Adrenal steroids and plasticity of hippocampal neurons: toward an understanding of underlying cellular and molecular mechanisms

Blocking CRH receptors in adults mitigates age-related memory impairments provoked by early-life adversity

In humans, early-life adversity is associated with impairments in learning and memory that may emerge later in life. In rodent models, early-life adversity directly impacts hippocampal neuron structure and connectivity with progressive deficits in long-term potentiation and spatial memory function. Previous work has demonstrated that augmented release and actions of the stress-activated neuropeptide, CRH, contribute to the deleterious effects of early-life adversity on hippocampal dendritic arborization, synapse number and memory-function. Early-life adversity increases hippocampal CRH expression, and blocking hippocampal CRH receptor type-1 (CRHR1) immediately following early-life adversity prevented the consequent memory and LTP defects. Here, we tested if blocking CRHR1 in young adults ameliorates early-life adversity-provoked memory deficits later in life. A weeklong course of a CRHR1 antagonist in 2-month-old male rats prevented early-life adversity-induced deficits in object recognition memory that emerged by 12 months of age. Surprisingly, whereas the intervention did not mitigate early-life adversity-induced spatial memory losses at 4 and 8 months, it restored hippocampus-dependent location memory in 12-month-old rats that experienced early-life adversity. Neither early-life adversity nor CRHR1 blockade in the adult influenced anxiety- or depression-related behaviors. Altogether, these findings suggest that cognitive deficits attributable to adversity during early-life-sensitive periods are at least partially amenable to interventions later in life.

Synaptic changes in the hippocampus of adolescent female rodents associated with resilience to anxiety and suppression of food restriction-evoked hyperactivity in an animal model for anorexia nervosa

Anorexia nervosa is a mental illness that emerges primarily during early adolescence, with mortality rate that is 200 times higher than that of suicide. The illness is characterized by intense fear of gaining weight, heightened anxiety, obstinate food restriction, often accompanied by excessive exercise, in spite of mounting hunger. The illness affects females nine times more often than males, suggesting an endocrine role in its etiology. Its relapse rate exceeds 25%, yet there are no accepted pharmacological treatments to prevent this. Here, we summarize studies from this laboratory that have used adolescent female rodents in activity-based anorexia (ABA), an animal model of anorexia nervosa, with the goal of identifying neurobiological underpinnings of this disease. We put forth a hypothesis that a GABAergic mechanism within the hippocampus is central to regulating an individual׳s anxiety which, in turn, strongly influences the individual׳s resilience/vulnerability to ABA. In particular, we propose that ionotropic GABAA receptors containing the subunits alpha4 and delta, are at play for exerting shunting inhibition upon hippocampal pyramidal neurons that become more excitable during ABA. Since these receptors confer insensitivity to benzodiazepines, this pharmacological profile of ABA fits with lack of report indicating efficacy of benzodiazepines in reducing the anxiety experienced by individuals with anorexia nervosa. The idea that the GABAergic system of the hippocampus regulates resilience/vulnerability to anorexia nervosa complements current opinions about the important roles of the prefrontal cortex, amygdala, striatum, gustatory pathways and feeding centers of the hypothalamus and of the neuromodulators, serotonin and dopamine, in the etiology of the disease. This article is part of a Special Issue entitled SI: Adolescent plasticity.

Developmental exposure to SSRIs, in addition to maternal stress, has long-term sex-dependent effects on hippocampal plasticity

RATIONALE

During pregnancy and postpartum period, 20 % of women are affected by depression, which is a growing health concern. Selective serotonin reuptake inhibitor (SSRI) medications are popular treatments for maternal depression; however, the effect of maternal depression and perinatal SSRI exposure on offspring's neural development needs further investigation.

OBJECTIVES

This study aims to determine the role of developmental fluoxetine exposure on hippocampal plasticity in the adult offspring.

METHODS

Sprague-Dawley rat offspring were exposed to fluoxetine beginning on postnatal day 1. Offspring were also exposed to prenatal maternal stress. Four groups of male and female offspring were used: (1) prenatal stress + fluoxetine, (2) prenatal stress + vehicle, (3) fluoxetine alone, and (4) vehicle alone. Hippocampi were analyzed for levels of cell proliferation, immature neurons, and new cell survival (3 weeks after 5-bromo-2-deoxyuridine injection) in the granule cell layer, as well as synaptophysin density in the CA3 region and granule cell layer. TPH staining was assessed in the dorsal raphe nucleus.

RESULTS

Developmental fluoxetine exposure to prenatally stressed offspring reversed the effect of prenatal stress or fluoxetine exposure alone on the number of immature neurons. Prenatal stress alone, regardless of developmental exposure to fluoxetine, markedly decreased hippocampal cell proliferation and tended to decrease new cell survival. Furthermore, in adult female offspring, developmental fluoxetine exposure greatly increased new cell survival and significantly decreased synaptophysin density in the granule cell layer.

CONCLUSIONS

There are long-term effects of developmental SSRI exposure on hippocampal plasticity that is differentially affected by expose to maternal adversity and offspring sex.

Hippocampal dysfunctions in tumor-bearing mice

Individuals with cancer are particularly susceptible to depression and cognitive impairment. However, the precise mechanisms underlying cancer-induced hippocampal dysfunction are poorly understood. We investigated the effects of a peripheral tumor on emotional behavior, hippocampus-dependent memory and associated molecular and cellular features using an experimental animal model. Behavioral alterations were examined; stress-related parameters measured; hippocampal neurogenesis evaluated; and the levels of pro-inflammatory cytokines, brain-derived neurotrophic factor (BDNF) and cyclooxygenase-2 (COX-2) assayed, 2 weeks after inoculation of adult BALB/c mice with cells of a colon carcinoma cell line (CT26). As the tumors developed, CT26-inoculated mice showed significant increases in the depression-like behavior (measured using the tail suspension test) and memory impairment (in terms of object recognition) compared with vehicle-inoculated controls. The presence of a peripheral tumor significantly elevated the hippocampal levels of mRNAs encoding interleukin-6 (IL-6) and tumor necrosis factor-α, as well as plasma IL-6 and corticosterone levels. Additionally, the adrenal glands became enlarged, and the numbers of Ki-67-positive proliferating hippocampal cells and doublecortin-positive immature progenitor neurons, as well as the constitutive levels of mRNAs encoding BDNF and COX-2 were significantly reduced. Therefore, a peripheral tumor alone may be sufficient to induce hippocampal dysfunction, possibly by reducing the rate of neurogenesis and the levels of BDNF and COX-2 in that tissue and also by increasing stress-related parameters and the circulating levels of pro-inflammatory cytokines.

