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Chromogranins as markers of altered hippocampal circuitry in temporal lobe epilepsy.

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Chromogranins as Markers of Altered
Hippocampal Circuitry in Temporal
Lobe Epilepsy
Susanne Pirker, MD,1,2 Thomas Czech, MD,2 Christoph Baumgartner, MD,3 Hans Maier, MD,4
Klaus Novak, MD,2 Sabine Fürtinger, MSc,1 Reiner Fischer-Colbrie, PhD,1 and Günther Sperk, PhD1
Chromogranins are polypeptides which are widely expressed in the central nervous system. They are stored in dense core
vesicles of nerve terminals, from where they are released upon stimulation. Using immunocytochemistry, we investigated
the distribution of chromogranin A, chromogranin B, secretoneurin, and, for comparison, dynorphin in hippocampal
specimens removed at routine surgery from patients with drug-resistant mesial temporal lobe epilepsy and in autopsy
tissues from nonneurologically deceased subjects. In post mortem controls (n ⴝ 21), immunoreactivity for all 4 peptides
(most prominently for chromogranin B and dynorphin) was observed in the terminal field of mossy fibers. For chromogranins, staining was observed also in sectors CA1 to CA3 and in the subiculum. Chromogranin B immunoreactivity
was found in the inner molecular layer of the dentate gyrus, the area of terminating associational-commissural fibers.
Secretoneurin and dynorphin immunoreactivity labeled the outer molecular layer and the stratum lacunosum moleculare
of sectors CA1 to CA3, where projections from the entorhinal cortex terminate. In specimens with Ammon’s horn
sclerosis (n ⴝ 25), staining for all 3 chromogranins and for dynorphin was reduced in the hilus of the dentate gyrus.
Instead, intense staining was observed in the inner molecular layer, presumably delineating terminals of sprouted mossy
fibers. Specimens obtained from temporal lobe epilepsy patients without Ammon’s horn sclerosis (n ⴝ 4) lacked this
pronounced rearrangement of mossy fibers. In the stratum lacunosum moleculare of sector CA1, secretoneurin and
dynorphin immunoreactivity was reduced in sclerotic, but not in nonsclerotic, specimens, paralleling the partial loss of
fibers arising from the entorhinal cortex. Instead, presumably sprouted secretoneurin-immunoreactive fibers were found
in the outer dentate molecular layer in sclerotic specimens. These changes in staining patterns for chromogranins and
dynorphin mark profound plastic and functional rearrangement of hippocampal circuitry in temporal lobe epilepsy.
Ann Neurol 2001;50:216 –226
More than a century ago, the selective loss of hippocampal neurons, termed Ammon’s horn sclerosis,
was described in mesial temporal lobe epilepsy
(TLE).1,2 Typically, neurons of the hippocampal subfields CA1 and CA3 and the hilus of the dentate gyrus
become severely damaged, whereas other neurons, such
as granule cells and CA2 neurons, are relatively spared.
At the same time, mossy fibers, the axons of granule
cells, undergo pronounced reorganization as revealed
by specific labeling with Timm’s stain or dynorphinlike immunoreactivity (IR).3–5 Mossy fibers normally
innervate neurons in the hilus of the dentate gyrus and
in the stratum lucidum of CA3. Presumably due to a
partial loss of granule cells and/or of postsynaptic targets, they appear to be reduced in TLE. Instead, a
prominent innervation of the inner molecular layer of
the dentate gyrus by collaterals of mossy fibers is observed.3– 6
The relevance of this “mossy fiber reorganization”
for the pathophysiology of TLE is still uncertain. It has
been suggested that “self-innervation” of granule cells
by their axons could contribute fundamentally to the
increased excitability of the hippocampal formation.7
Indeed, synaptic contacts between sprouted mossy fiber
terminals and dendrites of granule cells have been
found by electron microscopy.8 –10 Therefore, neurotransmitters released from sprouted mossy fiber terminals may act on granule cell dendrites and may have an
important impact on the altered signal transduction in
the epileptic hippocampus.
The main transmitter of mossy fibers is glutamate.11
The neuropeptide dynorphin is a cotransmitter in these
From the 1Department of Pharmacology, University of Innsbruck,
Innsbruck, 2Department of Neurosurgery, and 3Department of
Neurology, University of Vienna, Vienna, and 4Department of Pathology, University of Innsbruck, Innsbruck, Austria.
Published online May 25, 2001.
Received Dec 5, 2000, and in revised form Apr 2, 2001. Accepted
for publication Apr 2, 2001.
216
© 2001 Wiley-Liss, Inc.
Address correspondence to Dr Sperk, Department of Pharmacology,
Peter-Mayr-Strasse 1a, A-6020 Innsbruck, Austria.
