Neuropeptide-mediated excitability: a key triggering mechanism for seizure generation in the developing brain

The Interplay between the Hippocampus and Amygdala in Regulating Aberrant Hippocampal Neurogenesis during Protracted Abstinence from Alcohol Dependence

The development of alcohol dependence involves elevated anxiety, low mood, and increased sensitivity to stress, collectively labeled negative affect. Particularly interesting is the recent accumulating evidence that sensitized extrahypothalamic stress systems [e.g., hyperglutamatergic activity, blunted hypothalamic-pituitary-adrenal (HPA) hormonal levels, altered corticotropin-releasing factor signaling, and altered glucocorticoid receptor signaling in the extended amygdala] are evident in withdrawn dependent rats, supporting the hypothesis that pathological neuroadaptations in the extended amygdala contribute to the negative affective state. Notably, hippocampal neurotoxicity observed as aberrant dentate gyrus (DG) neurogenesis (neurogenesis is a process where neural stem cells in the adult hippocampal subgranular zone generate DG granule cell neurons) and DG neurodegeneration are observed in withdrawn dependent rats. These correlations between withdrawal and aberrant neurogenesis in dependent rats suggest that alterations in the DG could be hypothesized to be due to compromised HPA axis activity and associated hyperglutamatergic activity originating from the basolateral amygdala in withdrawn dependent rats. This review discusses a possible link between the neuroadaptations in the extended amygdala stress systems and the resulting pathological plasticity that could facilitate recruitment of new emotional memory circuits in the hippocampus as a function of aberrant DG neurogenesis.

Elevation of tau protein levels in the cerebrospinal fluid of children with West syndrome

PURPOSE

West syndrome is an epileptic encephalopathy with a poor developmental outcome. Tau protein levels in the cerebrospinal fluid (CSF) are reported to be markers of axonal damage and neurodegeneration. This study aimed to investigate axonal damage and the effects of adrenocorticotropic hormone (ACTH) therapy on axons in West syndrome, as measured by tau protein levels in CSF.

METHODS

Tau protein levels in CSF before and after ACTH therapy were determined by an enzyme-linked immunosorbent assay in 26 children with West syndrome. Of these 26 children, 18 were symptomatic, and 8 had a cryptogenic form of West syndrome. A group of 41 unaffected children was included in the study as a control group.

RESULTS

The levels of tau protein in CSF were significantly higher in children with West syndrome than in the control group, and these levels remained high after ACTH therapy. ACTH therapy was effective for 20 of the 26 children with West syndrome, and their CSF tau protein levels were significantly higher after ACTH therapy than before therapy.

CONCLUSION

Our results suggest that axonal damage occurs in West syndrome, as judged by tau protein levels in CSF.

Effects of HIV and early life stress on amygdala morphometry and neurocognitive function

Both HIV infection and high levels of early life stress (ELS) have been related to abnormalities in frontal-subcortical structures, yet the combined effects of HIV and ELS on brain structure and function have not been previously investigated. In this study we assessed 49 non-demented HIV-seropositive (HIV+) and 47 age-matched HIV-seronegative healthy control (HC) adults. Levels of ELS exposure were quantified and used to define four HIV-ELS groups: HC Low-ELS (N = 20); HC High-ELS (N = 27); HIV+ Low-ELS (N = 24); HIV+ High-ELS (N = 25). An automated segmentation tool measured volumes of brain structures known to show HIV-related or ELS-related effects; a brief neurocognitive battery was administered. A significant HIV-ELS interaction was observed for amygdala volumes, which was driven by enlargements in HIV+ High-ELS participants. The HIV+ High-ELS group also demonstrated significant reductions in psychomotor/processing speed compared with HC Low-ELS. Regression analyses in the HIV+ group revealed that amygdala enlargements were associated with higher ELS, lower nadir CD4 counts, and reduced psychomotor/processing speed. Our results suggest that HIV infection and high ELS interact to increase amygdala volume, which is associated with neurocognitive dysfunction in HIV+ patients. These findings highlight the lasting neuropathological influence of ELS and suggest that high ELS may be a significant risk factor for neurocognitive impairment in HIV-infected individuals.

Neurobehavioral risk is associated with gestational exposure to stress hormones

The developmental origins of disease or fetal programming model predict that early exposures to threat or adverse conditions have lifelong consequences that result in harmful outcomes for health. The maternal endocrine 'fight or flight' system is a source of programming information for the human fetus to detect threats and adjust their developmental trajectory for survival. Fetal exposures to intrauterine conditions including elevated stress hormones increase the risk for a spectrum of health outcomes depending on the timing of exposure, the timetable of organogenesis and the developmental milestones assessed. Recent prospective studies, reviewed here, have documented the neurodevelopmental consequences of fetal exposures to the trajectory of stress hormones over the course of gestation. These studies have shown that fetal exposures to biological markers of adversity have significant and largely negative consequences for fetal, infant and child emotional and cognitive regulation and reduced volume in specific brain structures.

Human amygdala development in the absence of species-expected caregiving

In altricial species, like the human, caregiver presence is necessary for typical emotional development. Children who have been raised in institutional care early in life experience caregiver deprivation and are at significantly elevated risk for emotional difficulties. The current manuscript examines the non-human and human literatures on amygdala development following caregiver deprivation and presents an argument that in the absence of the species-expected caregiver presence, human amygdala development exhibits rapid development and perhaps premature engagement that results in some of the emotional phenotypes observed following early institutional care.

Tuning synaptic transmission in the hippocampus by stress: the CRH system

To enhance survival, an organism needs to remember—and learn from—threatening or stressful events. This fact necessitates the presence of mechanisms by which stress can influence synaptic transmission in brain regions, such as hippocampus, that subserve learning and memory. A major focus of this series of monographs is on the role and actions of adrenal-derived hormones, corticosteroids, and of brain-derived neurotransmitters, on synaptic function in the stressed hippocampus. Here we focus on the contribution of hippocampus-intrinsic, stress-activated CRH-CRH receptor signaling to the function and structure of hippocampal synapses. Corticotropin-releasing hormone (CRH) is expressed in interneurons of adult hippocampus, and is released from axon terminals during stress. The peptide exerts time- and dose-dependent effects on learning and memory via modulation of synaptic function and plasticity. Whereas physiological levels of CRH, acting over seconds to minutes, augment memory processes, exposure to presumed severe-stress levels of the peptide results in spine retraction and loss of synapses over more protracted time-frames. Loss of dendritic spines (and hence of synapses) takes place through actin cytoskeleton collapse downstream of CRHR₁ receptors that reside within excitatory synapses on spine heads. Chronic exposure to stress levels of CRH may promote dying-back (atrophy) of spine-carrying dendrites. Thus, the acute effects of CRH may contribute to stress-induced adaptive mechanisms, whereas chronic or excessive exposure to the peptide may promote learning problems and premature cognitive decline.

