Cord serum cytokines at birth and children's trajectories of mood dysregulation symptoms from 3 to 8 years: The EDEN birth cohort

There is growing evidence that in utero imbalance immune activity plays a role in the development of neurodevelopmental and psychiatric disorders in children. Mood dysregulation (MD) is a debilitating transnosographic syndrome whose underlying pathophysiological mechanisms could be revealed by studying its biomarkers using the Research Domain Criteria (RDoC) model. Our aim was to study the association between the network of cord serum cytokines, and mood dysregulation trajectories in offsprings between 3 and 8 years of age. We used the data of a study nested in the French birth cohort EDEN that took place from 2003 to 2014 and followed mother-child dyads from the second trimester of pregnancy until the children were 8 years of age. The 2002 mother-child dyads were recruited from the general population through their pregnancy follow-up in two French university hospitals. 871 of them were included in the nested cohort and cord serum cytokine levels were measured at birth. Children's mood dysregulation symptoms were assessed with the Strengths and Difficulties Questionnaire Dysregulation Profile at the ages 3, 5 and 8 years in order to model their mood dysregulation trajectories. Out of the 871 participating dyads, 53% of the children were male. 2.1% of the children presented a high mood dysregulation trajectory whereas the others were considered as physiological variations. We found a significant negative association between TNF-α cord serum levels and a high mood dysregulation trajectory when considering confounding factors such as maternal depression during pregnancy (adjusted Odds Ratio (aOR) = 0.35, 95% Confidence Interval (CI) [0.18-0.67]). Immune imbalance at birth could play a role in the onset of mood dysregulation symptoms. Our findings throw new light on putative immune mechanisms implicated in the development of mood dysregulation and should lead to future animal and epidemiological studies.

Prenatal maternal negative life events associated with child emotional and behavioral problems in the French EDEN cohort

INTRODUCTION

Prenatal negative life events (NLEs) have been linked to adverse health outcomes in children. However, few studies examine this relationship during late childhood using trajectory analyses. Additionally, the impact of specific NLEs domains on child development remains unclear. This study aims to longitudinally explore the association between NLEs (cumulative score and specific NLEs domains) and child outcomes from birth to late childhood.

METHODS

1135 mother-child pairs from the French EDEN cohort were followed from 24 to 28 weeks of pregnancy up to 11 years of age. Maternal self-reports of prenatal NLEs were collected immediately after birth, then analyzed as a cumulative score and by NLEs domain. Children's emotional and behavioral symptoms were assessed at 4 timepoints through the Strengths and Difficulties Questionnaire.

RESULTS

Children of mothers exposed to ≥3 NLEs were more likely to follow trajectories of high levels of peer relationship problems (aOR [95 % CI] = 5.69 [1.74-18.69]), emotional symptoms (aOR [95 % CI] = 3.05 [1.08-8.63]), and conduct problems (aOR [95 %] = 3.53 [1.20-10.42]). Among the domains of NLEs, only events related to housing, finance, and living conditions were significantly associated with high emotional and behavioral difficulties trajectories (aOR [95%CI] = 2.71[1.26-5.81]).

LIMITATIONS

Potential attrition bias due to a higher dropout rate for children experiencing early indications of emotional and behavioral difficulties.

CONCLUSION

Findings support the relationship between prenatal NLEs and child outcomes, underscoring the importance of assessing prenatal stressors across life domains to identify mothers who might be in need of support.

Longitudinal effects of maternal depressive and anxious symptomatology on child hair cortisol and cortisone from pregnancy to 5-years: The EDEN mother-child cohort

Exposure to maternal depressive and anxious symptomatology in utero and after birth can affect child outcomes. One proposed mechanism is through changes in child stress hormone levels, however current studies present inconsistent findings, and further research is needed to better understand the impact of maternal mental health on child stress response. This study aims to add to the limited literature by analysing longitudinal data ranging from 24 weeks amenorrhea to 5 years postpartum among 281 mother-child pairs from the French EDEN mother-child birth cohort. Hair cortisol and cortisone data were collected from children at four time points: birth, 1, 3, and 5 years. Mothers reported depressive symptomatology via the Center for Epidemiologic Studies Depression Scale (CES-D) (at 24-weeks amenorrhea, 3-, and 5-year follow-up), and the Edinburgh Postnatal Depression Scale (EPDS) (at 4, 8 and 12 months postpartum). Prenatal anxiety symptomatology was measured via the State Anxiety Inventory (STAI) at 24 weeks amenorrhea. Group-based trajectory modelling indicated a 1-cluster classification of longitudinal child hair cortisol, cortisone and cortisol-to-cortisone ratio, as analyses did not reveal a classification by subgroups representing different child profiles. After inverse probability weighting, small effects showed prenatal depressive symptomatology was significantly associated to higher levels of child hair cortisone at one year. Prenatal anxiety symptomatology was significantly linked to higher levels of child cortisol measured at birth and cortisone at birth and at 1 year. Postpartum depressive symptomatology at 8 months was related to higher levels of cortisone among 3-year-olds. These effects were not moderated by child sex or maternal socio-economic status. Further research is needed to understand why there are associations at some time points and not others to determine any potential buffering factors.

Maternal Mental Health Care Matters: The Impact of Prenatal Depressive and Anxious Symptoms on Child Emotional and Behavioural Trajectories in the French EDEN Cohort

Few studies have investigated longitudinal trajectories of child socioemotional and behavioural development in relation to maternal prenatal mental health exposure or taken into consideration of the potential buffering effects of psychological intervention during pregnancy. Using data from 1135 mother-child dyads from the EDEN cohort from the general French population, Group-based trajectory modelling was used to model trajectories of behavioural and emotional characteristics measured at four timepoints via a parent-administered Strengths and Difficulties Questionnaire. Using propensity scores and inverse probability weighting to account for confounding factors, multinomial logistic regressions were used to quantify the associations with maternal symptoms of prenatal depression and anxiety. Stratified analyses were conducted by reporting psychologist and psychiatrist consultations during pregnancy. Compared to those without psychological problems, children of mothers with comorbid anxiety and depression retained a higher probability of following high and intermediate trajectories of emotional problems and a high trajectory of conduct problems throughout childhood. This increased risk was not present in the children of mothers who sought support through a prenatal psychologist or psychiatrist consultation. This article adds to a body of evidence underlining the importance of mental health care for expecting mothers.

Vangl2, a Core Component of the WNT/PCP Pathway, Regulates Adult Hippocampal Neurogenesis and Age-Related Decline in Cognitive Flexibility

Decline in episodic memory is one of the hallmarks of aging and represents one of the most important health problems facing Western societies. A key structure in episodic memory is the hippocampal formation and the dentate gyrus in particular, as the continuous production of new dentate granule neurons in this brain region was found to play a crucial role in memory and age-related decline in memory. As such, understanding the molecular processes that regulate the relationship between adult neurogenesis and aging of memory function holds great therapeutic potential. Recently, we found that Vang-Gogh like 2 (Vangl2), a core component of the Planar Cell Polarity (PCP) signaling pathway, is enriched in the dentate gyrus of adult mice. In this context, we sought to evaluate the involvement of this member of the Wnt/PCP pathway in both adult neurogenesis and memory abilities in adult and middle-aged mice. Using a heterozygous mouse model carrying a dominant-negative mutation in the Vangl2 gene, called Looptail (Vangl2Lp), we show that alteration in Vangl2 expression decreases the survival of adult-born granule cells and advances the onset of a decrease in cognitive flexibility. The inability of mutant mice to erase old irrelevant information to the benefit of new relevant ones highlights a key role of Vangl2 in interference-based forgetting. Taken together, our findings show that Vangl2 activity may constitute an interesting target to prevent age-related decline in hippocampal plasticity and memory.

