O . Peredery et al. Brain Research 881 2000 9 –17
11
for the later stages of the status epilepticus and the two regions of the diencephalon and telencephalon following
measures of damage in our study. the induction of status epilepticus by lithium and pilocar-
pine. Only the reticulata component of the substantia nigra 2.5. Latency before injection of acepromazine
SNR was damaged within the mesencephalon. Neuronal dropout and diffuse gliosis was found in many regions of
To assess if the injection of acepromazine was in- the thalamus, amygdala, SNR, hippocampus and basal
strumental in the stabilization of the seizure-induced brain ganglia. The neuropathology within the SNR was always
damage, an additional 10 rats were injected with acep- located in the lozenger-shaped region that receives
romazine between 0 and 6 h after the injection of the thalamic inputs. After about 20 days following the seizure
pilocarpine. These rats were killed 48 h later; the brains induction, there was minimal gliosis and maximal neuronal
were removed and processed as specified earlier. Bivariate dropout within this region.
correlations Pearson r were completed for the time in h Severe neuronal loss and gliosis were found almost
between the pilocarpine–acepromazine injections and the always within the CA1 region of the hippocampus Fig. 1.
amount of total damage within each structure. All statisti- Within the amygdala, neuronal dropout and gliosis were
cal analyses involved SPSS software on a VAX 4000 distributed diffusely throughout specific nuclear structures
computer. while other structures, such as the central group, were not
affected. Near-complete neuronal dropout, with cystic lesions, was found only within the limbic cortices such as
3. Results the entorhinal and piriform regions Fig. 2.
Neuronal dropout and gliosis occurred within 10 days of 3.1. Qualitative patterns
the seizure induction in most structures. After about 20 days, within many thalamic nuclei, a second phenomenon
Different types of neuronal damage dominated different evolved. Darkly staining Nissl material was accumulated
Fig. 1. Photomicrograph 403 of the hippocampal formation Ammon’s Horn for a control A and for a rat in which lithium pilocarpine seizures had been induced B showing loss of neurons in the dentate gyrus and CA1. Section C 1003 shows the cells within the dentate gyrus left and CA1 right
for a normal rat, while Section D 1003 shows their absence in the brain of a seized rat.
12 O
Fig. 2. Photomicrographs 403 of the entorhinal cortices below the A and the amygdala arrow for a control brain and of the entorhinal cortices with cystic lesions below the B and the amygdala arrow for a seized brain. The gliosis within the amygdala of the seized brain D, 1003 is not evident in
the amygdala C, 1003 of the normal brain.
within discrete thalamic structures. By postseizure day 50, around and including the suprageniculate nucleus. The
these diffuse bluish areas slowly resolved into dense reuniens and paratenial nuclei of the thalamus deserve
formations; about half of them displayed crystalline special attention because of their extremely frequent
characteristics Fig. 3 which were similar to those shown .90 devastation of neuronal populations. The least
[11] to contain dense calcium deposits embedded within a .2 but ,15 damaged structures were the ventral
mucopolysaccharide matrix. portions of the lateral and medial geniculate, the reticular
nucleus and the limbic thalamic nuclei. Neocortices 3.2. Semiquantitative patterns over time
showed a moderate 40 frequency of damage; the temporal and parietal cortices were damaged significantly
The percentages of brains n 5 62 that displayed any P , 0.05 more often than the frontal, occipital, insular or
discernable neuronal
dropout within
the amygdala,
perirhinal cortices. There was almost total neuronal drop- thalamus, and other structures are shown in Table 1. The
out within the piriform, retrosplenial, and entorhinal total damage score, defined as the sum of all types of
cortices. damage, for each structure is also shown. Within the
Neuronal dropout primarily pyramidal cells was most amygdala the neuronal dropout occurred most frequently
extreme within the CA1 sector of the hippocampal forma- .70 of the brains within the posterior, lateroventral
tion. This type of damage decreased progressively within and basomedial groups. The central nucleus was never
the CA2, CA3 and CA4 regions, respectively. Moderate observably damaged.