Depression, stress, epilepsy and adult neurogenesis

Epilepsy and depression share an unusually high coincidence suggestive of a common etiology. Disrupted production of adult-born hippocampal granule cells in both disorders may contribute to this high coincidence. Chronic stress and depression are associated with decreased granule cell neurogenesis. Epilepsy is associated with increased production - but aberrant integration - of new cells early in the disease and decreased production late in the disease. In both cases, the literature suggests these changes in neurogenesis play important roles in their respective diseases. Aberrant integration of adult-generated cells during the development of epilepsy may impair the ability of the dentate gyrus to prevent excess excitatory activity from reaching hippocampal pyramidal cells, thereby promoting seizures. Effective treatment of a subset of depressive symptoms, on the other hand, may require increased granule cell neurogenesis, indicating that adult-generated granule cells can modulate mood and affect. Given the robust changes in adult neurogenesis evident in both disorders, competing effects on brain structure are likely. Changes in relative risk, disease course or response to treatment seem probable, but complex and changing patterns of neurogenesis in both conditions will require sophisticated experimental designs to test these ideas. Despite the challenges, this area of research is critical for understanding and improving treatment for patients suffering from these disorders.

Exposure to prenatal psychobiological stress exerts programming influences on the mother and her fetus

BACKGROUND/AIMS

Accumulating evidence from a relatively small number of prospective studies indicates that exposure to prenatal stress profoundly influences the developing human fetus with consequences that persist into childhood and very likely forever.

METHODS

Maternal/fetal dyads are assessed at ∼20, ∼25, ∼31 and ∼36 weeks of gestation. Infant assessments begin 24 h after delivery with the collection of cortisol and behavioral responses to the painful stress of the heel-stick procedure and measures of neonatal neuromuscular maturity. Infant cognitive, neuromotor development, stress and emotional regulation are evaluated at 3, 6 12 and 24 months of age. Maternal psychosocial stress and demographic information is collected in parallel with infant assessments. Child neurodevelopment is assessed with cognitive tests, measures of adjustment and brain imaging between 5 and 8 years of age.

RESULTS

Psychobiological markers of stress during pregnancy, especially early in gestation, result in delayed fetal maturation, disrupted emotional regulation and impaired cognitive performance during infancy and decreased brain volume in areas associated with learning and memory in 6- to 8-year-old children. We review findings from our projects that maternal endocrine alterations that accompany pregnancy and influence fetal/infant/child development are associated with decreased affective responses to stress, altered memory function and increased risk for postpartum depression.

CONCLUSIONS

Our findings indicate that the mother and her fetus both are influenced by exposure to psychosocial and biological stress. The findings that fetal and maternal programming occur in parallel may have important implications for long-term child development and mother/child interactions.

Early life stress enhancement of limbic epileptogenesis in adult rats: mechanistic insights

Background

Exposure to early postnatal stress is known to hasten the progression of kindling epileptogenesis in adult rats. Despite the significance of this for understanding mesial temporal lobe epilepsy (MTLE) and its associated psychopathology, research findings regarding underlying mechanisms are sparse. Of several possibilities, one important candidate mechanism is early life ‘programming’ of the hypothalamic-pituitary-adrenal (HPA) axis by postnatal stress. Elevated corticosterone (CORT) in turn has consequences for neurogenesis and cell death relevant to epileptogenesis. Here we tested the hypotheses that MS would augment seizure-related corticosterone (CORT) release and enhance neuroplastic changes in the hippocampus.

Methodology/Principal Findings

Eight-week old Wistar rats, previously exposed on postnatal days 2–14 to either maternal separation stress (MS) or control brief early handling (EH), underwent rapid amygdala kindling. We measured seizure-induced serum CORT levels and post-kindling neurogenesis (using BrdU). Three weeks post-kindling, rats were euthanized for histology of the hippocampal CA3c region (pyramidal cell counts) and dentate gyrus (DG) (to count BrdU-labelled cells and measure mossy fibre sprouting). As in our previous studies, rats exposed to MS had accelerated kindling rates in adulthood. Female MS rats had heightened CORT responses during and after kindling (p<0.05), with a similar trend in males. In both sexes total CA3c pyramidal cell numbers were reduced in MS vs. EH rats post-kindling (p = 0.002). Dentate granule cell neurogenesis in female rats was significantly increased post-kindling in MS vs. EH rats.

Conclusions/Significance

These data demonstrate that early life stress results in enduring enhancement of HPA axis responses to limbic seizures, with increased hippocampal CA3c cell loss and augmented neurogenesis, in a sex-dependent pattern. This implicates important candidate mechanisms through which early life stress may promote vulnerability to limbic epileptogenesis in rats as well as to human MTLE and its associated psychiatric disorders.

Evaluation of candidate genes from orphan FEB and GEFS+ loci by analysis of human brain gene expression atlases

Febrile seizures, or febrile convulsions (FEB), represent the most common form of childhood seizures and are believed to be influenced by variations in several susceptibility genes. Most of the associated loci, however, remain ‘orphan’, i.e. the susceptibility genes they contain still remain to be identified. Further orphan loci have been mapped for a related disorder, genetic (generalized) epilepsy with febrile seizures plus (GEFS+).

We show that both spatially mapped and ‘traditional’ gene expression data from the human brain can be successfully employed to predict the most promising candidate genes for FEB and GEFS+, apply our prediction method to the remaining orphan loci and discuss the validity of the predictions. For several of the orphan FEB/GEFS+ loci we propose excellent, and not always obvious, candidates for mutation screening in order to aid in gaining a better understanding of the genetic origin of the susceptibility to seizures.

