Effect of neonatal handling on age-related impairments associated with the hippocampus

MK-801 administration during neonatal ethanol withdrawal attenuates interpositus cell loss and juvenile eyeblink conditioning deficits

Binge-level doses of ethanol have been demonstrated to severely disrupt the cerebellum and cerebellum-dependent tasks when administered to rodent subjects during the early postnatal period. N-methyl-d-aspartic acid (NMDA) receptor-mediated excitotoxicity associated with ethanol withdrawal has been implicated as a significant component contributing to neurotoxic effects resulting from early ethanol exposure, and studies using MK-801 (dizocilpine) have reported protection from ethanol-induced damage. The present study examined whether the administration of MK-801 during ethanol withdrawal would ameliorate ethanol-associated cell death in the interpositus nucleus of the cerebellum and behavioral deficits in a cerebellar dependent task. Long Evans rat pups were treated with ethanol (5.25 g/kg) in a binge-like manner on postnatal day 6 using intragastric intubation. Subjects then received an injection of MK-801 (0.5mg/kg) or vehicle during withdrawal, 30h after ethanol exposure. Rats were then trained on an eyeblink classical conditioning task as juveniles (40 days of age), and cerebellar interpositus nucleus numbers were assessed after conditioning. Ethanol-exposed subjects exhibited reductions in neuronal populations and behavioral deficits during eyeblink conditioning. However, MK-801 administration significantly attenuated observed deficiencies, suggesting a protective effect resulting from MK-801 treatment during ethanol withdrawal. These results support the role of NMDA receptor-mediated excitotoxicity as a component mechanism by which ethanol produces teratogenicity. Additionally, our findings support previous reports that have shown correlations between dependent measures of eyeblink classical-conditioning behavior and unbiased cell counts in the interpositus nucleus.

Childhood socioeconomic status and adult health

Socioeconomic status (SES) exposures during childhood are powerful predictors of adult cardiovascular morbidity, cardiovascular mortality, all-cause mortality, and mortality due to a range of specific causes. However, we still know little about when childhood SES exposures matter most, how long they need to last, what behavioral, psychological, or physiological pathways link the childhood SES experience to adult health, and which specific adult health outcomes are vulnerable to childhood SES exposures. Here, we discuss the evidence supporting the link between childhood and adolescent SES and adult health, and explore different environmental, behavioral, and physiological pathways that might explain how early SES would influence adult health. We also address the ages when SES exposures matter most for setting adult health trajectories as well as the role of exposure duration in SES influences on later health. While early childhood exposures seem to be potent predictors of a range of health outcomes, we emphasize that later childhood and adolescent exposures are risks for other health outcomes.

Transitions in sensitive period attachment learning in infancy: the role of corticosterone

Survival of altricial infants, including humans and rats, depends on attachment to the caregiver - a process that requires infants to recognize, learn, and remember their attachment figure. The demands of a dynamic environment combined with a maturing organism require frequent neurobehavioral reorganization. This restructuring of behavior and its supporting neural circuitry can be viewed through the unique lens of attachment learning in rats in which preference learning is enhanced and aversion learning is attenuated. Behavioral restructuring is well adapted to securing the crucial infant-caregiver relationship regardless of the quality of care. With maturation and the end of the infant-caregiver attachment learning period, the complex interplay of neural structures, hormones, and social behavior coordinates the developing rat's eventual transition to life outside of the nest. Nevertheless, early-life environmental and physiological stressors can alter the resilient nature of this system, particularly with respect to the amygdala, and these changes may provide important clues to understanding the lasting effects of early stress.

Neonatal handling impairs spatial memory and leads to altered nitric oxide production and DNA breaks in a sex specific manner

Early life events lead to behavioral and neurochemical changes in adulthood. The aim of this study is to verify the effects of neonatal handling on spatial memory, nitric oxide (NO) production, antioxidant enzymatic activities and DNA breaks in the hippocampus of male and female adult rats. Litters of rats were non-handled or handled (10 min/day, days 1-10 after birth). In adulthood they were subjected to a Morris water maze or used for biochemical evaluations. Female handled rats showed impairment in spatial learning. They also showed decreased NO production, while no effects were observed in these parameters in male rats. No effects were observed on the number of hippocampal NADPH diaphorase positive cells. In the Comet Assay, male handled rats showed increased DNA breaks index when compared to non-handled ones. We conclude that neonatal handling impairs learning performance in a sex-specific manner, what may be related to NO decreased levels.

Early environmental predictors of the affective and interpersonal constructs of psychopathy

Early childhood maltreatment (i.e., physical, sexual, emotional abuse) and caregiver disruptions are hypothesized to be instrumental in altering the neurobiology of the brain, particularly the amygdala, and contributing to the development of the affective deficits examined in individuals with psychopathy. Exposure to early untoward life events in models of rodent and nonhuman primates changes the neurobiology of the stress response. It is hypothesized that these changes may permanently shape brain regions that mediate stress and emotion and therefore play a role in the etiology of affective disorders in humans. The significance of experience (e.g., the intensity/severity, chronicity/duration, and developmental timing of experiences) and how the accompanying changes in the activity of the hypothalamic-pituitary-adrenocortical system affect alterations in the amygdala are discussed as critical contributors to the etiology of psychopathy. A model is proposed in which early maltreatment experiences contribute to alterations to the amygdala and produce a blunted or dissociative response to stress, a key factor in the affective deficits observed in psychopaths.

Hippocampal neurogenesis as a target for the treatment of mental illness: a critical evaluation

Over one-quarter of adult Americans are diagnosed with a mental illness like Major Depressive Disorder (MDD), Post-Traumatic Stress Disorder (PTSD), schizophrenia, and Alzheimer's Disease. In addition to the exceptional personal burden these disorders exert on patients and their families, they also have enormous cost to society. Although existing pharmacological and psychosocial treatments alleviate symptoms in many patients, the comorbidity, severity, and intractable nature of mental disorders strongly underscore the need for novel strategies. As the hippocampus is a site of structural and functional pathology in most mental illnesses, a hippocampal-based treatment approach has been proposed to counteract the cognitive deficits and mood dysregulation that are hallmarks of psychiatric disorders. In particular, preclinical and clinical research suggests that hippocampal neurogenesis, the generation of new neurons in the adult dentate gyrus, may be harnessed to treat mental illness. There are obvious applications and allures of this approach; for example, perhaps stimulating hippocampal neurogenesis would reverse the overt and noncontroversial hippocampal atrophy and functional deficits observed in Alzheimer's Disease and schizophrenia, or the more controversial hippocampal deficits seen in MDD and PTSD. However, critical examination suggests that neurogenesis may only correlate with mental illness and treatment, suggesting targeting neurogenesis alone is not a sufficient treatment strategy. Here we review the classic and causative links between adult hippocampal neurogenesis and mental disorders, and provide a critical evaluation of how (and if) our basic knowledge of new neurons in the adult hippocampus might eventually help combat or even prevent mental illness.