A Baldwin interpretation of adult hippocampal neurogenesis: from functional relevance to physiopathology

Hippocampal adult neurogenesis has been associated to many cognitive, emotional, and behavioral functions and dysfunctions, and its status as a selected effect or an "appendix of the brain" has been debated. In this review, we propose to understand hippocampal neurogenesis as the process underlying the "Baldwin effect", a particular situation in evolution where fitness does not rely on the natural selection of genetic traits, but on "ontogenetic adaptation" to a changing environment. This supports the view that a strong distinction between developmental and adult hippocampal neurogenesis is made. We propose that their functions are the constitution and the lifelong adaptation, respectively, of a basic repertoire of cognitive and emotional behaviors. This lifelong adaptation occurs through new forms of binding, i.e., association or dissociation of more basic elements. This distinction further suggests that a difference is made between developmental vulnerability (or resilience), stemming from dysfunctional (or highly functional) developmental hippocampal neurogenesis, and adult vulnerability (or resilience), stemming from dysfunctional (or highly functional) adult hippocampal neurogenesis. According to this hypothesis, developmental and adult vulnerability are distinct risk factors for various mental disorders in adults. This framework suggests new avenues for research on hippocampal neurogenesis and its implication in mental disorders.

Cord Serum Cytokines at Birth and Children's Anxiety-Depression Trajectories From 3 to 8 Years: The EDEN Mother-Child Cohort

BACKGROUND

Recent research suggests that immune dysregulation in pregnancy could be a risk factor for anxiety and depression symptoms in offspring. Whereas animal studies have demonstrated the importance of the link between perinatal cytokines and abnormal behaviors in offspring, human epidemiological studies in this area remain limited. The objectives of the study were to describe the network of cord serum cytokines at birth and test whether they are associated with subsequent anxiety and depression symptom trajectories in offspring.

METHODS

We used data and biological samples from 871 mother-child pairs followed up from pregnancy to 8 years of age and participating in the French mother-child cohort EDEN (a study on the pre- and early postnatal determinants of child health and development). Cord serum cytokines were measured at birth. Children's symptoms of anxiety and depression were assessed with the emotional difficulties subscore of the Strength and Difficulties Questionnaire at ages 3, 5, and 8 years, from which trajectories of anxiety-depression symptoms were derived.

RESULTS

Results showed a significant association between cord serum interleukin-7 at birth and the trajectories of children's anxiety-depression symptoms between ages 3 to 8 years (adjusted odds ratio, 0.73; 95% confidence interval, 0.57-0.93). The associations considered relevant confounders, including prenatal maternal depressive symptoms.

CONCLUSIONS

Early immune changes may contribute to subsequent anxiety and depression symptoms in childhood. Beyond the understanding of mechanisms underlying the occurrence of emotional difficulties in children, our findings open avenues for future research in human and animals.

The atypical Rho GTPase Rnd2 is critical for dentate granule neuron development and anxiety-like behavior during adult but not neonatal neurogenesis

Despite the central role of Rho GTPases in neuronal development, their functions in adult hippocampal neurogenesis remain poorly explored. Here, by using a retrovirus-based loss-of-function approach in vivo, we show that the atypical Rho GTPase Rnd2 is crucial for survival, positioning, somatodendritic morphogenesis, and functional maturation of adult-born dentate granule neurons. Interestingly, most of these functions are specific to granule neurons generated during adulthood since the deletion of Rnd2 in neonatally-born granule neurons only affects dendritogenesis. In addition, suppression of Rnd2 in adult-born dentate granule neurons increases anxiety-like behavior whereas its deletion in pups has no such effect, a finding supporting the adult neurogenesis hypothesis of anxiety disorders. Thus, our results are in line with the view that adult neurogenesis is not a simple continuation of earlier processes from development, and establish a causal relationship between Rnd2 expression and anxiety.

Sox11 is an Activity-Regulated Gene with Dentate-Gyrus-Specific Expression Upon General Neural Activation

Neuronal activity initiates transcriptional programs that shape long-term changes in plasticity. Although neuron subtypes differ in their plasticity response, most activity-dependent transcription factors (TFs) are broadly expressed across neuron subtypes and brain regions. Thus, how region- and neuronal subtype-specific plasticity are established on the transcriptional level remains poorly understood. We report that in young adult (i.e., 6-8 weeks old) mice, the developmental TF SOX11 is induced in neurons within 6 h either by electroconvulsive stimulation or by exploration of a novel environment. Strikingly, SOX11 induction was restricted to the dentate gyrus (DG) of the hippocampus. In the novel environment paradigm, SOX11 was observed in a subset of c-FOS expressing neurons (ca. 15%); whereas around 75% of SOX11+ DG granule neurons were c-FOS+, indicating that SOX11 was induced in an activity-dependent fashion in a subset of neurons. Environmental enrichment or virus-mediated overexpression of SOX11 enhanced the excitability of DG granule cells and downregulated the expression of different potassium channel subunits, whereas conditional Sox11/4 knock-out mice presented the opposite phenotype. We propose that Sox11 is regulated in an activity-dependent fashion, which is specific to the DG, and speculate that activity-dependent Sox11 expression may participate in the modulation of DG neuron plasticity.

Juvenile mild traumatic brain injury elicits distinct spatiotemporal astrocyte responses

Mild-traumatic brain injury (mTBI) represents ~80% of all emergency room visits and increases the probability of developing long-term cognitive disorders in children. To date, molecular and cellular mechanisms underlying post-mTBI cognitive dysfunction are unknown. Astrogliosis has been shown to significantly alter astrocytes' properties following brain injury, potentially leading to significant brain dysfunction. However, such alterations have never been investigated in the context of juvenile mTBI (jmTBI). A closed-head injury model was used to study jmTBI on postnatal-day 17 mice. Astrogliosis was evaluated using glial fibrillary acidic protein (GFAP), vimentin, and nestin immunolabeling in somatosensory cortex (SSC), dentate gyrus (DG), amygdala (AMY), and infralimbic area (ILA) of prefrontal cortex in both hemispheres from 1 to 30 days postinjury (dpi). In vivo T2-weighted-imaging (T2WI) and diffusion tensor imaging (DTI) were performed at 7 and 30 dpi to examine tissue level structural alterations. Increased GFAP-labeling was observed up to 30 dpi in the ipsilateral SSC, the initial site of the impact. However, vimentin and nestin expression was not perturbed by jmTBI. The morphology of GFAP positive cells was significantly altered in the SSC, DG, AMY, and ILA up to 7 dpi that some correlated with magnetic resonance imaging changes. T2WI and DTI values were significantly altered at 30 dpi within these brain regions most prominently in regions distant from the impact site. Our data show that jmTBI triggers changes in astrocytic phenotype with a distinct spatiotemporal pattern. We speculate that the presence and time course of astrogliosis may contribute to pathophysiological processes and long-term structural alterations following jmTBI.