Delta opioid receptors colocalize with corticotropin releasing factor in hippocampal interneurons

The hippocampal formation (HF) is an important site at which stress circuits and endogenous opioid systems intersect, likely playing a critical role in the interaction between stress and drug addiction. Prior study findings suggest that the stress-related neuropeptide corticotropin releasing factor (CRF) and the delta opioid receptor (DOR) may localize to similar neuronal populations within HF lamina. Here, hippocampal sections of male and cycling female adult Sprague-Dawley rats were processed for immunolabeling using antisera directed against the DOR and CRF peptide, as well as interneuron subtype markers somatostatin or parvalbumin, and analyzed by fluorescence and electron microscopy. Both DOR- and CRF-labeling was observed in interneurons in the CA1, CA3, and dentate hilus. Males and normal cycling females displayed a similar number of CRF immunoreactive neurons co-labeled with DOR and a similar average number of CRF-labeled neurons in the dentate hilus and stratum oriens of CA1 and CA3. In addition, 70% of DOR/CRF dual-labeled neurons in the hilar region co-labeled with somatostatin, suggesting a role for these interneurons in regulating perforant path input to dentate granule cells. Ultrastructural analysis of CRF-labeled axon terminals within the hilar region revealed that proestrus females have a similar number of CRF-labeled axon terminals that contain DORs compared to males but an increased number of CRF-labeled axon terminals without DORs. Taken together, these findings suggest that while DORs are anatomically positioned to modulate CRF immunoreactive interneuron activity and CRF peptide release, their ability to exert such regulatory activity may be compromised in females when estrogen levels are high.

Prenatal programming of human neurological function

The human placenta expresses the genes for proopiomelanocortin and the major stress hormone, corticotropin-releasing hormone (CRH), profoundly altering the "fight or flight" stress system in mother and fetus. As pregnancy progresses, the levels of these stress hormones, including maternal cortisol, increase dramatically. These endocrine changes are important for fetal maturation, but if the levels are altered (e.g., in response to stress), they influence (program) the fetal nervous system with long-term consequences. The evidence indicates that fetal exposure to elevated levels of stress hormones (i) delays fetal nervous system maturation, (ii) restricts the neuromuscular development and alters the stress response of the neonate, (iii) impairs mental development and increases fearful behavior in the infant, and (iv) may result in diminished gray matter volume in children. The studies reviewed indicate that fetal exposure to stress peptides and hormones exerts profound programming influences on the nervous system and may increase the risk for emotional and cognitive impairment.

Stress and epilepsy: multiple models, multiple outcomes

Human studies show a link between stress and epilepsy, with stress causing an increase in seizure frequency and severity in patients with epilepsy. Many different animal model systems have been used to better understand this connection and the possible mechanisms involved. This review highlights the results of such studies relating stress and seizure susceptibility, with a focus on the hypothalamic-pituitary-adrenal axis and its relationship to seizure generation. The effects of hypothalamic-pituitary-adrenal axis mediators, acute stress, chronic stress, and early life stress on the seizure phenotype are summarized. Results suggest that stress has both anticonvulsive and proconvulsive properties, depending on the animal strain and the stress/seizure induction paradigm used. Attempts to interpret the stress-epilepsy literature must take these variables into account. The growing availability of genetically modified mice that carry either human epilepsy mutations or mutations in stress pathway genes now provide the opportunity to examine the relationship between stress and epilepsy more directly.

An Etiological Model for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Kindling might represent a heuristic model for understanding the etiology of Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS). Kindling occurs when an organism is exposed repeatedly to an initially sub-threshold stimulus resulting in hypersensitivity and spontaneous seizure-like activity. Among patients with ME/CFS, chronically repeated low-intensity stimulation due to an infectious illness might cause kindling of the limbic-hypothalamic-pituitary axis. Kindling might also occur by high-intensity stimulation (e.g., brain trauma) of the limbic-hypothalamic-pituitary axis. Once this system is charged or kindled, it can sustain a high level of arousal with little or no external stimulus and eventually this could lead to hypocortisolism. Seizure activity may spread to adjacent structures of the limbic-hypothalamic-pituitary axis in the brain, which might be responsible for the varied symptoms that occur among patients with ME/CFS. In addition, kindling may also be responsible for high levels of oxidative stress, which has been found in patients with ME/CFS.

Electrophysiological insights into the enduring effects of early life stress on the brain

Increasing evidence links exposure to stress early in life to long-term alterations in brain function, which in turn have been linked to a range of psychiatric and neurological disorders in humans. Electrophysiological approaches to studying these causal pathways have been relatively underexploited. Effects of early life stress on neuronal electrophysiological properties offer a set of potential mechanisms for these susceptibilities, notably in the case of epilepsy. Thus, we review experimental evidence for altered cellular and circuit electrophysiology resulting from exposure to early life stress. Much of this work focuses on limbic long-term potentiation, but other studies address alterations in electrophysiological properties of ion channels, neurotransmitter systems, and the autonomic nervous system. We discuss mechanisms which may mediate these effects, including influences of early life stress on key components of brain synaptic transmission, particularly glutamate, GABA and 5-HT receptors, and influences on neuroplasticity (primarily neurogenesis and synaptic density) and on neuronal network activity. The existing literature, although small, provides strong evidence that early life stress induces enduring, often robust effects on a range of electrophysiological properties, suggesting further study of enduring effects of early life stress employing electrophysiological methods and concepts will be productive in illuminating disease pathophysiology.

The role of inflammation in epilepsy

Epilepsy is the third most common chronic brain disorder, and is characterized by an enduring predisposition to generate seizures. Despite progress in pharmacological and surgical treatments of epilepsy, relatively little is known about the processes leading to the generation of individual seizures, and about the mechanisms whereby a healthy brain is rendered epileptic. These gaps in our knowledge hamper the development of better preventive treatments and cures for the approximately 30% of epilepsy cases that prove resistant to current therapies. Here, we focus on the rapidly growing body of evidence that supports the involvement of inflammatory mediators-released by brain cells and peripheral immune cells-in both the origin of individual seizures and the epileptogenic process. We first describe aspects of brain inflammation and immunity, before exploring the evidence from clinical and experimental studies for a relationship between inflammation and epilepsy. Subsequently, we discuss how seizures cause inflammation, and whether such inflammation, in turn, influences the occurrence and severity of seizures, and seizure-related neuronal death. Further insight into the complex role of inflammation in the generation and exacerbation of epilepsy should yield new molecular targets for the design of antiepileptic drugs, which might not only inhibit the symptoms of this disorder, but also prevent or abrogate disease pathogenesis.

