Multiple Pilocarpine‐Induced Status Epilepticus in Developing Rats: A Long‐Term Behavioral and Electrophysiological Study

Abstract

Summary:Purpose: Animal models are useful for the study of status epilepticus (SE)-induced epileptogenesis and neurological sequelae, especially during early brain development. Here, we show several permanent abnormalities in animals subjected to multiple SE during early development.Methods: Wistar pup rats (7 to 9 days old) were subjected to three consecutive episodes of SE induced by systemic pilocarpine injections. To study the long-lasting consequences of early-induced SE, chronic electroencephalographic recordings were made from the hippocampus and cortex and several behavioral tests (inhibitory step-down avoidance, rota-rod, open field, elevated plus-maze, and Skinner box) were performed at postnatal days 30 to 90. We also investigated in vitro electrophysiological responses of the CA 1 area using extracellular recordings in hippocampal slices. A histological analysis was done using cresyl violet staining 24 hours and several months after SE induction. Apoptotic cell death was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL staining) 24 hours after the last SE episode.Results: Electroencephalographic recordings from 30-to 90-day-old rats that had been subjected to multiple SE episodes in early life showed marked changes compared with those from nontreated controls. These included frequent episodes of continuous complex spiking activity and high-voltage ictal discharges, with a small percentage of these rats presenting spontaneous behavioral seizures. These animals also presented evidence of severe cognitive deficit in adulthood. In vitro, a persistent hyperexcitability of the CAI area was detected in experimental animals. Histological analysis of the brains did not reveal any major long-term pathological changes. Nevertheless, an increased number of TUNEL-positive nuclei were present in some animals in both the hippocampus and the thalamus.Conclusions: These data show persistent abnormalities in animals subjected to multiple SE episodes during early postnatal development. SE may result in important plastic changes in critical periods of brain maturation leading to long-lasting epileptogenesis, as manifested by electrographic epileptiform discharges, behavioral deficits, and in vitro hyperexcitability of hippocampal networks.

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

“…These changes could underlie the behavioral deficits and generalized epileptic discharges observed in adulthood (15,16). The most prominent changes observed were (a) altered intracortical microcircuitry development; (b) anticipated PV immunoreactivity in neocortical interneurons; (c) increased GAD-65 immunoreactivity; and (d) altered neocortical apoptotic process.…”

“…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 hippocampal damage and complex partial seizures (17), developing rats treated at P7-9 develop generalized electrographic seizures without marked hippocampal damage (15,16). These findings suggest a diffuse involvement of the neocortical areas after neonatal (P7-9) seizures.…”

Postnatal Proteasome Inhibition Induces Neurodegeneration and Cognitive Deficiencies in Adult Mice: A New Model of Neurodevelopment Syndrome

“…Thus, rats exposed to neurotoxic compounds during the first few weeks of postnatal development display spontaneous recurrent seizure activity upon reaching adulthood, evident both behaviourally and in electroencephalographic analyses [8], [9]. Exposure to such toxins also provokes the formation of a hyperexcitable hippocampal network in vitro [10], [11]. Similarly, deprivation of maternal care during the first week of life provokes emotional and cognitive behavioural alterations in rodents that are ultimately manifested in adults [12].…”

Use of a new antiepileptic drug or an old one as first drug for treatment of absence epilepsy

“…Although status epilepticus early in life produces acute changes in terms of metabolic disturbances, it does not necessarily increase the probability to manifest spontaneous seizures later in life (Okada, et al 1984;Stafstrom, et al 1993;Santos, et al 2000;Roch, et al 2002;Raol et al 2003;Kubova, et al 2004;Raffo, et al 2004;Galanopoulou 2008). When spontaneous seizures are recorded, they are few (dos Santos, et al 2000;Raol et al 2003;Kubova et al 2004).…”

“…Multiple pilocarpine-induced episodes of status epilepticus in very young rats between 7 and 9 days of age are associated with the development of absence-like epilepsy later on (Ferreira, et al 2003) and these rats show less exploratory activity as well as memory and learning problems (Santos et al 2000). Neuroanatomical studies show no gross pathologic changes but there are progressive, subtle site-specific alterations of intracortical and hippocampal circuitries especially in the expression and the location of GABAergic neurons (da Silva, et al 2005).…”