incidences of damage occurred within the subiculum and The thalamic structures displayed a marked variability in
dentate gyrus. Other subcortical telencephalic structures the severity of damage. Structures that displayed the most
that displayed similar damage involved the claustrum, frequent neuronal dropout included most of the mediodor-
lateral septal nucleus dorsal part and the globus pallidus. sal group, the lateral and posterior nuclei and the regions
The incidence of neuronal dropout within the ventral
O . Peredery et al. Brain Research 881 2000 9 –17
13
Fig. 3. Photomicrographs 403 of the lateral portion of the thalamus in a control brain A and a brain B in which seizures had been induced about 50 days previously. The largest aggregate of crystalline material noted in B is magnified 1003 in D. For comparison, a comparable area of the thalamus is
magnified 1003 in the control brain.
striatum was sparse, while the dorsolateral region which MGD, MGM and the centrolateral, gelatinosus and
represents the forelimbs displayed discernable cell dropout; gustatory nuclei of the thalamus. Enhanced dropout was
the entopeduncular nucleus was mildly affected but there evident within the occipital, temporal, frontal, perirhinal,
were no discernable changes within the nucleus accum- insular agranular and cingulate cortices and within sever-
bens, substantia innominata, and the region surrounding al subcortical telencephalic structures; damage within the
and including the Islands of Calleja. CA3 region during this period was notable. The only
Table 2 shows only those structures that displayed conspicuous increase in anomalous histomorphology that
postseizure, time-dependent changes in the incidence of occurred between postseizure days 1 through 20 vs. day 50
neuronal dropout between postseizure days: a 1 through 5 was evident for the total damage score and involved for the
vs. 10, b 1 through 10 vs. 15 through 18 and c 1 most part those structures in which aggregates of calcium
through 18 vs. 50. A ‘1’ refers to an increased incidence deposits had been observed previously [11] in other brains.
of neuronal dropout, while a ‘2’ refers to a decrease; the criterion was a
f coefficient of greater than 0.40 P , 3.3. Quantification and validity of measures
0.05; a ‘0’ reflects no statistically significant change. In general, the results suggested little additional dropout
The means and standard deviations for neuronal cell
2
between days 1 through 5 and days 10 after the first stage density cells mm within 10 thalamic nuclei, that dis-
of pathology which was evident within 24 h. played the range in percentage incidence of damage within
However, between postseizure days 10 and 18, when our population of brains, are shown in Table 3. Means and
most of the peculiar rat behaviors began to emerge standard deviations for control brains are also indicated as
2
[2,3,17,19–21], there were conspicuous increases in neuro- well as the F-value and the strength of the effect
h , i.e. nal dropout within the lateral LaVM, LaVL and medial
the amount of variance in numbers of neurons explained Me amygdaloid groups, the medial geniculate group
by the treatment compared to no treatment. The amount of
14 O
Table 1 Table 2
Percentage of brains that displayed neuronal dropout or any form of Structures in which there was a significant change 1, increase; 2,
necrosis within specific structures. Abbreviations are from Paxinos and decrease in neuronal dropout or total damage in brains of rats that were
Watson [16] killed various times in days after seizure induction. Abbreviations are
from Paxinos and Watson [16] Structure
Dropout Any
Structure Dropout
Any damage
damage Structure
Neuronal dropout Total damage
,20 vs. 50 Amygdala
Thalamus ,5 vs. 10
,10 vs. 18–20 ,20 vs. 50
,20 vs. 50 PMCo
84 87
Rh 18
18 Amygdala
AHiPA 34
37 Hb
42 42
PMCo 1
PLCo 73
77 Re
92 97
PLCo 2
BLP 60
60 VL
55 63
BLP 2
2 LaDL