Gestational stress influences cognition and behavior

The developmental origins of disease or fetal programming model predicts that early exposures to threat or adverse conditions have lifelong consequences that result in harmful outcomes for health. The vast majority of the studies in support of the programming model in human beings are retrospective and most rely on surrogate measures of early experience such as birth weight or preterm birth. Recently, a small number of prospective studies have been reported that have documented the developmental consequences of exposures to stressful intrauterine conditions. These studies of gestational stress have clearly shown that fetal exposures to psychosocial and/or biological markers of adversity have significant and largely negative consequences for fetal, infant and child neurological development. Fetal exposure to stress, especially early in gestation, results in delayed fetal maturation and impaired cognitive performance during infancy and results in decreased brain volume in areas associated with learning and memory in children. The accumulating evidence supports the conclusion that fetal exposure to stress profoundly influences the nervous system, with consequences that persist into childhood and perhaps beyond.

Maternal separation modulates short-term behavioral and physiological indices of the stress response

Early-life stress produces an anxiogenic profile in adulthood, presumably by activating the otherwise quiescent hypothalamic-pituitary-adrenal (HPA) axis during the vulnerable 'stress hyporesponsive period'. While the long-term effects of such early-life manipulations have been extensively characterized, little is known of the short-term effects. Here, we compared the short-term effects of two durations of maternal separation stress and one unseparated group (US) on behavioral and physiological indices of the stress response in rat pups. Separations included 3h on each of 12days, from postnatal day (PND) 2 to 13 (MS2-13) and 3days of daily, 6-h separation from PND11-13 (MS11-13). On PND14 (Experiment 1), both MS2-13 and MS11-13 produced marked reductions in freezing toward an adult male conspecific along with reduced levels of glucocorticoid type 2 (GR) and CRF type-1 (CRF(1)) receptor mRNA in the hippocampus. Group MS2-13 but not MS11-13 produced deficits in stressor-induced corticosterone secretion, accompanied by reductions in body weight. Our results suggest that GR and/or CRF(1) levels, not solely the magnitude of corticosterone secretion, may be involved in the modulation of freezing. In a second experiment, we aimed to extend these findings by testing male and female separated and unseparated pups' unconditioned defensive behaviors to cat odor on PND26, and subsequent cue+context conditioning and extinction throughout postnatal days 27-32. Our results show that maternal separation produced reductions in unconditioned freezing on PND26, with MS2-13 showing stronger deficits than MS11-13. However, separation did not affect any other defensive behaviors. Furthermore, separated rats failed to show conditioned freezing, although they did avoid the no-odor block conditioned cue. There were no sex differences other than weight. We suggest that maternal separation may have produced these changes by disrupting normal development of hippocampal regions involved in olfactory-mediated freezing, not in mechanisms of learning and memory per se. These findings may have direct relevance for understanding the mechanisms by which early-life adverse experiences produce short-term and lasting psychopathologies.

Neurobehavioral consequences of stressor exposure in rodent models of epilepsy

Both normal, non-epileptic as well as seizure-prone rodents exhibit a spectrum of anxiogenic-like behaviors in response to stressor exposure. Comparative analysis reveals that the same set of emotionality dependent measures is sensitive to both stress reactivity in normal rodents as well as stress hyperreactivity typically seen in seizure-prone rodents. A variety of unconditioned, exploratory tasks reflect global sensitivity to stressor exposure in the form of behavioral inhibition of locomotor output. Moreover, well chosen stressors can trigger de novo seizures with or without a history of seizure incidence. Seizures may be elicited in response to stressful environmental stimuli such as noxious noises, tail suspension handling, or home cage disturbance. Stress reactivity studies in rodents with a genetic predisposition to seizures have yielded important clues regarding brain substrates that mediate seizure ontogeny and modulate ictogenesis. Brains of seizure susceptible rodents reflect elevated content of the stress-related neuropeptide, corticotropin-releasing factor (CRF) in several nuclei relative to non-susceptible controls and neutralization of brain CRF attenuates seizure sensitivity. Findings outlined in this review support a diathesis-stress hypothesis in which behavioral- and neuro-pathologies of genetically seizure susceptible rodents arise in part due to multifaceted hyperreactivity to noxious environmental stimuli.

Go "West," young man...The quest for animal models of infantile spasms (West syndrome)

Model of Infantile Spasms Induced by N-methyl-D-aspartic Acid in Prenatally Impaired Brain. Velisek L, Jehle K, Asche S, Veliskova J. Ann Neurol 2007;61(2):109–119. OBJECTIVE: Infantile spasms (a catastrophic epileptic syndrome of childhood) are insensitive to classic antiepileptic drugs. New therapies are limited by lack of animal models. Here we develop a new model of flexion spasms based on prenatal exposure to betamethasone combined with postnatal administration of N-methyl-D-aspartic acid (NMDA) and determine brain structures involved in the induction of flexion spasms. METHODS: Pregnant rats received two doses of betamethasone on day 15 of gestation. Offspring was injected with NMDA on postnatal day 15. Effects of adrenocorticotropin therapy on the development of age-specific flexion spasms were determined and electroencephalographic correlates recorded. C-fos immunohistochemistry and [14C]2-deoxyglucose imaging identified brain structures involved in the development of flexion spasms. RESULTS: Prenatal betamethasone exposure sensitizes rats to development of NMDA-induced spasms and, most importantly, renders the spasms sensitive to adrenocorticotropin therapy. Ictal electroencephalogram results correspond to human infantile spasms: electrodecrement or afterdischarges were observed. Imaging studies defined three principal regions involved in NMDA spasms: limbic areas (except the dorsal hippocampus), hypothalamus, and the brainstem. INTERPRETATION: Despite certain limitations, our new model correlates well with current infantile spasm hypotheses and opens an opportunity for development and testing of new effective drugs.

Interictal cerebral blood flow abnormality in cryptogenic West syndrome

PURPOSE

To elucidate the abnormality of interictal regional cerebral blood flow (rCBF) of West syndrome at the onset.

