Neuronal and glial pathological changes during epileptogenesis in the mouse pilocarpine model

Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia, United States
Experimental Neurology (Impact Factor: 4.7). 08/2003; 182(1):21-34. DOI: 10.1016/S0014-4886(03)00086-4
Source: PubMed


The rodent pilocarpine model of epilepsy exhibits hippocampal sclerosis and spontaneous seizures and thus resembles human temporal lobe epilepsy. Use of the many available mouse mutants to study this epilepsy model would benefit from a detailed neuropathology study. To identify new features of epileptogenesis, we characterized glial and neuronal pathologies after pilocarpine-induced status epilepticus (SE) in CF1 and C57BL/6 mice focusing on the hippocampus. All CF1 mice showed spontaneous seizures by 17-27 days after SE. By 6 h there was virtually complete loss of hilar neurons, but the extent of pyramidal cell death varied considerably among mice. In the mossy fiber pathway, neuropeptide Y (NPY) was persistently upregulated beginning 1 day after SE; NPY immunoreactivity in the supragranular layer after 31 days indicated mossy fiber sprouting. beta2 microglobulin-positive activated microglia, normally absent in brains without SE, became abundant over 3-31 days in regions of neuronal loss, including the hippocampus and the amygdala. Astrogliosis developed after 10 days in damaged areas. Amyloid precursor protein immunoreactivity in the thalamus at 10 days suggested delayed axonal degeneration. The mortality after pilocarpine injection was very high in C57BL/6 mice from Jackson Laboratories but not those from Charles River, suggesting that mutant mice in the C57BL/6(JAX) strain will be difficult to study in the pilocarpine model, although their neuropathology was similar to CF1 mice. Major neuropathological changes not previously studied in the rodent pilocarpine model include widespread microglial activation, delayed thalamic axonal death, and persistent NPY upregulation in mossy fibers, together revealing extensive and persistent glial as well as neuronal pathology.

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Available from: Karin Borges, Nov 20, 2014
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    ABSTRACT: Pilocarpine-induced status epilepticus (SE) is a widely used seizure model in mice, and the Racine scale has been used to index seizure intensity. The goal of this study was to analyze electroencephalogram (EEG) quantitatively using fast Fourier transformation (FFT) and statistically evaluate the correlation of electrographic seizures with convulsive behaviors. Simultaneous EEG and video recordings in male mice in a mixed genetic background were conducted and pilocarpine was administered intraperitoneally to induce seizures. The videos were graded using the Racine scale and the root-mean-square (RMS) power analysis of EEG was performed with Sirenia Seizure Pro software. We found that the RMS power was very weakly correlated with convulsive behavior induced by pilocarpine. Convulsive behaviors appeared long before electrographic seizures and showed a strong negative correlation with theta frequency activity and a moderate positive correlation with gamma frequency activity. Racine scores showed moderate correlations with RMS power across multiple frequency bands during the transition from first electrographic seizure to SE. However, there was no correlation between Racine scores and RMS power during the SE phase except a weak correlation with RMS power in the theta frequency. Our analysis reveals limitations of the Racine scale as a primary index of seizure intensity in status epilepticus, and demonstrates a need for quantitative analysis of EEG for an accurate assessment of seizure onset and severity.
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    • "Reactive astrocytes are generated in the hippocampus of animal models of epilepsy (Borges et al., 2003; Shapiro et al., 2008) and in the hippocampus of humans with temporal lobe epilepsy (Cohen-Gadol et al., 2004). These reactive changes in astrocytes, termed astrocytosis, generally involve increases in astrocyte size and number (Borges et al., 2003; Shapiro et al., 2008) and are often accompanied with neuronal loss and synaptic rearrangements (Borges et al., 2003; Kron et al., 2010). Reactive astrocytes exhibit an increased expression of GFAP, which is thus used to assess the development of reactive astrocytosis (Pekny and Nilsson, 2005; Wilhelmsson et al., 2004). "
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    • "activation and exacerbate neuroinflammation (Vezzani et al., 2011). In pilocarpine-treated mice evidence of neuroinflammation appears well before injury to most neurons (except perhaps those of the dentate hilus (Borges et al., 2003)), suggesting that in this model the initial cytokine burst elicited by seizures is not caused by neuron loss. In the future it would be worthwhile to explore pharmacological inhibition of EP2 in other models of neuronal injury such as ischemia, AD, PD and ALS. "
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