Neonatal handling and gender modulate brain monoamines and plasma corticosterone levels following repeated stressors in adulthood

Schizophrenia-relevant social, attentional and cognitive traits in female RHA vs. RLA rats: Effects of neonatal handling

The Roman high- (RHA) and low-avoidance (RLA) rats were bidirectionally selected and bred for, respectively, their rapid vs. extremely poor acquisition in the two-way active avoidance task. Consistent between-strain neurobehavioural differences have been found in anxiety- and stress-linked traits, as well as in schizophrenia-related phenotypes. RLAs display enhanced anxious- and stress-related phenotypes, whereas RHA rats show impulsivity, hyperactivity and attention/cognition-related impairments. Many of these typical behavioural phenotypes have been reported to be positively modulated by environmental treatments such as neonatal handling (NH). However, most studies on the Roman rat strains have been carried out in males. Thus, the present study for the first time focused on the joint evaluation of differences in novel object exploration (NOE), social interaction (SI), prepulse inhibition of the startle response (PPI), and cognitive performance and flexibility in various spatial tasks (using the Morris water maze, MWM) in females of both Roman rat strains. We also aimed at evaluating the long-lasting effects of NH treatment on the RHA vs. RLA profiles in these tests/tasks. Results show that anxiety-related behavior, as measured by the NOE test and self-grooming in the SI test, was increased in RLA rats, and dramatically reduced by NH. In the SI test RLA rats displayed diminished social interaction, which was rescued by NH. RHA females exhibited a deficit of PPI, which was not affected by NH. Spatial tasks in the MWM showed impairments of working memory, reference learning/memory and spatial reversal learning (i.e., cognitive flexibility) in RHA females. Spatial reference learning and cognitive flexibility (i.e., reversal task) showed some improvement in rats (mainly in RHAs) that had received NH during the first three weeks of life. With the exception of the SI test, the pattern of differences between female RHA vs. RLA profiles was overall consistent with what has previously been found in males of both strains, and NH treatment was able to enduringly improve some emotion-related and (spatial) cognitive outcomes in both strains.

Sex-dependent worsening of NMDA-induced responses, anxiety, hypercortisolemia, and organometry of early peripheral immunoendocrine impairment in adult 3xTg-AD mice and their long-lasting ontogenic modulation by neonatal handling

The neuroimmunomodulation hypothesis for Alzheimer's disease (AD) postulates that alterations in the innate immune system triggered by damage signals result in adverse effects on neuronal functions. The peripheral immune system and neuroimmunoendocrine communication are also impaired. Here we provide further evidence using a longitudinal design that also studied the long-lasting effects of an early life sensorial intervention (neonatal handling, from postnatal day 1-21) in 6-month-old (early stages of the disease) male and female 3xTg-AD mice compared to age- and sex-matched non-transgenic (NTg) mice with normal aging. The behavioral patterns elicited by the direct exposure to an open field, and the motor depression response evoked by NMDA (25 mg/kg, i.p) were found correlated to the organometry of peripheral immune-endocrine organs (thymus involution, splenomegaly, and adrenal glands' hypertrophy) and increased corticosterone levels, suggesting their potential value for diagnostic and biomonitoring.The NMDA-induced immediate and depressant motor activity and endocrine (corticosterone) responses were sensitive to sex and AD-genotype, suggesting worse endogenous susceptibility/neuroprotective response to glutamatergic excitotoxicity in males and in the AD-genotype. 3xTg-AD females showed a reduced immediate response, whereas the NTg showed higher responsiveness to subsequent NMDA-induced depressant effect than their male counterparts. The long-lasting ontogenic modulation by handling was shown as a potentiation of NMDA-depressant effect in NTg males and females, while sex × treatment effects were found in 3xTg-AD mice. Finally, NMDA-induced corticosterone showed sex, genotype and interaction effects with sexual dimorphism enhanced in the AD-genotype, suggesting different endogenous vulnerability/neuroprotective capacities and modulation of the neuroimmunoendocrine system.