Transcriptional Dysregulation in Postnatal Glutamatergic Progenitors Contributes to Closure of the Cortical Neurogenic Period

Progenitors of cortical glutamatergic neurons (Glu progenitors) are usually thought to switch fate before birth to produce astrocytes. We used fate-mapping approaches to show that a large fraction of Glu progenitors persist in the postnatal forebrain after closure of the cortical neurogenesis period. Postnatal Glu progenitors do not accumulate during embryonal development but are produced by embryonal radial glial cells that persist after birth in the dorsal subventricular zone and continue to give rise to cortical neurons, although with low efficiency. Single-cell RNA sequencing reveals a dysregulation of transcriptional programs, which parallels changes in m⁶A methylation and correlates with the gradual decline in cortical neurogenesis observed in vivo. Rescuing experiments show that postnatal progenitors are partially permissive to genetic and pharmacological manipulations. Our study provides an in-depth characterization of postnatal Glu progenitors and identifies potential therapeutic targets for promoting brain repair.

LAMP5 Fine-Tunes GABAergic Synaptic Transmission in Defined Circuits of the Mouse Brain

LAMP5 is member of the LAMP family of membrane proteins. In contrast to the canonical members of this protein family, LAMP1 and LAMP2, which show widespread expression in many tissues, LAMP 5 is brain specific in mice. In C. elegans, the LAMP5 ortholog UNC-46 has been suggested to act a trafficking chaperone, essential for the correct targeting of the nematode vesicular GABA-transporter UNC-47. We show here that in the mouse brain LAMP5 is expressed in subpopulations of GABAergic forebrain neurons in the striato-nigral system and the olfactory bulb. The protein was present at synaptic terminals, overlapping with the mammalian vesicular GABA-transporter VGAT. In LAMP5-deficient mice localization of the transporter was unaffected arguing against a conserved role in VGAT trafficking. Electrophysiological analyses in mutants showed alterations in short term synaptic plasticity suggesting that LAMP5 is involved in controlling the dynamics of evoked GABAergic transmission. At the behavioral level, LAMP5 mutant mice showed decreased anxiety and deficits in olfactory discrimination. Altogether, this work implicates LAMP5 function in GABAergic neurotransmission in defined neuronal subpopulations.

[Early life stressful experiences and neuropsychiatric vulnerability: evidences from human and animal models]

The human newborn is highly dependent on parental care for its survival but also for the healthy development of its brain. A large body of literature demonstrates the impact of early life adversity, even during the prenatal period, on the adult's health. The susceptibility to neuropsychiatric diseases is often potentiated by early stress. If there is an agreement that a critical developmental period exists, the mechanisms underlying the long term effects of early life adversity are still poorly understood. Recent studies in animals highlight the involvement of epigenetic processes in the transmission of such vulnerabilities, notably via modifications in germ cells, which can be transmitted in the next generations.

Running per se stimulates the dendritic arbor of newborn dentate granule cells in mouse hippocampus in a duration-dependent manner

Laboratory rodents provided chronic unlimited access to running wheels display increased neurogenesis in the hippocampal dentate gyrus. In addition, recent studies indicate that such an access to wheels stimulates dendritic arborization in newly formed neurons. However, (i) the presence of the running wheel in the housing environment might also bear intrinsic influences on the number and shape of new neurons and (ii) the dendritic arborization of new neurons might be insensitive to moderate daily running activity (i.e., several hours). In keeping with these uncertainties, we have examined neurogenesis and dendritic arborization in newly formed granular cells in adult C57Bl/6N male mice housed for 3 weeks under standard conditions, with a locked wheel, with a running wheel set free 3 h/day, or with a running wheel set permanently free. The results indicate that the presence of a blocked wheel in the home cage increased cell proliferation, but not the number of new neurons while running increased in a duration-dependent manner the number of newborn neurons, as assessed by DCX labeling. Morphological analyses of the dendritic tree of newborn neurons, as identified by BrdU-DCX co-staining, revealed that although the presence of the wheel stimulated their dendritic architecture, the amplitude of this effect was lower than that elicited by running activity, and was found to be running duration-dependent.

Gene-environment interaction in programming hippocampal plasticity: focus on adult neurogenesis

Interactions between genes and environment are a critical feature of development and both contribute to shape individuality. They are at the core of vulnerability resiliency for mental illnesses. During the early postnatal period, several brain structures involved in cognitive and emotional processing, such as the hippocampus, still develop and it is likely that interferences with this neuronal development, which is genetically determined, might lead to long-lasting structural and functional consequences and increase the risk of developing psychopathology. One particular target is adult neurogenesis, which is involved in the regulation of cognitive and emotional processes. Insights into the dynamic interplay between genes and environmental factors in setting up individual rates of neurogenesis have come from laboratory studies exploring experience-dependent changes in adult neurogenesis as a function of individual’s genetic makeup. These studies have implications for our understanding of the mechanisms regulating adult neurogenesis, which could constitute a link between environmental challenges and psychopathology.

Ocytocine et comportement maternel : de l’adaptation à la pathologie

L’ocytocine est connue pour son implication dans le développement des relations d’attachement entre individus en général, et dans le cas qui nous intéressera plus particulièrement ici, entre une mère et sa progéniture. Ces relations s’expriment à travers la mise en place d’un comportement maternel dont la qualité va conditionner le devenir phénotypique de l’enfant, chez l’Homme comme chez l’animal. Comprendre donc, à travers les modèles animaux, les mécanismes qui gouvernent la mise en place et le maintien de ce comportement apparaît fondamental. Dans ce contexte, nous ferons le point des connaissances acquises chez le rongeur sur les liens entre ocytocine et soin maternel, en conditions physiologiques et pathologiques. En particulier, nous dresserons un bilan de la littérature associant le niveau d’activité du système ocytocinergique central au niveau de soin maternel prodigué par les mères et détaillerons les structures mises en jeu. Nous évaluerons également le rôle de l’ocytocine dans la transmission du profil comportemental maternel d’une génération à la suivante. Enfin, nous nous intéresserons aux modèles de gestations pathologiques qui peuvent entraîner des troubles du post-partum se traduisant par un déficit d’attachement. Nous testerons sur ces modèles l’hypothèse selon laquelle une altération du système ocytocinergique pourrait être impliquée dans l’apparition des troubles de l’attachement, suggérant que ce système pourrait constituer une cible thérapeutique importante dans de telles pathologies.

Interplay of maternal care and genetic influences in programming adult hippocampal neurogenesis

BACKGROUND

Adult hippocampal neurogenesis, which is involved in the physiopathology of hippocampal functions, is genetically determined and influenced by early life events. However, studies on the interaction of these determining forces are lacking. This prompted us to investigate whether adult hippocampal neurogenesis can be modulated by maternal care and whether this influence depends upon the genetic background of the individual.

METHODS

We used a model of fostering that allows singling out the influence of the genetic make-up of the pups on the outcome of maternal behavior. Mice from two different inbred strains (C57BL/6J and DBA/2J) known to differ in their baseline neurogenesis as well as in their sensitivity to the influence of environmental experiences were raised by nonrelated mothers from the AKR/Ola (AKR) and C3H/He (C3H) strains exhibiting low- and high-pup-oriented behavior, respectively. Neurogenesis was then assessed in the dentate gyrus of the adult adopted C57BL/6J and DBA/2J mice.

RESULTS

We show that both the number and the morphological features of newborn granule cells in the dentate gyrus are determined by the maternal environment to which mice were exposed as pups and that this sensitivity to maternal environment is observed only in genetically vulnerable subjects.