METHODS

Quantitative measurement of rCBF with an autoradiography method using N-isopropyl-((123)I) p-iodoamphetamine single photon emission computed tomography (SPECT) was performed on 14 infants with cryptogenic West syndrome. Regions of interest (ROIs) for rCBF were placed automatically using an automated ROI analysis software (three-dimensional stereotactic ROI template), and were grouped into 12 segments: callosomarginal, precentral, central, parietal, angular, temporal, posterior cerebral, pericallosal, lenticular nucleus, thalamus, hippocampus, and cerebellum. We compared rCBF between the patients and seven age-matched infants with cryptogenic focal epilepsy as a control group. The patients were divided into two groups according to the duration from onset to SPECT, to compare rCBF.

RESULTS

Quantitative analysis revealed cerebral hypoperfusion in cryptogenic West syndrome with normal SPECT images under visual inspection. In bilateral central, posterior cerebral, pericallosal, lenticular nucleus, and hippocampus, and in the left parietal, temporal, and cerebellum, and in the right angular and thalamus segments there were statistical differences (p < 0.05). Compared with the duration from onset to SPECT, there were no significant differences of rCBF in all segments.

DISCUSSION

Broad cerebral hypoperfusion with posterior predominance involving the hippocampus and lenticular nucleus implies that even cryptogenic West syndrome has a widespread cerebral dysfunction at least transiently, which would correspond to clinical manifestations of hypsarrhythmia and epileptic spasms. Hippocampal hypoperfusion suggests the dysfunction of hippocampal circuitry in the brain adrenal axis, and may contribute to subsequent cognitive impairment of cryptogenic West syndrome.

A review of adversity, the amygdala and the hippocampus: a consideration of developmental timing

A review of the human developmental neuroimaging literature that investigates outcomes following exposure to psychosocial adversity is presented with a focus on two subcortical structures – the hippocampus and the amygdala. Throughout this review, we discuss how a consideration of developmental timing of adverse experiences and age at measurement might provide insight into the seemingly discrepant findings across studies. We use findings from animal studies to suggest some mechanisms through which timing of experiences may result in differences across time and studies. The literature suggests that early life may be a time of heightened susceptibility to environmental stressors, but that expression of these effects will vary by age at measurement.

High pregnancy anxiety during mid-gestation is associated with decreased gray matter density in 6-9-year-old children

Because the brain undergoes dramatic changes during fetal development it is vulnerable to environmental insults. There is evidence that maternal stress and anxiety during pregnancy influences birth outcome but there are no studies that have evaluated the influence of stress during human pregnancy on brain morphology. In the current prospective longitudinal study we included 35 women for whom serial data on pregnancy anxiety was available at 19 (+/-0.83), 25 (+/-0.9) and 31 (+/-0.9) weeks gestation. When the offspring from the target pregnancy were between 6 and 9 years of age, their neurodevelopmental stage was assessed by a structural MRI scan. With the application of voxel-based morphometry, we found regional reductions in gray matter density in association with pregnancy anxiety after controlling for total gray matter volume, age, gestational age at birth, handedness and postpartum perceived stress. Specifically, independent of postnatal stress, pregnancy anxiety at 19 weeks gestation was associated with gray matter volume reductions in the prefrontal cortex, the premotor cortex, the medial temporal lobe, the lateral temporal cortex, the postcentral gyrus as well as the cerebellum extending to the middle occipital gyrus and the fusiform gyrus. High pregnancy anxiety at 25 and 31 weeks gestation was not significantly associated with local reductions in gray matter volume.This is the first prospective study to show that a specific temporal pattern of pregnancy anxiety is related to specific changes in brain morphology. Altered gray matter volume in brain regions affected by prenatal maternal anxiety may render the developing individual more vulnerable to neurodevelopmental and psychiatric disorders as well as cognitive and intellectual impairment.

Neonatal seizures: an update on mechanisms and management

The lifespan risk of seizures is highest in the neonatal period. Current therapies have limited efficacy. Although the treatment of neonatal seizures has not changed significantly in the last several decades, there has been substantial progress in understanding developmental mechanisms that influence seizure generation and responsiveness to anticonvulsants. This article provides an overview of current approaches to the diagnosis and treatment of neonatal seizures, and some of the recent insights about the pathophysiology of neonatal seizures that may provide the foundation for better treatment are identified.

Early life stress as an influence on limbic epilepsy: an hypothesis whose time has come?

The pathogenesis of mesial temporal lobe epilepsy (MTLE), the most prevalent form of refractory focal epilepsy in adults, is thought to begin in early life, even though seizures may not commence until adolescence or adulthood. Amongst the range of early life factors implicated in MTLE causation (febrile seizures, traumatic brain injury, etc.), stress may be one important contributor. Early life stress is an a priori agent deserving study because of the large amount of neuroscientific data showing enduring effects on structure and function in hippocampus and amygdala, the key structures involved in MTLE. An emerging body of evidence directly tests hypotheses concerning early life stress and limbic epilepsy: early life stressors, such as maternal separation, have been shown to aggravate epileptogenesis in both status epilepticus and kindling models of limbic epilepsy. In addition to elucidating its influence on limbic epileptogenesis itself, the study of early life stress has the potential to shed light on the psychiatric disorder that accompanies MTLE. For many years, psychiatric comorbidity was viewed as an effect of epilepsy, mediated psychologically and/or neurobiologically. An alternative – or complementary – perspective is that of shared causation. Early life stress, implicated in the pathogenesis of several psychiatric disorders, may be one such causal factor. This paper aims to critically review the body of experimental evidence linking early life stress and epilepsy; to discuss the direct studies examining early life stress effects in current models of limbic seizures/epilepsy; and to suggest priorities for future research.

The neuro-symphony of stress

The impact of stress on brain function is increasingly recognized. Various substances are released in response to stress and can influence distinct neuronal circuits, but the functional advantages of having such a diversity of stress mediators remain unclear. Individual neurotransmitter, neuropeptide and steroid stress mediators have specific spatial and temporal niches, but these niches also overlap. In addition, the effects of individual mediators on neuronal function and plasticity are integrated, and emerging evidence suggests that there is crosstalk between them. Together, this results in the stress instruments producing an orchestrated 'symphony' that enables fine-tuned responses to diverse challenges.

