Elsevier

Epilepsy & Behavior

Volume 29, Issue 1, October 2013, Pages 19-27
Epilepsy & Behavior

Prenatal transport stress, postnatal maternal behavior, and offspring sex differentially affect seizure susceptibility in young rats

https://doi.org/10.1016/j.yebeh.2013.06.017Get rights and content

Highlights

  • Innate seizure susceptibility is influenced by many prenatal and postnatal factors.

  • Transportation of dams during gestation modifies offspring characteristics.

  • Variations in maternal care appeared to impact litter health and pup seizure susceptibility.

  • Maternal care and seizure provocation are influenced by offspring sex.

  • Differential patterns of neuronal activation were more prominent in the ventral rather than in the dorsal hippocampus.

Abstract

Epilepsy is a heterogeneous and chronic neurological condition of undefined etiology in the majority of cases. Similarly, the pathogenesis of the unprovoked seizures that lead to epilepsy is not known. We are interested in the factors that modify inherent seizure susceptibility, with a particular focus on those occurring during the prenatal and early postnatal periods. Female Sprague–Dawley rats were bred in-house or transported during pregnancy at one of two gestational days (G9 or G16). The effects of transport stress, maternal behavior, and offspring sex were then examined in terms of how they were related to provoked seizure susceptibility to kainic acid (KA) or a model of febrile convulsions (FCs) on postnatal day 14 (P14). We also examined the pattern of neuronal activation in the hippocampus and amygdala as indicated by the density of FosB protein immunoreactivity (FosB-ir). Results demonstrated only a small and inconsistent effect of transport alone, suggesting that the groups differed slightly prior to experimental manipulations. However, the influence of maternal behaviors such as licking and grooming (LG), arched back nursing (ABN), and dam-off time (DO) exerted a much stronger effect on the offspring. Dams designated as high LG gave birth to smaller litters, had pups that weighed less, had greater seizure susceptibility and severity, and had more FosB-ir neurons predominantly in the ventral hippocampus and the medial subnucleus of the amygdala (MeA). We also found a sex-dependent effect such that P14 males were smaller than their female littermates and had a greater seizure susceptibility and severity. Taken together, these results suggest an impact of prenatal and postnatal factors, as well as sex, on seizure susceptibility in young animals.

Introduction

Pediatric epilepsy is a relatively common neurological disorder [1], and seizures are thought to affect approximately 2–5% of all children [2]. While there are a large number of recognized causal factors, a significant proportion of children with epilepsy still have an unknown etiology despite extensive investigations [3]. As such, many studies have focused on determining the factors underlying seizure susceptibility and epileptogenesis, necessitating the development of animal models.

Various strategies exist for development of these models including genetic manipulation, focal lesions, and brain injury (including various forms of insult such as chemical, electrical, or traumatic) to normal neural substrates, all in the pursuit of studying the process of acquired epilepsy [4]. Although highly informative, these models are not designed to examine either innate susceptibility or the process of spontaneous epileptogenesis, both of which imply that the process of neurodevelopment is compromised. In the present study, we examine the effects of altered neurodevelopment by manipulating critical perinatal factors (prenatal stress and postnatal maternal care) and assessing male and female offspring seizure susceptibility. Using such a neurodevelopmental approach, as opposed to models that utilize adult animals, provided much more power to make inferences about pediatric epilepsy; a phenomenon that has a well-described strong developmental stage specificity [5], [6], [7]. Further, a large percentage of studies restrict analysis to males, which is problematic for extrapolating findings to females as sex differences in many neurological disorders are now widely accepted [8], [9], [10].