Vulnerability to stroke: implications of perinatal programming of the hypothalamic-pituitary-adrenal axis

Chronic stress is capable of exacerbating each major, modifiable, endogenous risk factor for cerebrovascular and cardiovascular disease. Indeed, exposure to stress can increase both the incidence and severity of stroke, presumably through activation of the hypothalamic-pituitary-adrenal (HPA) axis. Now that characterization of the mechanisms underlying epigenetic programming of the HPA axis is well underway, there has been renewed interest in examining the role of early environment on the evolution of health conditions across the entire lifespan. Indeed, neonatal manipulations in rodents that reduce stress responsivity, and subsequent life-time exposure to glucocorticoids, are associated with a reduction in the development of neuroendocrine, neuroanatomical, and cognitive dysfunctions that typically progress with age. Although improved day to day regulation of the HPA axis also may be accompanied by a decrease in stroke risk, evidence from rodent studies suggest that an associated cost could be increased susceptibility to inflammation and neuronal death in the event that a stroke does occur and the individual is exposed to persistently elevated corticosteroids. Given its importance in regulation of health and disease states, any long-term modulation of the HPA axis is likely to be associated with both benefits and potential risks. The goals of this review article are to examine (1) the clinical and experimental data suggesting that neonatal experiences can shape HPA axis regulation, (2) the influence of stress and the HPA axis on stroke incidence and severity, and (3) the potential for neonatal programming of the HPA axis to impact adult cerebrovascular health.

Long-term effects of neonatal handling on mu-opioid receptor levels in the brain of the offspring

Neonatal handling is an experimental paradigm of an early experience which permanently alters hypothalamic-pituitary-adrenal axis function resulting in increased ability to cope with stress, and decreased emotionality. In the present work we investigated the effect of neonatal handling on adult rat brain mu-opioid receptor levels, since the opioid system is known to play an important role in emotional processing, anxiety and stress responses. Neonatal handling resulted in increased levels of mu-opioid receptors in the basolateral and central amygdaloid nuclei, in the CA3 and CA4 hippocampal areas, in the ventral tegmental area, the nucleus accumbens and the prefrontal cortex. Handled animals of both sexes had lower anxiety as measured in the elevated plus maze. The increased mu receptor levels could participate in the molecular mechanisms underlying the well-documented decreased stress and anxiety responses of handled animals.

The pathways from mother's love to baby's future

Together with genetic factors, early-life experience governs the expression and function of stress-related genes throughout life. This, in turn, contributes to either resilience or vulnerability to depression and to aging-related cognitive decline. In humans and animal models, both the quality and quantity of early-life maternal care has been shown to be a predominant signal triggering bi-directional and enduring changes in expression profiles of genes including glucocorticoids and corticotropin releasing factor (CRH; hypothalamic and hippocampal), associated with the development of resilient or vulnerable phenotypes. However, many crucial questions remain unresolved. For examples, how is the maternal-derived signal transmitted to specific neuronal populations where enduring (likely epigenetic) regulation of gene expression takes place? What is the nature of this information? In other words, how do neurons know to ‘turn on’ epigenetic machinery? What are the direct functional consequences of altered gene expression? This review describes the voyage of recurrent bursts of sensory input from the mother (‘mother's love’) to CRH-expressing hypothalamic neurons that govern the magnitude of the response to stress. In addition, the acute and enduring effects of both nurturing and fragmented maternal care on the structure, cellular signaling and function of specific hippocampal and hypothalamic neurons are discussed. The evolving understanding of the processes initiated by the early life experience of ‘mother's love’ suggest novel molecular targets for prevention and therapy of stress-related affective and cognitive disorders.

Brain development under stress: hypotheses of glucocorticoid actions revisited

One of the conundrums in today's stress research is why some individuals flourish and others perish under similar stressful conditions. It is recognized that this individual variability in adaptation to stress depends on the outcome of the interaction of genetic and cognitive/emotional inputs in which glucocorticoid hormones and receptors play a crucial role. Hence one approach towards understanding individual variation in stress coping is how glucocorticoid actions can change from protective to harmful. To address this question we focus on four hypotheses that are connected and not mutual exclusive. First, the classical Glucocorticoid Cascade Hypothesis, in which the inability to cope with chronic stress causes a vicious cycle of excess glucocorticoid and downregulation of glucocorticoid receptors (GR) in the hippocampus triggering a feed-forward cascade of degeneration and disease. Second, the Balance Hypothesis, which takes also the limbic mineralocorticoid receptors (MR) into account and proposes that an integral limbic MR:GR imbalance is causal to altered processing of information in circuits underlying fear, reward, social behaviour and resilience, dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and impairment of behavioural adaptation. The MR:GR balance is altered by gene variants of these receptor complexes and experience-related factors, which can induce lasting epigenetic changes in the expression of these receptors. A particular potent epigenetic stimulus is the maternal environment which is fundamental for the Maternal Mediation Hypothesis. The outcome of perinatal gene x environment interaction, and thus of MR:GR-mediated functions depends however, on the degree of 'matching' with environmental demands in later life. The Predictive Adaptation Hypothesis therefore presents a conceptual framework to examine the role of glucocorticoids in understanding individual phenotypic differences in stress-related behaviours over the lifespan.