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

ACTH therapy in refractory generalized epilepsy

Adrenocorticotropic hormone (ACTH) has a long track record for the treatment of infantile spasms. However, there is paucity of data on the use of ACTH in the treatment of epilepsy beyond infantile spasms. We report the use of ACTH in two children with refractory generalized epilepsy. Both patients responded well. ACTH may be considered as a useful adjunctive therapy in patients with intractable generalized seizures. Side effects and cost however, remain important concerns.

Kindling and Oxidative Stress as Contributors to Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) is one of the more complex illnesses involving multiple systems within the body. Onset of ME/CFS frequently occurs quickly, and many patients report a prior exposure to a viral infection. This debilitating illness can affect the immune, neuroendocrine, autonomic, and neurologic systems. Abnormal biological findings among some patients have included aberrant ion transport and ion channel activity, cortisol deficiency, sympathetic nervous system hyperactivity, EEG spike waves, left ventricular dysfunction in the heart, low natural killer cell cytotoxicity, and a shift from Th1 to Th2 cytokines. We propose that the kindling and oxidative stress theories provide a heuristic template for better understanding the at times conflicting findings regarding the etiology and pathophysiology of this illness.

Postnatal inflammation increases seizure susceptibility in adult rats

There are critical postnatal periods during which even subtle interventions can have long-lasting effects on adult physiology. We asked whether an immune challenge during early postnatal development can alter neuronal excitability and seizure susceptibility in adults. Postnatal day 14 (P14) male Sprague Dawley rats were injected with the bacterial endotoxin lipopolysaccharide (LPS), and control animals received sterile saline. Three weeks later, extracellular recordings from hippocampal slices revealed enhanced field EPSP slopes after Schaffer collateral stimulation and increased epileptiform burst-firing activity in CA1 after 4-aminopyridine application. Six to 8 weeks after postnatal LPS injection, seizure susceptibility was assessed in response to lithium-pilocarpine, kainic acid, and pentylenetetrazol. Rats treated with LPS showed significantly greater adult seizure susceptibility to all convulsants, as well as increased cytokine release and enhanced neuronal degeneration within the hippocampus after limbic seizures. These persistent increases in seizure susceptibility occurred only when LPS was given during a critical postnatal period (P7 and P14) and not before (P1) or after (P20). This early effect of LPS on adult seizures was blocked by concurrent intracerebroventricular administration of a tumor necrosis factor alpha (TNFalpha) antibody and mimicked by intracerebroventricular injection of rat recombinant TNFalpha. Postnatal LPS injection did not result in permanent changes in microglial (Iba1) activity or hippocampal cytokine [IL-1beta (interleukin-1beta) and TNFalpha] levels, but caused a slight increase in astrocyte (GFAP) numbers. These novel results indicate that a single LPS injection during a critical postnatal period causes a long-lasting increase in seizure susceptibility that is strongly dependent on TNFalpha.

Prenatal stress and epilepsy in later life: a nationwide follow-up study in Denmark

PURPOSE

To examine whether prenatal exposure to maternal bereavement is associated with an increased risk of epilepsy in the first decades of life.

METHODS

We conducted a population-based cohort study of children (N=1,553,966) born in Denmark from 1978 to 2004. A total of 39,867 children born to women who lost a close relative while pregnant or within 1 year before the pregnancy were included in the exposed cohort. The main outcome of interest was hospitalization due to epilepsy (ICD 8 codes 345.00-345.99, ICD 10 codes G40.0-G41.9). We used log-linear Poisson models to estimate incidence rate ratios (IRRs).

RESULTS

The exposed children had a risk of epilepsy similar to that of unexposed children (IRR 1.06, 95% CI 0.96-1.18). The IRRs were 1.08 (95% CI 0.89-1.31) for the children of women who lost a child, and 1.02 (95% CI 0.91-1.15) for the children of women who lost a partner, parent or sibling. The IRRs did not differ according to the timing of exposure or the causes of death (unexpected causes and other causes).

CONCLUSIONS

Our data do not suggest any strong association between prenatal stress and epilepsy in the first decades of life.

Behavioral measures in animal studies: relevance to patients with epilepsy

The relevance of behavioral endpoints in animal seizure models to clinical epilepsy is outlined and enhanced in the present review by linking specific preclinical dependent measures with a quality-of-life scale that serves as an index of the health and welfare of patients with epilepsy (Quality of Life in Epilepsy inventory). This preclinical-to-clinical translation is possible based on existing literature within at least three behavioral domains: (1) physical and motor actions, (2) affective and emotional responses to environmental challenge, and (3) social, sexual, and parental functions. Face valid commonalities in observable behaviors are emphasized with the goal of engaging basic and applied researchers in collaborative research projects to accelerate the pace of discovery in the behavioral phenotyping of epilepsy field.

Role of brain inflammation in epileptogenesis

Inflammation is known to participate in the mediation of a growing number of acute and chronic neurological disorders. Even so, the involvement of inflammation in the pathogenesis of epilepsy and seizure-induced brain damage has only recently been appreciated. Inflammatory processes, including activation of microglia and astrocytes and production of proinflammatory cytokines and related molecules, have been described in human epilepsy patients as well as in experimental models of epilepsy. For many decades, a functional role for brain inflammation has been implied by the effective use of anti-inflammatory treatments, such as steroids, in treating intractable pediatric epilepsy of diverse causes. Conversely, common pediatric infectious or autoimmune diseases are often accompanied by seizures during the course of illness. In addition, genetic susceptibility to inflammation correlated with an increased risk of epilepsy. Mounting evidence thus supports the hypothesis that inflammation may contribute to epileptogenesis and cause neuronal injury in epilepsy. We provide an overview of the current knowledge that implicates brain inflammation as a common predisposing factor in epilepsy, particularly childhood epilepsy.

The central corticotropin releasing factor system during development and adulthood

Corticotropin releasing factor (CRH) has been shown to contribute critically to molecular and neuroendocrine responses to stress during both adulthood and development. This peptide and its receptors are expressed in the hypothalamus, as well as in limbic brain areas including amygdala and hippocampus. This is consistent with roles for CRH in mediating the influence of stress on emotional behavior and cognitive function. The expression of CRH and of its receptors in hypothalamus, amygdala and hippocampus is age-dependent, and is modulated by stress throughout life (including the first postnatal weeks). Uniquely during development, the cardinal influence of maternal care on the central stress response governs the levels of central CRH expression, and may alter the 'set-point' of CRH-gene sensitivity to stress in a lasting manner.

