Effect of neonatal isolation on outcome following neonatal seizures in rats—The role of corticosterone
Introduction
The immature brain is more susceptible to seizures yet less vulnerable to seizure-induced injury than the adult brain (Dube et al., 2001, Lai et al., 2002, Sarkisian et al., 1997, Schmid et al., 1999, Stafstrom et al., 1993). The patterns of neuronal injuries from seizures are age-specific; their extent and severity increase with age (Druga et al., 2005, Kubova et al., 2004, Sankar et al., 1998). Lithium-pilocarpine (Li-Pilo)-induced status epilepticus (SE) in adult rats produces the features of human temporal lobe epilepsy (TLE) in some aspects, such as hippocampal sclerosis. However, when SE is induced at postnatal day 10 (P10) – which is roughly equivalent to a human newborn (Romijn et al., 1991) – rats do not become epileptic (Dube et al., 2001, Priel et al., 1996) nor develop neuronal loss, interictal hypometabolism (Dube et al., 2000, Dube et al., 2001) or cognitive deficits (Zhang et al., 2004). While the immature brain appears to be less vulnerable to the adverse effects of prolonged seizures than the mature brain (Holmes et al., 2002), seizures early in life can be associated with later cognitive and behavioral disturbances, even in the absence of overt structural neuronal damage (Lynch et al., 2000, Majak and Pitkanen, 2004, Sayin et al., 2004, Stafstrom, 2002). In addition, Mathern et al. (1995) found that an initial precipitating injury, especially if occurring before age 5 years, was probably critical to the pathophysiological process of TLE. Given the increasing apparent age-specific brain damage from seizures, it is critical to determine under what circumstances early life seizures produce enduring neurological sequelae.
Considerable evidence demonstrates that the early environment modifies the development of hypothalamic–pituitary–adrenal (HPA) axis, subsequent brain function and behavior (Francis et al., 2002, Levine, 1994, Lissau and Sorensen, 1994, Liu et al., 1997, Matthews, 2002, McCormick et al., 1998, McEwen, 2000, Meaney, 2001, Plotsky and Meaney, 1993, Roceri et al., 2004, Weaver et al., 2004). Exposure of the developing brain to severe and/or prolonged stress may result in hyperactivity of the stress system with resultant hyperactivation of the HPA axis (upregulation of corticotrophin-releasing hormone (CRH) mRNA expression in the hypothalamus and amygdale) (Avishai-Eliner et al., 2002, Brunson et al., 2001, Hatalski et al., 1998, Plotsky and Meaney, 1993, Wadhwa et al., 2001), amygdala hyperfunction (fear reaction) (Meaney, 2001, Moriceau et al., 2004), and hippocampal dysfunction (defective glucocoticoid negative feedback, impaired learning and memory) (Liu et al., 1997; Matthews, 2002; McEwen, 2000). The importance of parental care as a mediator of the effects of early environmental adversity on neural development has been well established. In particular, normal maternal behavior is a key regulator during the stress hyporesponsive period (SHRP), lasting from neonatal day 2–3 until the second week of age, and influences the development of the HPA axis (Levine, 1994, Mathern et al., 1998, Sapolsky and Meaney, 1986, Weaver et al., 2004). Weaver et al. (2004) demonstrated that maternal behavior produces enduring alterations of DNA methylation at the glucocorticoid receptor (GR) gene promoter, and the offspring of mothers that exhibit less licking and grooming of pups, as adults, show less GR gene expression in the hippocampus, and an increase of plasma CORT response to acute stress. Furthermore, both early life stress and high CORT levels increase the risk for the development of seizures (Chadda and Devaud, 2004, Haut et al., 2003).
In most studies published to date, neonatal seizures have been induced in the experimental animals under normal handling and environmental conditions. For humans, most early life seizures occur in premature and sick neonates (Miller et al., 2002, Scher, 2003, Scher et al., 1993) who are hospitalized and separated from their mothers, usually in a stressful environment. We have previously showed that rats subjected to repetitive neonatal isolation (NI) can exacerbate cognitive deficits following recurrent seizures (Huang et al., 2002). The precise mechanism by which NI increases neuronal vulnerability to neonatal seizures is not clear. Although the stress response is a complex biochemical cascade involving the release of diverse chemicals that can affect various aspects of neuro-physiological processes, glucocorticoids (GCs) are thought to be the primary candidate for programming of the fetal HPA axis during early life experience (Matthews, 2002). In addition, excessive GCs increase neuronal vulnerability, particularly in the presence of concomitant excitatory challenges (Kaufer et al., 2004).