Decreased social interaction in the RHA rat model of schizophrenia-relevant features: Modulation by neonatal handling

The Roman-Low (RLA) and High-Avoidance (RHA) rat strains have been bidirectionally selected and bred, respectively, for extremely poor vs. rapid acquisition of the two-way active avoidance task. Over 50 years of selective breeding have led to two strains displaying many differential specific phenotypes. While RLAs display anxious-related behaviours, RHA rats show impulsivity, and schizophrenia-like positive and cognitive symptoms or phenotypes. Neonatal handling (NH) is an environmental treatment with long-lasting anxiolytic-like and anti-stress effects. NH also reduces symptoms related to schizophrenia, such as pre-pulse inhibition (PPI) impairment and latent inhibition (LI) deficits, and improves spatial working memory and cognitive flexibility. The present work was aimed at exploring whether RHAs also display negative schizophrenia-like symptoms (or phenotypes), such as lowered preference for social interaction (i.e. asociality), and whether NH would reduce these deficits. To this aim, we evaluated naïve inbred RHA and RLA rats in a social interaction (SI) test after either long- or short-term habituation to the testing set up (studies 1-2). In Study 3 we tested untreated and NH-treated RHA and RLA rats in novel object exploration (NOE) and SI tests. Compared with RHAs, RLA rats displayed increased anxiety-related behaviours in the NOE (i.e. higher behavioural inhibition, lesser exploration of the novel object) and SI (i.e. higher levels of self-grooming) tests which were dramatically reduced by NH treatment, thus supporting the long-lasting anxiolytic-like effect of NH. Remarkably, RHA rats showed decreased social preference in the SI test compared with RLAs, evidencing that RHAs would present a relative asociality, which is thought to model some negative symptomatology (i.e. social withdrawal) of schizophrenia. NH increased absolute levels of social behaviour in both strains, but with a more marked effect in RHA rats, especially in the first 5 min of the SI test. Thus, it is hypothesized that, apart from its effects on anxiety-related behaviours, NH might have long-lasting positive effects on behavioural and neurobiological processes that are impaired in schizophrenia.

Neonatal Handling Produces Sex Hormone-Dependent Resilience to Stress-Induced Muscle Hyperalgesia in Rats

Neonatal handling (NH) of male rat pups strongly attenuates stress response and stress-induced persistent muscle hyperalgesia in adults. Because female sex is a well established risk factor for stress-induced chronic muscle pain, we explored whether NH provides resilience to stress-induced hyperalgesia in adult female rats. Rat pups underwent NH, or standard (control) care. Muscle mechanical nociceptive threshold was assessed before and after water avoidance (WA) stress, when they were adults. In contrast to male rats, NH produced only a modest protection against WA stress-induced muscle hyperalgesia in female rats. Gonadectomy completely abolished NH-induced resilience in male rats but produced only a small increase in this protective effect in female rats. The administration of the antiestrogen drug fulvestrant, in addition to gonadectomy, did not enhance the protective effect of NH in female rats. Finally, knockdown of the androgen receptor by intrathecal antisense treatment attenuated the protective effect of NH in intact male rats. Together, these data indicate that androgens play a key role in NH-induced resilience to WA stress-induced muscle hyperalgesia.

PERSPECTIVE

NH induces androgen-dependent resilience to stress-induced muscle pain. Therefore, androgens may contribute to sex differences observed in chronic musculoskeletal pain and its enhancement by stress.

Early postnatal handling and environmental enrichment improve the behavioral responses of 17-month-old 3xTg-AD and non-transgenic mice in the Forced Swim Test in a gender-dependent manner

Forced Swimming Test (FST) models behavioural despair in animals by loss of motivation to respond or the refusal to escape. The present study was aimed at characterizing genetic (genotype and gender) and environmental factors (age/stage of disease and rearing conditions: C, standard; H, early postnatal handling; EE, environmental enrichment consisting in physical exercise as well as social and object enrichment) that may modulate the poor behavioural and cognitive flexibility response we have recently described in 12-month-old male 3xTg-AD mice in the FST. The comprehensive analysis of the ethogram shown in the FST considered the intervals of the test (0-2 and 2-6min), all the elicited behavioural responses (immobility, swimming and climbing) and their features (total duration and frequency of episodes). The long persistence of behaviours found in 17-month-old (late-stages of disease) 3xTg-AD mice was comparable to that recently described in males at 12 months of age (beginning of advanced stages) but also suggested increased age-dependent frailty in both genotypes. The poor behavioral flexibility of 3xTg-AD mice to elicit the behavioural despair shown by the NTg mice, was also found in the female gender. Finally, the present work demonstrates that early-life interventions were able to improve the time and frequency of episodes of immobility, being more evident in the female gender of both old NTg and 3xTg-AD mice. Ontogenic modulation by early-postnatal handling resulted in a more effective long-term improvement of the elicited behaviours in the FST than that achieved by environmental enrichment. The results talk in favor of the beneficence of early-life interventions on ageing in both healthy and disease conditions.

