts. Sections (immersed in
fixative) were stored at 4°C.
Silver-staining (dark-neuron) method. This method has been
described earlier (Gallyas et al., 1990). Briefly, after dehydration in
50, 75, and 100% propanol, sections were esterified with propanol containing 0.8% sulfuric acid. Sections were rehydrated through 50 and
25% propanol and distilled water, treated with 3% acetic acid for 5 min, and developed for 10 min. The fresh developing solution consisted
of equal volumes of 10% Na2CO3 and a solution composed of 0.2% AgNO3, 0.25%
NH4NO3, 2% tungstosilicic acid, and
0.4% formaldehyde. When developed, sections were dehydrated and
coverslipped.
Semithin sections and electron microscopy methods. Unstained
sections adjacent to those containing argyrophilic neurons were post-fixed with 1% osmium tetroxide, dehydrated, and embedded in Epon.
Semithin, 2 µm sections were cut and stained with 1% toluidine blue
to identify deeply basophilic neurons. For electron microscopy (EM)
analysis, ultrathin sections were obtained from the same tissue blocks,
subjected to uranyl acetate and lead citrate, and examined with a
transmission EM. Electron-dense neuronal profiles and their synapses
were further examined in serial sections to confirm their
identification.
Semiquantitative neuronal analysis. For counting both
silver- and Nissl-stained neurons, sections were analyzed without
knowledge of treatment ("blindly"). Based on the limbic
phenomenology of hyperthermia-induced seizures (Ben-Ari et al., 1981;
Baram et al., 1997), the examination of argyrophilic neurons focused on the amygdala, hippocampus, and cortical regions interconnected with
these structures. For determining the fate of most argyrophilic neurons, an estimate of their number was undertaken in the most affected structure, the lateral division (CE-L) of the central nucleus
of the amygdala (ACE). For purposes of neuronal counting, the
anatomical boundaries of the CE-L were defined using Sherwood and
Timiras (1970). Rostral and caudal boundaries were selected to permit
an easily identifiable coronal profile of the nucleus. The rostral
boundary was at the level of the anterior paraventricular hypothalamic
nucleus and the rostral border of the hippocampal CA3 (5.0 mm anterior
to bregma in the 39-d-old rat); the caudal boundary was defined at the
level of the infundibulum (4.1 mm anterior to bregma). The lateral
boundary of the ACE was defined by the clearly visible teardrop-shaped
lateral nucleus of the amygdala. The medial border was defined by the
cell-poor white matter of the internal capsule. Within the ACE, the
CE-L was defined according to Tuunanen et al. (1996). Briefly, the
tightly packed capsular region was defined laterally, and the
crescent-shaped medial division was distinguished medially (see Figs.
3, 5). Because a determination of the absolute, unbiased number of
argyrophilic neurons was not needed for the purposes of this study, a
modified profile sampling method was used [for a recent discussion,
see Popken and Farel (1997); Saper (1997)]. A grid reticule of 100 frames covering an area of 250 × 250 µm was centered over every sixth section of the CE-L, and all frames were subjected to counting for cell bodies throughout the depth of the section (Popken and Farel,
1997). The resulting number was multiplied to yield an estimate of the
overall number of argyrophilic neurons in the CE-L as defined above.
For Nissl-stained sections, every ninth 20 µm section was subjected
to cell counts. To minimize the bias of the "splitting" of large
cell bodies resulting in an overestimate of counts, we counted nucleoli
(Popken and Farel, 1997). Counts of each section were averaged to yield
an estimate of variance, and the overall neuronal numbers in the CE-L,
as defined above, were obtained for each experimental animal. The
statistical significance of differences among the three treatment
groups used ANOVA (PRISM statistical software; GraphPad, San Diego,
CA).
| |
RESULTS |
Using ISEL, hyperthermic seizures lead to little immediate
cell death
Direct evidence of DNA fragmentation associated with several forms
of neuronal death, including death induced by kainic acid-induced status epilepticus (Pollard et al., 1994), was studied using ISEL. After hyperthermic seizures, only occasional amygdala and hippocampal neurons were labeled in sections derived from rats subjected to hyperthermic seizures and permitted to survive for 1, 4, 8.5, 20, or 48 hr (Fig. 1, Table
1). Sections from adult rats subjected to
kainic acid-induced status epilepticus and allowed a 20 hr survival
time, which were run in parallel, contained abundant labeled neurons in
hippocampal CA3 and most amygdala nuclei, confirming the validity of
the ISEL method (data not shown).
View larger version (70K):
[in this window]
[in a new window]
|
Figure 1.