Adolescent female C57BL/6 mice with vulnerability to activity-based anorexia exhibit weak inhibitory input onto hippocampal CA1 pyramidal cells

Anorexia nervosa (AN) is an eating disorder characterized by self-imposed severe starvation and often linked with excessive exercise. Activity-based anorexia (ABA) is an animal model that reproduces some of the behavioral phenotypes of AN, including the paradoxical increase in voluntary exercise following food restriction (FR). Although certain rodents have been used successfully in this animal model, C57BL/6 mice are reported to be less susceptible to ABA. We re-examined the possibility that female C57BL/6 mice might exhibit ABA vulnerability during adolescence, the developmental stage/sex among the human population with particularly high AN vulnerability. After introducing the running wheel to the cage for 3 days, ABA was induced by restricting food access to 1h per day (ABA1, N=13) or 2 h per day (ABA2, N=10). All 23 exhibited increased voluntary wheel running (p<0.005) and perturbed circadian rhythm within 2 days. Only one out of five survived ABA1 for 3 days, while 10 out of 10 survived ABA2 for 3 days and could subsequently restore their body weight and circadian rhythm. Exposure of recovered animals to a second ABA2 induction revealed a large range of vulnerability, even within littermates. To look for the cellular substrate of differences in vulnerability, we began by examining synaptic patterns in the hippocampus, a brain region that regulates anxiety as well as plasticity throughout life. Quantitative EM analysis revealed that CA1 pyramidal cells of animals vulnerable to the second ABA2 exhibit less GABAergic innervation on cell bodies and dendrites, relative to the animals resilient to the second ABA (p<0.001) or controls (p<0.05). These findings reveal that C57BL/6J adolescent females can be used to capture brain changes underlying ABA vulnerability, and that GABAergic innervation of hippocampal pyramidal neurons is one important cellular substrate to consider for understanding the progression of and resilience to AN.

Pregnancy or stress decrease complexity of CA3 pyramidal neurons in the hippocampus of adult female rats

Pregnancy is a time of distinct neural, physiological and behavioral plasticity in the female. It is also a time when a growing number of women are vulnerable to stress and experience stress-related diseases, such as depression and anxiety. However, the impact of stress during gestation on the neurobiology of the mother has yet to be determined, particularly with regard to changes in the hippocampus; a brain area that plays an important role in stress-related diseases. Therefore, the aim of the present study was to understand how stress and reproductive state may alter dendritic morphology of CA1 and CA3 pyramidal neurons in the hippocampus. To do this, adult age-matched pregnant and virgin female Wistar rats were divided into two conditions: (1) control and (2) stress. Females in the stress condition were restrained for 1h/day for the last 2 weeks of gestation and at matched time-points in virgin females. Females were sacrificed the day after the last restraint session and brains were processed for Golgi impregnation. Dendritic length and number of branch points were quantified for apical and basal regions of CA1 and CA3 pyramidal neurons. Results show that regardless of reproductive state, stressed females had significantly shorter apical dendrites and fewer apical branch points in CA3 pyramidal cells. In addition, pregnant females, regardless of stress exposure, had less complex CA3 pyramidal neurons, as measured by Sholl analysis. No differences between conditions were seen in morphology of CA1 pyramidal neurons. This work shows that both repeated restraint stress and pregnancy affect dendritic morphology by decreasing complexity of CA3, but not CA1, neurons in the hippocampus.

Direction-dependent effects of chronic "jet-lag" on hippocampal neurogenesis

Disruptions in circadian rhythms, as seen in human shift workers, are often associated with many health consequences including impairments in cognitive functions. However, the mechanisms underlying these affects are not well understood. The objective of the present study is to explore the effects of circadian disruption on hippocampal neurogenesis, which has been implicated in learning and memory and could serve as a potential pathway mediating the cognitive consequences associated with rhythm disruption. Circadian rhythm disruptions were introduced using a weekly 6 h phase shifting paradigm, in which male Wistar rats were subjected to either 6 h phase advances (i.e. traveling eastbound from New York to Paris) or 6 h phase delays (i.e. traveling westbound from Paris to New York) in their light/dark schedule every week. The effects of chronic phase shifts on hippocampal neurogenesis were assessed using doublecortin (DCX), a microtubule binding protein expressed in immature neurons. The results revealed that chronic disruption in circadian rhythms inhibits hippocampal neurogenesis, and the degree of reduction in neurogenesis depends upon the direction and duration of the shifts. In two cohorts of animals that experienced phase shifts for either 4 or 8 weeks, a greater decrease in neurogenesis was observed when the phase was advanced versus delayed in both groups. The direction-dependent effect mirrors the findings on clock gene expression in the SCN, suggesting a causal link between the reduction in hippocampal neurogenesis and a disrupted SCN circadian clock.

Hippocampal neurogenesis and dendritic plasticity support running-improved spatial learning and depression-like behaviour in stressed rats

Exercise promotes hippocampal neurogenesis and dendritic plasticity while stress shows the opposite effects, suggesting a possible mechanism for exercise to counteract stress. Changes in hippocampal neurogenesis and dendritic modification occur simultaneously in rats with stress or exercise; however, it is unclear whether neurogenesis or dendritic remodeling has a greater impact on mediating the effect of exercise on stress since they have been separately examined. Here we examined hippocampal cell proliferation in runners treated with different doses (low: 30 mg/kg; moderate: 40 mg/kg; high: 50 mg/kg) of corticosterone (CORT) for 14 days. Water maze task and forced swim tests were applied to assess hippocampal-dependent learning and depression-like behaviour respectively the day after the treatment. Repeated CORT treatment resulted in a graded increase in depression-like behaviour and impaired spatial learning that is associated with decreased hippocampal cell proliferation and BDNF levels. Running reversed these effects in rats treated with low or moderate, but not high doses of CORT. Using 40 mg/kg CORT-treated rats, we further studied the role of neurogenesis and dendritic remodeling in mediating the effects of exercise on stress. Co-labelling with BrdU (thymidine analog) /doublecortin (immature neuronal marker) showed that running increased neuronal differentiation in vehicle- and CORT-treated rats. Running also increased dendritic length and spine density in CA3 pyramidal neurons in 40 mg/kg CORT-treated rats. Ablation of neurogenesis with Ara-c infusion diminished the effect of running on restoring spatial learning and decreasing depression-like behaviour in 40 mg/kg CORT-treated animals in spite of dendritic and spine enhancement. but not normal runners with enhanced dendritic length. The results indicate that both restored hippocampal neurogenesis and dendritic remodelling within the hippocampus are essential for running to counteract stress.

Effect of treadmill exercise on blood glucose, serum corticosterone levels and glucocorticoid receptor immunoreactivity in the hippocampus in chronic diabetic rats

Abnormal excess of glucocorticoid is one of feature characteristics in type 2 diabetes. In the present study, we investigated the effect of treadmill exercise at chronic diabetic stages on glucocorticoid receptor (GR) immunoreactivity in the hippocampal CA1 region and dentate gyrus, which are very vulnerable to diabetes. For this study, we used Zucker diabetic fatty (ZDF) rats and Zucker lean control (ZLC) rats. Twenty-three-week-old ZLC and ZDF rats were put on the treadmill with or without running for 7 weeks and sacrificed at 30 weeks of age. Treadmill exercise significantly decreased diabetes-induced blood glucose and serum corticosteroid levels although they did not drop to control levels. In sedentary ZLC rats, GR immunoreactivity was detected in pyramidal cells of the CA1 region as well as in granule cells of the dentate gyrus. In the sedentary ZDF rats, GR immunoreactivity was significantly increased in these regions. However, treadmill exercise significantly decreased GR immunoreactivity in these regions. These results indicate that treadmill exercise in chronic diabetic rats significantly decreased GR immunoreactivity in the hippocampal CA1 region and dentate gyrus, although blood glucose and serum corticosteroid levels did not fully recover to normal state.