E-mail: guenther.sperk@uibk.ac.at
neurons.12 It is present in normal mossy fibers and
those sprouted to the inner molecular layer of TLE patients.4,9,13 Also, chromogranins have been identified
in mossy fibers of rats and humans.14 –17 Chromogranins are a family of acidic polypeptides, which are
widely distributed in nervous and endocrine tissues.14
They comprise chromogranin A (CgA), CgB, and secretogranin II and were originally isolated from secretory granules of chromaffin cells in the adrenal medulla. In the nervous system, they are stored in large
dense core vesicles and processed by peptidases to numerous smaller peptides,18 which are released upon
nerve stimulation.14 Peptides derived from chromogranins may exert neurotransmitter-like or trophic
functions.14 Thus, for secretoneurin cleaved from secretogranin II,19 dopamine release–enhancing and chemoattractant actions have been established.14,20 In the
kainic acid model of TLE in rats, conspicuous changes
in the gene expression of chromogranin mRNAs have
been observed.21,22
We investigated by immunocytochemistry the distribution of CgA, CgB, and secretoneurin in hippocampal
specimens from patients with drug-resistant TLE with
and without hippocampal sclerosis and in post mortem
tissue from nonneurologically deceased subjects as controls. Our aim was to study chromogranin-IR as an
immunocytochemical marker of neuronal elements of
the hippocampal circuitry, notably of mossy fibers.
Changes in distribution were compared with changes
in dynorphin-IR, an established immunocytochemical
marker for mossy fibers.4,9 Specimens from four TLE
patients without Ammon’s horn sclerosis were included
to investigate the relationship between neuronal cell loss
and the observed anatomical changes.
region. Patients without obvious Ammon’s horn sclerosis
were defined as nonsclerotic. They suffered from cortical dysplasia (n ⫽ 1) or cryptogenic TLE (n ⫽ 3). Mean age [⫾
standard error of mean (SEM)] at surgery was 34.5 ⫾ 1.9
years. Twelve females and 17 males were included in the
study. The epileptic focus was on the left side in 14 patients
and on the right side in 15 patients. Mean duration of epilepsy was 21.4 ⫾ 2.2 and 14.8 ⫾ 5.2 years in patients with
and without hippocampal sclerosis, respectively. All patients
were taking antiepileptic drugs in mono- or polytherapy. The
most frequent antiepileptic drugs were carbamazepine (83%),
lamotrigine (28%), valproate (24%), clobazam (21%), and
vigabatrin (14%).
As control tissues, 21 hippocampi from patients without
known history of neurological or psychiatric disease were obtained at routine autopsy (mean age 57.7 ⫾ 3.5 years). Each
brain was studied by a neuropathologist, to confirm the absence of a brain lesion. The time from death to fixation of
brain specimens ranged from 8 to 36 hours (mean 17.2 ⫾
3.8 hours). Five cases were females and 16 males. Eleven
specimens were taken from the right hemisphere, 5 from the
left. In 5 cases, the side investigated was unknown. Causes of
death were pneumonia, lung cancer, pharyngeal cancer, laryngeal cancer, breast cancer, liver cancer, liver cirrhosis,
melanoma, myocardial infarction, pulmonary embolism, cardiovascular arrest, lymphoma, tracheal cancer, stomach cancer, or renal failure.
Surgical specimens of the hippocampal body (middle segment) from TLE patients and autopsy tissue were sectioned
perpendicularly to the hippocampal axis into 5-mm-thick
blocks and immersed in 4% paraformaldehyde, 50 mM
phosphate-buffered saline (PBS, pH 7.4) for 4 to 5 days.
After stepwise immersion in sucrose (range 5%–20%) over 2
days, specimens were frozen and stored at –70°C. Microtom
sections (40 ␮m) were collected and stored in PBS/0.1% sodium azide at 5°C.
Immunohistochemistry
Patients and Methods
Presurgical evaluation of TLE patients included detailed clinical examinations, prolonged video-electroencephalographic
monitoring with scalp and sphenoidal electrodes, and neuropsychological tests, including a Wada test. Neuroimaging
studies comprised high-resolution magnetic resonance imaging (MRI) and single-photon emission computed tomography. When the epileptogenic zone was localized to the medial temporal region, patients were referred to selective
amygdalohippocampectomy or anteromedial temporal lobe
resection.
Approval for the study was obtained from the University
of Vienna, and informed consent was obtained from patients
providing specimens. Surgical specimens of all patients were
examined by routine pathology, and in accordance with presurgical examination, they were grouped into those with hippocampal sclerosis (n ⫽ 25) and those without (n ⫽ 4).
Specimens with hippocampal sclerosis originated from patients with selectively damaged hippocampus as assessed by
MRI and confirmed by the presence of distinct hippocampal
sclerosis in the neuropathological examination.23 In these patients, seizures presumably arose from the medial temporal
Monoclonal CgA antiserum (clone LK2H10) was purchased
from Boehringer-Mannheim (Mannheim, Germany). Antisera for CgB and secretoneurin were raised in rabbits against
synthetic peptides corresponding to amino acids 554 –564 of
human CgB24 and 154 –186 of rat secretogranin II (differing
only in 1 position from the human sequence),25 respectively,
and coupled to keyhole-limpet hemocyanin. The antisera
recognized the respective chromogranin and processing products but did not cross-react with other chromogranins or a
variety of neuropeptides.15,19 The rabbit antisera for dynorphin A(1– 8) and ␣-neoendorphin were donated by Dr. P.