How postnatal insults may program development: studies in animal models

During the postnatal period, the nervous system is modified and shaped by experience, in order to adjust it to the particular environment in which the animal will live. This plasticity, one of the most remarkable characteristics of the nervous system, promotes adaptive changes, but it also makes brain more vulnerable to insults. This chapter will focus on the effects of interventions during the postnatal development in animal models of neonatal handling (usually up to 15 min of handling) and maternal separation (usually at least for 3 h). Sex-specific changes and effects of prepubertal stress such as social isolation later on in life were also considered. These interventions during development induce long-lasting traces in the pups' nervous system, which will be reflected in changes in neuroendocrine functions, including the hypothalamus-pituitary-adrenal and hypothalamus-pituitary-gonadal axes; anxiety and cognitive performance; and feeding, sexual, and social behavior. These enduring changes may be adaptive or maladaptive, depending on the environment in which the animal will live. The challenge researchers facing now is to determine how to reverse the deleterious effects that may result from early-life stress exposure.

Brief neonatal handling alters sexually dimorphic behaviors in adult rats

Several effects of neonatal handling on brain and behavior have been reported. We investigated the effects of neonatal handling on behaviors that have been shown to be sexually dimorphic in rats using an open-field test. "Gender differences" were observed in locomotor activity, exploratory behavior and grooming in the handled group. However, clear gender differences in these behaviors were not observed in the non-handled group. Our findings show that brief daily handling sessions (~ 1 min) in the first 2 weeks of postnatal life increased locomotor activity and exploratory behavior, and that these effects were more pronounced in females. Moreover, many rats in the non-handling group exhibited an increase in defecation relative to the handling group during the 10-min observation period. This suggests that the non-handling group experienced more stress in response to the novel open-field arena, and that this resulted in the absence of gender differences. Notably, this anxiety-related response was attenuated by neonatal handling. Our study underscores the impact of brief neonatal handling on sexually dimorphic behaviors, and indicates that caution should be exercised in controlling for the effects of handling between experimental groups, particularly in neurotoxicological studies that evaluate gender differences.

Bizarre behaviors and risk assessment in 3xTg-AD mice at early stages of the disease

Bizarre behaviors (stereotyped stretching, stereotyped rearing, backward movements and jumps) were conspicuously elicited in classical unconditioned tests with different levels of anxiogenic conditions. They were characterized for the first time as early-BPSD-like symptoms in 6 month-old male and female 3xTg-AD mice. The pattern of these behaviors differed from that exhibited by their age- and gender-matched NTg counterparts. Confrontation of an open and illuminated field was the best trigger of such behaviors as compared to mild neophobia in the corner test or the choice between two compartments in the dark-light box. Here we also report that increased freezing, delayed thigmotaxis and enhancement of emotional behaviors were early BPSD-like symptoms indicative of their response to low-stressful environments. Independently of the genotype, consistent gender effects pointed toward the relevance of female gender to study bizarre behaviors and risk assessment. The identification of items of behavior and its gender component were relevant to find out bidirectional and selective behavioral long-lasting effects of postnatal handling. This early life treatment reduced freezing and most of the bizarre behaviors whereas potentiated risk assessment and the horizontal locomotor activity. In contrast, vertical exploratory activity was not modified by the treatment. The results also talk in favor of the beneficence of early-life interventions on the behavioral outcome in adulthood in both healthy and disease conditions. As shown, the consideration of bizarre behaviors and risk assessment may become an additional tool for evaluating BPSD-like symptoms in relation to preventive and/or therapeutical strategies targeted at AD. It may also have a role in the evaluation of the potential risk factors for the disease.

Denial of reward in the neonate shapes sociability and serotonergic activity in the adult rat

Background

Manipulations of the early environment are linked to long-lasting alterations of emotionality and social capabilities. Denial of rewarding mother-pup interactions in early life of rats could serve as model for child neglect. Negative consequences for social competence in later life, accompanied by changes in the serotonergic system would be expected. In contrast, rewarding mother-pup contact should promote adequate social abilities.