Rare acute neuronal death after hyperthermic
seizures in the immature rat. A, In situ
end labeling reveals two hippocampal CA3 neurons
(arrows) undergoing DNA fragmentation from an animal
killed 20 hr after hyperthermic seizures. B, Higher
magnification shows the typical DNA fragmentation in a pyramidal layer
neuron (arrow corresponding to the lower neuron in
A). Run in parallel, sections from normothermic controls
did not contain labeled neurons, whereas, as expected, sections from
kainic acid-treated mature rats revealed numerous dying cells (data not
shown). s.o., Stratum oriens; s.p.,
stratum pyramidale; s.r., stratum radiatum. Scale bars:
A, 50 µm; B, 10 µm.
|
|
Hyperthermic seizures lead to neuronal injury in discrete
hippocampal and amygdala regions
Sections from animals killed 24 hr after hyperthermic seizures
contained significant populations of silver-stained, dark neurons. Figure 2 demonstrates clusters of stained
neurons in the hippocampus. All subfields of the CA3 pyramidal cell
layer were involved, as well as the entire extent of CA1 and occasional
granule cells (Fig. 2A). Affected neurons were
interspersed among normal ones, and their stained apical and basal
dendrites indicated that they were pyramidal cells. No argyrophilic
neurons were apparent in control sections (Fig. 2C) or in
sections from animals pretreated with anticonvulsants before
hyperthermia induction (Fig. 2B). Higher
magnifications of the silver-stained neurons, revealing pronounced
physicochemical alterations (shrunken appearance; Gallyas et al.,
1992a), are shown in Figure 2, D and E.
View larger version (169K):
[in this window]
[in a new window]
|
Figure 2.
Acute induction of silver-stained neurons in
hippocampal sections from immature rats subjected to hyperthermic
seizures (A), hyperthermia without seizures
(B), or normothermia (C) is
shown. Animals were killed 24 hr after treatment, and sections were
stained using the Gallyas dark-neuron method. Abundant stained neurons
are evident in the CA1 and all three subfields of the CA3 pyramidal
cell layers (CA3a-CA3c) of an animal
with seizures (A) but not in hyperthermic or
normothermic controls (B, C). Higher
magnifications (D, E) provide
morphological detail of the affected neurons in the CA1 pyramidal layer
(D) and in CA3c (E),
demonstrating altered physicochemical properties of both the cell body
and processes. DG, Dentate gyrus; s.l.m.,
stratum lacunosum moleculare; s.o., stratum oriens;
s.p., stratum pyramidale; s.r., stratum
radiatum. Scale bars: A-C, 1 mm;
D, E, 50 µm.
|
|
The remarkable involvement of the lateral division of the ACE is
evident in Figure 3. Sections from rats
killed 24 hr after hyperthermia and seizures (Fig. 3A)
revealed an abundance of argyrophilic neurons, whereas sections from
both of the control groups [hyperthermia without seizures (Fig.
3B) and normothermia (Fig. 3C)] did not contain
affected cells. Semiquantitative analysis of affected neurons in the
CE-L suggested that the number of injured neurons was in the order of
185.8 ± 10.1 per 100-µm-thick section or 1645.5 ± 178 within the defined anatomical boundaries of this nucleus (see Materials
and Methods). The distribution of hyperthermic seizures-induced
argyrophilic neurons included also the medial and lateral basal
amygdala nuclei (Fig. 3D), as well as a delimited portion of
the perirhinal cortex (Fig. 3E).
View larger version (179K):
[in this window]
[in a new window]
|
Figure 3.
Neuronal injury induced by hyperthermic seizures
in the amygdala, demonstrated using the Gallyas dark-neuron method.
A, Significant involvement of the lateral division of
the central amygdaloid nucleus (CE-L) is manifested by
large numbers of densely silver-stained neurons. B,
C, Sections from hyperthermic (B)
or normothermic (C) controls contain few stained
neurons. D, The distribution of silver-stained neurons
in other amygdaloid nuclei, the basomedial (ABM)
and basolateral (ABL) nuclei, is shown.
E, The presence of argyrophilic neurons in the
perirhinal cortex is evident. ALA, Lateral amygdala
nucleus; IC, internal capsule; rf, rhinal
fissure. Scale bars: A-C, 500 µm;
D, E, 200 µm.
|
|
EM was used to show the ultrastructural features of the silver-stained
neurons in the hippocampal CA1 and the amygdaloid CE-L. Figure
4 demonstrates a hyperelectron-dense
shrunken pyramidal cell (Fig. 4B). Intact synapses
are apparent along the surfaces of the soma and the shrunken, spiny
dendrites of this neuron (Fig. 4C), which are postsynaptic
to immature axon terminals. In the CE-L, the electron-dense cells
maintained intact cell membranes and contained distinct organelles
including Golgi complexes and endoplasmic reticulum (Fig.
4D,E).
View larger version (179K):
[in this window]
[in a new window]
|
Figure 4.
Light and electron micrographs of
hyperelectron-dense neurons in the hippocampal CA1
(A-C) and the lateral division of the
central amygdaloid nucleus (CE-L) (D,
E). A, B, A shrunken,
deeply basophilic neuron in A appears electron-dense in
B compared with a normal neuron
(N). The hyperelectron-dense nucleus
(n) and apical dendrite (d)
with a spine (arrow) of this neuron, as well as abnormal
processes (curved arrows) and a glial cell
(G), are shown in B.
