Disruption of Cortical Development as a Consequence of Repetitive Pilocarpine‐induced Status Epilepticus in Rats

Abstract

Summary: Purpose:The aim of the present study was to observe possible cortical abnormalities after repetitive pilocarpineinduced status epilepticus (SE) in rats during development.Methods: Wistar rats received intraperitoneal injection of pilocarpine hydrochloride 2% (380 mg/kg) at P7, P8, and P9. All experimental rats displayed SE after pilocarpine injections. Rats were killed at P10 and P35, and immunocytochemistry procedures were performed on 50-µm vibratome sections, by using antibodies against nonphosphorylated neurofilament (SMI-311), parvalbumin (PV), calbindin (CB), calretinin (CR), and glutamate decarboxylase (GAD-65). Selected sections were used for the TUNEL method and double-labeling experiments, with different mixtures of the same markers. Results:The major findings of the present work were (a) altered intracortical circuitry development; (b) anticipation of PV immunoreactivity in neocortical interneurons; (c) increased GAD-65 immunoreactivity; and (d) reduced neocortical apoptotic process.Conclusions: From these results, we suggest that previously healthy brain, without genetic abnormalities, might develop an "acquired" disruption of cortical development whose evolution reproduces some characteristics of the childhood epilepsies associated with cognitive impairment. Key Words: Immature brain-Early insult-Apoptosis-Neocortex-Interneurons.In humans, the incidence of seizures is higher in the first year of life and decreases until adulthood (1,2). Although most of the early-life seizures are inherently benign, symptomatic febrile or hypoxic seizures are present in the history of many patients with temporal lobe epilepsy (TLE) and are believed to be associated with an underlying progressive epileptogenic process (3). Despite increasing knowledge of basic epileptology, the role of early-life seizures in the development of TLE remains an open question.In rats, neonatal seizures induce a range of hippocampal changes, such as glia activation and cytokine increase (4), altered glutamate and γ -aminobutyric acid (GABA)(A)-receptor gene immunoreactivity (5), persistent changes in intrinsic properties of CA1 cells (6), long-term behavioral deficits (7), and reduced hippocampal neurogenesis (8). Nevertheless, several studies have shown that the immature brain is resistant to seizure-induced hippocampal neuronal cell loss (9-12) and synaptic reorganization (11,13,14). Despite hippocampal resistance to neuronal Address correspondence and reprint requests to Dr. A. V. Silva at Lab Neurologia Experimental UNIFESP-EPM, Rua Botucatú, 862, CEP 04023-900 São Paulo, SP, Brazil. E-mail: valotta.nexp@epm.br damage during early development, Santos and colleagues (15,16) recently demonstrated that multiple episodes of pilocarpine-induced status epilepticus (SE) in developing rats (P7-P9) led to progressive neocortical/hippocampal epileptiform activity, persistent in vitro hyperexcitability, increased hippocampal/thalamic apoptosis, and severe cognitive impairment in adulthood.In contrast to adult rats that develop hippocam...

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“…In control mice, SMI 311 labeled a defined subpopulation of weakly pS6ϩ pyramidal neurons belonging to cortical layers III, V, and (rarely) nonpyramidal layer VI neurons (Fig. 6 A-D) (Ulfig et al, 1998;da Silva et al, 2005). This staining was particularly strong in the retrosplenial granular (RSG) cortex (Fig.…”

Altered anxiety-related and abnormal social behaviors in rats exposed to early life seizures

“…Our study brings an important contribution to demonstrate that sequels of neonatal seizures extending beyond the learning and memory deficits, increased anxiety and loss in cognitive flexibility. Animals studies reveal that early life seizures can disrupt some brain structure such as the hippocampus (Holmes et al, 1998; Lynch et al, 2000; Santos et al, 2000; Villeneuve et al, 2000; Sogawa et al, 2001; Cornejo et al, 2007; Nishimura et al, 2011) neocortex (da Silva et al, 2005; Isaeva et al, 2010), prefrontal cortex (PFC) (Kleen et al, 2011) and thalamus (Santos et al, 2000; Kubová et al, 2001) allowing the argument that the behavioral implications are broad, impacting the cognitive, and adaptive performance. In human condition, different neonatal conditions are likely to cause neurological damage e alter brain development.…”

The multimodal prospects for neuroprotection and disease modification in epilepsy: Relationship to its challenging neurobiology

“…Also, synaptic reorganization did not occur until after the third postnatal week (Haas et al, 2001;Wasterlain et al, 2002). Repeated episodes of pilocarpine-induced SE during post-natal days 7-9 did not result in abnormal distribution of neocortical inter-neurons at postnatal day 35 (da Silva et al, 2005). Some authors found occasional hippocampal damage in rats from the second post-natal week onwards but the pattern was different from that in adult rats, however, they suggested that this damage was not due to seizure itself but to the stress associated with seizure (Ribak et al, 1996).…”