Neural development proceeds according to a timed series of events [11]. Deviations from this programming result in aberrations of neurodevelopment ranging from structural abnormalities to cellular and subcellular functional impairment. Teratogenicity can result from a wide variety of factors that can be broadly divided into exogenous or endogenous etiologies. Endogenous teratogenicity can be further subdivided into factors related to maternal and fetal physiology and those related to maternal psychological factors. This is not a clean dichotomy as psychological stressors often involve a physiological response including activation of the hypothalamic–pituitary–adrenal axis [12]. While psychological stress undeniably affects the individual, studies have shown a significant impact of maternal psychological stress on fetal neurodevelopment in humans and animals (for reviews, see [13], [14]). Offspring effects are manifested as alterations in cognitive and behavioral function, as well as in structural and molecular changes in the brain [15], [16], [17], [18], [19]. The exact mechanisms underlying these effects are not fully known, but a role of the HPA axis and associated glucocorticoid release is supported by studies using administration of prenatal exogenous steroids noting similar changes in the neurobiology and behavior of the offspring [9]. However, as could be predicted, the changes associated with exogenous steroids are not exactly the same as those induced by exposure to stressors, a finding that may be a result of the latter also incorporating activation of the autonomic and immunological systems as part of the stress response.

Many different prenatal stress models have been used to examine developmental outcomes, all of which appear to have slightly different fetal and newborn outcomes. In another study in our lab, we examined the effect of prenatal immune challenge on newborn seizure susceptibility and found a significant difference in the seizure susceptibility of control postnatal day 14 (P14) pups as a function of the gestational timing of dam transport [20]. As this variable has significant potential to impact experimental outcomes, we sought to determine, more specifically, whether maternal-timed pregnant transport in and of itself modifies seizure susceptibility. We chose to focus on the effect of prenatal stress from a single day (gestational (G) day 9 or 16) as these two time points represent critical periods of brain development, hypothesizing that significant perturbations may induce different but long-lasting effects on neurodevelopment.

While prenatal stress is gaining a wider appreciation as a neurodevelopmental regulator, postnatal factors such as maternal behavior have also been shown to significantly impact neurodevelopment [6], [8], [21] and reshape prior experiences [22]. These effects have been noted at the cellular level as well as in terms of behavioral outcomes [22]. Although these effects have been largely investigated in animal models, the potential significance in human neurodevelopment is evident [15], [17]. However, the effect of the postnatal environment is also dependent somewhat on the prenatal experience not only in terms of the direct effect on the offspring but also with respect to the subsequent impact on maternal behavior [23]. Therefore, we monitored maternal behavior in all groups and analyzed its relationship to seizure susceptibility.

In summary, prior literature has clearly demonstrated that prenatal stress has the ability to significantly modify neurodevelopment. However, offspring outcomes have largely focused on behavioral, cognitive, or cellular changes, while less is known about the possible impact prenatal stress may have on seizure susceptibility and epilepsy. Therefore, we sought to investigate the sex-dependent effects of prenatal transport stress and postnatal maternal behavior on seizure susceptibility in P14 rat pups.

Section snippets

Animals and transport stress

Ten adult male and ten adult female Sprague–Dawley rats were ordered from Charles River (Quebec, Canada) prior to being bred in-house (IH). For IH bred dams, estrous cycle was determined daily (between 1030 h and 1100 h) with vaginal smears starting 2 days after arrival in the vivarium until 2 days before mating. The vaginal epithelial sample was collected and smeared on to SuperFrost slides, left at room temperature to dry, then fixed and stained using Diff-Quik staining kit (VWR, Canada). After

Control groups

There were no significant differences in litter size or pup weight as a function of maternal transport alone. However, other differences were noted in the pups at baseline and following stimuli (saline, LPS, KA, and FC) as determined by the amount of FosB-ir labeling (Figs. 1A and B). In the vDG (Fig. 1A), a significant difference was found between the transport groups [F(2,18) = 14.74, p < 0.01] where the IH baseline FosB-ir level was higher compared to G9 [t = 2.92, p < 0.05] and G16 [t = 5.36, p < 

Discussion

In this study, we initially sought to determine whether maternal transport during pregnancy affected seizure susceptibility of offspring. Because maternal behavior plays an important role in neurodevelopment, we also examined the moderating effect of various maternal behaviors on the same outcome. Our results suggest that transporting dams during gestation alters pup characteristics, compared to those of IH-bred dams from the same strain and supplier and may, therefore, impact further