C, Higher magnification of the dendritic spine
(s; arrow in B) reveals
two axodendritic synapses (arrows) formed by
vesicle-containing axon terminals (t1 and
t2). D, Three
hyperelectron-dense neurons with intact nuclei
(n), Golgi complex, and endoplasmic reticulum are
shown. E, Enlargement of an axosomatic synapse
(arrow in D) shows synaptic vesicles and
a multivesicular body (m) within the
electron-dense soma. Scale bars: A, 20 µm;
B, D, 2 µm; C,
E, 0.1 µm.
|
|
Hyperthermic seizures, but not the hyperthermia per se, lead to
neuronal injury
Seizure duration in the hyperthermic seizure group averaged
19.13 ± 1.21 min. Animals pretreated with pentobarbital before hyperthermia induction did not have behavioral seizures, although the
degree of hyperthermia, as defined by maximal core temperature, and the
duration of hyperthermia were comparable with those of non-pretreated
pups (Table 1). Sections from anticonvulsant-pretreated animals who did
not develop seizures and were killed either 24 hr or a week
subsequently did not contain silver-stained neurons (see below). A
broad correlation between seizure duration and the extent of neuronal
injury was evident. Thus, sections from one of two animals, in whom
short seizures (<2 min) developed despite diazepam pretreatment,
contained occasional silver-stained neurons (data not shown).
Neuronal changes induced by hyperthermic seizures persist for at
least 2 weeks
Altered structural neuronal properties, manifested as silver
staining of affected neurons, persisted in the regions in which they
were noted within 24 hr after the seizures. Figure
5 demonstrates clusters of injured
neurons in the hippocampus of an immature rat surviving for 1 week
(Fig. 5A) or 2 weeks (Fig. 5B) after hyperthermic
seizures. In the CE-L, another region with abundant dark neurons,
persistent staining was also observed. Figure 5C demonstrates abundant stained neurons in the CE-L of an animal surviving for a week after hyperthermic seizures. A section from a rat
surviving for 2 weeks is shown in Figure 5D, suggesting decreasing abundance of stained neurons at the latter time point.
View larger version (165K):
[in this window]
[in a new window]
|
Figure 5.
Persistent injury to hippocampal and amygdaloid
neurons after hyperthermic seizures. Sections obtained from immature
rats killed 1 week (A, C) or 2 weeks
(B, D) after hyperthermic seizures are
shown. Silver-stained neurons are evident in the CA1 pyramidal cell
layer (A, B) and in the lateral division
of the central nucleus of the amygdala (CE-L)
(C, D) at both time points. Decreased
numbers of affected neurons are apparent at the 2-week time point
(B, D). DG, Dentate gyrus;
IC, internal capsule; s.p., stratum
pyramidale. Scale bar, 50 µm.
|
|
Hyperthermic seizures do not result in the dropout of a significant
number of neurons
Sections from 12 animals surviving for 4 weeks after hyperthermic
seizures, hyperthermia alone, or no treatment were subjected to
neuronal counts by an investigator unaware of treatment (blinded). Because an abundance of argyrophilic, injured neurons occurred in the
CE-L, this region was chosen for semiquantitative assessment of
neuronal dropout. The three experimental groups did not differ significantly in total neuronal number in the anatomically defined CE-L
(4295 ± 97, 4358 ± 139, and 4428 ± 54 cells per CE-L
for the hyperthermic seizures, hyperthermia alone, and normothermic groups, respectively). Variance among samples was small, and the maximal difference in CE-L neurons among groups was an order of magnitude lower than was the estimated number of argyrophilic, injured
neurons in this structure (see above). These results do not exclude
death of some injured neurons; however, they indicate that the majority
of hyperthermic seizures-induced argyrophilic neurons do not die and
drop out.
| |
DISCUSSION |
The principal findings of this study are the following: (1)
Hyperthermic seizures alter the structure of select neuronal
populations in the hippocampus and the amygdala. (2) These changes are
predicated on the presence of the seizures rather than on hyperthermia
per se. (3) The distribution of affected neurons provides the first reported topographical "map" of neuronal vulnerability to febrile seizures. (4) In regions where the physicochemical changes induced by
hyperthermic seizures are highly abundant, few neurons manifest apoptotic changes, i.e., DNA fragmentation. (5) Although significant numbers of neurons are rendered argyrophilic for at least 2 weeks after
the seizures, particularly in the amygdaloid CE-L, no significant neuronal dropout can be demonstrated by 4 weeks after the seizures.
Hyperthermic seizures produce injury of discrete limbic
neuronal populations
The current study demonstrates significant and prolonged
alterations in the physicochemical properties of neurons in the
pyramidal layer of the hippocampal CA1 and all of the CA3
subfields. In addition, a large proportion of pyramidal and
nonpyramidal neurons in the CE-L are consistently rendered argyrophilic
by this febrile seizures model. The distribution of the argyrophilic
neurons is consistent with both the behavioral and the
electrophysiological characteristics of hyperthermic seizures (Baram et
al., 1997). The behavioral aspects, freezing and oral automatisms,
indicate a limbic onset in the amygdala (Gloor, 1992) or the
hippocampus (Ben-Ari, 1985). Our electrophysiological studies of the
seizures in this model revealed epileptiform discharges in the amygdala and the hippocampus but not the neocortex (Baram et al., 1997). Thus
the pattern of distribution of the argyrophilic neurons, taken together
with the earlier studies, constitutes a map of the propagation of
hyperthermic seizures. At a minimum, the distribution of injured
neurons provides the neuroanatomic matrix of neuronal vulnerability to
febrile seizures in this model. In this context, it is interesting that
electrophysiological and anatomical data regarding the distribution of
human febrile seizures are scarce, because the seizures are
unpredictable, short, and ethically impossible to induce (Morimoto et
al., 1991).