Early-life experience alters response of developing brain to seizures

Prolonged seizures during childhood are associated with behavior problems, memory impairment and school failure. No effective treatment currently exists after seizures to mitigate neuronal injury and long-term neurological sequelae for children with epilepsy. We studied the therapeutic efficacy of early-life environment on seizure-induced behavioral deficits, neuronal injury and the inflammatory reaction using the kainic acid (KA) seizure model. Two rearing conditions, maternal separation for 3 h daily versus maternal care in an enriched environment, were followed by single housing for the former (Deprived) and group housing in an enriched environment for the latter (Enriched). To examine the influence of differential rearing on the behavioral effects of early-life seizures, KA was injected on P21. On P28, marked reduction in exploratory behavior was noted after seizures only in the Deprived group. To investigate seizure-induced hippocampal injury, a separate group of rats were injected with KA on P35 since consistent seizure-induced neuronal injury is observed only in mature rats. Brains of rats sacrificed on P37 displayed a significant reduction in DNA fragmentation and microglial activation in Enriched compared to Deprived animals. Our results suggest that a nurturing early environment can enhance the ability of the developing brain to recover from seizures and provide a buffer against their damaging effects. While the nurturing environment was neuroprotective, the combination of deprived rearing and the insult of early-life seizures resulted in significant behavioral deficits, an increase in neuronal injury and activation of microglia in young rats.

Effects of neonatal handling on social memory, social interaction, and number of oxytocin and vasopressin neurons in rats

Early-life environmental events can induce profound long-lasting changes in several behavioral and neuroendocrine systems. The neonatal handling procedure, which involves repeated brief maternal separations followed by experimental manipulations, reduces stress responses and sexual behavior in adult rats. The purpose of this study was to analyze the effects of neonatal handling on social behaviors of male and female rats in adulthood, as manifest by the results of social memory and social interaction tests. The number of oxytocin (OT) and vasopressin (VP) neurons in the paraventricular (PVN) and supraoptic (SON) nuclei of hypothalamus were also analyzed. The results did not demonstrate impairment of social memory. Notwithstanding, handling did reduce social investigative interaction and increase aggressive behavior in males, but did not do so in females. Furthermore, in both males and females, handling was linked with reduced number of OT-neurons in the parvocellular region of the PVN, while no differences were detected in the magnocellular PVN or the SON. On the other hand, handled males exhibited increased number of VP-neurons in the magnocellular zone of the PVN. We may conclude that the repeated brief maternal separations can reduce affiliative social behavior in adult male rats. Moreover, the disruption of the mother-infant relationship caused by the handling procedure induced long-lasting morphological changes in critical neuroendocrine areas that are involved in social bonding in mammals.

(+/-)3,4-Methylenedioxymethamphetamine (MDMA) dose-dependently impairs spatial learning in the morris water maze after exposure of rats to different five-day intervals from birth to postnatal day twenty

During postnatal days (PD) 11-20, (+/-)3,4-methylenedioxymethamphetamine (MDMA) treatment impairs egocentric and allocentric learning, and reduces spontaneous locomotor activity; however, it does not have these effects during PD 1-10. How the learning impairments relate to the stress hyporesponsive period (SHRP) is unknown. To test this association, the preweaning period was subdivided into 5-day periods from PD 1-20. Separate pups within each litter were injected subcutaneously with 0, 10, 15, 20, or 25 mg/kg MDMA x4/day on PD 1-5, 6-10, 11-15, or 16-20, and tested as adults. The 3 highest MDMA dose groups showed reduced locomotor activity during the first 10 min (of 60 min), especially in the PD 1-5 and 6-10 dosing regimens. MDMA groups in all dosing regimens showed impaired allocentric learning in the Morris water maze (on acquisition and reversal, all MDMA groups were affected; on the small platform phase, the 2 high-dose groups were affected). No effects of MDMA were found on anxiety (elevated zero maze), novel object recognition, or egocentric learning (although a nonsignificant trend was observed). The Morris maze results did not support the idea that the SHRP is critical to the effects of MDMA on allocentric learning. However, since no effects on egocentric learning were found, but were apparent after PD 11-20 treatment, the results show that these 2 forms of learning have different exposure-duration sensitivities.

Insecure attachment style is associated with chronic widespread pain

Individuals with “insecure” adult attachment styles have been shown to experience more pain than people with secure attachment, though results of previous studies have been inconsistent. We performed a cross-sectional study on a large population-based sample to investigate whether, compared to pain free individuals, subjects with chronic widespread pain were more likely to report insecure adult attachment style. Subjects in a population-based cross-sectional study completed a self-rated assessment of adult attachment style. Attachment style was categorised as secure (i.e., normal attachment style); or preoccupied, dismissing or fearful (insecure attachment styles). Subjects completed a pain questionnaire from which three groups were identified: pain free; chronic widespread pain; and other pain. Subjects rated their pain intensity and pain-related disability on an 11 point Likert scale. Subjects (2509) returned a completed questionnaire (median age 49.9 years (IQR 41.2–50.0); 59.2% female). Subjects with CWP were more likely to report a preoccupied (RRR 2.6; 95%CI 1.8–3.7), dismissing (RRR 1.9; 95%CI 1.2–3.1) or fearful attachment style (RRR 1.4; 95%CI 1.1–1.8) than those free of pain. Among CWP subjects, insecure attachment style was associated with number of pain sites (Dismissing: RRR 2.8; 95%CI 1.2–2.3, Preoccupied: RRR = 1.8, 95%CI 0.98–3.5) and degree of pain-related disability (Preoccupied: RRR = 2.1, 95%CI 1.0–4.1), but not pain intensity. These findings suggest that treatment strategies based on knowledge of attachment style, possibly using support and education, may alleviate distress and disability in people at risk of, or affected by, chronic widespread pain.

The impact of early environmental rearing condition on the discriminative stimulus effects and Fos expression induced by cocaine in adult male and female rats

RATIONALE

A number of environmental manipulations, including maternal separation (MS), have been shown to alter behavioral responses to drugs of abuse.

OBJECTIVES

This study assessed if MS affected the stimulus and Fos-inducing effects of cocaine.

MATERIALS AND METHODS

In experiment 1, male and female Sprague-Dawley rats were exposed to brief maternal separations (BMS), long maternal separations (LMS), or animal facility rearing (AFR) and then trained as adults to discriminate cocaine (10 mg/kg, intraperitoneally) from saline. Following training, generalization tests to novel doses of cocaine and other dopaminergic compounds were performed. Assessments of variations in training dose pretreatment times were also made. In experiment 2, male and female rats exposed to MS conditions were administered cocaine or saline for 14 days, and Fos expression in the mesolimbic system was measured.