Methodology/Principal Findings

Male Wistar rats trained in a T-maze during postnatal days 10–13 under denial (DER) or permission (RER) of maternal contact were tested for play behavior in adolescence and for coping with defeat in adulthood. We estimated serotonin (5-HT) levels in the brain under basal conditions and following defeat, as well as serotonin receptor 1A (5-HT1A) and serotonin transporter (SERT) expression. DER rats exhibited increased aggressive-like play behavior in adolescence (i.e. increased nape attacks, p<0.0001) and selected a proactive coping style during defeat in adulthood (higher sum of proactive behaviors: number of attacks, flights, rearings and defensive upright posture; p = 0.011, p<0.05 vs RER, non-handled-NH). In adulthood, they had lower 5-HT levels in both the prefrontal cortex (p<0.05 vs RER) and the amygdala (p<0.05 vs NH), increased 5-HT levels following defeat (PFC p<0.0001) and decreased serotonin turnover (amygdala p = 0.008). The number of 5-HT1A immunopositive cells in the CA1 hippocampal area was increased (p<0.05 DER, vs RER, NH); SERT levels in the amygdala were elevated (p<0.05 vs RER, NH), but were lower in the prefrontal cortex (p<0.05 vs NH).

Conclusions/Significance

Denial of expected maternal reward early in life negatively affects sociability and the serotonergic system in a complex manner. We propose that our animal model could contribute to the identification of the neurobiological correlates of early neglect effects on social behavior and coping with challenges, but also in parallel with the effects of a rewarding early-life environment.

Maternal separation as a model of brain-gut axis dysfunction

RATIONALE

Early life stress has been implicated in many psychiatric disorders ranging from depression to anxiety. Maternal separation in rodents is a well-studied model of early life stress. However, stress during this critical period also induces alterations in many systems throughout the body. Thus, a variety of other disorders that are associated with adverse early life events are often comorbid with psychiatric illnesses, suggesting a common underlying aetiology. Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is thought to involve a dysfunctional interaction between the brain and the gut. Essential aspects of the brain-gut axis include spinal pathways, the hypothalamic pituitary adrenal axis, the immune system, as well as the enteric microbiota. Accumulating evidence suggest that stress, especially in early life, is a predisposing factor to IBS.

OBJECTIVE

The objective of this review was to assess and compile the most relevant data on early life stress and alterations at all levels of the brain gut axis.

RESULTS

In this review, we describe the components of the brain-gut axis individually and how they are altered by maternal separation. The separated phenotype is characterised by alterations of the intestinal barrier function, altered balance in enteric microflora, exaggerated stress response and visceral hypersensitivity, which are all evident in IBS.

CONCLUSION

Thus, maternally separated animals are an excellent model of brain-gut axis dysfunction for the study of disorders such as IBS and for the development of novel therapeutic interventions.

Early-life blockade of 5-HT(1A) receptors alters adult anxiety behavior and benzodiazepine sensitivity

BACKGROUND

Early-life stress may affect 5-HT(1A) receptor circuitry, which could result in increased anxiety in later life. An increased anxiety phenotype in 5-HT(1A) receptor KO mice (1AKO) mice has been ascribed to 5-HT(1A) receptor absence during the early postnatal period. Thus, subtle and transient serotonergic changes during the early postnatal period may lead to an increased risk for developing stress-related disorders during adulthood.

METHODS

Wildtype and 1AKO mice on a Swiss-Webster (SW) background were treated during the early postnatal period with vehicle or the 5-HT(1A) receptor antagonist WAY-100,635.

RESULTS

Pharmacologic 5-HT(1A) receptor blockade during the early postnatal period induced long-lasting effects on anxiety and benzodiazepine sensitivity in adolescent and adult mice on a Swiss-Webster background and resembles the SW 1AKO phenotype. Furthermore, WAY-100,635-treated mice had increased cortical gamma-aminobutyric acid-A receptor (GABA(A)R) alpha(1) and alpha(3) subunit levels and increased hippocampal GABA(A)R alpha(2) subunit levels.

CONCLUSIONS

Absence of 5-HT(1A)R signaling during early stages of brain maturation predisposes an organism to affective dysfunction later in life. Because early-life treatment with WAY-100,635 in Swiss-Webster mice reduced diazepam sensitivity and increased GABA(A)R alpha subunit levels in the prefrontal cortex and hippocampus, our data suggest a putative link between early-life disruption of the serotonergic system and the emergence of increased anxiety and decreased benzodiazepine responsivity at adult age. Moreover, early-life 5-HT(1A) receptor functionality appears to be essential for the development of normal GABA(A)R functionality. This study may have clinical implications for psychoactive drug use during pregnancy and for the pharmacogenetic background of benzodiazepine sensitivity.