Unique aspects of the distribution of neuronal injury in the
febrile seizures model
The distribution of neuronal injury observed in this study
possesses features both common to and distinct from injury found with
other limbic seizure types. In the hippocampus, major involvement of
CA3 and CA1 pyramidal cell layers and relative sparing of the granule
cell layer and subiculum are consistent with vulnerability patterns in
adult models of kainic acid- (Nadler et al., 1978; Sperk et al., 1983;
Pollard et al., 1994) and pilocarpine-induced status epilepticus
(Clifford et al., 1987). In the amygdala, however, the almost exclusive
involvement of CE-L neurons distinguishes the injury pattern in this
model from the adult pilocarpine and kainic acid seizure models, in
which neuronal death was found preferentially in the cortical, medial,
and lateral nuclei (Clifford et al., 1987) and in the basal nuclear
group, respectively (Schwob et al., 1980; Sperk et al., 1983).
Involvement of the ACE has been documented (Ben-Ari et al., 1981), and
a detailed analysis of amygdala neuropathology after kainic acid
seizures suggests that within the ACE, most argyrophilic neurons occur
in the CE-L (Tuunanen et al., 1996). Thus, although predominant ACE
injury in limbic excitotoxicity models is unusual, the preferential
involvement of the CE-L in this febrile seizures model is supported by
the argyrophilia pattern documented in a different (adult) model of limbic epilepsy.
The mechanism for the unique vulnerability of ACE neurons in this model
of febrile seizures may involve the preferential activation of this
nucleus during the hyperthermic stress (Gray, 1993; Tkacs et al.,
1997). Stress leads to rapid immediate-early-gene induction in the
ACE (Clark et al., 1991; Honkaniemi et al., 1992), followed by
activation of a cluster of neurons producing corticotropin-releasing hormone (CRH) (Clark et al., 1991; Gray, 1993). CRH is capable of
producing neuronal death in the amygdala of the immature rat (Baram and
Ribak, 1995; Ribak and Baram, 1996), so that a local release of CRH in
the ACE may account for the observed neuronal injury.
Neuronal injury in the immature, as compared with the
adult, brain
The spatiotemporal evolution of neuronal changes observed in the
current studies provides a useful perspective into issues of
seizure-induced cell death in the immature brain. Although prolonged
and severe seizures typically occur when convulsants such as kainic
acid or pilocarpine are administered to immature rats (younger than
20 d), it is generally considered that they are not followed by
neuropathological changes (Nitecka et al., 1984; Sperber et al., 1992;
Chang and Baram, 1994; but see Wasterlain, 1997). The present study,
revealing profound but transient alterations of neuronal integrity in
regions known to be affected by other limbic seizure paradigms, may
provide a mechanism to reconcile conflicting reports regarding the
effects of developmental limbic seizures on neuronal survival.
Specifically, our findings suggest that similar neuronal populations
share vulnerability to limbic seizures in both the immature and mature
rat, but immature neurons may undergo injury followed by recovery,
whereas mature neurons progress from injury to death (Chang and Baram,
1994; Owens et al., 1997). In addition, as has been shown for
eosinophilic acid fuchsin staining (Chang and Baram, 1994), neuronal
argyrophilia may carry a different significance regarding neuronal fate
in the immature, as compared with the adult, CNS. Along the same lines,
ISEL may underestimate neuronal death particularly in the immature
brain, leading to the limited cell death found in the current studies.
The ISEL time course study and the lack of significant neuronal dropout
using an independent method at the 4 week time point, however, render
this possibility less likely (and see below).
An intriguing feature of the distribution of affected neurons after
hyperthermic seizures in this study is their concordance with the
neuropathological features of human temporal lobe (limbic) epilepsy
known as mesial temporal sclerosis. Within the hippocampus, the most
common sites of neuronal loss are the CA3 and CA4 (of which the hilus
is the rodent counterpart) (Sagar and Oxbury, 1987; Bruton, 1988). Less
is known regarding the precise topography of neuronal loss in the TLE
amygdala (Gloor, 1992), and most studies refer to gliosis in the
"basal" nuclear group (Cavanagh and Meyer, 1956; Bruton, 1988;
Gloor, 1992). The amygdala is preferentially affected, however, when
TLE is caused by lesions outside the hippocampus (Cavanagh and Meyer,
1956; Gloor, 1992).
Hyperthermic seizures lead to neuronal injury without evidence of
significant neuronal dropout
The hyperthermic seizures-induced neuronal injury demonstrated in
this study was not associated with significant DNA fragmentation, as
determined by ISEL. DNA cleavage is generally considered a marker of
cell death (Wyllie, 1993), although the type of cell death (apoptosis
vs necrosis) may be unsettled (Kure et al., 1991; Pollard et al.,
1994). The advantage of ISEL and similar techniques derives from the
resulting positive stain, which renders even single cells highly
visible, in contrast to cell counts, which determine a decrease in
overall cell numbers. A significant disadvantage of methods using DNA
fragmentation markers stems from the short temporal "window"
(within the process of neuronal death) during which such DNA
fragmentation may be detectable. Thus, these methods tend to
underestimate neuronal death, particularly when cells do not die
synchronously (Voyvodic, 1996). However, the current study included
several time points spanning 1-48 hr after seizure induction, so that
temporal underestimation of the number of dying neurons is less likely.