RESULTS

In males, BMS retarded the acquisition of the cocaine discrimination. Generalization to novel doses of cocaine did not differ among rearing conditions, but the training dose cue lasted longer in LMS. Distinct generalization and ED(50) profiles were found between male rearing conditions for all dopamine compounds. While BMS females had higher cocaine ED(50) estimates, no other differences were found in females. LMS males and females, as well as AFR females, had significant increases in Fos expression after cocaine in a region-specific manner. No differences were found with other rearing groups.

CONCLUSION

Early environmental variables altered the stimulus effects (in a sex-dependent manner) as well as the neuronal responsiveness to cocaine, which may be mediated by the dopamine system.

Developmental psychobiology of cyclic affective illness: Implications for early therapeutic intervention

The recurrent affective disorders are discussed from the perspective of accumulating inherited and experiential effects on gene expression. Stress and episodes of affective illness are viewed as leaving biochemical and microstructural residues in the central nervous system (CNS) in relation to their patterning, severity, and recurrence. Comorbid factors such as substance abuse and developmental disturbances may also interact with these illness-related variables. In addition to the primary pathological processes, secondary adaptive changes can also be induced, which, in concert with pharmacological interventions, may be sufficient to counter episode occurrences and illness progression. We postulate that the balance of primary pathological and secondary adaptive changes at multiple levels of CNS regulation accounts for recurrence and cyclicity in the affective disorders. The importance of early, effective, long-term interventions in the recurrent affective disorders and the therapeutic potential of several new treatment modalities including repeated transcranial magnetic stimulation (rTMS) are discussed.

Trajectories of maternal depressive symptoms over her child's life span: relation to adrenocortical, cardiovascular, and emotional functioning in children

Maternal depression has a number of adverse effects on children. In the present study, maternal depressive symptoms were assessed (using the Center for Epidemiological Studies Depression Scale) when their child was 3 months, 6 months, 1 year, 2 years, 4.25 years, 6 years, 7 years, 8 years, and 10 years of age. At 9.5 years of age, children's (94 females, 82 males) depressive symptoms as well as cardiovascular and cortisol levels during baseline and two psychologically stressful tasks were measured. Using multilevel modeling, maternal depressive symptom trajectories were considered in relation to their child's adrenocortical and cardiovascular responses to acute stress. Our goal was to determine maternal depressive symptom trajectories for children with elevated cardiovascular and cortisol reactivity to acute stress and elevated depressive symptoms. In general, those mothers with chronically elevated depressive symptoms over their child's life span had children with lower initial cortisol, higher cardiac output and stroke volume in response to acute stress, lower vascular resistance during acute stress tasks, and significantly more depressive symptoms at 9.5 years of age. These results are discussed in the context of established associations among hypothalamic-pituitary-adrenal axis dysregulation, depression, and cardiovascular disease.

Effects of (+)-methamphetamine on path integration and spatial learning, but not locomotor activity or acoustic startle, align with the stress hyporesponsive period in rats

Rats treated with (+)-methamphetamine (MA) on postnatal days (P) 11-20 exhibit long-term spatial and path integration (Morris water maze (MWM) and Cincinnati water maze (CWM)) learning deficits whereas those treated on P1-10 do not. MA treatment increases corticosterone release in an age-dependent U-shaped pattern that corresponds to the stress hyporesponsive period (SHRP; P4-15). Here we tested the hypothesis that the cognitive effects induced by MA are associated with treatment that begins within the SHRP. Three treatment regimens were compared, P1-10, P6-15, and P11-20. One male/female pair/litter received 0, 10, or 25mg/kg MA/dose (four doses/day at 2h intervals given s.c. with 19-21 litters/regimen). Locomotor activity and acoustic startle were tested as behaviors not predicted to be associated with the SHRP. Cincinnati and Morris water maze findings were consistent with the hypothesis in that MA-treated animals exposed from P6-15 or P11-20 showed impaired learning compared to those exposed from P1-10; however, on probe trials in the Morris water maze, MA-induced memory impairments were not regimen-specific and were contributed to by all treatment regimens. All MA treatment regimens induced reductions in locomotor activity and acoustic startle facilitation as expected. No differential effect on prepulse trials was seen suggesting no impairment in sensory gating. Cognitive deficits from neonatal MA treatment are associated with the SHRP and may be the product of hypothalamic-pituitary-adrenal (HPA) axis dysregulation during critical periods of brain development.

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.

Coregulation in Salivary Cortisol During Maternal Holding of Premature Infants

Purpose: The purpose of this study was to examine coregulation between mothers and preterm infants in hypothalamic-pituitary-adrenocortical (HPA) system activity, as indicated by salivary cortisol levels, while mothers held their infants. The research questions were (a) does mother—infant coregulation in HPA activity occur during holding? and (b) if mother— infant coregulation in HPA activity exists during holding, do type of holding, antenatal steroids, sound level, and maternal touch influence this coregulation? Sample: The sample consisted of 20 mother— infant dyads with infants at a mean postconceptional age of 34.7 weeks (+0.7) and average postnatal age of 15 days (+9) at the time of cortisol sampling. Design: The design was exploratory using convenience sampling. Maternal and infant cortisol levels were obtained at Time 1 (baseline) and Time 2 (end of holding); at each time, the absolute differences in levels between mother and infant were determined. Coregulation was operationalized as less difference between maternal-infant cortisol levels immediately after holding (Time 2) as compared to before holding (Time 1). Results: The two variables with the highest correlation with the Time 1/Time 2 difference score included antenatal steroids and ambient sound level, which were entered into a linear regression equation as predictor variables. A coregulatory relationship in cortisol levels existed between mothers and infants during holding, which was moderated by sound levels. Nurses in the neonatal intensive care unit (NICU) can facilitate the mother—infant relationship, as reflected in coregulatory measures, by promoting a quiet environment, particularly around mothers who are holding their infants.