Neurobiological adaptations to violence across development

Developmental adaptations to violent environments involve a multitude of cascading effects spanning many levels of analysis from genes to behavior. In this review, we (a) examine the potentiating effects of violence on genetic vulnerabilities and the functioning of neurotransmitter systems in producing both internalizing and externalizing psychopathology; (b) describe implications of violence exposure for brain development, particularly within the hippocampus and prefrontal cortex; and (c) consider the effects of violence on developing human stress and startle responses. This review integrates literatures on the developmental effects of violence among rodents, nonhuman primates, and humans. Many neurobiological changes that are adaptive for survival in violent contexts become maladaptive in other environments, conferring life-long risk for psychopathology.

Sex differences in corticolimbic dopamine and serotonin systems in the rat and the effect of postnatal handling

Stress-related psychopathology is particularly prevalent in women, although the neurobiological reason(s) for this are unclear. Dopamine (DA) and serotonin (5-HT) systems however, are known to play important adaptive roles in stress and emotion regulation. The aims of the present study included examination of sex differences in stress-related behaviour and neuroendocrine function as well as post mortem neurochemistry, with the main hypothesis that corticolimbic DA and 5-HT systems would show greater functional activity in males than females. Long-Evans rats of both sexes were employed. Additional factors incorporated included differential postnatal experience (handled vs. nonhandled) and adult mild stress experience (acute vs. repeated (5) restraint). Regional neurochemistry measures were conducted separately for left and right hemispheres. Behaviourally, females showed more exploratory behaviour than males in the elevated plus maze and an openfield/holeboard apparatus. Females also exhibited significantly higher levels of adrenocorticotrophic hormone and corticosterone at all time points in response to restraint stress than males across treatment conditions, although both sexes showed similar habituation in stress-induced ACTH activation with repeated mild stress. Neurochemically, females had significantly higher levels of DA (in ventromedial prefrontal cortex (vmPFC), insular cortex and n. accumbens) and 5-HT (in vmPFC, amygdala, dorsal hippocampus and insula) than males. In contrast, males had higher levels of the DA metabolite DOPAC or DOPAC/DA ratios than females in all five regions and higher levels of the 5-HT metabolite 5-HIAA or 5-HIAA/5-HT ratios in vmPFC, amygdala and insula, suggesting greater neurotransmitter utilization in males. Moreover, handling treatment induced a significant male-specific upregulation of 5-HT metabolism in all regions except n. accumbens. Given the adaptive role of 5-HT and DAergic neurotransmission in stress and emotion regulation, the intrinsic sex differences we report in the functional status of these systems across conditions, may be highly relevant to the differential vulnerability to disorders of stress and emotion regulation.

Neonatal handling and the maternal odor preference in rat pups: involvement of monoamines and cyclic AMP response element-binding protein pathway in the olfactory bulb

Early-life environmental events, such as the handling procedure, can induce long-lasting alterations upon several behavioral and neuroendocrine systems. However, the changes within the pups that could be causally related to the effects in adulthood are still poorly understood. In the present study, we analyzed the effects of neonatal handling on behavioral (maternal odor preference) and biochemical (cyclic AMP response element-binding protein (CREB) phosphorylation, noradrenaline (NA), and serotonin (5-HT) levels in the olfactory bulb (OB)) parameters in 7-day-old male and female rat pups. Repeated handling (RH) abolished preference for the maternal odor in female pups compared with nonhandled (NH) and the single-handled (SH) ones, while in RH males the preference was not different than NH and SH groups. In both male and female pups, RH decreased NA activity in the OB, but 5-HT activity increased only in males. Since preference for the maternal odor involves the synergic action of NA and 5-HT in the OB, the maintenance of the behavior in RH males could be related to the increased 5-HT activity, in spite of reduction in the NA activity in the OB. RH did not alter CREB phosphorylation in the OB of both male and females compared with NH pups. The repeated handling procedure can affect the behavior of rat pups in response to the maternal odor and biochemical parameters related to the olfactory learning mechanism. Sex differences were already detected in 7-day-old pups. Although the responsiveness of the hypothalamic-pituitary-adrenal axis to stressors is reduced in the neonatal period, environmental interventions may impact behavioral and biochemical mechanisms relevant to the animal at that early age.