Therefore, the discrepancy between the large numbers of argyrophilic
neurons and the rare ISEL-labeled cells indicates that argyrophilia in
the current study does not constitute evidence of "irreversible
injury" or death (Gallyas et al., 1992b; Toth et al., 1997) in the
majority of neurons.
A major advantage of the silver-staining method used in the current
study lies in its ability to demonstrate substantial populations of
injured hippocampal and ACE neurons. The precise alterations in the
physicochemical properties of injured neurons that lead to their
enhanced affinity to the silver stain has not been resolved (Gallyas et
al., 1992b). However, aside from the ISEL data, two additional lines of
evidence point against equating argyrophilia with neuronal death.
First, Toth et al. (1997) demonstrated that fluid percussion trauma can
lead to the formation of argyrophilic neurons even when applied to a
dead animal. Second, the number of argyrophilic neurons observed in the
current study, at least in the CE-L (~1700), far exceeded any
potential cell loss determined by cell counts 4 weeks later (~150
neurons, maximal intergroup difference). Counts were performed without
knowledge of treatment, minimizing a systematic bias, but inherent
estimation errors cannot be excluded (Popken and Farel, 1997). However,
in the context of the current study, even a 100% error in counting
(Popken and Farel, 1997; Saper, 1997) would not alter the conclusion
that the majority of argyrophilic, injured neurons induced by
hyperthermic seizures do not drop out.
Implications for human febrile seizures
The studies described provide a prospective analysis of the
spatiotemporal profile of neuronal changes induced by hyperthermic seizures, in an appropriate-age model of human febrile seizures. Febrile seizures, the most common human seizures, affect at least 500,000 individuals per year (Hauser, 1994). These seizures are essentially restricted to the developmental period of infancy and early
childhood (Knudsen, 1996). The contribution of febrile seizures to the
development of TLE has remained controversial (Cendes et al., 1993;
Knudsen, 1996) and has centered on the issue of induction of limbic
neuronal death by these seizures (Sagar and Oxbury, 1987; Gloor, 1991).
These fundamental issues of developmental epilepsy are difficult to
study in the human. The current study relied on an appropriate-age
model in which seizures can be induced in >93% of animals, thus
eliminating any concerns of genetic predisposition and pre-existing
lesions. Using this model, we have demonstrated the pattern of
vulnerability of hippocampal and amygdala neuronal populations to
hyperthermic seizures. The absence of neuronal injury (argyrophilia) in
hyperthermic rats in whom the seizures were prevented confirms the
specificity of these neuronal changes to the seizures themselves. In
addition, the results of this study suggest that the majority of
injured neurons do not progress to death. Thus, these data do not
support the supposition that early-life febrile seizures result
directly in hippocampal cell death, the neuropathological lesion found
in human TLE. However, the widespread and prolonged neuronal injury
demonstrated in this study may lead to significant alterations of the
function and electrophysiology of the affected neuronal circuits (Kapur
and Coulter, 1995), which could lead eventually to an epileptic
state.
| |
FOOTNOTES |
Received Nov. 7, 1997; revised March 5, 1998; accepted March 10, 1998.
This work was supported by National Institutes of Health Grants NS28912
and NS35439 to T.Z.B. and NS15669 to C.E.R. The technical assistance of
L. Schultz and M. Shiba-Noz is appreciated. We thank Drs. G. Popken and
I. Soltesz for helpful discussions, and A. Owens for her help with this
manuscript.
Correspondence should be addressed to Dr. Tallie Z. Baram, Departments
of Anatomy and Neurobiology and Pediatrics, ZOT 4475, University of
California, Irvine, Irvine, CA 92697-4475.
| |
REFERENCES |
-
Albala BJ,
Moshe SL,
Okada R
(1984)
Kainic acid-induced seizures: a developmental study.
Brain Res
315:139-148[Medline].
-
Baram TZ,
Ribak CE
(1995)
Peptide-induced status epilepticus causes neuronal death and synaptic reorganization.
NeuroReport
6:277-280[Web of Science][Medline].
-
Baram TZ,
Gerth A,
Schultz L
(1997)
Febrile seizures: an age appropriate model.
Brain Res Dev Brain Res
246:134-143.
-
Ben-Ari Y
(1985)
Limbic seizure and brain damage produced by kainic acid: mechanisms and relevance to human temporal lobe epilepsy.
Neuroscience
14:375-403[Web of Science][Medline].
-
Ben-Ari Y,
Tremblay E,
Riche D,
Ghilini G,
Naquet R
(1981)
Electrographic, clinical and pathological alterations following systemic administration of kainic acid, bicuculline or pentetrazole: metabolic mapping using the deoxyglucose method with special reference to the pathology of epilepsy.
Neuroscience
6:1361-1391[Web of Science][Medline].
-
Berg AT,
Shinnar S,
Hauser WA,
Alemany M,
Shapiro ED,
Salomon ME,
Crain EF
(1992)
A prospective study of recurrent febrile seizures.
N Engl J Med
327:1122-1127[Abstract].