Programming neuroendocrine stress axis activity by exposure to glucocorticoids during postembryonic development of the frog, Xenopus laevis

Exposure to elevated glucocorticoids during early mammalian development can have profound, long-term consequences for health and disease. However, it is not known whether such actions occur in nonmammalian species, and if they do, whether the molecular physiological mechanisms are evolutionarily conserved. We investigated the effects of dietary restriction, which elevates endogenous corticosterone (CORT), or exposure to exogenous CORT added to the aquarium water of Xenopus laevis tadpoles on later-life measures of growth, feeding behavior, and neuroendocrine stress axis activity. Dietary restriction of prometamorphic tadpoles reduced body size at metamorphosis, but juvenile frogs increased food intake, showed catch-up growth through 21 d after metamorphosis, and had elevated whole-body CORT content compared with controls. Dietary restriction causes increased CORT in tadpoles, so to mimic this increase, we treated tadpoles with 100 nm CORT or vehicle for 5 or 10 d and then reared juvenile frogs to 2 months after metamorphosis. Treatment with CORT decreased body weight at metamorphosis, but juvenile frogs showed catch-up growth and had elevated basal plasma (CORT). Immunohistochemical analysis showed that CORT exposure as a tadpole led to decreased glucocorticoid receptor immunoreactivity in brain regions involved with stress axis regulation and in the anterior pituitary gland of juvenile frogs. The elevated CORT in juvenile frogs, which could result from decreased negative feedback owing to down-regulation of glucocorticoid receptor, may drive the hyperphagic response. Taken together, our findings suggest that long-term, stable phenotypic changes in response to elevated glucocorticoids early in life are an ancient and conserved feature of the vertebrate lineage.

The neuropsychology of conduct disorder

This article reviews evidence from neuropsychological tests that brain dysfunction is a correlate of conduct disorder. Most studies report consistent findings of differential neuropsychological deficits for antisocial samples in verbal and “executive” functions. Neuropsychological measures are related to some of the best indicators of poor outcome for children with conduct symptoms, such as early onset, stability across time, hyperactive symptoms, and aggressiveness. Neuropsychological tests statistically predict variance in antisocial behavior independently of appropriate control variables. This article argues that neuropsychological variables warrant further study as possible causal factors for conduct disorder and presents one developmental perspective on how neuropsychological problems might contribute risk for conduct disorder.

Recurrent affective disorder: Roots in developmental neurobiology and illness progression based on changes in gene expression

Electrophysiological kindling and behavioral sensitization to psychomotor stimulants and stress provide paradigms for understanding how repeated acute events can leave neurobiological residues in gene expression, accounting for the observed long-lasting alterations in behavioral responsivity. Kindling helps conceptualize how repeated electrical stimulation of the brain can progressively evoke increased behavioral and convulsive responsivity, leading to spontaneous seizures in the absence of exogenous stimulation following sufficient stimulations. As kindling unfolds, a complex spatiotemporal cascade of events occurs and includes the induction of immediate early genes (e.g.,c-fos) and late effector genes (including peptides and growth factors) possibly associated with the observed changes in brain microstructure (e.g., synapse formation, axonal and dendritic sprouting, apoptosis). Behavioral sensitization to psychomotor stimulants and stress has also been shown to induce related but different cascades of effects on immediate early and late effector gene expression. These may be associated with the observed long-lasting alterations in behavioral responsivity based on prior experience. If these types of alterations are put into a developmental context, this would provide a paradigm for understanding how early life events could exert profound and behaviorally relevant biochemical and microstructural effects on the central nervous system of the developing organism. The conceptual overview offered by the sensitization and kindling models suggests that environmentally triggered neurobiological processes do not form a single or static residue but, instead, engage processes related to developmental neurobiology and learning and memory and whose substrate is constantly evolving over an organism's lifetime.

Neonatal handling reduces the number of cells in the medial preoptic area of female rats

Early-life events may induce alterations in neuronal function in adulthood. A crucial aspect in studying long-lasting effects induced by environmental interventions imposed to the animal several weeks before is finding a stable change that could be causally related to the phenotype observed in adulthood. In order to explain an adult trait, it seems necessary to look back to early life and establish a temporal line between events. The neonatal handling procedure is an experimental tool to analyze the long-lasting impact of early-life events. Aside from the neuroendocrine response to stress, neonatal handling also alters the functionality of the hypothalamus-pituitary-gonad (HPG) axis. Reductions in ovulation and surge of the luteinizing hormone (LH) on the proestrous day were shown in female rats. Considering the importance of the medial preoptic area (MPA) for the control of ovulation, the present study aimed to verify the effects of neonatal handling on the numerical density and cell size in the MPA in 11-day-old and 90-day-old female rats. Cellular proliferation was also assessed using BrdU (5-bromo-2'-deoxyuridine) in 11-day-old pups. Results showed that neonatal handling induces a stable reduction in the number of cells and in the size of the cell soma, which were lower in handled females than in nonhandled ones at both ages. Cellular proliferation in the MPA was also reduced 24 h after the last manipulation. The repeated mother-infant disruption imposed by the handling procedure "lesioned" the MPA. The dysfunction in the ovulation mechanisms induced by the handling procedure could be related to that neuronal loss. The study also illustrates the impact of an environmental intervention on the development of the brain.

Hypothalamic-pituitary-adrenal (HPA) axis function in 3-month old infants with prenatal selective serotonin reuptake inhibitor (SSRI) antidepressant exposure

BACKGROUND

Prenatal exposure to stress and selective serotonin reuptake inhibitors (SSRIs) alter hypothalamic-pituitary-adrenal (HPA) stress reactivity in offspring, however, the effects of combined exposure to HPA activity in human infants is unknown.

OBJECTIVE

To examine HPA basal levels and stress responsiveness in 3-month olds with prenatal exposure to SSRIs.

METHODS

Salivary cortisol levels in infants of SSRI treated mothers (n=31, mean exposure 230.2+/-72.2 days) were compared with non-SSRI exposed (n=45) infants in response to a challenge (infant-controlled habituation task) and under basal conditions in the late afternoon/early evening. Mode of feeding, to account for possible postnatal drug exposure via breast milk, as well as measures of pre and postnatal maternal mood, were included as covariates.