Effect of neonatal handling on serotonin 1A sub-type receptors in the rat hippocampus

Serotonin 1A sub-type receptors play an important role in the etiopathogenesis of depression, which is known to occur more often in females than males. Early experiences can be a predisposing factor for depression; however, the underlying cellular processes remain unknown. In an effort to address such issues, we employed neonatal handling, an experimental model of early experience, which has been previously shown to render females more vulnerable to display enhanced depression-like behavior in response to chronic stress, while it increases the ability of males to cope. In rat pre-pubertal (30 days of age) and adult (90 days) hippocampus, of both males and females, the effect of neonatal handling on serotonin 1A sub-type receptor mRNA and protein levels was determined by in situ hybridization and immunohistochemistry, respectively, while the number of binding sites was determined by in vitro autoradiography using [(3)H]8-hydroxy-2(di-n-propylamino)tetralin as the ligand. Our results revealed a significant sex difference in serotonin 1A sub-type receptor mRNA, protein and binding sites, with females having higher levels than males. Handling resulted in statistically significant decreased numbers of cells positive for serotonin 1A sub-type receptor mRNA or protein, as well as [(3)H]8-hydroxy-2(di-n-propylamino)tetralin binding sites in the area 4 of Ammon's horn and dentate gyrus of both pre-pubertal males and females. In adult animals the number of serotonin 1A sub-type receptor mRNA positive cells was increased as a result of handling in the area 1 of Ammon's horn, area 4 of Ammon's horn and dentate gyrus of males, while it was decreased only in the area 4 of Ammon's horn of females. Furthermore, the number of serotonin sub-type 1A receptor immunopositive cells, as well as [(3)H]8-hydroxy-2(di-n-propylamino)tetralin binding sites was increased in the area 1 of Ammon's horn, area 4 of Ammon's horn and dentate gyrus of handled males, whereas it was decreased in these same brain areas in the handled females. We can thus infer that neonatal handling results in alterations in postsynaptic serotonergic neurotransmission, which may contribute to the sex dimorphic effects of handling as to the vulnerability toward depression-like behavior in response to chronic stressful stimuli.

Role of sex and sex steroids in mediating pituitary-adrenal responses to acute buspirone treatment in sheep

Systematic characterisation of sex differences in the serotonergic modulation of the hypothalamic-pituitary-adrenal (HPA) axis may assist with our understanding of why stress-related disorders are disproportionately represented in women. In this study, we examined the acute effects of buspirone, a serotonergic 1A receptor subtype agonist, on the endocrine endpoints of adrenocorticotrophin (ACTH) and cortisol secretion in gonadectomised male and female sheep. Each sheep was treated with an acute i.v. injection containing vehicle or buspirone (0.03, 0.1 and 0.3 mg/kg) in the presence and absence of sex steroid replacement (SSR). In males, SSR treatment consisted of testosterone (2 x 200 mg s.c. pellets) and, in females, the mid-luteal phase of the oestrus cycle was simulated by treatment with oestradiol (1 cm s.c. implant) and an intravaginal controlled internal drug release device containing 0.3 g progesterone. ACTH, cortisol, testosterone and progesterone were measured in jugular blood. Basal ACTH levels were higher in males, whereas basal cortisol levels were higher in females, regardless of sex steroid status. The magnitude of the increase in ACTH and cortisol secretion following buspirone treatment was dose-dependent. There were no differences in the ACTH responses of males and females to buspirone treatment, either in the presence or absence of sex steroid replacement. However, although the cortisol response to buspirone was greater in females, there was no discernable effect of sex steroid status in addition to this sex difference on either basal or buspirone-stimulated cortisol release. We conclude that the larger basal and buspirone-stimulated cortisol response measured in females may reflect a sex difference, either in the sensitivity of the adrenal gland to ACTH or in the catecholaminergic innervation of the adrenal gland. The lack of effect of sex and sex steroids in the ACTH secretory response to buspirone may indicate that the sex differences in serotonergic modulation of the HPA axis, as reported previously by our group, were mediated via serotonergic receptor subtypes other than the 1A receptor.