Partial deficiency or short-term inhibition of 11beta-hydroxysteroid dehydrogenase type 1 improves cognitive function in aging mice

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) regenerates active glucocorticoids (GCs) from intrinsically inert 11-keto substrates inside cells, including neurons, thus amplifying steroid action. Excess GC action exerts deleterious effects on the hippocampus and causes impaired spatial memory, a key feature of age-related cognitive dysfunction. Mice with complete deficiency of 11β-HSD1 are protected from spatial memory impairments with aging. Here, we tested whether lifelong or short-term decreases in 11β-HSD1 activity are sufficient to alter cognitive function in aged mice. Aged (24 months old) heterozygous male 11β-HSD1 knock-out mice, with ∼60% reduction in hippocampal 11β-reductase activity throughout life, were protected against spatial memory impairments in the Y-maze compared to age-matched congenic C57BL/6J controls. Pharmacological treatment of aged C57BL/6J mice with a selective 11β-HSD1 inhibitor (UE1961) for 10 d improved spatial memory performance in the Y-maze (59% greater time in novel arm than vehicle control). These data support the use of selective 11β-HSD1 inhibitors in the treatment of age-related cognitive impairments.

Hippocampal volume deficits associated with exposure to psychological trauma and posttraumatic stress disorder in adults: a meta-analysis

Trauma exposure itself in the absence of posttraumatic stress disorder (PTSD) may be associated with hippocampal volume deficits. We meta-analytically compared hippocampal volumes in PTSD subjects, in trauma-exposed subjects without PTSD, and in trauma-unexposed subjects. Using the words and phrases PTSD, neuroimaging, hippocampus, brain, violence, trauma, abuse, rape, war, combat, accident, and disaster, we searched major computerized databases to obtain candidate studies through 2008 for inclusion. We identified 39 hippocampal volumetric studies in adults with PTSD compared to control groups consisting of either trauma-exposed controls without PTSD or trauma-unexposed controls, or both. We meta-analytically compared left, right, and total hippocampal volumes between 1) PTSD subjects and a trauma-unexposed group, 2) PTSD subjects and a trauma-exposed group without PTSD, and 3) a trauma-unexposed group and a trauma-exposed group without PTSD. Hippocampal volumes were smaller in the PTSD group and trauma-exposed group without PTSD compared to the trauma-unexposed group. Further, the right hippocampus was smaller in the PTSD group compared to the trauma-exposed group without PTSD. Additionally, the right hippocampus was larger than the left in the PTSD and trauma-unexposed groups but not in the trauma-exposed group without PTSD. Hippocampal volume reduction is associated with trauma exposure independent of PTSD diagnosis, albeit additional hippocampal reduction was found in PTSD compared to the trauma-exposed group without PTSD.

Differential regulation of the serotonin 1 A transcriptional modulators five prime repressor element under dual repression-1 and nuclear-deformed epidermal autoregulatory factor by chronic stress

Chronic stress is known to affect brain areas involved in learning and emotional responses. These changes, thought to be related to the development of cognitive deficits are evident in major depressive disorder and other stress-related pathophysiologies. The serotonin-related transcription factors (Freud-1/CC2D1A; five prime repressor element under dual repression/coiled-coil C2 domain 1a, and NUDR/Deaf-1; nuclear-deformed epidermal autoregulatory factor) are two important regulators of the 5-HT1A receptor. Using Western blotting and quantitative real-time polymerase chain reaction (qPCR) we examined the expression of mRNA and proteins for Freud-1, NUDR, and the 5-HT1A receptor in the prefrontal cortex (PFC) of male rats exposed to chronic restraint stress (CRS; 6 h/day for 21 days). After 21 days of CRS, significant reductions in both Freud-1 mRNA and protein were observed in the PFC (36.8% and 32%, respectively; P<0.001), while the levels of both NUDR protein and mRNA did not change significantly. Consistent with reduced Freud-1 protein, 5-HT1A receptor mRNA levels were equally upregulated in the PFC, while protein levels actually declined, suggesting post-transcriptional receptor downregulation. The data suggest that CRS produces distinct alterations in the serotonin system specifically altering Freud-1 and the 5-HT1A receptor in the PFC of the male rat while having no effect on NUDR. These results point to the importance of understanding the mechanism for the differential regulation of Freud-1 and NUDR in the PFC as a basis for understanding the related effects of chronic stress on the serotonin system (serotonin-related transcription factors) and stress-related disorders like depression.

Repeated brief social defeat episodes in mice: effects on cell proliferation in the dentate gyrus

Stressful experiences can affect hippocampal structure and function and can suppress new cell birth in the adult hippocampus in several species. Here we examine how repeated intermittent social defeat affects cell proliferation in the dentate gyrus (DG) in mice. Adult male CFW mice were subjected to 10 daily social defeat episodes, 3 defeat episodes within one day or a single defeat episode. Intruder mice were injected with 5-bromo-2'-deoxyuridine (BrdU, 200mg/kg, i.p.) 1h after the last fight, and incorporation of BrdU into proliferating cells in the DG was quantified. In a third experiment, aggressive resident mice were allowed to fight with an intruder mouse every day for 10 days, and these residents were injected with BrdU 1h after the last aggressive encounter. There was a significant decrease in cell proliferation in mice that received 10 social defeats, confirming and extending earlier results. This decrease is correlated with the intensity of the defeat experiences, as quantified by frequency of attack bites. Cell proliferation was slightly inhibited after a single defeat, although this effect was not significant. Three defeats within a 5-h period had no effect on levels of proliferation. Offensive aggressive stress in the residents did not result in any changes in hippocampal cell proliferation. These data indicate that repeated intermittent social defeat experienced over multiple days suppresses proliferation in the DG, and this may have important implications for our understanding of hippocampal changes related to stress psychopathologies.

Cerebrospinal fluid ACTH and cortisol in opsoclonus-myoclonus: effect of therapy

Opsoclonus-myoclonus syndrome is one of a few corticotropin (ACTH)-responsive central nervous system disorders of childhood. We measured cerebrospinal fluid ACTH and cortisol in 69 children with opsoclonus-myoclonus and 25 age- and sex-matched control subjects to determine endogenous levels and look for hypothesized differential hormonal effects of ACTH and corticosteroid treatment. Cerebrospinal fluid cortisol was 10-fold higher with ACTH treatment (n = 26), but was unchanged with oral steroid treatment (n = 18) or no treatment (n = 25). It was significantly higher in children receiving daily high-dose ACTH than alternate day ACTH. In ACTH-treated children, cerebrospinal fluid and serum cortisol were highly correlated (r = 0.96, P = 0.0001), with a mean ratio of cerebrospinal fluid to serum cortisol of approximately 1:10. Cerebrospinal fluid ACTH concentration did not differ significantly between untreated opsoclonus-myoclonus and control subjects but was lower with ACTH (-29%) or steroid treatment (-36%), suggesting feedback inhibition of ACTH release. These data delineate differences in the central effects of ACTH and corticosteroid therapy, as well as between high and low ACTH doses, and support the integrity of the brain-adrenal axis in pediatric opsoclonus-myoclonus.