CONCLUSIONS

Altogether, our data indicate interplay between early environment and the genetic envelop of an individual in determining adult hippocampal neurogenesis. Our experimental approach could thus contribute to the identification of factors determining the neurogenic potential of the adult hippocampus.

Acute cannabinoids impair working memory through astroglial CB1 receptor modulation of hippocampal LTD

Impairment of working memory is one of the most important deleterious effects of marijuana intoxication in humans, but its underlying mechanisms are presently unknown. Here, we demonstrate that the impairment of spatial working memory (SWM) and in vivo long-term depression (LTD) of synaptic strength at hippocampal CA3-CA1 synapses, induced by an acute exposure of exogenous cannabinoids, is fully abolished in conditional mutant mice lacking type-1 cannabinoid receptors (CB(1)R) in brain astroglial cells but is conserved in mice lacking CB(1)R in glutamatergic or GABAergic neurons. Blockade of neuronal glutamate N-methyl-D-aspartate receptors (NMDAR) and of synaptic trafficking of glutamate α-amino-3-hydroxy-5-methyl-isoxazole propionic acid receptors (AMPAR) also abolishes cannabinoid effects on SWM and LTD induction and expression. We conclude that the impairment of working memory by marijuana and cannabinoids is due to the activation of astroglial CB(1)R and is associated with astroglia-dependent hippocampal LTD in vivo.

A new chapter in the field of memory: adult hippocampal neurogenesis

Understanding the cellular mechanisms underlying learning and memory is a major challenge in neurobiology. Structural and functional changes occurring in the hippocampus such as synaptic remodeling and long-term potentiation are key signatures of long-term memory processes. The discovery of a de novo hippocampal production of neurons in the adult brain has been a breakthrough in the field of plasticity and memory, introducing a new actor that could sustain memory processes. Here we will review our current knowledge on the role of these adult new neurons in memory. In particular we will provide evidence showing that they are required for learning and memory and that an alteration in their production rate or maturation leads to memory impairments. Through a thorough survey of the literature, we will also acknowledge that there are many controversies regarding the specific role played by newborn neurons. The emerging picture is that they are involved in the establishment of spatiotemporal relationships among multiple environmental cues for the flexible use of the acquired information. Indeed, newborn neurons have been found to be required for separating events based on their spatial and temporal characteristics, a process that preserves the uniqueness of a memory representation. Thus, adult-born neurons are required for allocentric space representation, for long-term memory retention and for flexible inferential memory expression. Finally, we will conclude by highlighting directions for future research, emphasizing that the exact participation of newborn neurons in memory processes will not be approached without considering the hippocampal network in general.

Conditional reduction of adult neurogenesis impairs bidirectional hippocampal synaptic plasticity

Adult neurogenesis is a process by which the brain produces new neurons once development has ceased. Adult hippocampal neurogenesis has been linked to the relational processing of spatial information, a role attributed to the contribution of newborn neurons to long-term potentiation (LTP). However, whether newborn neurons also influence long-term depression (LTD), and how synaptic transmission and plasticity are affected as they incorporate their network, remain to be determined. To address these issues, we took advantage of a genetic model in which a majority of adult-born neurons can be selectively ablated in the dentate gyrus (DG) and, most importantly, in which neurogenesis can be restored on demand. Using electrophysiological recordings, we show that selective reduction of adult-born neurons impairs synaptic transmission at medial perforant pathway synapses onto DG granule cells. Furthermore, LTP and LTD are largely compromised at these synapses, probably as a result of an increased induction threshold. Whereas the deficits in synaptic transmission and plasticity are completely rescued by restoring neurogenesis, these synapses regain their ability to express LTP much faster than their ability to express LTD. These results demonstrate that both LTP and LTD are influenced by adult neurogenesis. They also indicate that as newborn neurons integrate their network, the ability to express bidirectional synaptic plasticity is largely improved at these synapses. These findings establish that adult neurogenesis is an important process for synaptic transmission and bidirectional plasticity in the DG, accounting for its role in efficiently integrating novel incoming information and in forming new memories.

Adult-born neurons are necessary for extended contextual discrimination

New neurons are continuously produced in the adult dentate gyrus of the hippocampus. It has been shown that one of the functions of adult neurogenesis is to support spatial pattern separation, a process that transforms similar memories into nonoverlapping representations. This prompted us to investigate whether adult-born neurons are required for discriminating two contexts, i.e., for identifying a familiar environment and detect any changes introduced in it. We show that depleting adult-born neurons impairs the animal's ability to disambiguate two contexts after extensive training. These data suggest that the continuous production of new dentate neurons plays a crucial role in extracting and separating efficiently contextual representation in order to discriminate features within events.

Age-dependent effect of prenatal stress on hippocampal cell proliferation in female rats

Stressors occurring during pregnancy can alter the developmental trajectory of offspring and lead to, among other deleterious effects, cognitive deficits and hyperactivity of the hypothalamo-pituitary-adrenal axis. A recent feature of the prenatal stress (PS) model is its reported influence on structural plasticity in hippocampal formation, which sustains both cognitive functions and stress responsiveness. Indeed, we and others have previously reported that males exposed to stress in utero are characterized by a decrease in hippocampal cell proliferation, and consequently neurogenesis, from adolescence to senescence. Recent studies in females submitted to PS have reported conflicting results, ranging from no effect to a decrease in cell proliferation. We hypothesized that changes in cell proliferation in PS female rats are age dependent. To address this issue, we examined the impact of PS on hippocampal cell proliferation in juvenile, young, middle-aged and old females. As hypothesized, we found an age-dependent effect of PS in female rats as cell proliferation was significantly decreased only when animals reached senescence, a time when adrenal gland weight also increased. These data suggest that the deleterious effects of PS on hippocampal cell proliferation in females are either specific to senescence or masked during adulthood by protective factors.

Spatial relational memory requires hippocampal adult neurogenesis

The dentate gyrus of the hippocampus is one of the few regions of the mammalian brain where new neurons are generated throughout adulthood. This adult neurogenesis has been proposed as a novel mechanism that mediates spatial memory. However, data showing a causal relationship between neurogenesis and spatial memory are controversial. Here, we developed an inducible transgenic strategy allowing specific ablation of adult-born hippocampal neurons. This resulted in an impairment of spatial relational memory, which supports a capacity for flexible, inferential memory expression. In contrast, less complex forms of spatial knowledge were unaltered. These findings demonstrate that adult-born neurons are necessary for complex forms of hippocampus-mediated learning.

Impact of intra- and interstrain cross-fostering on mouse maternal care

The importance of maternal care in shaping an individual's phenotype in health and disease is becoming more and more apparent in both human and animal studies. However, in mouse studies using inbred strains or knockout mice to analyze the genetic influences on the development of normal and aberrant behavioral phenotypes, maternal behavior is very poorly characterized and often ignored. This study provides an extensive analysis of spontaneous maternal behavior of inbred mice in three conditions: (1) comparing two commonly used strains, (2) analyzing the impact of adopting pups from the same strain (intrastrain cross-fostering) and (3) analyzing the impact of adopting pups from a different strain (interstrain cross-fostering). For each condition, maternal behavior was analyzed continuously over 23-h periods on postnatal days 2, 4, 6 and 9. We report that (1) the maternal behavior of C57BL/6J and DBA/2J dams toward their biological offspring is highly similar, (2) intrastrain cross-fostering has minimal impact on maternal behavior of C57BL/6J and DBA/2J dams, (3) interstrain cross-fostering does not modify the strain differences in maternal care observed between AKR and C3H/He mothers and (4) the pup strain does influence the amount of maternal behavior shown by both mothers in interstrain cross-fostering. These latter findings demonstrate that both mother strain and pup strain are key determinants of maternal behavior.