Ciofi (INSERM U 156, Neuroendocrinologie Cellulaire,
Lille, France). Immunocytochemical staining was abolished
by 50 ␮M dynorphin(1– 8) and ␣-neoendorphin, respectively, but not dynorphin A(1–18), met-enkephalin, and leuenkephalin or the other respective opioid peptides (not
shown). Antisera did not cross-react with a variety of other
neuropeptides.26
Incubations were performed on free-floating sections. For
dynorphin and ␣-neoendorphin immunohistochemistry, sections were pretreated with target retrieval solution (pH 6.0;
Dako, Vienna, Austria) at 70°C and then at room tempera-
Pirker et al: Chromogranins in TLE
217
ture for 20 minutes each. In all instances, the avidin-biotinperoxidase method was used according to the supplier’s protocol (Vectastain Standard ABC kit; Vector, Burlingame,
CA). Only for ␣-neoendorphin was a horseradish peroxidase–coupled secondary antibody used (P0448, 1:250;
Dako). Depending on the host of the secondary antibody,
sections were preincubated for 90 minutes with 10% normal
goat serum (Margaritella, Vienna, Austria) when processed
for dynorphin, ␣-neoendorphin, CgB, and secretoneurin or
with 10% normal horse serum (GIBCO, Paisley, UK) in 50
mM Tris-HCl–buffered saline (pH 7.2, TBS) for CgA immunohistochemistry. This step was followed by incubation
with the respective primary antibody (dynorphin 1:20,000,
␣-neoendorphin 1:1,000, CgA 1:2,500, CgB 1:15,000, secretoneurin 1:5,000) for 48 to 72 hours at 4°C in the same
buffer. Sections were then incubated in 0.6% H2O2, 20%
methanol in TBS for 20 minutes to reduce endogenous peroxidase activity and then with secondary biotinylated antibodies (1:200, Vectastain) against mouse (CgA) or rabbit
(CgB, secretoneurin, dynorphin) and the avidin-biotinhorseradish peroxidase solution (1:100, Vectastain) for 30
minutes at room temperature. They were then reacted with
0.4 mM 3,3⬘-diaminobenzidine (Sigma, Munich, Germany)
and 0.01% H2O2 in TBS for 4 to 6 minutes, mounted on
slides, air-dried, dehydrated, and coverslipped. After each incubation step, except the preincubation with normal goat or
horse serum, 3 5-minute washes with TBS were included. All
buffers and antibody dilutions (except for washing after target retrieval solution, the peroxidase block, and diaminobenzidine) contained 0.4% Triton X-100. In each experiment,
sections without primary antibody were included; they did
not show immunopositive elements. Sections from control
and epilepsy cases were processed simultaneously. Age and
length of post mortem time did not affect immunostaining.
Data Analysis
Staining intensities for CgB- and dynorphin-IR were evaluated using a calibrated image analysis system (MetaMorph3;
Visitron Systems, Munich, Germany). After imaging the sections, gray values were evaluated in the inner and outer
thirds of the molecular layer and converted to relative optical
densities. Data are expressed as ratios of the relative optical
densities in these areas (Table). Differences in cell counts and
ratios of relative optical densities between autopsies and sclerotic and nonsclerotic specimens were calculated by analysis
of variance and further compared between individual groups
using a Dunnett test.
Cell counts were performed in 20-␮m-thick Nissl-stained
sections using an ocular grid at 200⫻ magnification. Areas
of 250 ⫻ 50 and 200 ⫻ 200 ␮m were evaluated in the
granule cell and CA2 pyramidal cell layer, respectively. Hilar
interneurons were counted in an area of 500 ⫻ 500 ␮m.
Data were calculated as neurons/mm3 ⫾ SEM as described.27
Granule cell dispersion was defined as a pattern in which
the normally close apposition of granule cells was dissolved.
The clear boundary between the granule cell layer and the
molecular layer was not observed, and granule cells were scattered into the molecular layer.28
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Table. Ratios of Relative Optical Densities for
Chromogranin B (CgB) and Dynorphin in Sclerotic and
Nonsclerotic Specimens
Ratios of Relative Optical Densities
(IML/OML)
Tissue
CgB
Dynorphin
n
Autopsy
Sclerotic
Nonsclerotic
1.52 ⫾ 0.05
2.07 ⫾ 0.10a
1.69 ⫾ 0.10
0.67 ⫾ 0.02
2.10 ⫾ 0.09a
0.72 ⫾ 0.12
21
25
4
Ratios of relative optical densities of CgB and dynorphin immunoreactivity in the inner (IML) vs. the outer molecular layer (OML)
are shown (mean ⫾ SEM). Note that in autopsies CgB labels more
intensely the IML and dynorphin the OML. In sclerotic, but not in
nonsclerotic, tissue, labeling of the IML considerably increases for
both peptides (compared with OML), reflecting the zone of
sprouted mossy fibers.