Cellular mechanisms underlying an effect of “early handling” on pCREB and BDNF in the neonatal rat hippocampus

Early experiences have long-term effects on brain function and behavior. However, the precise mechanisms involved still remain elusive. In an effort to address this issue, we employed the model of "early handling", which is known to affect the ability of the adult organism to respond to stressful stimuli, and determined its effects on hippocampal pCREB and BDNF 2, 4, and 8 h later. 8 h following "handling" on postnatal day 1, there was an increase in pCREB and BDNF positive cells in the hippocampus, a brain area which is a specific target of "handling". On the other hand, vehicle injection resulted in decreased pCREB and BDNF in both handled and non-handled animals 2 and 4 h later. The "handling"-induced increase of pCREB and BDNF was cancelled by inhibition of NMDA, AMPA/kainate, GABA-A, 5-HT1A or 5-HT2A/C receptors, as well as L-type voltage-gated Ca(2+) channels. It thus appears that "early handling" activates these neurotransmitter receptors, leading to increased intracellular Ca(2+), phosphorylation of the transcription factor CREB, and increased BDNF expression. BDNF can then exert its morphogenetic effects and thus "imprint" the effects of "handling" on the brain.

Early life genetic, epigenetic and environmental factors shaping emotionality in rodents

Childhood trauma is known to increase risk for emotional disorders and addiction. However, little is currently understood about the neurodevelopmental basis of these effects, or how genetic and epigenetic factors interact with the environment to shape the systems subserving emotionality. In this review, we discuss the use of rodent models of early life emotional experience to study these issues in the laboratory and present some of our pertinent findings. In rats, postnatal maternal separation can produce lasting increases in emotional behavior and stressor-reactivity, together with alterations in various brain neurotransmitter systems implicated in emotionality, including corticotropin-releasing factor, serotonin, norepinephrine, and glutamate. Genetic differences between inbred mouse strains have been exploited to further study how maternal behavior affects emotional development using techniques such as cross-fostering and generation of inter-strain hybrids. Together with our own recent data, the findings of these studies demonstrate the pervasive influence of maternal and social environments during sensitive developmental periods and reveal how genetic factors determine how these early life experiences can shape brain and behavior throughout life.

Effect of androgens on sexual differentiation of pituitary gamma-aminobutyric acid receptor subunit GABA(B) expression

Previous work demonstrated a sexually dimorphic ontogenic expression of gamma-aminobutyric acid receptors (GABA(B)R) in rat pituitary. As sex steroids determine sex-specific expression patterns, we now studied the effect of sex hormones on pituitary GABA(B)R expression. GABA(B)R subunits, measured by Western blot and by semi-quantitative RT-PCR and luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone measured by RIA were determined in two experimental designs: First experimental design: 8- and 15-day-old females (8F, 15F); 8F and 15F treated with 100 mug testosterone propionate (TP) on day 1 of life (8F100TP, 15F100TP), 8- and 15-day-old males (8M, 15M) and 8M and 15M castrated on day 1 (8MC, 15MC). Second experimental design: 8-day-old female and male animals: 8F, 8F100TP, 8F treated with 1 mug/day TP on days 1-4 (8F1TP), 8F treated with the androgen antagonist Flutamide (Flut: 2.5 mg/100 g BW of pregnant mother on days E17-E23) (8F-Flut), 8M, 8MC, 8M treated with Flut as above (8M-Flut) and 8MC-Flut. In these animals, in addition, GABA, glutamate, aspartate and taurine were measured by HPLC in hypothalami and cortex. In the first set of experiments, GABA(B1)R mRNA/protein expression was higher in 8F than in 15F, 8M or 15M. In 8F100TP, GABA(B1)R mRNA/protein decreased to male levels. TP treatment did not alter GABA(B1)R expression in 15F. There was no difference in GABA(B1)R expression between 8M and 15M and neonatal castration did not modify its expression. In the second set of experiments, TP (1 mug) or Flut did not modify GABA(B1)R in 8F, while 100 microg TP continued to decrease GABA(B1)R expression. In 8M, Flut, alone or with castration, increased GABA(B1)R mRNA/protein expression to 8F. Hypothalamic GABA content followed the same pattern as pituitary GABA(B)R expression in 8-day-old animals, suggesting a cross-regulation. With regard to hormonal levels, 100 microg, but not 1 microg TP altered gonadotropins at 8 days, although both treatments effectively androgenized females as evidenced by lack of cycling. We conclude that androgens, acting pre- and postnatally, decrease pituitary GABA(B)R subunit expression.