-
Bruton CJ
(1988)
In: The neuropathology of temporal lobe epilepsy. New York: Oxford UP.
-
Cavanagh JB,
Meyer A
(1956)
Aetiological aspects of Ammon's horn sclerosis associated with temporal lobe epilepsy.
Br Med J
2:1403-1407.
-
Cendes F,
Andermann F,
Dubeau F,
Gloor P,
Evans A,
Jones-Gotman M,
Olivier A,
Andermann E,
Robitaille Y,
Lopes-Cendes I
(1993)
Early childhood prolonged febrile convulsions, atrophy and sclerosis of mesial structures, and temporal lobe epilepsy: an MRI volumetric study.
Neurology
43:1083-1087[Abstract/Free Full Text].
-
Chang D,
Baram TZ
(1994)
Status epilepticus results in reversible neuronal injury in infant rat hippocampus: novel use of a marker.
Brain Res Dev Brain Res
77:133-136[Medline].
-
Clark M,
Weiss SR,
Post RM
(1991)
Expression of c-fos mRNA in rat brain after intracerebroventricular administration of corticotropin-releasing hormone.
Neurosci Lett
132:235-238[Web of Science][Medline].
-
Clifford DB,
Olney JW,
Maniotis A,
Collins RC,
Zorumski CF
(1987)
The functional anatomy and pathology of lithium-pilocarpine and high-dose pilocarpine seizures.
Neuroscience
23:953-968[Web of Science][Medline].
-
Dobbing J,
Sands J
(1973)
Quantitative growth and development of human brain.
Arch Dis Child
48:757-767[Abstract/Free Full Text].
-
Falconer MA,
Serafetinides EA,
Corsellis JAN
(1964)
Etiology and pathogenesis of temporal lobe epilepsy.
Arch Neurol
10:233-248.
-
Gallyas F,
Guldner FH,
Zoltay G,
Wolff JR
(1990)
Golgi-like demonstration of "dark" neurons with an argyrophil III method for experimental neuropathology.
Acta Neuropathol (Berl)
79:620-628[Medline].
-
Gallyas F,
Zoltay G,
Balas I
(1992a)
An immediate light microscopic response of neuronal somata, dendrites and axons to contusing concussive head injury in the rat.
Acta Neuropathol (Berl)
83:394-401[Medline].
-
Gallyas F,
Zoltay G,
Dames W
(1992b)
Formation of "dark" (argyrophilic) neurons of various origins proceeds with a common mechanism of biophysical nature (a novel hypothesis).
Acta Neuropathol (Berl)
83:504-509[Medline].
-
Gloor P
(1991)
Mesial temporal sclerosis: historical background and an overview from a modern perspective.
In: Epilepsy surgery (Luders HO,
ed), pp 689-703. New York: Raven.
-
Gloor P
(1992)
Role of the amygdala in temporal lobe epilepsy.
In: The amygdala: neurobiological aspects of emotion, memory, and mental dysfunction (Aggleton JP,
ed), pp 505-538. New York: Wiley-Liss.
-
Gray TS
(1993)
Amygdaloid CRF pathways. Role in autonomic, neuroendocrine, and behavioral responses to stress.
Ann NY Acad Sci
697:53-60[Web of Science][Medline].
-
Hauser WA (1994) The prevalence and incidence of convulsive
disorders in children. Epilepsia 35 [Suppl] 2:S1-S6.
-
Holmes GL
(1997)
Epilepsy in the developing brain: lessons from the laboratory and clinic.
Epilepsia
38:12-30[Web of Science][Medline].
-
Holmes GL,
Thompson JL
(1988)
Effects of kainic acid on seizure susceptibility in the developing brain.
Brain Res
467:51-59[Medline].
-
Honkaniemi J,
Pelto-Huikko M,
Rechardt L,
Isola J,
Lammi A,
Fuxe K,
Gustafsson JA,
Wikstrom AC,
Hokfelt T
(1992)
Colocalization of peptide and glucocorticoid receptor immunoreactivities in rat central amygdaloid nucleus.
Neuroendocrinology
55:451-459[Web of Science][Medline].
-
Jensen FE,
Applegate CD,
Holtzman D,
Belin TR,
Burchfiel JL
(1991)
Epileptogenic effect of hypoxia in the immature rodent brain.
Ann Neurol
29:629-637[Web of Science][Medline].
-
Kapur J,
Coulter DA
(1995)
Experimental status epilepticus alters gamma-aminobutyric acid type A receptor function in CA1 pyramidal neurons.
Ann Neurol
38:893-900[Web of Science][Medline].
-
Knudsen FU
(1996)
Febrile seizures-treatment and outcome.
Brain Dev
18:438-449[Web of Science][Medline].
-
Kure S,
Tominaga T,
Yoshimoto T,
Tada K,
Narisawa K
(1991)
Glutamate triggers internucleosomal DNA cleavage in neuronal cells.
Biochem Biophys Res Commun
179:39-45[Web of Science][Medline].
-
Morimoto T,
Nagao H,
Sano N,
Takahashi M,
Matsuda H
(1991)
Electroencephalographic study of rat hyperthermic seizures.
Epilepsia
32:289-293[Web of Science][Medline].
-
Nadler JV,
Perry BW,
Cotman CW
(1978)
Intraventricular kainic acid preferentially destroys hippocampal pyramidal cells.