Statistics were performed by analysis of variance with subsequent
individual comparisons by a Dunnett test.
p ⬍ 0.001 in hippocampal sclerosis vs. controls.
a
Results
Pathology and Dispersion of Granule Cells
In accordance with previous observations,27 extensive
cell losses were detected in sectors CA1 and CA3/CA4
of sclerotic, but not nonsclerotic, specimens. There was
a 77 ⫾ 7.8 % ( p ⬍ 0.01) reduction of neurons in the
dentate hilus of sclerotic specimens, whereas the number of neurons in nonsclerotic specimens was reduced
by 8 ⫾ 4.7% (not significant) only. Considerable cell
losses were also seen in areas relatively resistant to
epilepsy-induced cell damage, such as granule cells (55
⫾ 2.0%) and CA2 pyramidal cells (38 ⫾ 2.2 %, both
p ⬍ 0.01) in specimens with hippocampal sclerosis but
not significantly in nonsclerotic tissues (10 ⫾ 4.1 and
6 ⫾ 2.6%, respectively). In 9 patients with hippocampal sclerosis, granule cell dispersion was observed.28
The granule cell layer was wider than in other TLE
patients and bilaminar in 3 patients. None of the post
mortem controls or nonsclerotic hippocampi investigated showed a dispersion of granule cells.
Distribution of CgA-IR, CgB-IR, Secretoneurin-IR,
and Dynorphin-IR in the Hippocampus of Post
Mortem Controls
CGA. In controls, CgA-IR was characterized by prominent staining of CA2 pyramidal cells and stratum lucidum of CA3 (Fig 1a). Punctate structures were seen
throughout the hilus and stratum pyramidale (Figs 1a,
2a). In the dentate gyrus, some granule cells were
CgA-IR (Fig 2a). The molecular layer was nearly devoid of staining (Figs 1a, 2a). Single CgA-IR perikarya
and fibers, however, were seen in the molecular layer
and in the hilus of the dentate gyrus (not shown).
Faint, diffuse staining was present in the stratum lacunosum moleculare; it was slightly more intense in area
Fig 1. Chromogranin A (CgA; a, b), chromogranin B (CgB; c, d), secretoneurin (SN; e, f), and dynorphin (Dyn; g, h) immunoreactivity (IR) in the hippocampus of specimens with Ammon’s horn sclerosis and in post mortem controls. In controls (a, c, e, g), IR
for all 4 peptides (notably for CgB and dynorphin) is present in the dentate hilus and extends to the strata lucidum and pyramidale of sector CA3, representing the terminal field of mossy fibers. Arrowheads mark borders of the granule cell layer and borders
between inner and outer parts of the dentate molecular layer and the granule cell layer, respectively. In autopsies, the inner molecular layer is immunoreactive for CgB (c). Note the prominent dynorphin-IR (g) and secretoneurin-IR (e) bands labeling the outer
molecular layer and extending to the stratum lacunosum moleculare of CA3 and CA1. The stratum radiatum shows CgB-IR (c)
but not dynorphin-IR (g). In sclerotic specimens (b, d, f, h), these staining patterns become rearranged: staining in the polymorph
cell layer adjacent to the granule cell layer is reduced; instead, pronounced labeling of the inner molecular layer of the dentate gyrus
is seen (arrows). Note augmented CgB-IR (d) and secretoneurin-IR (f) in hilar interneurons of epileptic specimens. H, hilus; o,
outer two-thirds of molecular layer; I, inner third of molecular layer; lm, stratum lacunosum moleculare; sr, stratum radiatum.
Scale bar ⫽ 500 ␮m
Pirker et al: Chromogranins in TLE
219
Fig 2. Chromogranin A (CgA), chromogranin B (CgB), secretoneurin (SN), and dynorphin (Dyn) immunoreactivity (IR) in dentate
gyrus of post mortem controls (a–d) and in nonsclerotic (e–h) and sclerotic specimens (i–l) of temporal lobe epilepsy patients.