Conclusion

In essence, our results suggest that several factors including prenatal maternal stress, postnatal maternal behavior, offspring sex, and the seizure induction model affect seizure susceptibility in young rats. Although a routinely carried out event, transportation of pregnant dams introduces significant variability into experimental studies involving offspring development, and in our study, it influenced litter pup characteristics and baseline FosB-ir. Even more pronounced than the prenatal

Acknowledgments

The authors would like to thank Kay Murphy and Donna Goguen for their technical assistance, as well as Drs. Aylin Reid, James Heida, and Lisa Wright for conceptual help in various portions of the study. The study was funded by the William Dennis Chair and Research Fund in Pediatric Epilepsy (MJE), an IWK research grant (MJE), an Alberta Children's Hospital research grant (MJE, QJP), the Dalhousie Medical Research Foundation (MJE), and the Heart and Stroke Foundation of New Brunswick (RWC).

References (62)

  • A.L. Vivinetto et al.

    Neurobiological effects of neonatal maternal separation and post-weaning environmental enrichment

    Behav Brain Res

    (2013)
  • L.C. Schmued et al.

    Fluoro-Jade C results in ultra high resolution and contrast labeling of degenerating neurons

    Brain Res

    (2005)
  • M. Kuwagata et al.

    Observation of fetal brain in rat valproate-induced autism model: a developmental neurotoxicity study

    Int J Dev Neurosci

    (2009)
  • M. DelCerro et al.

    Maternal care counteracts behavioral effects of prenatal environmental stress in female rats

    Behav Brain Res

    (2010)
  • M. Meaney et al.

    Maternal care as a model for experience-dependent chromatin plasticity?

    Trends Neurosci

    (2005)
  • C. Caldji et al.

    Variations in maternal care in infancy regulate the development of stress reactivity

    Biol Psychiatry

    (2000)
  • A. Harris et al.

    Glucocorticoids, prenatal stress and the programming of disease

    Horm Behav

    (2011)
  • M. Fanselow et al.

    Are the dorsal and ventral hippocampus functionally distinct structures?

    Neuron

    (2010)
  • P. Lee et al.

    Prenatal stress generates deficits in rat social behaviour: reversal by oxytocin

    Brain Res

    (2007)
  • H. Edwards et al.

    Prenatal stress alters seizure thresholds and the development of kindled seizures in infant and adult rats

    Horm Behav

    (2002)
  • M.M. Sadaghiani et al.

    Prenatal stress potentiates pilocarpine-induced epileptic behaviors in infant rats both time and sex dependently

    Epilepsy Behav

    (2010)
  • N. Young et al.

    Exogenous antenatal glucocorticoid treatment reduces susceptibility for hippocampal kindled and maximal electroconvulsive seizures in infant rats

    Exp Neurol

    (2006)
  • Y. Diz-Chaves et al.

    Prenatal stress increases the expression of proinflammatory cytokines and exacerbates the inflammatory response to LPS in the hippocampal formation of adult male mice

    Brain Behav Immun

    (2013)
  • E. Merlot et al.

    Prenatal stress, fetal imprinting and immunity

    Brain Behav Immun

    (2008)
  • S.A. Cavigelli et al.

    Within-litter variance in rat maternal behaviour

    Behav Process

    (2010)
  • F.N. van Hasselt et al.

    Within-litter variation in maternal care received by individual pups correlates with adolescent social play behaviour in male rats

    Physiol Behav

    (2012)
  • F.A. Champagne

    Maternal imprints and the origins of variation

    Horm Behav

    (2011)
  • F.A. Champagne

    Interplay between social experiences and the genome: epigenetic consequences for behavior

    Adv Genet

    (2012)
  • P. Banjeree et al.

    The descriptive epidemiology of epilepsy: a review

    Epilepsy Res

    (2009)
  • W. Hauser

    The prevalence and incidence of convulsive disorders in children

    Epilepsia

    (1994)
  • S. Shinnar et al.

    Update on the epidemiology and prognosis of pediatric epilepsy

    J Child Neurol

    (2002)
  • Cited by (0)

    View full text