Exercise-induced promotion of hippocampal cell proliferation requires beta-endorphin

Adult hippocampal neurogenesis is influenced by a variety of stimuli, including exercise, but the mechanisms by which running affects neurogenesis are not yet fully understood. Because beta-endorphin, which is released in response to exercise, increases cell proliferation in vitro, we hypothesized that it could exert a similar effect in vivo and mediate the stimulatory effects of running on neurogenesis. We thus analyzed the effects of voluntary wheel-running on adult neurogenesis (proliferation, differentiation, survival/death) in wild-type and beta-endorphin-deficient mice. In wild-type mice, exercise promoted cell proliferation evaluated by sacrificing animals 24 h after the last 5-bromo-2'-deoxyuridine (BrdU) pulse and by using endogenous cell cycle markers (Ki67 and pH(3)). This was accompanied by an increased survival of 4-wk-old BrdU-labeled cells, leading to a net increase of neurogenesis. Beta-endorphin deficiency had no effect in sedentary mice, but it completely blocked the running-induced increase in cell proliferation; this blockade was accompanied by an increased survival of 4-wk-old cells and a decreased cell death. Altogether, adult neurogenesis was increased in response to exercise in knockout mice. We conclude that beta-endorphin released during running is a key factor for exercise-induced cell proliferation and that a homeostatic balance may regulate the final number of new neurons.

Sex Differences in Sleep: the Response to Sleep Deprivation and Restraint Stress in Mice

STUDY OBJECTIVES

Numerous clinical studies and sleep surveys have shown pronounced sex differences in the occurrence of insomnia and other sleep pathologies. It has been suggested that sex differences in sleep, while subtle under baseline conditions, may increase in magnitude under biological or environmental challenges. However, controlled and experimental studies on sleep under challenged conditions rarely include female subjects. In this context, we examined sex differences in sleep in the mouse, not only under baseline conditions, but also after sleep deprivation and restraint stress.

DESIGN

Adult male and female C57BL/6J mice were implanted with electrodes to record sleep-wake architecture and sleep electroencephalogram under baseline conditions and after 6 hours of sleep deprivation or 1 hour of restraint stress at the beginning of the daily light phase.

RESULTS

Although baseline sleep patterns slightly differed between the sexes, the homeostatic recovery response to sleep deprivation was similar. In contrast, the changes in sleep after restraint stress were markedly different between male and female mice, with males displaying a stronger initial suppression of sleep and a stronger rebound of rapid-eye-movement sleep later in the recovery phase.

CONCLUSIONS

In mice, the fundamental homeostatic properties of sleep regulation may not differ between the sexes, but the way sleep is affected and disrupted by environmental influences may be sex dependent. The latter may reflect sex differences in stress sensitivity.

Adult neurogenesis: from precursors to network and physiology

The discovery that the adult mammalian brain creates new neurons from pools of stemlike cells was a breakthrough in neuroscience. Interestingly, this particular new form of structural brain plasticity seems specific to discrete brain regions, and most investigations concern the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampal formation (HF). Overall, two main lines of research have emerged over the last two decades: the first aims to understand the fundamental biological properties of neural stemlike cells (and their progeny) and the integration of the newly born neurons into preexisting networks, while the second focuses on understanding its relevance in brain functioning, which has been more extensively approached in the DG. Here, we propose an overview of the current knowledge on adult neurogenesis and its functional relevance for the adult brain. We first present an analysis of the methodological issues that have hampered progress in this field and describe the main neurogenic sites with their specificities. We will see that despite considerable progress, the levels of anatomic and functional integration of the newly born neurons within the host circuitry have yet to be elucidated. Then the intracellular mechanisms controlling neuronal fate are presented briefly, along with the extrinsic factors that regulate adult neurogenesis. We will see that a growing list of epigenetic factors that display a specificity of action depending on the neurogenic site under consideration has been identified. Finally, we review the progress accomplished in implicating neurogenesis in hippocampal functioning under physiological conditions and in the development of hippocampal-related pathologies such as epilepsy, mood disorders, and addiction. This constitutes a necessary step in promoting the development of therapeutic strategies.

Effects of Gamma-Hydroxybutyrate (GHB) on Vigilance States and EEG in Mice

STUDY OBJECTIVES

Gamma-hydroxybutyrate (GHB) is an endogenous neuromodulator that appears to have wide-ranging effects on vigilance and behavior. In the present study, we examined the effects of GHB on sleep-wake behavior and EEG in mice. In addition, we measured effects of GHB on body temperature and arousal or stress hormones.

DESIGN

Adult male BALB/c mice were implanted with electroencephalographic and electromyographic electrodes to record vigilance states and an intraperitoneal transmitter to record body temperature. After recovery from surgery and habituation to the recording procedure, the mice were intraperitoneally injected with saline or GHB (50, 150 or 250 mg/kg) half an hour after light onset. Blood samples to measure effects of GHB on corticosterone and prolactin levels were collected in a separate group of mice.

SETTING

N/A PATIENTS: N/A INTERVENTIONS: N/A RESULTS: At the lowest dose, GHB had no conspicuous effects on behavioral vigilance and electroencephalogram, nor on body temperature and endocrine measures. At the 2 higher doses, GHB induced a short period of electroencephalographic hypersynchrony in parallel to complete behavioral inactivity, an unnatural flat body posture, and nonresponsiveness to stimulation. After the highest dose of GHB, this state of reduced vigilance was associated with a decrease in body temperature, while prolactin and corticosterone levels were strongly increased.

CONCLUSIONS

The results do not indicate a clear sleep-promoting effect of GHB in mice, but, at higher doses, it caused electroencephalographic hypersynchronization together with a coma-like state.

Environmentally induced long-term structural changes: cues for functional orientation and vulnerabilities

Environmental challenges profoundly modify phenotypes and disrupt inherent developmental programs both at functional and structural levels. As an example, we have studied the impact of these environmental influences on adult neurogenesis in the dentate gyrus. Neurogenesis results from an inherent program, participates to hippocampal network organization and, as a consequence, to the various functional abilities depending on this region, including memories. In preclinical studies of aging we have shown that phenotypes vulnerable to the development of spatial memory disorders are characterized by lower hippocampal neurogenesis. We have hypothesized that these interindividual variations in functional expression of neurogenesis in senescent subjects could be predicted early in life. Indeed, a behavioral response (novelty-induced locomotor reactivity) and a biological trait (hypothalamo-pituitary-adrenal axis activity), which are predictive of cognitive impairments later in life, are related to neurogenesis in young adult rats. This suggests that subjects starting off with an impaired neurogenesis, here rats that are high reactive to stress, are predisposed for the development of age-related cognitive disorders. We have further shown that these inter-individual differences result from early deleterious life events. Indeed, prenatal stress orients neurogenesis in pathological ways for the entire life, and precipitates age-related cognitive impairments. Altogether these data suggest first that hippocampal neurogenesis plays a pivotal role in environmentally-induced vulnerability to the development of pathological aging, and second that environmental challenges and life events orient structural developments, leading to different phenotypes.