CgA-IR labels some granule cells and punctate structures in the dentate hilus of controls (a). CgB-IR (b) and dynorphin-IR (d) label prominently granule cells, fiber bundles, individual fibers, and cells in the hilus. Labeling of granule cells is enhanced in epileptic specimens for CgA (e, i), CgB (f, j), and dynorphin (h, l). Whereas the inner molecular layer is lightly labeled only by CgB-IR
in autopsies (b), dense CgB-IR (j) and dynorphin-IR (l) are seen there in sclerotic specimens. Generally, labeling is reduced in the
dentate hilus, where well-stained cells become visible (j, l). Secretoneurin-IR (c) and dynorphin-IR (d) label the outer molecular
layer with a clear-cut border to the inner molecular layer in autopsies, a pattern which is lost in sclerotic (k, l), but not in nonsclerotic (g, h), specimens. Note a plexus of secretoneurin-IR fibers in the supragranular molecular layer of autopsies (arrow in c),
secretoneurin-IR cells in the nonsclerotic (g) and sclerotic hilus (k), and fibers extending to the outer molecular layer in sclerotic
specimens (k). H, hilus; o, outer two-thirds of molecular layer; i, inner third of molecular layer. Scale bar ⫽ 100 ␮m.
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CA1 and gradually declined in sectors CA2 and CA3
(Fig 1a).
Pronounced CgB-IR was observed in the terminal field of mossy fibers and throughout the hippocampus proper (especially in the strata pyramidale and radiatum) and the subicular complex of all autopsies
(Figs 1c). Bundles of CgB-IR fibers, presumably mossy
fibers, arising from the granule cell layer, formed a
dense network in the adjacent hilus (Figs 1c, 2b, 3a,d)
and dissolved to more punctate structures deeper in
sector CA4 (Fig 3d) and the strata lucidum and pyramidale CA3 (Fig 1c). Weaker, diffuse staining was observed in the inner third of the dentate molecular layer
and in the stratum radiatum of area CA3 (Figs 1c, 2b;
Table). At high magnification, single fibers were found
throughout the molecular layer (not shown). Numerous granule cells were CgB-IR; also, CA2 pyramidal
cells were CgB-IR, though less so than for CgA (Figs
1c, 2b, 3a).
CGB.
SECRETONEURIN. In post mortem controls, secretoneurinIR was present in the outer two-thirds of the molecular
layer, the supragranular layer, and the polymorph cell
region and extended to the entire CA3 field terminating at the border to CA2 (Fig 1e). IR structures were
especially dense in the supragranular layer (Fig 2c, arrow). In the molecular layer, secretoneurin-IR exhibited a laminar distribution (Figs 1e, 2c). The outer
two-thirds of the molecular layer were considerably
more intensely stained than the inner third (Fig 1e).
Single immunopositive fibers were seen throughout the
molecular layer, and single moderately stained neurons
were found in the molecular and granule cell layers at
high magnification (Figs 2c, 3c). In the polymorph cell
layer, secretoneurin-IR was found in numerous fibers
(presumably mossy fibers) and in single perikarya
(Fig 3c).
In the hippocampus proper, diffuse secretoneurinpositive staining was observed throughout the stratum
lacunosum moleculare and equally in the strata pyramidale and lucidum of area CA3 (Fig 1e).
Secretoneurin-IR fibers were present in CA1 and even
more numerous in regions CA2 and CA3. Single moderately stained neurons were seen in sectors CA1 to
CA3, especially in the strata oriens, pyramidale, and
radiatum (not shown).
DYNORPHIN. The distribution patterns of dynorphinand ␣-neoendorphin-IR were essentially identical. We
therefore refrain from describing ␣-neoendorphin-IR.
In autopsies, dark dynorphin-IR was observed in the
terminal field of mossy fibers and in granule cells (Fig
1g). Mossy fibers were marked by dark dynorphin-IR
structures of punctate appearance, which were particularly dense in the dentate hilus and strata lucidum and
pyramidale of CA3 (Figs 1g, 2d). In addition, single
somata and many thin fibers were observed in the hilus
(Fig 2d). Whereas the inner third of the dentate molecular layer was devoid of dynorphin-IR, its outer
two-thirds were labeled by diffuse staining with a sharp
IR band delineating the border to the inner layer (Figs
1g, 2d; Table). Single dark fibers and perikarya were
found in all parts of the molecular layer. Light diffuse
staining was observed also in the subgranular layer and
the stratum lacunosum moleculare of sectors CA1 to
CA3 (Fig 1g)
CgA-IR, CgB-IR, Secretoneurin-IR, and DynorphinIR in Specimens with Hippocampal Sclerosis
Marked changes in CgA-IR were observed in
sclerotic hippocampi. In most cases (23/25), the number of granule cells labeled appeared to be increased
compared with autopsies (Fig 2i). In contrast to post
mortem controls, faint CgA-IR was present in the molecular layer of most cases with hippocampal sclerosis
(22/25), presumably contained in terminals of sprouted
mossy fibers (arrow in Fig 1b). In addition, scattered
fibers and somata were observed in all parts of the molecular layer and hilus (Fig 2i). The intensity and width
of CgA-IR in the inner molecular layer varied between
individual samples. In one-third of patients, staining
was light and restricted to the inner third of the dentate molecular layer (Figs 1b, 2i). In another third of
sclerotic specimens (9/25), slight CgA-IR extended to
the middle and outer thirds of the molecular layer (not
shown).