Nature
271:676-677[Medline].
-
Nelson KB,
Ellenberg JH
(1976)
Predictors of epilepsy in children who have experienced febrile seizures.
N Engl J Med
295:1029-1033[Abstract].
-
Nitecka L,
Tremblay E,
Charton G,
Bouillot JP,
Berger ML,
Ben-Ari Y
(1984)
Maturation of kainic acid seizure-brain damage syndrome in the rat.
Neuroscience
13:1073-1094[Web of Science][Medline].
-
Owens JJ,
Robbins CA,
Wenzel HJ,
Schwartzkroin PA
(1997)
Acute and chronic effects of hypoxia on the developing hippocampus.
Ann Neurol
41:187-199[Web of Science][Medline].
-
Pollard H,
Charriaut-Marlangue C,
Cantagrel S,
Represa A,
Robain O,
Moreau J,
Ben-Ari Y
(1994)
Kainate-induced apoptotic cell death in hippocampal neurons.
Neuroscience
63:7-18[Web of Science][Medline].
-
Popken GJ,
Farel PB
(1997)
Sensory neuron number in neonatal and adult rats estimated by means of stereologic and profile-based methods.
J Comp Neurol
386:8-15[Web of Science][Medline].
-
Ribak CE,
Baram TZ
(1996)
Selective death of hippocampal CA3 pyramidal cells with mossy fiber afferents after CRH-induced status epilepticus in infant rats.
Brain Res Dev Brain Res
91:245-251[Medline].
-
Sagar HJ,
Oxbury JM
(1987)
Hippocampal neuron loss in temporal lobe epilepsy: correlation with early childhood convulsions.
Ann Neurol
22:334-340[Web of Science][Medline].
-
Sakhi S,
Bruce A,
Sun N,
Tocco G,
Baudry M,
Schreiber SS
(1994)
p53 induction is associated with neuronal damage in the central nervous system.
Proc Natl Acad Sci USA
91:7525-7529[Abstract/Free Full Text].
-
Saper CB
(1997)
Counting on our reviewers to set the standards.
J Comp Neurol
386:1[Web of Science].
-
Schwob JE,
Fuller T,
Price JL,
Olney JW
(1980)
Widespread patterns of neuronal damage following systemic or intracerebral injections of kainic acid: a histological study.
Neuroscience
5:991-1014[Web of Science][Medline].
-
Sherwood NM,
Timiras PS
(1970)
In: A stereotaxic atlas of the developing rat brain. Berkeley, CA: University of California.
-
Shinnar S
(1990)
Febrile seizures.
In: Current therapy in neurological disease (Johnson RT,
ed), pp 29-32. Philadelphia: Decker.
-
Sperber EF,
Haas KZ,
Stanton PK,
Moshe SL
(1991)
Resistance of the immature hippocampus to seizure-induced synaptic reorganization.
Brain Res Dev Brain Res
60:88-93[Medline].
-
Sperber EF,
Stanton PK,
Haas K,
Ackerman RF,
Moshe SL
(1992)
Developmental differences in the neurobiology of epileptic brain damage.
In: Molecular neurobiology of epilepsy, pp 67-81. Amsterdam: Elsevier.
-
Sperk G,
Lassmann H,
Baran H,
Kish SJ,
Seitelberger F,
Hornykiewicz O
(1983)
Kainic acid-induced seizures: neurochemical and histopathological changes.
Neuroscience
10:1301-1315[Web of Science][Medline].
-
Tkacs NC,
Li J,
Strack AM
(1997)
Central amygdala Fos expression during hypotensive or febrile, nonhypotensive endotoxemia in conscious rats.
J Comp Neurol
379:592-602[Web of Science][Medline].
-
Toth Z,
Hollrigel GS,
Gorcs T,
Soltesz I
(1997)
Instantaneous perturbation of dentate interneuronal networks by a pressure wave-transient delivered to the neocortex.
J Neurosci
17:8106-8117[Abstract/Free Full Text].
-
Tuunanen J,
Halonen T,
Pitkanen A
(1996)
Status epilepticus causes selective regional damage and loss of GABAergic neurons in the rat amygdaloid complex.
Eur J Neurosci
8:2711-2725[Web of Science][Medline].
-
Verity CM,
Butler NR,
Golding J
(1985)
Febrile convulsions in a national cohort followed up from birth. Prevalence and recurrence in the first five years of life.
Br Med J
290:1307-1310.
-
Voyvodic JT
(1996)
Cell death in cortical development: how much? Why? So what?
Neuron
16:693-696[Web of Science][Medline].
-
Wasterlain CG
(1997)
Recurrent seizures in the developing brain are harmful.
Epilepsia
38:728-734[Web of Science][Medline].
-
Wyllie AH
(1993)
Apoptosis.
Br J Cancer
67:205-208[Web of Science][Medline].
-
Yi SJ,
Baram TZ
(1994)
Corticotropin-releasing hormone mediates the response to cold stress in the neonatal rat without compensatory enhancement of the peptide's gene expression.
Endocrinology
135:2364-2368[Abstract].