RESULTS

Lower post-stress cortisol levels were observed in non-SSRI exposed/non-breastfed infants compared with non-SSRI exposed infants who were breastfed at 3 months of age. Stress reactivity patterns among SSRI exposed infants did not differ with mode of feeding. The cortisol reactivity slope (CRS) was significantly lower among non-SSRI exposed non-breastfed infants compared with non-SSRI exposed breastfed infants. Early evening basal cortisol levels were lower in SSRI exposed infants than in non-SSRI exposed infants, controlling for maternal mood and mode of feeding. Postnatal SSRI exposure (infant SSRI drug levels) via breast milk was not associated with stress or basal cortisol levels. Total cortisol, reflected by the AUC measure, did not differ significantly between exposure groups.

CONCLUSIONS

Prenatal SSRI exposure altered HPA stress response patterns and reduced early evening basal cortisol levels. Stress challenge HPA response differences only became apparent when the moderating effect of method of feeding was accounted for. These findings suggest an early "programming" effect of antenatal maternal mood, prenatal SSRI exposure and postnatal maternal care giving on the HPA system.

Effects of early postnatal sibling deprivation on anxiety and vulnerability to cocaine in offspring rats

RATIONALE

Early-life experience has long-term consequences on affective behavior and drug abuse in adults. While many manipulations used to study these consequences alter mother-infant interactions, the effects of sibling interactions are less well characterized.

OBJECTIVES

To examine the long-term effects of early postnatal sibling deprivation (EPSD) on anxiety-like behavior, sucrose preference and behavioral responses to cocaine in adult rats.

MATERIALS AND METHODS

After EPSD manipulation, in which litters were culled to one pup on postnatal day 1 (PN1) or 7 (PN7), the dams' maternal behavior was observed. After the pups reached adulthood, we tested their behavioral responses in the elevated plus maze and sucrose consumption, and to cocaine conditioned place preference and cocaine sensitization.

RESULTS

The pups with EPSD on PN1 received more maternal licking/grooming during the first postnatal week. EPSD on PN1 but not PN7 enhanced locomotor activity in the open field test and exploration of open arms in the elevated plus maze in both female and male offspring. While EPSD had no effect on sucrose intake in adult rats, it decreased vulnerability to cocaine sensitization and cocaine conditioned place preference in male but not female rats.

CONCLUSION

Our findings that early postnatal sibling deprivation influences maternal licking/grooming behavior, as well as anxiety-like behavior and vulnerability to drugs in pups that have grown to adulthood, suggests that both sibling interaction and maternal behavior, play critical roles in individual development.

HPA system regulation and adult attachment anxiety: individual differences in reactive and awakening cortisol

Early life experiences can influence hypothalamus-pituitary-adrenal (HPA) axis regulation in adulthood, in both animals and humans. In humans, they have also been shown to influence adult attachment styles. However, the relationship between adult attachment styles and HPA axis regulation is largely unexplored. The present study investigated the relationship among varying levels of attachment anxiety and avoidance with both the cortisol response to acute stress (CRS) and the cortisol response to awakening (CRA) in 48 adult women. Attachment-unrelated stress was induced by a laboratory stress task. Saliva for free cortisol assessment was sampled before and after the stress task in the laboratory and at home on 2 consecutive days in the morning after awakening. We found that attachment anxiety but not attachment avoidance was associated with cortisol measures. Attachment anxiety was positively correlated with CRS and negatively with CRA. Finally, the two cortisol parameters were negatively associated with one another. The results are discussed with respect to (1) recent findings suggesting that the HPA system and hippocampus are programmed during critical development periods, establishing a certain trajectory of physiological responsiveness throughout life, and (2) a model that links development of the hippocampus with self development.

Effect of neonatal handling on adult rat spatial learning and memory following acute stress

Brief neonatal handling permanently alters hypothalamic-pituitary-adrenal axis function resulting in increased ability to cope with stress. Since stress is known to affect cognitive abilities, in the present study we investigated the effect of brief (15 min) handling on learning and memory in the Morris water maze, following exposure to an acute restraint stress either before training or recall. Exposure of non-handled rats to the acute stress prior to training resulted in quicker learning of the task, than in the absence of the stressor. When acute stress preceded acquisition, male handled rats showed an overall better learning performance, and both sexes of handled animals were less impaired in the subsequent memory trial, compared to the respective non-handled. In addition, the number of neurons immunoreactive for GR was higher in all areas of Ammon's horn of the handled rats during the recall. In contrast, the number of neurons immunoreactive for MR was higher in the CA1 and CA2 areas of the non-handled males. When the acute restraint stress was applied prior to the memory test, neonatal handling was not effective in preventing mnemonic impairment, as all animal groups showed a similar deficit in recall. In this case, no difference between handled and non-handled rats was observed in the number of GR positive neurons in the CA2 and CA3 hippocampal areas during the memory test. These results indicate that early experience interacts with sex and acute stress exposure in adulthood to affect performance in the water maze. Hippocampal corticosterone receptors may play a role in determining the final outcome.

Neonatal tactile stimulation enhances spatial working memory, prefrontal long-term potentiation, and D1 receptor activation in adult rats

Environmental stimuli during neonatal periods play an important role in the development of cognitive function. In this study, we examined the long-term effects of neonatal tactile stimulation (TS) on spatial working memory (SWM) and related mechanisms. We also investigated whether TS-induced effects could be counteracted by repeated short periods of maternal separation (MS). Wistar rat pups submitted to TS were handled and marked transiently per day during postnatal days 2-9 or 10-17. TS/MS pups were stimulated in the same way as TS pups and then individually separated from their mother for 1h/day. Their nontactile stimulated (NTS) siblings served as controls. In adulthood, TS and TS/MS rats showed better performance in two versions of the delayed alternation task and superior in vivo long-term potentiation of the hippocampo-prefrontal cortical pathway when compared with controls. Furthermore, there were more doses of A77636 (a selective dopamine D1 agonist) to significantly improve SWM performance in TS and TS/MS rats than in NTS rats, suggesting that activation of prefrontal D1 receptors in TS and TS/MS rats is more optimal for SWM function than in NTS rats. MS did not counteract TS-induced effects because no significant difference was found between TS/MS and TS animals. These data indicate that in early life, external tactile stimulation leads to long-term facilitative effects in SWM-related neural function.