To address the importance of early life maternal–infant interaction on the development and vulnerability of the brain, we investigated the effects of NI on early life SE and explored the role of CORT on the pathogenesis of neurological sequelae associated with NI followed by seizures. In this study, we examined the influence of NI on plasma CORT levels at baseline and in response to seizures, and determined whether NI exacerbated neonatal seizure-induced long-term neurological damage, focusing on spatial learning and memory, and the hippocampal phosphorylated cyclic adenosine monophosphate (cAMP)-responsive element-binding protein at serine-133 (pCREBSer-133), an important transcription factor underlying learning and memory (Lonze and Ginty, 2002, Silva et al., 1998). Seizure thresholds, spontaneous seizures, and hippocampal neuronal loss were examined, too. We also evaluated whether the immediate suppression of the SE-induced rise in plasma CORT by metyrapone, a CORT synthesis inhibitor, can reverse the deleterious effects of NI on neonatal SE-induced long-term consequences.
Section snippets
Overview of experiments
To investigate whether NI compromises the developing brain following a prolonged seizure, and whether increased CORT after SE played a role in the deleterious effects of NI on SE, the rats were assigned randomly to five groups: control (CONT) rats, rats experiencing neonatal isolation (NI), rats subjected to Li-Pilo-induced SE (SE), rats subjected to NI plus SE (NIS), and a subset of NIS rats treated with metyrapone (NISM). We subjected rat pups to normal rearing (non-isolated) or NI (isolated)
Determine the test-dosage of metyrapone
In unpublished data, we found that that metyrapone given immediately after the induction of seizures exerted a pharmacological protection on cognitive deficits at both 100 mg/kg (NISM100) and 150 mg/kg (NISM150) with an optimal effect of 100 mg/kg, while metyrapone at 200 mg/kg (NISM200) had a mild detrimental effect. The time spent in the target quadrant (percentage) in the probe trial, a measure of strength of memory, was NIS = 28.02 ± 1.91%; NISM100 = 37.19 ± 2.70%; NISM150 = 35.2 ± 4.82%; NISM200 = 28.96 ±
Discussion
The current study presents evidence that NI increases the acute response of plasma CORT to SE, and subjects the immature brain to subsequent seizure-induced injury. First, the study demonstrates that the experience of NI does not influence the plasma CORT levels 24 h after the last isolation paradigm, but enhances the acute CORT response to SE. Second, sole NI or SE early in life does not result in enduring behavioral alterations or hippocampal neuronal loss. However, repeated NI prolongs
Acknowledgements
This study was supported by the National Science Council, Taiwan (NSC-93-2320-B-182A-003), National Heath Research Institute, Taiwan (NHRI-EX91-8909BP), National Institutes of Health, USA (NS27984 and NS44295). Chi-Mei Hospital, Taiwan, grant number: CMFHR9452, and Chang-Gung Memorial Hospital, Taiwan, grant number: CMRPG83044.
References (81)
- et al.
Stressed-out, or in (utero)?
Trends Neurosci.
(2002) - et al.
Sex differences in effects of mild chronic stress on seizure risk and GABAA receptors in rats
Pharmacol. Biochem. Behav.
(2004) - et al.
The functional anatomy and pathology of lithium-pilocarpine and high-dose pilocarpine seizures
Neuroscience
(1987) - et al.
Degenerative neuronal changes in the rat thalamus induced by status epilepticus at different developmental stages
Epilepsy Res.
(2005) - et al.
Progressive metabolic changes underlying the chronic reorganization of brain circuits during the silent phase of the lithium-pilocarpine model of epilepsy in the immature and adult rat
Exp. Neurol.
(2000) - et al.
Relationship between neuronal loss and interictal glucose metabolism during the chronic phase of the lithium-pilocarpine model of epilepsy in the immature and adult rat
Exp. Neurol.
(2001) Steroids, neuroactive steroids and neurosteroids in psychopathology
Prog. Neuropsychopharmacol. Biol. Psychiatr.
(2005)- et al.
Stress and epilepsy: a patient perception survey
Epilepsy Behav.
(2003) - et al.
Ontogenic study of lithium-pilocarpine-induced status epilepticus in rats
Brain Res.
(1992) - et al.
Seizure-induced damage in the developing human: relevance of experimental models
Prog. Brain Res.
(2002)
Long-term effects of early life malnutrition and status epilepticus: assessment by spatial navigation and CREBSer133 phosphorylation
Dev. Brain Res.