Adult neurogenesis: from precursors to network and physiology

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

The mossy fiber system of the hippocampal formation is decreased by chronic and postnatal but not by prenatal protein malnutrition in rats

We tested in 70-day-old Sprague-Dawley rats, whether malnutrition imposed during different periods of hippocampal development produced deleterious effects on the total reference volume of the mossy fiber system. Animals were treated under four nutritional conditions: (a) well nourished; (b) prenatal protein malnourished; (c) chronic protein malnourished and (d) postnatal protein malnourished. Timm's stained material was used in coronal hippocampal sections (40 microm) to estimate--using the Principle of Cavalieri--the total reference volume of the mossy fiber system in each experimental group. Our results show that chronic and postnatal protein malnourished, but not prenatal malnourished rats, decrease the mossy fiber system and the total reference volume of the mossy fiber system are selectively vulnerable to the type of dietary restriction. Thus, chronic and posnatal protein malnutrition produce deleterious effects, but only rats under prenatal protein malnutrition were able to reorganize synapses in this plexus. These findings raise the possibility that chronic malnutrition, as a long-term stressful factor, might be an important paradigm to test structural hippocampal changes that produce physiological and pathophysiological effects, or the possibility to recover its function for nutritional rehabilitation.

Long-term effects of social stress on brain and behavior: a focus on hippocampal functioning

In order to study mechanisms involved in the etiology of human affective disorders, there is an abundant use of various animal models. Next to genetic factors that predispose for psychopathologies, environmental stress is playing an important role in the etiology of these mental diseases. Since the majority of stress stimuli in humans that lead to psychopathology are of social nature, the study of consequences of social stress in experimental animal models is very valuable. The present review focuses on one of these models that uses the resident-intruder paradigm. In particular the long-lasting effects of social defeat in rats will be evaluated. Data from our laboratory on the consequences of social defeat on emotional behavior, stress responsivity and serotonergic functionality are presented. Furthermore, we will go into detail on hippocampal functioning in socially stressed rats. Very recent results show that there is a differential effect of a brief double social defeat and repetitive social defeat stress on dendritic remodeling in hippocampal CA3 neurons and that this has repercussions on hippocampal LTP and LTD. Both the structural and electrophysiological changes of principal neurons in the hippocampal formation after defeat are discussed as to their relationship with the maintenance in cognitive performance that was observed in socially stressed rats. The results are indicative of a large dynamic range in the adaptive plasticity of the brain, allowing the animals to adapt behaviorally to the previously occurred stressful situation with the progression of time.

Direct inhibitory effects of leptin on the neonatal adrenal and potential consequences for brain glucocorticoid feedback

Leptin is most studied for its primary role in the CNS control of energy balance and food intake in humans and rodents, yet it has functions on multiple target sites including the adrenal gland. In adult rodents, leptin has been shown to inhibit adrenal steroidogenesis and we have recently demonstrated that some of the mechanisms responsible for leptin-induced inhibition of adrenal glucocorticoid production, namely a reduction of StAR protein expression are already present in the neonatal adrenal gland. The effect of leptin on the neonatal adrenal gland integrates well with the previously demonstrated effect of this protein to inhibit stress responses, enhance glucocorticoid receptor expression in the CNS and sensitivity to glucocorticoid inhibitory feedback in neonates. The leptin receptor isoform and intracellular mechanisms involved in regulation of the adrenocortical activity at multiple levels might differ between target tissues (CNS vs periphery) and age (neonates vs adult). Neonatal leptin represents an important regulator of adrenocortical function during a critical period of brain development, which is exquisitely sensitive to circulating glucocortcoid concentrations. Since circulating leptin levels in neonates vary according to maternal diet, this protein can be viewed as a critical link between environmental and maternal factors and the developing physiology of the infant.

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

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

Suppressed proliferation and apoptotic changes in the rat dentate gyrus after acute and chronic stress are reversible

Acute stress suppresses new cell birth in the hippocampus in several species. Relatively little is known, however, on how chronic stress affects the turnover, i.e. proliferation and apoptosis, of the rat dentate gyrus (DG) cells, and whether the stress effects are lasting. We investigated how 3 weeks of chronic unpredictable stress would influence the structural dynamic plasticity of the rat DG, and studied newborn cell proliferation, survival, apoptosis, volume and cell number in 10-week-old animals. To study lasting effects, another group of animals was allowed to recover for 3 weeks. Based on two independent parameters, bromodeoxyuridine (BrdU) and Ki-67 immunocytochemistry, our results show that both chronic and acute stress decrease new cell proliferation rate. The reduced proliferation after acute stress normalized within 24 h. Interestingly, chronically stressed animals showed recovery after 3 weeks, albeit with still fewer proliferating cells than controls. Apoptosis, by contrast, increased after acute but decreased after chronic stress. These results demonstrate that, although chronic stress suppresses proliferation and apoptosis, 3 weeks of recovery again normalized most of these alterations. This may have important implications for our understanding of the reversibility of stress-related hippocampal volume changes, such as occur, for example, in depression.

Implication of corticosteroid receptors in the regulation of hippocampal structural plasticity

The dentate gyrus is one of the few areas of the adult brain that continues to produce neurons and to express the embryonic polysialylated isoforms of neuronal cell adhesion molecules (PSA-NCAM). The stress hormone corticosterone exerts a complex modulation on neurogenesis and PSA-NCAM, and previous studies have shown that mature granule cells require corticosterone for their survival. Thus, the aim of our work was to investigate the respective role of the different corticosteroid receptors on these three parameters in adrenalectomized rats. It was found that treatment with a low dose of the mineralocorticoid receptor agonist, aldosterone, prevents only the adrenalectomy-induced increase in cell death. Treatment with a higher dose of aldosterone normalized cell proliferation whereas PSA-NCAM expression was normalized only by treatment with the glucocorticoid receptor agonist, RU 28362. It is concluded that stimulation of the mineralocorticoid receptor is sufficient to mediate the effects of corticosterone on neurogenesis and to protect mature cells from cell death whereas stimulation of the glucocorticoid receptor is necessary to modulate PSA-NCAM expression.

Effects of estrogens on choline-acetyltransferase immunoreactivity and GAP-43 mRNA in the forebrain of young and aging male rats

1. Previous work demonstrated that estradiol (E2) treatment prevented the abnormal response to stress and the reduction of glucocorticoid receptors (GR) in hippocampus from aging male rats. The mechanisms originating these effects were unknown. 2. In the present work, we investigated the E2 effects on the cholinergic, growth-associated protein (GAP-43) expressing neurons of the medial septum (MS) and vertical limb of diagonal band of Broca (VDB). These areas project to the hippocampus, and may be involved in the mentioned E2 effects in aging animals. Therefore, the response to E2 of choline-acetyltransferase (ChAT) in neurons and cell processes and GAP-43 mRNA as a marker of neurite outgrowth was studied in young and old male rats. 3. Young (3-4 months) and old (18-20 months) male Sprague-Dawley rats remained untreated or were implanted s.c. with a 14 mg pellet of E2 benzoate during 6 weeks. We used immoucytochemistry to determine ChAT and isotopic in situ hybridization to analyze GAP-43 mRNA expression. 4. Aging males showed a reduction in the number and length of ChAT-immunoreactive cell processes, but not in the number of positive neurons in MS and VDB. E2 reverted both parameters in old rats to levels of young animals. Regarding basal levels of GAP-43 mRNA, they were similar in old and young animals, but E2 treatment up-regulated GAP-43 mRNA expression in MS and VDB of old animals only. 5. Our data suggest that prolonged E2 treatment may affect hippocampal function of aging male rats by regulating in part the plasticity of cholinergic, GAP-43 expressing neurones of the basal forebrain. Without discarding a direct E2 effect on the limbic tissue, effects on the cholinergic system may have a pronounced impact on the neuroendocrine and stress responses of the aging hippocampus.