Inhibition of serotonin but not norepinephrine transport during development produces delayed, persistent perturbations of emotional behaviors in mice

Serotonin (5-HT) acts as a neurotransmitter, but also modulates brain maturation during early development. The demonstrated influence of genetic variants on brain function, personality traits, and susceptibility to neuropsychiatric disorders suggests a critical importance of developmental mechanisms. However, little is known about how and when developmentally perturbed 5-HT signaling affects circuitry and resulting behavior. The 5-HT transporter (5-HTT) is a key regulator of extracellular 5-HT levels and we used pharmacologic strategies to manipulate 5-HTT function during development and determine behavioral consequences. Transient exposure to the 5-HTT inhibitors fluoxetine, clomipramine, and citalopram from postnatal day 4 (P4) to P21 produced abnormal emotional behaviors in adult mice. Similar treatment with the norepinephrine transporter (NET) inhibitor, desipramine, did not adversely affect adult behavior, suggesting that 5-HT and norepinephrine (NE) do not share the same effects on brain development. Shifting our period of treatment/testing to P90/P185 failed to mimic the effect of earlier exposure, demonstrating that 5-HT effects on adult behavior are developmentally specific. We have hypothesized that early-life perturbations of 5-HT signaling affect corticolimbic circuits that do not reach maturity until the peri-adolescent period. In support of this idea, we found that abnormal behaviors resulting from postnatal fluoxetine exposure have a post-pubescent onset and persist long after reaching adult age. A better understanding of the underlying 5-HT sensitive circuits and how they are perturbed should lead to new insights into how various genetic polymorphisms confer their risk to carriers. Furthermore, these studies should help determine whether in utero exposure to 5-HTT blocking drugs poses a risk for behavioral abnormalities in later life.

What do trajectories of childhood socioeconomic status tell us about markers of cardiovascular health in adolescence?

OBJECTIVE

The current study examined trajectories of socioeconomic status (SES) throughout childhood and their relationship to markers of cardiovascular health in adolescence. The goal was to determine whether early-life SES, current SES, cumulative SES, and/or social mobility best explained the relationship between SES experiences across an adolescent's life span and current blood pressure (BP), heart rate (HR), and body mass index (BMI).

DESIGN

One hundred two adolescents completed cardiovascular health assessments including systolic blood pressure, diastolic blood pressure, HR, and BMI. Parents reported on family SES, indicating the number of bedrooms in the family home for each year of the child's life.

RESULTS

Using Jones, Nagin, and Roeder's semiparametric group-based method, four distinct trajectories of childhood SES were identified. Trajectory groups were differentially related to adolescents' systolic blood pressure and diastolic blood pressure. A trajectory showing low early-life SES that increased through childhood was associated with the highest BP in adolescence. Partial correlation analyses specifically examining the various life-course scenarios similarly indicated that early-life SES was the strongest predictor of adolescents' BP. Trajectories of childhood SES were unrelated to HR and BMI.

CONCLUSIONS

Of the life-course models that we tested, an early-life SES model best explained adolescents' current BP. These findings point toward early-life developmental processes as potential candidates for explaining the relationship between SES and risk factors related to cardiovascular disease. They suggest that interventions designed to reduce SES health disparities should take place early in a child's life.

Gene-environment interaction affects substance P and neurokinin A in the entorhinal cortex and periaqueductal grey in a genetic animal model of depression: implications for the pathophysiology of depression

Evidence implies a role for corticotropin-releasing hormone (CRH) and tachykinins, e.g. substance P (SP) and neurokinin A (NKA) in the pathophysiology of depression. We have previously shown that SP- and NKA-like immunoreactivity (-LI) concentrations were altered in the frontal cortex and striatum of the congenitally 'depressed' Flinders Sensitive Line (FSL) compared to the Flinders Resistant Line (FRL) control rats. It is also known that environmental stress may affect brain levels of tachykinins. In view of these results we decided to superimpose maternal deprivation, an early life environmental stressor, onto the genetically predisposed 'depressed' FSL rats and the FRL control rats and use this paradigm as a model of gene-environment interaction. The adult animals were sacrificed, adrenal glands and brains dissected out and SP-, NKA- and CRH-LI levels were determined in ten discrete brain regions. Maternal deprivation led to a marked increase in SP-LI and NKA-LI levels in the periaqueductal grey (PAG) and entorhinal cortex of the 'depressed' FSL strain while it had no significant effect in the FRL controls. Furthermore, specific strain differences in peptide-LI content were confirmed. No difference was found in relative adrenal gland weight, which is consistent with the finding that CRH-LI levels in the hypothalamus were similar across strains, and insensitive to stress in either strain. Taken together, these data are in line with behavioural experiments showing ameliorating effects of NK1 and NK2 receptor antagonists against anxiety and depression-like symptoms in rodents, and therefore further implicate the tachykinin systems in the pathophysiology of depression and adult life psychopathology.

Sex- and age-dependent effects of early postnatal sibling deprivation on spatial learning and memory in adult rats

In this study, we investigated the effects of early postnatal sibling deprivation (EPSD) on spatial learning and memory in adult rats. Litters were culled to one pup with its mother on postnatal day (PN) 1 or 7 and their spatial learning and memory ability were examined with Morris water maze in adult. EPSD on PN1 improved, but on PN7 impaired performance of the spatial learning task in adult female rats. However, EPSD did not have any effect on the spatial learning ability in adult male rats.

Both infantile stimulation and exposure to sweet food lead to an increased sweet food ingestion in adult life

We have reported that neonatal handling leads to increased sweet food preference in adult life. Our aim was to verify if these differences in feeding behavior appear before puberty, and whether other types of intervention in periadolescence (such as exposure to toys) could interfere with sweet food consumption later in life. Nests of Wistar rats were (1) non-handled or (2) handled (10 min/day) on days 1-10 after birth. Males from these groups were subdivided in two subgroups: one was habituated to sweet food (Froot Loops-Kellogs) in a new environment for 4 days and tested for sweet food preference at age 27 days, before submitting to a new habituation and test for sweet food ingestion again in adult life. The other subgroup was habituated and tested only in adulthood. In another set of experiments, neonatally non-handled rats were exposed or not to a new environment with toys in periadolescence, and tested for sweet food ingestion as adults. Neonatal handling increases sweet food consumption only if the habituation and tests are performed after puberty. Interestingly, infant exposure to sweet food had a similar effect as neonatal handling, since controls that were exposed to sweet food at age 22 to 27 days increased their ingestion as adults. Exposure to toys in periadolescence had the same effect. We suggest that an intervention during the first postnatal days or exposure to an enriched environment later in the pre-pubertal period leads to behavioral alterations that persist through adulthood, such as increased sweet food ingestion.