In contrast to increased CgA-IR in granule cells and
the molecular layer, the extent of IR staining was often
reduced in the dentate hilus and stratum lacunosum
moleculare of CA1 (Fig 1b). As in controls, pyramidal
cells of CA2 were well labeled (Figs 1b, 3i). Their
number was, however, significantly reduced, by about
38%, compared to controls and nonsclerotic specimens. Single somata and fibers were seen throughout
the hippocampus proper. In the dentate hilus, the stratum lucidum, and less frequently other parts of the
hippocampus proper, numerous plaque-like structures
were labeled for all 3 chromogranins and dynorphin
(Fig 3e, j). They may result from degenerating (mossy)
fibers. Similar IR clusters were detected in sclerotic
specimens by immunocytochemistry for glutamate
receptors 2 and 3.29 Interestingly, CgA-IR and
secretoneurin-IR have been observed in senile plaques
of Alzheimer’s patients.30
CGA.
In patients with hippocampal sclerosis, increased
CgB-IR was observed in granule cells and well-stained
neurons were detected in parts of the hilus devoid of
CgB-IR mossy fibers (Figs 1d, 2j, 3b,g). In the hilus
and the hippocampus proper, the same neuronal struc-
CGB.
Pirker et al: Chromogranins in TLE
221
Fig 3. High-power photomicrographs of chromogranin B (CgB; a, b, d, e, g, h), secretoneurin (c, f), and chromogranin A (CgA; i,
j) immunoreactive (IR) structures in the hippocampus of autopsies and specimens with hippocampal sclerosis. Modest CgB-IR is seen
in granule cells of autopsies (a) with conspicuous fiber bundles arising from the layer (a) forming a dense network adjacent to the
granule cell layer (upper part of d) and dissolving into more punctate structures and IR clusters in CA4 (lower part of d). In sclerotic specimens, the number of fiber bundles is drastically reduced and numerous CgB-IR plaque-like structures (e) and neurons (g)
are seen. Plaque-like structures are also detected for CgA (j) and may reflect degenerating (mossy) fibers. Secretoneurin-IR neurons
are seen in the hilus of autopsies (c). Their labeling is augmented in sclerotic specimens, and they may give rise to sprouted fibers
(f). CgA-IR labels well CA2 pyramidal cells in controls (not shown) and sclerotic specimens (i). g, granule cell layer. Scale bars ⫽
150 ␮m (a, b, i, j) and 50 ␮m (c–h).
tures were present as in controls. However, their
abundance (but not their staining intensity) was considerably reduced (Fig 1d). Bundles of impressively
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stained fibers, presumably mossy fibers, were less frequently observed than in controls (Figs 2j, 3b,e). In
contrast, single fibers arising from the granule cell
layer were clearly detected in the subgranular layer
(Fig 3b).
The most conspicuous change was the strong increase in CgB-IR in the inner third of the dentate molecular layer, likely labeling sprouted mossy fiber terminals [Figs 1d (arrow), 2j], also reflected by a significant
increase in the ratio of relative optical densities in the
inner vs. the outer molecular layers (Table). The
CgB-IR band covered 16% to 56% (average 34 ⫾ 4%)
of the molecular layer. Thus, in 18 of the 25 cases
investigated, the moderate to dark IR band occupied
the inner third of the molecular layer (Fig 2j). In 6
cases, only a narrow dark IR band was observed in the
supragranular layer. On average, specimens with granule cell dispersion28 showed significantly ( p ⬍ 0.05)
broader labeling of the molecular layer (42 ⫾ 4%)
than those without dispersion. In 1 specimen with
granule cell dispersion, the IR band extended to the
middle and in another specimen to the entire molecular layer. There was an inverse correlation between the
extent of the molecular layer labeled by sprouted CgBpositive fibers and the number of neuropeptide Y
mRNA-positive neurons in the dentate hilus (not
shown), also indicating a correlation of the extent of
neurodegeneration and mossy fiber sprouting. In most
specimens, densely packed fibers were seen in the outer
molecular layer, which may arise from neurons in the
dentate hilus (Fig 3h). No clinical parameters, such as
febrile seizures, duration of epilepsy, or other possible
risk factors, were found to correlate with either the extent of neurodegeneration or sprouting (not shown).
SECRETONEURIN. Secretoneurin-IR was considerably
enhanced in the molecular layer of the dentate gyrus,
especially in its inner third, the area of sprouted mossy
fiber collaterals (Figs 1f, 2k). In contrast, in the stratum lacunosum moleculare of CA1, secretoneurin-IR
was less prominent than in controls (Fig 1f). Superimposed over diffuse immunostaining, numerous dark fibers were seen in the molecular layer (Fig 2k), presumably originating from intensely stained neurons in the
dentate hilus (Fig 3f). The number of fibers was increased compared to controls. In the polymorph cell
region, secretoneurin-IR was reduced in structures presumably formed by mossy fibers (Fig 2h). It was, however, frequently present in distinct fibers and somata
throughout the hilus and hippocampus proper of surgical specimens (Figs 1f, 2k 3f). In the stratum lacunosum moleculare, other than in controls, staining was
seen only in areas CA2 and CA3, not in CA1 (Fig 1f).