Endocrine abnormalities in healthy first-degree relatives of type 2 diabetes patients--potential role of steroid hormones and leptin in the development of insulin resistance

BACKGROUND

First-degree relatives of type 2 diabetes patients are at risk of developing diabetes and they display several metabolic and hormonal perturbations. The interplay between insulin resistance, steroid hormones and circulating leptin is, however, still not fully explored in this group.

DESIGN

Thirty-three healthy first-degree relatives of type 2 diabetic patients (relatives; M/F 19/14) were compared to 33 healthy subjects without a family history of diabetes (controls) and the groups were matched for gender, age and body mass index (BMI). We performed euglycaemic hyperinsulinaemic clamps and blood was sampled for hormone analyses.

RESULTS

Relatives exhibited decreased insulin sensitivity (index of metabolic clearance rate of glucose; MCRI) but when genders were analysed separately, this difference was significant only in males (11.3 +/- 1.3 vs. 15.0 +/- 1.5 units, means +/- SEM, P = 0.030). In male relatives morning cortisol and testosterone levels were lower, whereas leptin was higher than in male controls (P = 0.018, 0.008 and 0.063, respectively). In male relatives plasma testosterone levels were significantly associated with insulin sensitivity (r = 0.48, P = 0.040). Circulating leptin levels were inversely correlated with insulin sensitivity in all subject groups (r-values -0.49 to -0.66; P < 0.05, except in female control subjects P = 0.063). These associations were present also when age and BMI or waist:hip ratio were included in stepwise multiple regression analyses.

CONCLUSION

Male subjects genetically predisposed for type 2 diabetes display several endocrine abnormalities including leptin, cortisol and testosterone levels. Dysregulation of these hormones may be important in the development of insulin resistance and type 2 diabetes.

Multidrug resistance P-glycoprotein hampers the access of cortisol but not of corticosterone to mouse and human brain

In the present study, we investigated the role of the multidrug resistance (mdr) P-glycoprotein (Pgp) at the blood-brain barrier in the control of access of cortisol and corticosterone to the mouse and human brain. [(3)H]Cortisol poorly penetrated the brain of adrenalectomized wild-type mice, but the uptake was 3.5-fold enhanced after disruption of Pgp expression in mdr 1a(-/-) mice. In sharp contrast, treatment with [(3)H]corticosterone revealed high labeling of brain tissue without difference between both genotypes. Interestingly, human MDR1 Pgp also differentially transported cortisol and corticosterone. LLC-PK1 monolayers stably transfected with MDR1 complementary DNA showed polar transport of [(3)H]cortisol that could be blocked by a specific Pgp blocker, whereas [(3)H]corticosterone transport did not differ between transfected and host cells. Determination of the concentration of both steroids in extracts of human postmortem brain tissue using liquid chromatography mass spectrometry revealed that the ratio of corticosterone over cortisol in the brain was significantly increased relative to plasma. In conclusion, the data demonstrate that in both mouse and human brain the penetration of cortisol is less than that of corticosterone. This finding suggests a more prominent role for corticosterone in control of human brain function than hitherto recognized.

PSA-NCAM: an important regulator of hippocampal plasticity

The Neural Cell Adhesion Molecule (NCAM) serves as a temporally and spatially regulated modulator of a variety of cell-cell interactions. This review summarizes recent results of studies aimed at understanding its regulation of expression and biological function, thereby focussing on its polysialylated isoforms (PSA-NCAM). The detailed analysis of the expression of PSA and NCAM in the hippocampal mossy fiber system and the morphological consequences of PSA-NCAM deficiency in mice support the notion that the levels of expression of NCAM are important not only for the regulation and maintenance of structural changes, such as migration, axonal growth and fasciculation, but also for activity-induced plasticity. There is evidence that PSA-NCAM can specifically contribute to a presynaptic form of plasticity, namely long-term potentiation at hippocampal mossy fiber synapses. This is consistent with previous observations that NCAM-deficient mice show deficits in spatial learning and exploratory behavior. Furthermore, our data points to an important role of the hypothalamic-pituitary-adrenal axis, which is the principle adaptive response of the organism to environmental challenges, in the control of PSA-NCAM expression in the hippocampal formation. In particular, we evidence an inhibitory influence of corticosterone on PSA-NCAM expression.

The effects of prenatal stress on the development of hypothalamic paraventricular neurons in fetal rats

The present experiments focused on the influence of prenatal stress on the development of neurons of the hypothalamic paraventricular nucleus in the fetal rat, including corticotropin-releasing factor-containing neurons. Prenatal stress was administered by restraining pregnant rats in a small cage for either 30 (30-min stress group) or 240 min (240-min stress group) daily for three days from embryonic day 15 to 17, and the fetal brains were taken on embryonic day 18 for later analysis. Golgi-impregnated neurons of the paraventricular nucleus in the 240-min stress group revealed that the total length of the processes was significantly shorter than in the control (unstressed) and 30-min stress groups. In addition, the 240-min stress group showed an increase in the number of apoptotic cells in the fetal paraventricular nucleus. On the other hand, Golgi-impregnated neurons of the paraventricular nucleus in the 30-min stress group had a greater degree of cell differentiation as manifested by an increase in both the number of branch points and the total length of the processes from the cell body. Furthermore, the fetal paraventricular nucleus in the 30-min stress group showed enhanced corticotropin-releasing factor messenger RNA expression, while the varicosities of corticotropin-releasing factor-containing axons at the median eminence revealed more matured morphology such as shorter intervals between the varicosities. These findings suggest the duration-dependent effects of prenatal stress on the development of fetal hypothalamic paraventricular nucleus neurons, including corticotropin-releasing factor-containing neurons: long-lasting stress causes neurotoxic changes of fetal paraventricular nucleus neurons, whereas short-lasting stress facilitates the development of these fetal brain neurons. These morphological changes induced by prenatal stress may contribute to behavioral changes of the offspring after birth.

The stress-reaction process and the adaptive modification and reorganization of neuronal networks

On the basis of a comprehensive definition of the stress-reaction process (SRP), the neurobiological and psychological consequences of this process, which are elicited by either controllable or uncontrollable stress, are described. We conclude that controllable stress triggers the stabilization and facilitation of neuronal networks involved in the generation of appropriate patterns of appraisal and coping, whereas uncontrollable stress favors the extinction of inappropriate patterns and the reorganization of neuronal connections underlying certain inappropriate behaviors. Both controllable and uncontrollable stress-reaction processes are therefore inherent challenges to the development and essential prerequisites of the adaptation of an individual's behavior to the demands of the ever-changing external world. The overabundance, as well as the lack, of either kind of SRP may lead to different psychodevelopmental failures and psychiatric disturbances.