Copyright © 1998 Society for Neuroscience 0270-6474/98/18114285-10$05.00/0
This article has been cited by other articles:
|
|
|
|
 
A. K. Sharma, R. Y. Reams, W. H. Jordan, M. A. Miller, H. L. Thacker, and P. W. Snyder
Mesial Temporal Lobe Epilepsy: Pathogenesis, Induced Rodent Models and Lesions
Toxicol Pathol,
December 1, 2007;
35(7):
984 - 999.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Chen, A. Neu, A. L. Howard, C. Foldy, J. Echegoyen, L. Hilgenberg, M. Smith, K. Mackie, and I. Soltesz
Prevention of Plasticity of Endocannabinoid Signaling Inhibits Persistent Limbic Hyperexcitability Caused by Developmental Seizures
J. Neurosci.,
January 3, 2007;
27(1):
46 - 58.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. Dube, C. Richichi, R. A. Bender, G. Chung, B. Litt, and T. Z. Baram
Temporal lobe epilepsy after experimental prolonged febrile seizures: prospective analysis
Brain,
April 1, 2006;
129(4):
911 - 922.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Janszky, H. Jokeit, D. Heinemann, R. Schulz, F. G. Woermann, and A. Ebner
Epileptic activity influences the speech organization in medial temporal lobe epilepsy
Brain,
September 1, 2003;
126(9):
2043 - 2051.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. A. Bender, S. V. Soleymani, A. L. Brewster, S. T. Nguyen, H. Beck, G. W. Mathern, and T. Z. Baram
Enhanced Expression of a Specific Hyperpolarization-Activated Cyclic Nucleotide-Gated Cation Channel (HCN) in Surviving Dentate Gyrus Granule Cells of Human and Experimental Epileptic Hippocampus
J. Neurosci.,
July 30, 2003;
23(17):
6826 - 6836.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Janszky, F.G. Woermann, P. Barsi, R. Schulz, P. Halasz, and A. Ebner
Right hippocampal sclerosis is more common than left after febrile seizures
Neurology,
April 8, 2003;
60(7):
1209 - 1210.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. S. White
Animal models of epileptogenesis
Neurology,
November 12, 2002;
59(90095):
S7 - 14.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
C. L. Wellington, L. M. Ellerby, C.-A. Gutekunst, D. Rogers, S. Warby, R. K. Graham, O. Loubser, J. van Raamsdonk, R. Singaraja, Y.-Z. Yang, et al.
Caspase Cleavage of Mutant Huntingtin Precedes Neurodegeneration in Huntington's Disease
J. Neurosci.,
September 15, 2002;
22(18):
7862 - 7872.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Brewster, R. A. Bender, Y. Chen, C. Dube, M. Eghbal-Ahmadi, and T. Z. Baram
Developmental Febrile Seizures Modulate Hippocampal Gene Expression of Hyperpolarization-Activated Channels in an Isoform- and Cell-Specific Manner
J. Neurosci.,
June 1, 2002;
22(11):
4591 - 4599.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Shinnar and T. A. Glauser
Febrile Seizures
J Child Neurol,
January 1, 2002;
17(1_suppl):
S44 - S52.
[Abstract]
[PDF]
|
|
|
|
|
|
|
G. Golarai, A. C. Greenwood, D. M. Feeney, and J. A. Connor
Physiological and Structural Evidence for Hippocampal Involvement in Persistent Seizure Susceptibility after Traumatic Brain Injury
J. Neurosci.,
November 1, 2001;
21(21):
8523 - 8537.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Z. Baram and S. Shinnar
Do febrile seizures improve memory?
Neurology,
July 10, 2001;
57(1):
7 - 8.
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. C. Chang, N. W. Guo, S. T. Wang, C.C. Huang, and J.J. Tsai
Working memory of school-aged children with a history of febrile convulsions: A population study
Neurology,
July 10, 2001;
57(1):
37 - 42.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. K. McCabe, D. C. Silveira, M. R. Cilio, B. H. Cha, X. Liu, Y. Sogawa, and G. L. Holmes
Reduced Neurogenesis after Neonatal Seizures
J. Neurosci.,
March 15, 2001;
21(6):
2094 - 2103.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. T. Berg, S. Shinnar, S. R. Levy, and F. M. Testa
Childhood-onset epilepsy with and without preceding febrile seizures
Neurology,
November 1, 1999;
53(8):
1742 - 1742.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
M. Hornig, H. Weissenbock, N. Horscroft, and W. I. Lipkin
An infection-based model of neurodevelopmental damage
PNAS,
October 12, 1999;
96(21):
12102 - 12107.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Sankar, D. H. Shin, H. Liu, A. Mazarati, A. Pereira de Vasconcelos, and C. G. Wasterlain
Patterns of Status Epilepticus-Induced Neuronal Injury during Development and Long-Term Consequences
J. Neurosci.,
October 15, 1998;
18(20):
8382 - 8393.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. Kato, T. Kishi, T. Kamachi, M. Akisada, T. Oka, R. Midorikawa, K. Takio, N. Dohmae, P. I. Bird, J. Sun, et al.
Serine Proteinase Inhibitor 3 and Murinoglobulin I Are Potent Inhibitors of Neuropsin in Adult Mouse Brain
J. Biol. Chem.,
April 27, 2001;
276(18):
14562 - 14571.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
Top
Abstract
Introduction