Seizure susceptibility and locus ceruleus activation are reduced following environmental enrichment in an animal model of epilepsy

Alterations in the complexity of social and physical housing environments modulate seizure susceptibility in animal models of epilepsy. The studies described here tested the hypothesis that environmental enrichment would delay seizure onset in the epileptic (El) mouse. Neural activation measured via cFos expression, accumulation of the stress neuropeptide corticotropin-releasing factor (CRF), and behavioral seizure susceptibility were quantified in El mice to better understand the mechanisms of ictogenesis. Enrichment housing of El mice from Postnatal Days 21 to 49 produced a 100% decrease in seizure susceptibility relative to El controls. cFos expression increased in the primary motor cortex, locus ceruleus, and hippocampus of El mice relative to ddY controls, an effect attenuated by enrichment housing. CRF levels were elevated by enrichment in the hippocampus of ddY mice only. This study provides evidence that enrichment housing delays the onset of seizure susceptibility in El mice while altering the neuronal and stress-related responses in seizure-associated regions of the El brain.

GABA: a pioneer transmitter that excites immature neurons and generates primitive oscillations

Developing networks follow common rules to shift from silent cells to coactive networks that operate via thousands of synapses. This review deals with some of these rules and in particular those concerning the crucial role of the neurotransmitter gamma-aminobuytric acid (GABA), which operates primarily via chloride-permeable GABA(A) receptor channels. In all developing animal species and brain structures investigated, neurons have a higher intracellular chloride concentration at an early stage leading to an efflux of chloride and excitatory actions of GABA in immature neurons. This triggers sodium spikes, activates voltage-gated calcium channels, and acts in synergy with NMDA channels by removing the voltage-dependent magnesium block. GABA signaling is also established before glutamatergic transmission, suggesting that GABA is the principal excitatory transmitter during early development. In fact, even before synapse formation, GABA signaling can modulate the cell cycle and migration. The consequence of these rules is that developing networks generate primitive patterns of network activity, notably the giant depolarizing potentials (GDPs), largely through the excitatory actions of GABA and its synergistic interactions with glutamate signaling. These early types of network activity are likely required for neurons to fire together and thus to "wire together" so that functional units within cortical networks are formed. In addition, depolarizing GABA has a strong impact on synaptic plasticity and pathological insults, notably seizures of the immature brain. In conclusion, it is suggested that an evolutionary preserved role for excitatory GABA in immature cells provides an important mechanism in the formation of synapses and activity in neuronal networks.

The acceleration of amygdala kindling epileptogenesis by chronic low-dose corticosterone involves both mineralocorticoid and glucocorticoid receptors

We have previously demonstrated that low-dose corticosterone (CS) administration, used as a model of the effect of chronic stress, accelerates epileptogenesis in the electrical amygdala kindling rat model of temporal lobe epilepsy (TLE). This current study examined the relative contributions to this effect of mineralocorticoid (MR) and glucocorticoid (GR) subtypes of glucocorticoid receptors. Female non-epileptic wistar rats 10-13 weeks of age were implanted with a bipolar electrode into the left amygdala. Five treatment groups were subjected to rapid amygdala kindling: water-control (n=9), CS treated (6 mg/100 ml added to drinking water; n=9), CS+spironolactone (MR antagonist, 50 mg/kg sc; n=9), CS+mifepristone (GR antagonist, 25 mg/kg sc; n=9), and CS+both antagonists (n=7). Rats were injected with vehicle or the relevant antagonist twice daily for the entire kindling period. Experimental groups differed significantly in the number of stimulations required to reach the 'fully kindled state' (Racine, 1972) ANOVA, F(4,38)=2.73, p=0.04). Amygdala kindling was accelerated in the CS-treated group compared with water controls (mean stimulations for full kindling: 45.2 vs. 86.5, p<0.01). This acceleration was inhibited by both the MR and GR antagonist treatments (mean stimulations: 69.6 and 70.4, p=0.04 and 0.04 vs. CS group, respectively), with the kindling rates in these groups not significantly different from water-treated subjects (p=0.26 and 0.29, respectively). The kindling rates in the MR and GR antagonist treatment groups did not significantly differ from each other (p=0.93), nor from the combined treatment group (mean stimulations: 62.8, p=0.59 and 0.54, respectively). This study demonstrates that activation of both high-affinity (MR) and low-affinity (GR) glucocorticoid receptors are involved in mediating CS-induced acceleration of amygdala kindling epileptogenesis.

Acute stress increases interstitial fluid amyloid-beta via corticotropin-releasing factor and neuronal activity

Aggregation of the amyloid-beta (Abeta) peptide in the extracellular space of the brain is critical in the pathogenesis of Alzheimer's disease. Abeta is produced by neurons and released into the brain interstitial fluid (ISF), a process regulated by synaptic activity. To determine whether behavioral stressors can regulate ISF Abeta levels, we assessed the effects of chronic and acute stress paradigms in amyloid precursor protein transgenic mice. Isolation stress over 3 months increased Abeta levels by 84%. Similarly, acute restraint stress increased Abeta levels over hours. Exogenous corticotropin-releasing factor (CRF) but not corticosterone mimicked the effects of acute restraint stress. Inhibition of endogenous CRF receptors or neuronal activity blocked the effects of acute stress on Abeta. Thus, behavioral stressors can rapidly increase ISF Abeta through neuronal activity in a CRF-dependent manner, and the results suggest a mechanism by which behavioral stress may affect Alzheimer's disease pathogenesis.

Neuropeptide Y: potential role in recurrent developmental seizures

Seizures induce profound plastic changes in the brain, including altered expression of neuropeptide Y (NPY) and its receptors. Here, I discuss a potential role of NPY plasticity in the developmental brain: in a rat model of febrile seizures (FS), the most common type of seizures in infants and young children, NPY expression was up-regulated in hippocampus after experimentally induced FS. Interestingly, NPY up-regulation was associated with an increased seizure threshold for additional (recurrent) FS, and this effect was abolished when an antagonist against NPY receptor type 2 was applied. These findings suggest that inhibitory actions of NPY, released after seizures, exert a protective effect that reduces the risk of seizure recurrence in the developing brain.