Relationships among cortisol (CRT), dehydroepiandrosterone-sulfate (DHEAS), and memory in a longitudinal study of healthy elderly men and women

At test times 18 months apart (Time 1 and Time 2), men (n Time 1 = 31, Time 2 = 23), women estrogen-users (n Time 1 = 14, Time 2 = 10), and women estrogen non-users (n Time 1 = 41, Time 2 = 27), whose average age was 72.1 and 73.4 years at Time 1 and Time 2, respectively, were tested with a battery of neuropsychological tests measuring verbal memory, visual memory, concentration/attention, language fluency and semantic memory. Plasma levels of CRT and DHEAS were assayed by radioimmunoassay at both test times. The men had higher DHEAS levels than both groups of women at both test times (p < 0.001) and also had a higher DHEAS/CRT ratio compared to the estrogen non-users (p < 0.05). Although there were no group differences in CRT levels at either time, CRT levels increased in the estrogen non-using women from Time 1 to Time 2 (p < 0.001). Subjects with lower CRT levels performed better than those with higher levels on several tests of declarative memory (p < 0.05). Men and estrogen-users had higher Digit Span scores compared to female estrogen non-users at both test times (p < 0.01), and women estrogen-users also had higher Backward Digit Span scores than non-users (p < 0.05). Both groups of women performed better than men on Category Retrieval (p < 0.01). These findings suggest that higher CRT levels in elderly men and women are associated with poorer explicit memory functioning; however, these results failed to provide any evidence that DHEAS is protective against declarative memory decline with aging.

Hypothalamic arousal, insulin resistance and Type 2 diabetes mellitus

AIMS

Type 2 diabetes mellitus (DM) develops when insulin resistance overcomes the capacity of compensatory insulin secretion. Insulin resistance may be induced via psychoneuroendocrine pathways, a possibility which has received little previous attention.

METHODS

We have used salivary cortisol measurements to monitor the activity of the hypothalamic-pituitary-adrenal (HPA) axis, the major controller of hormones involved in the regulation of peripheral insulin sensitivity under everyday conditions. The influence of external challenges, as well as the sensitivity of feedback regulation, were followed in randomly selected middle-aged population samples.

RESULTS

In health there is a rhythmicity of cortisol secretion, with a high plasticity and efficient feedback control. In contrast, a group of subjects were identified with a flat, rigid day curve and poor feedback control, who showed consistent abnormalities in stress-related cortisol secretion, including inhibited secretions of sex steroids and growth hormone; insulin resistance; abdominal obesity; elevated leptin levels; hyperglycaemia; dyslipidaemia and hypertension with elevated heart rate. The endocrine abnormalities are probably responsible for the anthropometric and metabolic abnormalities. The circulatory perturbations seem to be induced by a parallel activation of the central sympathetic nervous system suggesting an 'hypothalamic arousal syndrome', gradually developing into an independent risk for disease. An associated cluster of environmental factors, including psychosocial and socio-economic stress, traits of depression and anxiety, alcohol consumption and smoking, all factors known to activate hypothalamic centres, has been identified. A polymorphism of the glucocorticoid receptor gene, with 13.7% homozygotes in the male Swedish population, parallels receptor dysfunction, and may be responsible for the associated insulin resistance, central obesity and hypertension.

CONCLUSIONS

This is the first detailed examination of psychoneuroendocrinological processes in the natural environment on a population basis in relation to somatic health. The results suggest that an hypothalamic arousal syndrome, with parallel activation of the HPA axis and the central sympathetic nervous system, is responsible for development of endocrine abnormalities, insulin resistance, central obesity, dyslipidaemia and hypertension, leading to frank disease, including Type 2 DM. We suggest that this syndrome is probably based on environmental pressures in genetically susceptible individuals.

Complex regulation of the expression of the polysialylated form of the neuronal cell adhesion molecule by glucocorticoids in the rat hippocampus

The gyrus dentatus is one of the few areas of the brain that continues to produce neurons after birth. The newborn cells differentiate into granule cells which project axons to their postsynaptic targets. This step is accompanied by the transient expression of the polysialylated isoforms of neuronal cell adhesion molecules (PSA-NCAM) by the developing neurons. Glucocorticoid hormones have been shown to inhibit neurogenesis. We noted a functional correlation between PSA-NCAM expression and glucocorticoid action after manipulation of corticosterone levels in the adrenalectomized rat. Adrenalectomy increased neurogenesis, evaluated from the incorporation of 5-bromo-2'-deoxyuridine in neuronal precursors, as well as PSA-NCAM expression. The increase in PSA-NCAM-immunoreactive (IR) cells in the gyrus dentatus, evidenced 72 h following adrenalectomy, persisted for at least a month. It was accompanied by enhanced dendritic arborization of PSA-NCAM-IR cells in the gyrus dentatus and by an increase in number of PSA-NCAM-IR fibres in the CA3 subfield. Neurogenesis was normalized by restitution of diurnal or nocturnal levels of corticosterone, whereas normalization of PSA-NCAM expression was only observed after simulation of the complete circadian fluctuation of the hormone. Our findings reveal the complex action of corticosterone in modulating the expression of PSA-NCAM in the gyrus dentatus of the hippocampal formation. They also highlight the importance of corticosterone fluctuations in the control of neurogenesis and plasticity in this structure.

Regulation of gene expression by corticoid hormones in the brain and spinal cord

Glucocorticoids (GC) and mineralocorticoids (MC) have profound regulatory effects upon the central nervous system (CNS). Hormonal regulation affects several molecules essential to CNS function. First, evidences are presented that mRNA expression of the alpha3 and beta1-subunits of the Na,K-ATPase are increased by GC and physiological doses of MC in a region-dependent manner. Instead, high MC doses reduce the beta1 isoform and enzyme activity in amygdaloid and hypothalamic nuclei, an effect which may be related to MC control of salt appetite. The alpha3-subunit mRNA of the Na,K-ATPase is also stimulated by GC in motoneurons of the injured spinal cord, suggesting a role for the enzyme in GC neuroprotection. Second, we provide evidences for hormonal effects on the expression of mRNA for the neuropeptide arginine vasopressin (AVP). Our data show that GC inhibition of AVP mRNA levels in the paraventricular nucleus is sex-hormone dependent. This sexual dimorphism may explain sex differences in the hypothalamic-pituitary-adrenal axis function between female and male rats. Third, steroid effects on the astrocyte marker glial fibrillary acidic protein (GFAP) points to a complex regulatory mechanism. In an animal model of neurodegeneration (the Wobbler mouse) showing pronounced astrogliosis of the spinal cord, in vivo GC treatment down-regulated GFAP immunoreactivity, whereas the membrane-active steroid antioxidant U-74389F up-regulated this protein. It is likely that variations in GFAP protein expression affect spinal cord neurodegeneration in Wobbler mice. Fourth, an interaction between neurotrophins and GC is shown in the injured rat spinal cord. In this model, intensive GC treatment increases immunoreactive low affinity nerve growth factor (NGF) receptor in motoneuron processes. Because GC also increases immunoreactive NGF, this mechanism would support trophism and regeneration in damaged tissues. In conclusion, evidences show that some molecules regulated by adrenal steroids in neurons and glial cells are not only involved in physiological control, but additionally, may play important roles in neuropathology.