Early and Later Adoptions Differently Modify Mother-Pup Interactions

Life events occurring during the perinatal period have strong long-term effects. In rats, prenatal stress, postnatal maternal separations, or adoptions at different periods are known to affect behavior and reactivity to stress in offspring. To determine the role of maternal factors on differential outcome adoptions, the authors investigated interactions between pups and the adopting mothers by assessing both pups' ultrasound emissions and maternal behavior. Early and late adoptions increased mother care at the moment of adoption and during mother-infant reunion after a separation procedure. However, although early adoption induced a decrease in pups' ultrasound emissions in response to a stressful separation, later adoptions enhanced it. Results suggest a sensitive period during which fostering may change pups' and dams' behavior.

Prenatal stress in rats predicts immobility behavior in the forced swim test

Prenatally-stressed (PS) rats are characterized by a general impairment of the hypothalamo-pituitary-adrenal (HPA) axis and sleep disturbances indicating that this model has face validity with some clinical features observed in a subpopulation of depressed patients. The prolonged corticosterone secretion shown by PS rats in response to stress was positively correlated with an increased immobility behavior in the forced swim test. To investigate the predictive validity of this model, a separate group of animals was chronically treated with the antidepressant tianeptine (10 mg/kg i.p. for 21 days). Such chronic treatment reduced in PS rats immobility time in the forced swim test. These findings suggest that the PS rat is an interesting animal model for the evaluation of antidepressant treatment.

Sleep in female mice: a strain comparison across the estrous cycle

STUDY OBJECTIVE

Studying inbred strains of mice has proven useful in uncovering genetic variation in the expression of sleep patterns. However, although genetic influence on many behaviors has been shown to be gender specific, to date, sleep patterns in different strains of female mice have not been reported. In order to perform such studies in female mice, the estrous cycle must be taken into account in view of the effects of reproductive hormones on sleep. The aim of this study was thus to determine sleep patterns in female mice of different inbred strains over the estrous cycle.

DESIGN

Three strains of mice were used. Vaginal smears were performed to determine the estrous cycle stage; electroencephalographic and electromyographic activity, as well as body temperature and locomotor activity collected during a full estrous cycle, were analyzed.

MEASUREMENTS AND RESULTS

We report a major impact of the genetic background in the regulation of non-rapid eye movement sleep over a 24-hour period and clear strain differences in rapid eye movement sleep distribution over the light-dark cycle. In contrast, the estrous cycle had less influence on non-rapid eye movement sleep and rapid eye movement sleep, and these effects were dependent on the genotype of the mice.

CONCLUSIONS

Sleep regulation in female mice is influenced primarily by genetic background and, to a lesser extent, by hormonal variations associated with the estrous cycle.

Measurement of hypocretin/orexin content in the mouse brain using an enzyme immunoassay: the effect of circadian time, age and genetic background

The hypocretins (1 and 2) have emerged as key regulators of sleep and wakefulness. We developed a high-throughput enzyme immunoassay (EIA) to measure total brain hypocretin levels from large numbers of mice. Hypocretin levels were not altered by circadian time or age. However, significant differences in one or both hypocretin peptides were observed between different mouse strains. We studied hypocretin levels in knockout and transgenic mouse models with obesity, circadian gene mutations or monoaminergic defects. Compared to controls, only histamine receptor knockouts had lower hypocretin levels. This was most pronounced in H1 receptor knockouts suggesting the existence of a positive feedback loop between hypocretin and histaminergic neurons.

Behavioral characterization of mice lacking histamine H(3) receptors

Brain histamine H(3) receptors are predominantly presynaptic and serve an important autoregulatory function for the release of histamine and other neurotransmitters. They have been implicated in a variety of brain functions, including arousal, locomotor activity, thermoregulation, food intake, and memory. The recent cloning of the H(3) receptor in our laboratory has made it possible to create a transgenic line of mice devoid of H(3) receptors. This paper provides the first description of the H(3) receptor-deficient mouse (H(3)(-/-)), including molecular and pharmacologic verification of the receptor deletion as well as phenotypic screens. The H(3)(-/-) mice showed a decrease in overall locomotion, wheel-running behavior, and body temperature during the dark phase but maintained normal circadian rhythmicity. H(3)(-/-) mice were insensitive to the wake-promoting effects of the H(3) receptor antagonist thioperamide. We also observed a slightly decreased stereotypic response to the dopamine releaser, methamphetamine, and an insensitivity to the amnesic effects of the cholinergic receptor antagonist, scopolamine. These data indicate that the H(3) receptor-deficient mouse represents a valuable model for studying histaminergic regulation of a variety of behaviors and neurotransmitter systems, including dopamine and acetylcholine.

Individual vulnerability to substance abuse and affective disorders: role of early environmental influences

One of the most important questions raised by modern psychiatry and experimental psychopathology is the origin of mental diseases. More concisely, clinical and experimental neurosciences are increasingly concerned with the factors that render one individual more vulnerable than another to a given pathological outcome. Animal models are now available to understand the sources of individual differences for specific phenotypes prone to behavioral disadaptations. Over the last 10 years we have explored the consequences of environmental perinatal manipulations in the rat. We have shown that prenatal stress is at the origin of a wide range of physiological and behavioral aberrances such as alterations in the activity of the hormonal stress axis, increased vulnerability to drug of abuse, emotional liability, cognitive impairments and predisposition to pathological aging. Taken together, these abnormalities define a bio-behavioral syndrome. Furthermore, the cognitive disabilities observed in prenatally-stressed rats were recently related to an alteration of neurogenesis in the dentate gyrus, thus confirming the impact of early life events on brain morphology. A second model (handling model) has also been developed in which pups are briefly separated from their mothers during early postnatal life. In contrast with prenatally-stressed animals, handled rats exhibited a reduced emotion response when confronted with novel situations and were protected against age-induced impairments of both the hormonal stress axis and cognitive functions. Taken together, the results of these investigations show that the bio-behavioral phenotype that characterizes each individual is strongly linked to the nature and timing of perinatal experience. Furthermore, data collected in prenatally-stressed animals indicate that this model could be used profitably to understand the etiology and pathophysiology of affective disorders.

The effect of restraint stress on paradoxical sleep is influenced by the circadian cycle

It is well known that the physiological impact imposed by events or behaviors displayed during the waking period determines the way organisms sleep. Among the situations known to affect sleep both in its duration and quality, stress has been widely studied and it is now admitted that its effects on sleep architecture depend on several factors specific to the stressor or the individual itself. Although numerous reports have highlighted the prominent role of the circadian cycle in the physiological, endocrine and behavioral consequences of restraint stress, a possible circadian influence in the effects of stress on the sleep-wake cycle has never been studied. Thus the present study was designed to compare the effects on sleep of a 1 h-lasting restraint stress applied at light onset to those observed after the same stressor was applied at light offset. We report that in both conditions stress induced a marked paradoxical sleep increase, whereas wakefulness displayed a moderate decrease and slow wave sleep a moderate augmentation. Although the effects of stress at lights on were of similar magnitude than those of stress at lights off, important differences in the sleep rebound latencies were observed: whatever the time of day the stress was applied, its effects on sleep always occurred during the dark period. This result thus shows that restraint stress could be efficiently used to study the interaction between the circadian and homeostatic components of sleep regulation.