DYNORPHIN. In all sclerotic specimens, dynorphin-IR
was detected in the molecular layer of the dentate gyrus
with a distribution similar to that of CgB-IR. In most
cases (14/25), a dark dynorphin-IR band was present
in the inner third of the molecular layer, whereas the
outer portions were only lightly stained (Figs 1h, 2l), as
also indicated by a markedly increased ratio of relative
optical densities in the inner vs. the outer molecular
layers (Table). No distinct border was detected between the inner and the outer molecular layers (Fig
1h). Similar to controls, many granule cells were intensely stained (Fig 2l). In the polymorphic cell region,
dynorphin-IR somata were considerably less numerous
than in autopsies (Fig 2l), being detected in 5 specimens only. The extent of punctate IR was reduced in
the hilus and the CA3 sector (Figs 1h, 2l).
Dynorphin-IR was also reduced in the stratum lacunosum moleculare of CA1 in most cases (Fig 1h). Essentially the same distribution pattern was observed for
␣-neoendorphin-IR (not shown).
Chromogranin-IR and Dynorphin-IR in Specimens
without Hippocampal Sclerosis
In TLE patients without hippocampal sclerosis, IR patterns in most instances were more like those in autopsies than in sclerotic specimens. In particular, no decrease in presumed mossy fiber staining was seen in the
dentate hilus (Fig 2e-h), only marginal additional staining was detected in the inner molecular layer for
dynorphin-IR, and the outer molecular layer was discretely labeled for secretoneurin and dynorphin (Fig
2g,h). However, labeling of hilar interneurons was enhanced as in sclerotic specimens, though without significant cell loss.
Numbers of CgA-IR granule cells and hilar neurons were increased compared to controls (Fig 2e).
CGA.
In 3 patients, very faint and diffuse CgB-IR was
found throughout the molecular layer (Fig 2f). In contrast to controls, dark punctate staining was observed
in the supragranular layer at the crest and tips of the
dentate gyrus. Staining in the hilus was slightly lighter
compared with autopsies. Pyramidal cells of area CA2
were stained in 3 of 4 cases (not shown).
CGB.
Secretoneurin-IR was similarly distributed, although generally less intensive, in nonsclerotic specimens compared with autopsies (Fig 2g). Labeling was, however, enhanced in hilar neurons (Figs
2g, 3f).
SECRETONEURIN.
DYNORPHIN. Staining patterns were similar to controls, though often more intense (Fig 2h). Specifically,
no prominent dynorphin-IR band was seen in the inner molecular layer. In contrast to autopsies, punctate
staining was seen at the crest of the dentate gyrus in
the supragranular layer of 3 cases. In the fourth case,
light diffuse staining was observed throughout the molecular layer. IR in the hilus was more intense than in
controls.
Pirker et al: Chromogranins in TLE
223
Discussion
Our data provide evidence for a wide and heterogeneous distribution of chromogranins within the human
hippocampal formation and for profound changes in
TLE. Comparisons between post mortem tissues and
surgical specimens have to be drawn with caution for
two reasons: mean age of patients at surgery was significantly lower than that of deceased subjects and the
time required from isolation of the hippocampal tissue
during surgery until its fixation was considerably
shorter (three to five hours) than the mean post mortem interval prior to autopsy (17.2 hours). However,
no correlation between post mortem times or age at
death with the intensity of immunolabeling could be
detected. In addition, tissue samples from patients
without hippocampal sclerosis to some extent served as
controls since they were obtained using the same protocol. Our surgical samples obtained from the hippocampal body (middle segment) were not large
enough to investigate possible differences in the rostral–caudal axis. Autopsy specimens were investigated
at the same part of the hippocampus.
Chromogranin-IR and Dynorphin-IR as
Neuroanatomical Markers in the Post
Mortem Hippocampus
Although significant overlap in the IR patterns was
seen for all chromogranins and dynorphin, characteristic differences were also noted. There is an interesting
segregation of IR in the molecular layer: whereas
CgB-IR faintly labels the entire inner third of the molecular layer following the pattern of associationalcommissural fiber innervation,31 secretoneurin-IR
forms a narrow band of intensely labeled individual fibers in the innermost supragranular layer, possibly arising from hilar neurons.
The outer two-thirds of the molecular layer (with its
distinct border to the inner third) and the stratum lacunosum moleculare are labeled for secretoneurin and
dynorphin, outlining terminal areas of entorhinal cortical afferents. High concentrations of dynorphin
mRNA in the entorhinal cortex32 indicate that the
peptide may be contained in the respective nerve terminals.