Early maternal separation increases NGF expression in the developing rat hippocampus

Nerve Growth Factor (NGF) is a neurotrophin involved in growth and differentiation of central cholinergic neurons. In this study a maternal separation paradigm was used to test whether levels of NGF might be affected by brief manipulations of rat pups early during ontogeny. The expression of NGF mRNA was examined in 3-day-old rat pups following 45 min maternal separation using in situ hybridization. Early maternal separation in neonatal rats resulted in increased expression of NGF mRNA in the dentate gyrus and the hilus of the hippocampus. NGF protein levels measured (by means of a sensitive ELISA assay) in the whole hippocampus the day following the separation procedure did not differ in separated vs. nonseparated pups. These data indicate that brief manipulations performed early during development can affect hippocampal NGF expression.

Serotonin regulates synaptic connections in the dentate molecular layer of adult rats via 5-HT1a receptors: evidence for a glial mechanism

The present study sought to verify effects of 5-HT on synaptic density at the ultrastructural level, to determine whether the 5-HT1a receptor is important for the maintenance of synaptic connections and to obtain evidence implicating S100 beta in the apparent neurotrophic actions of 5-HT. Reduction of hippocampal 5-HT with para-chloroamphetamine (PCA) resulted in a significant decline in the synaptic density of the dentate molecular layer. Reduction of norepinephrine with DSP-4 produced a slight decrease in the number of molecular layer synapses, but this difference was not statistically different from control values. 5-HT1a antagonist treatment resulted in a decline in synaptic density comparable to that observed following PCA treatment. These observations suggest that 5-HT functions to maintain synaptic connections in the dentate molecular layer via a 5-HT1a mechanism. To determine whether the change in synaptic density was due to the action of 5-HT on neuronal receptors or astrocytic receptors, a monoclonal antibody against S100 beta was infused into the lateral ventricle for seven days. Controls received infusions of normal goat serum. Half of the rats from the anti-S100 beta and control groups also received daily injections of NAN-190. Anti-S100 beta infusion resulted in a significant (p < 0.01) decrease in synapses compared to serum controls. Concomitant NAN-190 administration did not enhance synapse loss in the anti-S100 beta group. The results of this study suggest that the maintenance of synaptic connections in the dentate molecular layer is influenced by S100 beta levels that are controlled by 5-HT stimulation of astrocytic 5-HT1a receptors.

Corticosteroids influence the action potential firing pattern of hippocampal subfield CA3 pyramidal cells

Corticosteroids regulate gene expression through the activation of mineralocorticoid and glucocorticoid receptors. The hippocampus contains the highest density of mineralocorticoid and glucocorticoid receptors in the central nervous system. The modulation of neuron excitability by corticosteroids in hippocampal subfield CA1 is well documented. However, it is not known whether corticosteroids produce different effects across the various hippocampal subfields. Therefore, we used intracellular recording techniques to examine the actions of chronic corticosteroid treatment (2 weeks) on the electrophysiological properties of rat hippocampal subfield CA3 pyramidal cells. The treatment groups used in this investigation were: adrenalectomy (ADX), selective mineralocorticoid receptor activation with aldosterone (ALD), mineralocorticoid and glucocorticoid receptor activation with high levels of corticosterone (HCT), and SHAM. Corticosteroid treatment altered the percentage of nonburst and burst firing neurons. The percentages of nonbursting cells were 74 and 62% in tissue from ADX and HCT animals compared to 42 and 41% in ALD and SHAM animals, respectively. The corticosteroid-induced effect on the ratio of nonbursting to bursting cells does not appear to be secondary to changes in the cell's membrane input resistance, resting potential, time constant, action potential, slow-or fast-afterhyperpolarizing potential properties. Based on these results we conclude that corticosteroids are important for maintaining the ratio of nonburst and burst firing pyramidal neurons in subfield CA3. These novel results are distinct from those previously reported for subfield CA1, suggesting that corticosteroids have different effects across hippocampal subfields.

Localization of 11 beta-hydroxysteroid dehydrogenase: specific protector of the mineralocorticoid receptor in mammalian olfactory mucosa

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) plays a major role in the protection of the mineralocorticoid (type I) receptor. The cellular mechanism of aldosterone selectivity relies on the coexpression of mineralocorticoid receptors and 11 beta HSD in the same cells. In the current study, 11 beta HSD activity was localized in the mammalian olfactory mucosa by a histochemical technique which links steroid metabolism with the deposition of formazan. The histochemical reaction results from oxidation of the synthetic substrate 11 beta-hydroxyandrostenedione and is dependent on nicotine-adenine dinucleotide (NAD). This demonstrates the presence of a dehydrogenase activity separate from the nicotineamide-adenine dinucleotide phosphate (NADP)-dependent 11 beta HSD. In the olfactory mucosa, the presence of NAD-dependent 11 beta HSD activity is localized to the sustentacular cells and acinar cells of Bowman's glands. No definite NAD-dependent activity was demonstrated in the olfactory receptor neurons. These data suggest that mineralocorticoid receptors present in acinar cells and sustentacular cells are aldosterone selective.

Effects of neonatal stimulation on later cognitive function and hippocampal nerve growth factor

This study examined the behavioural and physiological effects of chronic mild stress on neonatally handled and non-handled rats. Neonatally handled and non-handled rats were exposed to chronic mild stress from weaning time to 6 months of age. They were behaviourally tested at 6 months of age, and sacrificed for analysis of nerve growth factor (NGF) in the hippocampus and hypothalamus. In contrast to the reported deleterious effect of acute strong stress, mild stress appeared to stimulate production of NGF in the hippocampus and improve spatial learning in both handled and nonhandled rats. Because neonatal handling produces neuroanatomical changes in the rat hippocampus and enhances cognitive function throughout the rats life span, these results implicate hippocampal NGF in the neuroprotective effects of handling.

Spatial training in a complex environment and isolation alter the spine distribution differently in rat CA1 pyramidal cells

The hippocampus is critically involved in spatial learning. Spatial training in adult rats, which improved their spatial learning ability, increased the number of excitatory hippocampal CA1 spine synapses on basal dendrites as compared with either isolated or standardly housed animals (Moser et al. [1994] Proc. Natl. Acad. Sci. USA 91:12673-12675). In this article, we report that spine synapses on oblique apical dendritic branches do not increase in density or number after the same type of training. When examining the variability of the spine density on basal CA1 dendrites by using variance component analysis, the variance associated with the cells was twice as large in all three groups as that coupled to the rats. Analysis of the spine density plots shows that the enhanced spine density after spatial training is found in most cells recorded from the trained group but that a small subset of CA1 neurones are particularly well supplied with spines. The trained group had a significant right-skewed tail of the spine distribution, i.e., training caused high spine density to occur in a small subset of dendritic segments. Conversely, the isolated group had a significant left-skewed spine distribution, indicating that some of the dendritic segments were undersupplied with spines, whereas the paired group displayed no asymmetry.