Epigenetic programming of the stress response in male and female rats by prenatal restraint stress

Exposure to hostile conditions results in a series of coordinated responses aimed at enhancing the probability of survival. The activation of the hypothalamo-pituitary-adrenocortical (HPA) axis plays a pivotal role in the stress response. While the short-term activation of the HPA axis allows adaptive responses to the challenge, in the long run this can be devastating for the organism. In particular, life events occurring during the perinatal period have strong long-term effects on the behavioral and neuroendocrine response to stressors. In male and female rats exposed to prenatal restraint stress (PRS), these effects include a long-lasting hyperactivation of the HPA response associated with an altered circadian rhythm of corticosterone secretion. Furthermore, male animals exhibit sleep disturbances. In males, these HPA dysfunctions have been reported in infant, young, adult and aged animals, thus suggesting a permanent effect of early stress. Interestingly, after exposure to an intense inescapable footshock, female PRS rats durably exhibit a blunted corticosterone secretion response to stress. In male PRS rats exposed to an alcohol challenge, the HPA axis is similarly hyporesponsive. Rats exposed to PRS also show behavioral disturbances. Both male and female PRS rats show high anxiety levels and depression-like behavior during adulthood, although some studies suggest that female PRS rats present low anxiety levels. With ageing, male and female PRS rats exhibit memory impairments in hippocampus-dependent tasks, while female PRS rats improve their memory performance during adulthood. The gender effect on behavior seems to be related to a reduction in hippocampal plasticity in male PRS rats, and an increase in female PRS rats. Despite the permanent imprinting induced by early stress, the dysfunctions observed after PRS can be reversed by environmental or pharmacological strategies such as environmental enrichment or antidepressive and neurotrophic treatments. Mechanisms underlying the effects of PRS on the offspring remain largely unknown. However, previous studies have demonstrated that maternal glucocorticoids during pregnancy play an important role in the HPA disturbances reported in male offspring. Finally, gestational stress has long-lasting effects on the HPA axis and on behavior in the dams. Alterations in maternal behavior could thus also make a strong contribution to the long-term effects of PRS, through epigenetic mechanisms.

11beta-HSD1, inflammation, metabolic disease and age-related cognitive (dys)function

11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is an intracellular amplifier of glucocorticoid action. By converting intrinsically inert glucocorticoids (cortisone, 11-dehydrocorticosterone) into their active forms (cortisol, corticosterone), 11beta-HSD1 increases glucocorticoid access to receptors. Glucocorticoid hormones modulate diverse physiological processes, linking circadian rhythms to food seeking, motivational and cognitive behaviours, as well as intermediary metabolism and immune responses. They are a key component of pathways that buffer the organism against stressful challenges. Here we review the part played in these processes by 11beta-HSD1, and discuss the promise of inhibitors of 11beta-HSD1 in alleviating disorders associated with cumulative stress.

Enhanced hippocampal long-term potentiation and spatial learning in aged 11beta-hydroxysteroid dehydrogenase type 1 knock-out mice

Glucocorticoids are pivotal in the maintenance of memory and cognitive functions as well as other essential physiological processes including energy metabolism, stress responses, and cell proliferation. Normal aging in both rodents and humans is often characterized by elevated glucocorticoid levels that correlate with hippocampus-dependent memory impairments. 11Beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) amplifies local intracellular ("intracrine") glucocorticoid action; in the brain it is highly expressed in the hippocampus. We investigated whether the impact of 11beta-HSD1 deficiency in knock-out mice (congenic on C57BL/6J strain) on cognitive function with aging reflects direct CNS or indirect effects of altered peripheral insulin-glucose metabolism. Spatial learning and memory was enhanced in 12 month "middle-aged" and 24 month "aged" 11beta-HSD1(-/-) mice compared with age-matched congenic controls. These effects were not caused by alterations in other cognitive (working memory in a spontaneous alternation task) or affective domains (anxiety-related behaviors), to changes in plasma corticosterone or glucose levels, or to altered age-related pathologies in 11beta-HSD1(-/-) mice. Young 11beta-HSD1(-/-) mice showed significantly increased newborn cell proliferation in the dentate gyrus, but this was not maintained into aging. Long-term potentiation was significantly enhanced in subfield CA1 of hippocampal slices from aged 11beta-HSD1(-/-) mice. These data suggest that 11beta-HSD1 deficiency enhances synaptic potentiation in the aged hippocampus and this may underlie the better maintenance of learning and memory with aging, which occurs in the absence of increased neurogenesis.

Increased daily handling of ovariectomized rats enhances performance on a radial-maze task and obscures effects of estradiol replacement

Estrogen impacts performance on tasks of learning and memory, although there are inconsistencies in the direction and magnitude of the reported effects. Contributory factors to the inconsistencies may be methodological differences associated with different regimens of treatment. The goal of the present experiment was to assess the effect of increased handling, such as that commonly associated with pharmacological or other experimental manipulations, on the ability of estrogen to influence working memory performance. Young adult rats were ovariectomized and implanted with capsules containing either cholesterol or 25% estradiol diluted in cholesterol. Half of each hormone treatment group received standard handling, which consisted of handling required to carry out experimental procedures and half received increased handling, which consisted of standard handling as well as 2 min of additional daily handling by the experimenter. Animals were trained daily on a working memory task on an eight-arm radial maze for 24 days of acquisition and for eight additional daily trials in which delays of either 1 min or 3 h were imposed between the fourth and fifth arm choices. Animals that received increased handling exhibited significantly enhanced performance during acquisition and delay trials compared to those that received standard handling. Estradiol significantly enhanced performance during delay trials in animals that received standard handling but had no effect in animals that received increased handling. These results suggest that the amount of handling that animals receive as part of experimental procedures may obscure the memory enhancing effects of estradiol replacement on certain tasks of cognition.