44 44
G 45
48 LaVM
1 LaVM
74 74
Ang 15
16 LaVl
1 LaVL
69 69
IAM 23
23 BLA
2 BLA
18 18
PVA 19
21 BM
1 2
CeL AM
63 71
Me 1
I AD
10 10
BLV 37
40 AVDM
8 8
Thalamus BM
69 71
AVVL 21
23 MGD
1 Me
39 39
PT 90
90 MGV
1 ACo
27 27
IAD 19
19 MGM
1 CeM
MD 68
73 SG
1 IMG
3 3
CM 47
48 PoT
1 IM
5 5
IMD 48
55 PLi
1 CxA
13 15
Hippocampal formation DLG
1 AA
5 5
S 44
45 LPMR
1 ASTR
23 23
DG 42
44 LPLR
1 Thalamus
CA1 92
92 Po
2 1
MGD 76
81 CA2
68 68
Gu 1
MGV 11
11 CA3
27 27
CL 2
1 MGM
39 40
CA4 11
11 LDVL
1 SG
84 87
Cerebral cortices LDDM
1 PoT
15 21
Pir 95
97 Hb
1 PLi
13 15
RSCx 71
73 Re
1 LPMC
66 68
PRh 39
40 G
1 DLG
77 77
Ent 73
85 Cortices
VLG 2
2 Oc
37 37
Oc 1
Eth 2
3 Par
45 45 LI, II
Te 1
2 2
LPMR 73
82 Te
47 47
Fr 1
2 2
LPLR 47
63 Fr
37 37
AI 1
MG 24
34 AI, GI
37 42
Cg 1
2 Po
76 87
Other subcortical structures VPM
44 48
DEn 90
90 Hippocampal formation
PF 44
45 VEn
82 85
S 1
1 Rt
Cl 40
40 CA1
1 VPL
52 53
CPu 61
61 CA3
1 Gu
29 31
LS 35
35 Other subcortical structures
CL 56
66 MS
Cl 1
VLG GP
48 50
CPu 1
LDVL 79
87 EP
24 24
LS 1
PC 61
66 LOT
8 8
GP 1
MDL 76
85 BSTI
19 19
VM 84
89 VP
2 2
LDDM 73
79 FStr
6 6
MDC 73
76 Mesencephalon
of 10 brains and the proportion of all n 5 62 brains that
MDM 77
82 SNR
94 97
displayed some form of damage.
SNC
3.4. Comparisons of 2-DG measures and neuronal dropout
variance in cell loss that could be attributed to the seizures ranged from minimal rhomboid nucleus to a maximum of
The factor loadings for the 2-DG activity in the 28 99 nucleus reuniens. A correlation
r of 0.86 P , shared structures specified in the Handforth and Treiman
0.001 existed between the percentages of cell loss rela- data [5,6] for the early and late stages of status epilepticus
tive to controls for each of the 10 thalamic nuclei average and neuronal dropout for each structure the mean of the
O . Peredery et al. Brain Research 881 2000 9 –17
15 Table 3
3.5. Damage and latency of acepromazine injection
3
Means and standard deviations for the cellular density of neurons 1310
2
cells mm for sample thalamic nuclei. Abbreviations are from Paxinos
The increased incidence and severity of neuronal drop-
and Watson [16]
out within the diencephalon and telencephalon as a func-
2
Nuclei Control
Seizure F-value
h
tion of the time 20.5 to 6 h between the seizure onset
M S.D.
M S.D.
and removal of the brain were qualitatively conspicuous. Statistically significant r . 0.60 correlations were evident
PF L 1.22
0.06 0.99
0.22 4.70
0.28 VM
0.47 0.04
0.29 0.13
7.22 0.38
for the entorhinal cortices, amygdaloid–hippocampal tran-
RH 2.26
0.11 1.94
0.32 3.56
0.23
sition area, basolateral nucleus anterior part of the
MD L 0.72
0.05 0.12
0.07 242.70
0.95
amygdala, anteroventral thalamic nucleus ventrolateral
LPMC 0.77
0.02 0.12
0.07 303.16
0.95
part and CA3 of the hippocampal formation. The severity
VPL 0.51
0.01 0.40
0.08 8.96
0.43
of damage rapidly increased when the acepromazine
Re 1.20
0.05 0.05
0.03 2830.86
0.99 IAM
1.21 0.18
0.28 0.20
66.60 0.85
injection was delayed for more than 2 h. Even when
AVVL 2.04
0.22 1.30
0.24 27.93
0.70
acepromazine was injected before the seizure onset within
VLG 0.99
0.10 0.83
0.07 11.22
0.48
seconds of the pilocarpine, pervasive neuronal dropout
P , 0.05, P , 0.01, P , 0.001.
was still discernable within 48 h for all brains for the following structures: piriform cortices, CA1 of the hip-
pocampus, the dorsal and ventral endopiriform nuclei, 62 brains in our major study are shown in Table 4. To be
basolateral nucleus of the amygdala anterior part, conservative, we accepted only loading coefficients that
mediodorsal thalamic nuclei medial and central part, the explained at least 50 of the variance r . 0.70 as
nucleus reuniens and the reticulata of the substantia nigra. statistically significant. The structures that showed the
greatest metabolic activation, as inferred by 2-DG, during waxing and waning and discrete spiking electrical seizures
4. Discussion