Sleep restriction alters the hypothalamic-pituitary-adrenal response to stress

Chronic sleep restriction is an increasing problem in many countries and may have many, as yet unknown, consequences for health and well being. Studies in both humans and rats suggest that sleep deprivation may activate the hypothalamic-pituitary-adrenal (HPA) axis, one of the main neuroendocrine stress systems. However, few attempts have been made to examine how sleep loss affects the HPA axis response to subsequent stressors. Furthermore, most studies applied short-lasting total sleep deprivation and not restriction of sleep over a longer period of time, as often occurs in human society. Using the rat as our model species, we investigated: (i) the HPA axis activity during and after sleep deprivation and (ii) the effect of sleep loss on the subsequent HPA response to a novel stressor. In one experiment, rats were subjected to 48 h of sleep deprivation by placing them in slowly rotating wheels. Control rats were placed in nonrotating wheels. In a second experiment, rats were subjected to an 8-day sleep restriction protocol allowing 4 h of sleep each day. To test the effects of sleep loss on subsequent stress reactivity, rats were subjected to a 30-min restraint stress. Blood samples were taken at several time points and analysed for adrenocorticotropic hormone (ACTH) and corticosterone. The results show that ACTH and corticosterone concentrations were elevated during sleep deprivation but returned to baseline within 4 h of recovery. After 1 day of sleep restriction, the ACTH and corticosterone response to restraint stress did not differ between control and sleep deprived rats. However, after 48 h of total sleep deprivation and after 8 days of restricted sleep, the ACTH response to restraint was significantly reduced whereas the corticosterone response was unaffected. These results show that sleep loss not only is a mild activator of the HPA axis itself, but also affects the subsequent response to stress. Alterations in HPA axis regulation may gradually appear under conditions of long total sleep deprivation but also after repeated sleep curtailment.

Long term neurodevelopmental and behavioral effects of perinatal life events in rats

Modern neurosciences are now able to open new avenues concerning an experimental approach to clinical neurosciences and psychiatry. Detection and prediction of potential vulnerabilities such as behavioral disturbances and neurodegenerative diseases, are urgent tasks leading to prevention that must be encouraged in parallel to the enormous efforts displayed for treatments. Besides possible genetic origins of diseases, environmental factors are now coming under scrutiny, and especially deleterious and challenging life events and stress occurring during prenatal and postnatal critical periods may orient brain functions towards deleterious developments. The hypothesis that will be examined is that early events might be at the origin of pathological transformations and symptoms after long periods of apparent normal abilities and behavioral homeostasis. We used models of prenatal stress and postnatal manipulations such as cross-fostering. It will be demonstrated that such events induce long-term changes, cognitive and emotional modifications appearing first, when offspring are adults, followed by cognitive defects later in life. Increased sensitivity of the hypothalamic pituitary-adrenal axis (HPA), the endocrine system controlling the secretion of stress hormones (corticoids), appears to be a major element of pathogenesis. HPA axis dysfunction appears very early after birth (3 days) and lasts for months. Cumulative exposure to high levels of hormones seems to be detrimental for some brain regions, especially the hippocampus and major neurotransmitter systems such as dopamine neurons. We evidenced that neuronal modifications in hippocampal region are correlated with behavioral and cognitive defects, relating environment, stress in early life, hormonal changes, long-term neuropathological processes and impaired cognition in aging. Moreover appears in offspring, when adults, a proneness to engage in drug dependence. These data emphasize the need to consider early environmental life events as etiological factors for delayed neuropsychiatric disturbances, neurodegenerative defects included. Moreover, they strengthen the interest for a longitudinal approach to promote experimental psychopathology.

Nicotine-induced locomotor activity is increased by preexposure of rats to prenatal stress

Genetic factors are believed to play a predominant role in the individual differences observed in behavioral and pharmacological responses to drugs of abuse. An increasing literature indicates, however, that epigenetic factors can be involved as well. In this report we examined whether developmental changes induced by prenatal stress could alter the way animals respond to the psychostimulant effect of nicotine when adults. The results show that nicotine induces a dose-dependent increase of locomotor activity in both groups, and that prenatally-stressed animals exhibit a higher behavioral response at all doses. This study emphasizes the importance of early environment in the later development of drug-related behavior.

Human 293 cell metabolism in low glutamine-supplied culture: interpretation of metabolic changes through metabolic flux analysis

Metabolic flux analysis is a useful tool to analyze cell metabolism. In this study, we report the use of a metabolic model with 34 fluxes to study the 293 cell, in order to improve its growth capacity in a DMEM/F12 medium. A batch, fed-batch with glutamine feeding, fed-batch with essential amino acids, and finally a fed-batch experiment with both essential and nonessential amino acids were compared. The fed-batch with glutamine led to a maximum cell density of 2.4x10(6) cells/ml compared to 1.8x10(6) cells/ml achieved in a batch mode. In this fed-batch with glutamine, it was also found that 2.5 mM ammonia was produced compared to the batch which had a final ammonia concentration of 1 mM. Ammonia was found to be growth inhibiting for this cell line at a concentration starting at 1 mM. During the fed-batch with glutamine, the flux analysis shows that a majority of amino acid fluxes and Kreb's cycle fluxes, except for glutamine flux, are decreased. This observation led to the conclusion that the main nutrient used is glutamine and that during the batch there is an overflow in the Kreb's cycle. Thus, a fed-batch with glutamine permits a better utilization of this nutrient. A fed-batch with essential amino acid without glutamine was also assayed in order to reduce ammonia production. The maximum cell density was increased further to 3x10(6) cells/ml and ammonia production was reduced below 1 mM. Flux analysis shows that the cells could adapt to a medium with low glutamine by increasing the amino acid fluxes toward the Kreb's cycle. Adding nonessential amino acids during this feeding strategy did not improve growth further and the nonessential amino acids accumulated in the medium.

Prenatal stress produces learning deficits associated with an inhibition of neurogenesis in the hippocampus

Early experiences such as prenatal stress significantly influence the development of the brain and the organization of behavior. In particular, prenatal stress impairs memory processes but the mechanism for this effect is not known. Hippocampal granule neurons are generated throughout life and are involved in hippocampal-dependent learning. Here, we report that prenatal stress in rats induced lifespan reduction of neurogenesis in the dentate gyrus and produced impairment in hippocampal-related spatial tasks. Prenatal stress blocked the increase of learning-induced neurogenesis. These data strengthen pathophysiological hypotheses that propose an early neurodevelopmental origin for psychopathological vulnerabilities in aging.

Pregnenolone sulfate increases hippocampal acetylcholine release and spatial recognition

The pregnenolone sulfate is a neurosteroid with promnesic properties. Recently, a correlation between endogenous levels of pregnenolone sulfate in the hippocampus and performance in a spatial memory task has been reported in aged rats. Cholinergic transmission is known to modulate memory processes and to be altered with age. In the present experiment we investigated the effect of increasing doses of pregnenolone sulfate on hippocampal acetylcholine release. Our results show that intracerebroventricular administrations of this neurosteroid induced a dose-dependent increase in acetylcholine release. Administration of 12 and 48 nmol of pregnenolone sulfate induced a short lasting (20 min) enhancement of acetylcholine output with a maximum around 120% over baseline and the administration of 96 and 192 nmol doses induced a long-lasting (80 min) increase that peaked around 300% over baseline. In a second experiment we have observed that the 12 nmol dose enhanced spatial memory performance, whereas the 192 nmol dose was inefficient. These results are consistent with previous work suggesting that, a modest increase in acetylcholine release facilitates memory processes, while elevation beyond an optimal level is ineffective. Nevertheless, neurosteroids may be of value for reinforcing depressed cholinergic transmission in certain age-related memory disorders.