Typical staining patterns for chromogranins were
also seen in the hippocampus proper. Pyramidal cells,
especially those in CA2, were preferentially labeled for
CgA. The pattern of CgB-IR in the hippocampus
proper and the subiculum follows the areas innervated
by Schaffer collaterals and axon terminals of CA1 pyramidal cells. This is consistent with the expression of
CgB mRNA throughout the pyramidal cell layer of the
rat.22
224
Annals of Neurology
Vol 50
No 2
August 2001
Reorganization of the Hippocampal Formation
in TLE
The most conspicuous characteristic of specimens with
hippocampal sclerosis is the dramatic reorganization of
mossy fibers, as indicated by marked reductions in IR
of all three chromogranins (most prominently visualized for CgB) and dynorphin in the dentate hilus and
strong increases in IR of chromogranins and dynorphin
in the inner molecular layer. In the 4 nonsclerotic TLE
specimens investigated, only discrete labeling of the inner molecular layer was detected, excluding extensive
sprouting into this area. This indicates that sprouting is
associated with neurodegeneration, supported by a high
correlation between the area of the inner molecular
layer occupied by sprouted mossy fibers and the extent
of neurodegeneration in the sclerotic specimens.4,33 Although mossy fiber sprouting may not be a prerequisite
for epilepsy (as indicated by the lack of sprouting in
nonsclerotic TLE specimens), it may augment recurrent seizures.34 However, we cannot exclude that patients without hippocampal sclerosis at surgery may not
have developed hippocampal sclerosis later. It is, however, interesting to note that the average time spent in
epilepsy was similar for our three adult patients without Ammon’s horn sclerosis as for those with sclerosis
(18.7 vs. 22.4 years). Mossy fiber sprouting has been
reported in aged controls.35 We did not observe, however, significant dynorphin-IR in autopsies, including
specimens of two older persons (92 and 80 years) otherwise not included in this study.
Another interesting observation is the apparent loss
of the sharp secretoneurin-IR and dynorphin-IR border
between the inner and outer two-thirds of the molecular layer in hippocampal sclerosis. This may be caused
by invading mossy fibers and possible reduction of perforant path terminals. The reduced staining in the stratum lacunosum moleculare CA1 to CA3 may be related to loss of entorhinal cortex neurons36 projecting
to this area and supports the assumption that the peptides may be contained in these fibers.
Dense secretoneurin-IR and CgB-IR fibers, likely
arising from hilar interneurons, invade the outer molecular layer of sclerotic TLE specimens, as also shown
for neuropeptide Y–containing fibers.13,37 Increased
chromogranin-IR in hilar interneurons, in granule cells
(CgA and CgB), and in pyramidal cells (CgA) of sclerotic and nonsclerotic specimens may reflect seizureinduced increases in the synthesis of the respective
polypeptides. This is consistent with increased chromogranin mRNA concentrations observed in hippocampal
neurons of epileptic rats.21,22 Interneurons seem to
overexpress chromogranins also in the nonsclerotic hippocampus, reflecting increased activity of presumable
GABAergic neurons and possibly contributing to endogenous anticonvulsive mechanisms. Progressive loss
of these vulnerable neurons could later propagate neurodegeneration.
During epileptic seizures, sprouted mossy fibers and
axons of hilar interneurons may release chromogranins
or peptides derived from them. Although little is
known about the physiological functions of chromogranins, actions of other neuropeptides are well established in animal models of TLE. Thus, neuropeptide Y
becomes overexpressed after epileptic seizures and may
serve as an endogenous anticonvulsant by suppressing
glutamate release from mossy fibers and Schaffer collaterals.38,39 Similarly, dynorphin exerts an inhibitory
action on glutamate release through ␬-receptors located
presynaptically on mossy fibers and perforant path terminals.40 Inhibitory action has been shown also for
dynorphin released from sprouted mossy fibers upon
␬-receptors on perforant path terminals.41
In conclusion, changes in IR of chromogranins mark
an impressive rearrangement of neuronal circuitries in
patients with TLE-induced Ammon’s horn sclerosis.
These include degenerative loss of chromogranin-IR
mossy fibers in the dentate hilus and sprouting of
mossy fibers. Distortion of the lamination of the molecular layer, as outlined by secretoneurin-IR and
dynorphin-IR and losses of IR in the stratum lacunosum moleculare, indicate impaired innervations from
the entorhinal cortex. Surviving hilar interneurons exhibit enhanced expression of secretoneurin and presumably give rise to fibers sprouting to the outer parts
of the dentate molecular layer. Chromogranins and
peptides derived from them may be released during epileptic seizures and may exert a functional role in the
epileptic hippocampus.
This project was funded by the Austrian Federal Ministry for Science and Transport (GZ 70.039/2-Pr/4/98) and the Austrian Science Foundation.
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We thank Anna Wieselthaler for excellent technical assistance and
C. Trawöger and Dr C. Schwarzer for valuable discussion.
18.
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