Neuronal Cell Death in a Rat Model for Mesial Temporal Lobe Epilepsy Is Induced by the Initial Status Epilepticus and Not by Later Repeated Spontaneous Seizures

Abstract

Summary:Purpose: To determine whether repeated seizures contribute to hippocampal sclerosis, we investigated whether cell loss in the (para) hippocampal region was related to the severity of chronic seizure activity in a rat model for temporal lobe epilepsy (TLE).Methods: Chronic epilepsy developed after status epilepticus (SE) that was electrically induced 3-5 months before. The presence of neuronal damage was assessed by using Fluoro-Jade and dUTP nick end-labeling (TUNEL) of brain sections counterstained with Nissl.Results: We found a negative correlation between the numbers of surviving hilar cells and the duration of the SE (r ‫ס‬ -0.66; p < 0.01). In the chronic phase, we could discriminate between rats with occasional seizures (0.15 ± 0.05 seizures per day) without progression and rats with progressive seizure activity (8.9 ± 2.8 seizures/day). In both groups, the number of TUNEL-positive cells in parahippocampal regions was similar and higher than in controls. In the hippocampal formation, this was not significantly different from controls. Fluoro-Jade staining showed essentially the same pattern at 1 week and no positive neurons in chronic epileptic rats.Conclusions: Cell death in this rat model is related to the initial SE rather than to the frequency of spontaneous seizures. These results emphasize that it is of crucial importance to stop the SE as soon as possible to prevent extended cell loss and further progression of the disease. They also suggest that neuroprotectants can be useful during the first week after SE, but will not be very useful in the chronic epileptic phase. Key Words: Necrosis-Apoptosis-Parahippocampal region-TUNEL-Fluoro-Jade-Sclerosis-EpileptogenesisProgression.Since the discovery that a specific neuropathologic syndrome of temporal lobe epilepsy (TLE) is associated with hippocampal mesial sclerosis, there has been a controversy whether the sclerosis is the cause or consequence of repeated complex partial seizures [reviewed in (1,2)]. Various reports on experimental TLE models, in particular the kindling model, suggest that repeated seizures cause progressive hippocampal damage (3,4). However, the kindling model is a model for repeated seizures in which seizures are triggered by electrical stimulation, whereas spontaneous seizures are rarely recorded. Moreover, kindling-induced damage is relatively mild, and the claim of cell loss due to repeated seizures is not always confirmed when cell densities are taken into account (5,6). Previous research in animal models in which chronic seizures developed after a pharmacologically or electrically induced status epilepticus (SE) have shown that extensive cell death occurs almost immediately after the SE in various brain regions (7-9). However, studies that investigated the effects of chronic seizures on cell death have relied mainly on morphologic/stereologic measurements (10,11), so that subtle seizure-induced cell loss might have remained undetected.In this study we used the post-SE model in which an SE was induced by electrical stimula...

In vitro status epilepticus but not spontaneous recurrent seizures cause cell death in cultured hippocampal neurons

“…In fact, aside from the cell death associated with the initial exposure to low Mg 2+ , there was no increase in neuronal cell death in cultures manifesting SREDs compared to age-matched control cultures for the life of the neurons in culture. The results are consistent with animal and human data that demonstrate that the majority of neuronal cell death is associated with SE and not with recurrent seizures (Duncan, 2002;Fujikawa, 2005;Fujikawa et al, 2000;Gorter et al, 2003;Holmes, 2002;Pitkanen et al, 2002). To our knowledge this study provides the first direct evidence in an in vitro model that continuous electrographic epileptiform activity is directly correlated with neuronal cell death in the absence of any other extracellular environmental effects on neuronal viability.…”

“…In vivo studies utilizing rat models of SE-induced temporal lobe epilepsy suggest that neuronal cell death is only associated with the initial injury from SE, but not with the subsequent spontaneous recurrent seizures (Gorter et al, 2003;Pitkanen et al, 2002); however, there is data showing that even a few evoked seizures in kindled rats produce TUNEL-positive hippocampal in hilar neurons (Bengzon et al, 1997) and hippocampal neuronal loss that increases with increasing numbers of kindled seizures (Cavazos et al, 1994). Clinical studies have demonstrated conflicting results with reports of increased serum and CSF levels of neuron-specific enolase, a marker of neuronal injury, after spontaneous seizures (Buttner et al, 1999).…”

“…Conversely, it is now widely accepted in animals and man that spontaneous recurrent seizures, occurring in the context of intractable epilepsy, do not cause significant brain injury (Fujikawa, 2005). Evidence is now accumulating especially from the in vivo models of epilepsy, suggesting that neuronal cell death is associated with initial epileptogenic insult and not with later spontaneous seizures (Gorter et al, 2003;Pitkanen et al, 2002). Understanding the effects of epileptiform discharges on neuronal viability is important in developing therapeutic strategies for treating SE and epilepsy.…”

Prenatal choline supplementation attenuates neuropathological response to status epilepticus in the adult rat hippocampus

“…Keywords choline; kainic acid; hippocampus; seizures; bromodeoxyuridine; growth factor; glutamic acid decarboxylase; glial fibrillary acidic protein; neuroprotection Status epilepticus (SE), a period of prolonged seizures, produces a host of plastic changes in the hippocampus that are thought to contribute to the development of temporal lobe epilepsy. SE results in substantial neuronal loss (Cavazos et al, 1994;Haas et al, 2001;Gorter et al, 2003), γ-aminobutyric acid (GABA) system alterations (e.g., Houser & Esclapez, 1996), reactive gliosis (Jorgensen et al 1993; Niquet et al, 1994a;Kang et al, 2006), mossy fiber innervation of the dentate gyrus (Sutula et al, 1988;Ben-Ari & Represa, 1990), changes in levels of growth factors (Khrestchatisky et al, 1995;Mudo et al, 1996;Schmidt-Kastner et al, 1996;Shetty et al, 2004), and a transient increase in cell proliferation and neurogenesis (Bengzon et al, 1997;Parent et al, 1997;Scharfman et al, 2000;Hattiangady et al, 2004). These SE-induced degenerative and regenerative changes in the hippocampus are also Corresponding author: Dr. Christina L. Williams, Department of Psychology and Neuroscience, 572 Research Drive, Box 91050, GSRB-II, Room 3022, Duke University, Durham, NC 27708, USA, Phone: 919-660-5638, Fax: 919-660-5798, Email: williams@psych.duke.edu.…”

“…SE results in substantial neuronal loss (Cavazos et al, 1994;Haas et al, 2001;Gorter et al, 2003), γ-aminobutyric acid (GABA) system alterations (e.g., Houser & Esclapez, 1996), reactive gliosis (Jorgensen et al 1993;Niquet et al, 1994a;Kang et al, 2006), mossy fiber innervation of the dentate gyrus (Sutula et al, 1988;Ben-Ari & Represa, 1990), changes in levels of growth factors (Khrestchatisky et al, 1995;Mudo et al, 1996;Schmidt-Kastner et al, 1996;Shetty et al, 2004), and a transient increase in cell proliferation and neurogenesis (Bengzon et al, 1997;Parent et al, 1997;Scharfman et al, 2000;Hattiangady et al, 2004). These SE-induced degenerative and regenerative changes in the hippocampus are also accompanied by deficits in hippocampal-dependent learning and memory (Stafstrom et al, 1993;Liu et al, 1994;Sarkisian et al, 1997;Hort et al, 1999;Mikati et al, 2001).…”