Prenatal stress alters circadian activity of hypothalamo-pituitary-adrenal axis and hippocampal corticosteroid receptors in adult rats of both gender

Prenatal stress impairs activity of the hypothalamo-pituitary-adrenal (HPA) axis in response to stress in adult offspring. So far, very few data are available on the effects of prenatal stress on circadian functioning of the HPA axis. Here, we studied the effects of prenatal stress on the circadian rhythm of corticosterone secretion in male and female adult rats. To evaluate the effects of prenatal stress on various regulatory components of corticosterone secretion, we also assessed the diurnal fluctuation of adrenocorticotropin, total and free corticosterone levels, and hippocampal corticosteroid receptors. Finally, in the search of possible maternal factors, we studied the effects of repeated restraint stress on the pattern of corticosterone secretion in pregnant female rats. Results demonstrate that prenatal stress induced higher levels of total and free corticosterone secretion at the end of the light period in both males and females, and hypercorticism over the entire diurnal cycle in females. No diurnal fluctuation of adrenocorticotropin was observed in any group studied. The effects of prenatal stress on corticosterone secretion could be mediated, at least in part, by a reduction in corticosteroid receptors at specific times of day. Results also show that prepartal stress alters the pattern of corticosterone secretion in pregnant females. Those data indicate that prenatally stressed rats exhibit an altered temporal functioning of the HPA axis, which, taken together with their abnormal response to stress, reinforces the idea of a general homeostatic dysfunction in those animals.

The neurosteroid pregnenolone sulfate increases cortical acetylcholine release: a microdialysis study in freely moving rats

The effects of pregnenolone sulfate (Preg-S) administrations (0, 12, 48, 96, and 192 nmol intracerebroventricularly) on acetylcholine (ACh) release in the frontal cortex and dorsal striatum were investigated by on-line microdialysis in freely moving rats. Following Preg-S administration, extracellular ACh levels in the frontal cortex increased in a dose-dependent manner, whereas no change was observed in the striatum. The highest doses (96 and 192 nmol) induced a threefold increase above control values of ACh release, the intermediate dose of 48 nmol led to a twofold increase, whereas after the dose of 12 nmol, the levels of ACh were not different from those observed after vehicle injection. The increase in cortical ACh reached a maximum 30 min after administration for all the active doses. Taken together, these results suggest that Preg-S interacts with the cortical cholinergic system, which may account, at least in part, for the promnesic and/or antiamnesic properties of this neurosteroid.

Corticotropin-releasing factor administered centrally, but not peripherally, stimulates hippocampal acetylcholine release

In addition to corticotropin-releasing factor's well-known role in mediating hormonal and behavioral responses to stress, this peptide also reportedly affects arousal and cognition, processes that classically have been associated with forebrain cholinergic systems. Corticotropin-releasing factor stimulation of cholinergic neurons might thus provide a mechanism for this peptide's cognitive effects. To examine this possibility, the present experiments characterize the effect of corticotropin-releasing factor on cholinergic neurotransmission, using in vivo microdialysis to measure hippocampal acetylcholine release. Corticotropin-releasing factor (0.5-5.0 microg/rat intracerebroventricularly) was found to increase dialysate concentrations of acetylcholine in a dose-dependent manner in comparison with a control injection, the ovine peptide having a greater effect than the same dose of the human/rat peptide. This effect was found to be centrally mediated, independent of the peripheral effects of an exogenous corticotropin-releasing factor injection; subcutaneous injections of the peptide increased plasma concentrations of corticosterone, the adrenal hormone ultimately secreted in the rat's stress response, to the same level as did the central injections, without affecting hippocampal acetylcholine release. These results demonstrate that corticotropin-releasing factor, acting centrally, regulates hippocampal cholinergic activity, and suggest that corticotropin-releasing factor/acetylcholine interactions may underlie some of the previously identified roles of these neurotransmitters in arousal, cognition, and stress.

Prenatal stress enhances stress- and corticotropin-releasing factor-induced stimulation of hippocampal acetylcholine release in adult rats

There is growing evidence that stressors occurring during pregnancy can impair biological and behavioral responses to stress in the adult offspring. For instance, prenatal stress enhances emotional reactivity, anxiety, and depressive-like behaviors associated with a prolonged stress-induced corticosterone secretion and a reduction in hippocampal corticosteroid receptors. Among the neurotransmitters involved in these hormonal and behavioral responses, acetylcholine may play a critical role. However, it is unknown whether prenatal stressful events also may influence the development of cholinergic systems. In the present study, hippocampal acetylcholine was measured, by in vivo microdialysis, in both male and female adult prenatally stressed rats, under basal conditions, after a mild stress (saline injection) or after intracerebroventricular administration of corticotropin-releasing factor (CRF; 0.1 nM). No difference in basal release of acetylcholine was observed between control and prenatally stressed rats of both genders. Mild stress was found to increase hippocampal acetylcholine release to a greater extent in prenatally stressed rats than in controls. In males, the CRF-induced increase in hippocampal acetylcholine release was larger in prenatally stressed rats, as compared with controls, during the first hour after the injection and in females during the third hour after the injection. These data indicate that prenatal stress has long-term effects on the development of forebrain cholinergic systems. The augmented increase in hippocampal acetylcholine release after the mild stress and CRF injection in prenatally stressed rats may be involved in some of the hormonal and behavioral abnormalities found in prenatally stressed rats.

Neurosteroids: deficient cognitive performance in aged rats depends on low pregnenolone sulfate levels in the hippocampus

Pregnenolone sulfate (PREG S) is synthesized in the nervous system and is a major neurosteroid in the rat brain. Its concentrations were measured in the hippocampus and other brain areas of single adult and aged (22-24 month-old) male Sprague-Dawley rats. Significantly lower levels were found in aged rats, although the values were widely scattered and reached, in about half the animals, the same range as those of young ones. The spatial memory performances of aged rats were investigated in two different spatial memory tasks, the Morris water maze and Y-maze. Performances in both tests were significantly correlated and, accompanied by appropriate controls, likely evaluated genuine memory function. Importantly, individual hippocampal PREG S and distance to reach the platform in the water maze were linked by a significant correlation, i.e., those rats with lower memory deficit had the highest PREG S levels, whereas no relationship was found with the PREG S content in other brain areas (amygdala, prefrontal cortex, parietal cortex, striatum). Moreover, the memory deficit of cognitively impaired aged rats was transiently corrected after either intraperitoneal or bilateral intrahippocampal injection of PREG S. PREG S is both a gamma-aminobutyric acid antagonist and a positive allosteric modulator at the N-methyl-D-aspartate receptor, and may reinforce neurotransmitter system(s) that decline with age. Indeed, intracerebroventricular injection of PREG S was shown to stimulate acetylcholine release in the adult rat hippocampus. In conclusion, it is proposed that the hippocampal content of PREG S plays a physiological role in preserving and/or enhancing cognitive abilities in old animals, possibly via an interaction with central cholinergic systems. Thus, neurosteroids should be further studied in the context of prevention and/or treatment of age-related memory disorders.