Regulation of dendritic spine density in cultured rat hippocampal neurons by steroid hormones

The effects of gonadal steroid hormones on dendritic spines were studied in hippocampal neurons that were dissociated and grown in culture for 2-3 weeks. Exposure to estradiol caused up to a twofold increase in dendritic spine density in these neurons. The effect of estradiol was stereospecific and blocked by the steroid antagonist tamoxifen. The estradiol-induced rise in spine density was blocked by the NMDA antagonist APV, but not by the AMPA/KA antagonist DNQX. The estradiol-induced rise in spine density was blocked by the serine/threonine kinase inhibitor H7, but not by the tyrosine kinase inhibitor genestein, and was partially mimicked by PMA, an activator of protein kinase C. Estradiol also caused an increase in the fluorescence intensity of synaptophysin-immunoreactive terminals, corresponding to presynaptic boutons. Finally, estradiol caused a rise in [Ca]i reactivity of the cultured neurons to topical application of glutamate. These studies are the first to examine receptor and second messenger regulation of dendritic spines, and they illustrate the viability of cultured neurons as a powerful test system to address issues related to the regulation of dendritic spine maturation.

CR16, a novel proline-rich protein expressed in rat brain neurons, binds to SH3 domains and is a MAP kinase substrate

CR16 is a glucocorticoid-regulated gene expressed in subpopulations of neurons in the brain, including the hippocampus. The CR16 open reading frame encodes a 45 kDa protein containing 32% proline. To begin characterizing the CR16 protein, a rabbit polyclonal antibody was raised against an Escherchia coli-produced fusion protein containing amino acids 370-438 of CR16. The antibody identifies a protein doublet of 68 and 72 kDa by sodium-dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) from hippocampal extracts and from insect cells expressing the CR16 open reading frame from a baculovirus construct. However, when hippocampal extracts are electrophoresed on nondenaturing polyacrylamide gels, the CR16 protein migrates as a 48 kDa protein that better correlates with the size of the open reading frame. Examination of the primary amino acid sequence reveals at least 12 sequence homologies to the abl-SH3 binding domain consensus sequence XPXXPPP psi XP. In addition, CR16 has at least 36 copies of the PXXP motif, which is contained in all known SH3 binding domains. Solution and filter binding assays confirm that CR16 selectively binds SH3 domains. The CR16 primary amino acid sequence also contains at least eight consensus MAP kinase phosphorylation sites, five of which are in the potential SH3 binding domains. The CR16 protein, immunoprecipitated from rat brain, is an in vitro substrate for the purified enzyme. However, phosphorylation of CR16 does not greatly affect the binding of the various SH3 domains in our assay system. These data strongly suggest that the function of CR16 is to mediate one or more signal transduction pathways in CNS neurons, in addition to being a glucocorticoid-regulated gene.

Chronic psychosocial stress causes apical dendritic atrophy of hippocampal CA3 pyramidal neurons in subordinate tree shrews

We have shown previously that repeated laboratory restraint stress or daily corticosterone administration affects the structure of CA3 hippocampal neurons in rats. In the present study, we investigated the effect of repeated daily psychosocial stress on the structure of hippocampal CA3 pyramidal neurons in male tree shrews (Tupaia belangeri). Male tree shrews develop social hierarchies in which subordinates show characteristic changes in physiological and behavioral parameters when confronted with a dominant. In the present experiments, subordinate animals lost body weight soon after starting the daily social conflict, and urinary excretion of cortisol was elevated throughout the experiment as compared with the control period. Golgi-impregnated brain tissue from subordinates exposed to 28 d (1 hr/d) of social confrontations was compared with that from control nonstressed animals. The apical dendrites of the CA3 pyramidal cells from subordinates had a decreased number of branch points and total dendritic length as compared with controls. No differences were observed in apical dendritic spine density or in the basal dendritic tree morphology. The stress-induced CA3 apical dendritic atrophy in subordinates was prevented by administering daily oral doses of the antiepileptic drug phenytoin (Dilantin, Sigma, St. Louis, MO) (200 mg/kg), which interferes with excitatory amino acid (EAA) action. These results suggest that the naturalistic stressor psychosocial stress induces specific structural changes in hippocampal neurons of subordinate male tree shrews. These changes, like those in the rat after glucocorticoid treatment or restraint stress, probably are mediated by activation of the hypothalamo-pituitary-adrenal-axis acting in concert with endogenous EAAs from mossy fiber input.

Inhibition of cortisol secretion by dexamethasone in relation to body fat distribution: a dose-response study

There is now evidence of a hypersensitive hypothalamo-pituitary-adrenal (HPA) axis in subjects with an elevated waist/hip circumference ratio (WHR), an indicator of the centralization of body fat stores. The activity of the HPA axis is regulated by central glucocorticoid receptors, whose activity can be tested by the administration of exogenous glucocorticoids, which normally inhibit cortisol secretion. In this study, dexamethasone (dex) was administered in random order in doses of 0.05, 0.125, 0.25 and 0.5 mg at 10 p.m. with measurements of serum cortisol in the morning (8 a.m.) of this and the following day. The test was performed on 22 apparently healthy men, 40 to 60 years of age, recruited from laboratory personnel, outpatient clinics or advertisements in a newspaper. Eight had a body mass index (BMI) (kg/m2) of < 25 and 14 of > 25. Twelve men had a waist hip ratio (WHR) of < 1.0 and 10 men had a WHR of > 1.0. Cortisol values at baseline were correlated inversely with WHR and were usually lower in men with a high (> 1.0) rather than a low than low (< 1.0) WHR after dex inhibition. There was apparently no inhibition by dex at 0.05 and 0.125 mg on average in men with a WHR of > 1.0. In addition, the inhibition at 0.5 mg dex correlated negatively with the WHR and was significantly lower (p < 0.05) in men with a WHR of > 1.0 than in men with a WHR of < 1.0. None of these differences or relationships was found to be dependent on BMI. It is concluded that men with an elevated WHR experience a decrease in the inhibition of cortisol secretion by dex. It is suggested that this could explain or contribute to the elevated sensitivity of their HPA axis. Furthermore, lower morning cortisol concentrations suggest a change in diurnal secretion patterns.

Cerebrospinal fluid corticotropin-releasing factor concentrations in patients with anxiety disorders and normal comparison subjects

Cerebrospinal fluid (CSF) concentrations of corticotropin-releasing factor (CRF) were measured in a group of patients with anxiety disorders and normal comparison subjects (NC) to explore the hypothesis that abnormalities in CRF neuronal regulation occur in patients with anxiety disorders. Analysis of variance (ANOVA) revealed no differences in CSF CRF concentrations between the four diagnostic categories: panic disorder (PD), generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), and NCs. Male OCD patients had higher CSF CRF concentrations than men with PD and GAD and male NCs. CSF CRF concentration was positively correlated with age in women but not in men. These findings suggest that central neuronal CRF regulation may be affected by both age and gender.