Cognitive performances and locomotor activity following dentate granule cell damage in rats: role of lesion extent and type of memory tested
Neurobiol. Learn Mem.
Recurrent bicuculline-induced seizures in rat pups cause long-term motor deficits and increase vulnerability to a subsequent insult
Epilepsy Behav.
Parental neglect during childhood and increased risk of obesity in young adulthood
Lancet
Suppression of hippocampal neurogenesis is associated with developmental stage, number of perinatal seizure episodes, and glucocorticoid level
Exp. Neurol.
Function and regulation of CREB family transcription factors in the nervous system
Neuron
The acute effects of corticosteroids on cognition: integration of animal and human model studies
Brain Res. Rev.
Early programming of the hypothalamo–pituitary–adrenal axis
Trend Endocrinol. Metab.
Corticosterone release in response to repeated, short episodes of neonatal isolation: evidence of sensitization
Int. J. Dev. Neurosci.
Effects of adverse experiences for brain structure and function
Biol. Psychiatr.
Corticosterone controls the developmental emergence of fear and amygdala to predator odors in infant rat pups
Int. J. Dev. Neurosci.
(−)-Nicotine ameliorates corticosterone's potentiation of N-methyl-d-aspartate receptor-mediated cornu ammonis 1 toxicity
Neuroscience
Early, postnatal experience alters hypothalamic corticotropin-releasing factor (CRF) mRNA, median eminence CRF content and stress-induced release in adult rats
Mol. Brain Res.
Modification of seizure activity by electrical stimulation. I. After-discharge threshold
Electroencephalogr. Clin. Neurophysiol.
Neonatal dexamethasone therapy: short- and long-term consequences
Trend Endocrinol. Metab.
Postnatal repeated maternal deprivation produces age-dependent changes of brain-derived neurotrophic factor expression in selected rat brain regions
Biol. Psychiatr.
At what ages is the developing cortex of the rat comparable to that of the full-term newborn baby?
Early Hum. Dev.
The memory-modulatory effects of glucocorticoids depend on an intact stria terminalis
Brain Res.
Neuroactive steroids: mechanisms of action and neuropsychopharmacological perspectives
Trends Neurosci.
Neonatal seizures and brain damage
Pediatr. Neurol.
Assessing the behavioral and cognitive effects of seizures on the developing brain
Prog. Brain Res.
Synergistic action of corticosterone on kainic acid-induced electrophysiological alterations in the hippocampus
Brain Res.
The neurobiology of stress in human pregnancy: implications for prematurity and development of the fetal central nervous system
Prog. Brain Res.
Lithium-pilocarpine-induced status epilepticus in immature rats result in long-term deficits in spatial learning and hippocampal cell loss
Neurosci. Lett.
Maternal deprivation in neonatal rats alters the expression of circadian system under light-dark cycles and restricted daily feeding in adulthood
Physiol. Behav.
Biosynthesis and metabolism of steroid hormones by human adrenal carcinomas
Braz. J. Med. Biol. Res.
Corticotropin (ACTH) acts directly on amygdala neurons to down-regulate corticotropin-releasing hormone gene expression
Ann. Neurol.
Circadian rhythm of corticosterone levels in rat brain
J. Endocrinol.
Long-term effects of status epilepticus in the immature brain are age- and model-specific
Epilepsia
Calorie restriction of a high-carbohydrate diet elevates the threshold of PTZ-induced seizures to values equal to those seen with a ketogenic diet
Epilepsy Res.
Cited by (64)
Sex differences in the developing brain impact stress-induced epileptogenicity following hyperthermia-induced seizures
2021, Neurobiology of DiseaseCitation Excerpt :However, not all patients with complex FS develop mTLE suggesting that other variables likely play a role in leading to epileptogenesis and mTLE. Environmental stressors, such as early life stress, are known to harbor persistent changes to the limbic system, including increased vulnerability to epileptogenesis (Huang et al., 2002; Jones et al., 2009; Kumar et al., 2011; Lai et al., 2006; Salzberg et al., 2007). Several animal models have shown that postnatal stress, through maternal separation or exogenous corticosterone administration, promote limbic epileptogenesis, possibly through HPA axis hyper-reactivity in adulthood (Huang et al., 2002; Koe et al., 2014).
Post-traumatic stress disorder (PTSD) in patients with epilepsy
2021, Epilepsy and BehaviorPre-clinical models of reward deficiency syndrome: A behavioral octopus
2020, Neuroscience and Biobehavioral ReviewsFebrile seizures and increased stress sensitivity in children: How it relates to seizure characteristics
2019, Epilepsy and Behavior