Antisocial and seizure susceptibility phenotypes in an animal model of epilepsy are normalized by impairment of brain corticotropin-releasing factor

Social interaction phenotyping is an unexplored niche in animal modeling of epilepsy despite the sensitivity of affiliative behaviors to emotionality and stress, which are known seizure triggers. Thus, the present studies examined the social phenotype of seizure-susceptible El and nonsusceptible ddY strains both in untreated animals and following preexposure to a handling stressor. The second aim of the present studies was to evaluate the dependence of sociability in El mice on the proconvulsive, stress neuropeptide corticotropin-releasing factor (CRF) using CRF-SAP, a conjugate of CRF and the toxin saporin, which selectively reduced CRF peptide levels in the basolateral amygdala of El mice. El mice exhibited lower social investigation times than ddY counterparts, whereas central administration of CRF-SAP normalized social investigation times relative to ddY controls. Moreover, handling-induced seizures in El mice were reduced by 50% following treatment with CRF-SAP relative to saporin alone-injected El controls. The results of this study suggest that tonically activated CRF systems in the El mouse brain suppress affiliative behavior and facilitate evoked seizures.

Neural, endocrine and electroencephalographic hyperreactivity to human contact: a diathesis-stress model of seizure susceptibility in El mice

The El mouse strain provides a non-induced model of idiopathic, multifactorial epilepsy in which seizures are elicited in response to stressful environmental stimuli such as tail suspension handling. In the present studies, genetically seizure susceptible El and non-susceptible ddY control mice were exposed to tail suspension, foot-shock and social stressors in order to test the hypothesis that neural and physiological responses to such stimuli would be exaggerated in the El strain. The first experiment assessed neural cell density, stress neuropeptide (corticotropin releasing factor--CRF) levels, and plasma corticosterone activation in El and ddY mice in an unhandled control condition or following exposure to tail suspension or foot-shock stressors. The second experiment assessed brain electroencephalographic activity using telemetrically monitored skull surface electrodes in El and ddY mice exposed to tail suspension or social interaction stressors. Assessment of El mouse brains revealed higher cell counts in amygdala and elevated CRF peptide content in the paraventricular thalamic nucleus relative to ddY controls. El mice exhibited significantly elevated plasma corticosterone levels 60 min following exposure to tail suspension and foot-shock stressors relative to ddY controls. Finally, El mice exhibited significantly elevated brain electroencephalographic (1-4 Hz) activity in response to tail suspension, but not social interaction, relative to ddY controls. These results indicate that potentiated neural, endocrine and physiological activation arises in the El strain following exposure to a known seizure trigger stimulus, involuntary tail suspension handling. The findings support a diathesis-stress hypothesis in which genetically seizure susceptible El mice exhibit a multifaceted hyperreactivity to noxious environmental stimuli.

Inhibition of Glutamate Transporters Results in a "Suppression-Burst" Pattern and Partial Seizures in the Newborn Rat

PURPOSE

To determine the electrophysiological pattern and propose a clinical relevance of a deficient glutamate transport in the developing brain.

METHODS

(a) Surface EEG-video monitoring in freely moving pups; (b) intracortical multiple unit activity (MUA) and local field potential recordings in 5- to 7-day-old rats after pharmacological inhibition of the glutamate transporters by DL-TBOA.

RESULTS

Glutamate transporters inhibition alters the background cortical electrical activity inducing a dominant and persistent pattern of bilateral recurrent paroxysmal bursts alternating with periods of hypoactivity and also partial seizures. Intracortical local field recordings show that paroxysmal bursts are associated with multiunits and gamma oscillations separated by periods of silence. This cortical activity involves the activation of ionotropic glutamate receptors and was not observed after kainate and pilocarpine administration.

CONCLUSIONS

We show that a dysfunction of glutamate transporters in immature rats leads to a singular cortical activity that is reminiscent of a "suppression-burst" pattern. We propose that an early deficiency of glutamate transport may underlie some early onset epilepsies.

Exposure to neonatal separation stress alters exploratory behavior and corticotropin releasing factor expression in neurons in the amygdala and hippocampus

Evidence is accumulating that early emotional experience interferes with the development of the limbic system, which is involved in perception and regulation of emotional behaviors as well as in learning and memory formation. Limbic brain regions, as well as hypothalamic regions and other, nonlimbic areas contain specific neuron subpopulations, which express and release corticotropin releasing factor (CRF). Since these neurons serve to connect limbic function to endocrine, stress-related responses, we proposed that stressful experience during early postnatal brain development should interfere with the development of CRF-containing neurons, particularly in brain regions essential for emotional regulation. Applying neonatal separation stress (daily 1 h separation from the parents and litter mates) as stressor, the number of immunocytochemically identified CRF-expressing neurons/fibers was quantified in the amygdala, hippocampus, paraventricular nucleus of the hypothalamus, piriform cortex, and the somatosensory cortex of 3-week-old stressed and nonstressed Octodon degus, a semi-precocial rodent. Compared to controls neonatally stressed animals showed significantly lower levels of CRF-positive fibers (-60%) in the central amygdala, significantly less CRF-positive neurons in the dentate gyrus (-28%) and the CA1 region (-29%) and significantly lower CRF cell densities in the somatosensory cortex (-26%). On the other hand, we found significantly higher numbers of CRF-immunoreactive neurons in the basolateral amygdaloid complex (+192%) of stressed animals compared to nonstressed controls. No differences in CRF-immunoreactive cell densities were detected in the other regions. Additional behavioral analysis revealed significantly elevated exploratory behavior (+34%) in stressed animals compared to controls, which might indicate reduced anxiety in the stressed animals.

Developmental factors regulating susceptibility to perinatal brain injury and seizures

PURPOSE OF REVIEW

To review the unique pattern of developmentally regulated factors that govern the susceptibility of the brain during the preterm and term windows of development.

RECENT FINDINGS

The neonatal brain shows unique regional differences in susceptibility to injury. In response to the common insult of hypoxia/ischemia, the preterm brain exhibits regional white matter susceptibility, while gray matter is affected in the term brain. Developmental regulation of specific cellular factors is likely to underlie these age-specific differences.

SUMMARY

A better understanding of these factors could contribute to the development of new age-specific therapeutic strategies with clinical potential for disorders such as periventricular leukomalacia in the preterm and neonatal seizures in the term infant.