Chronic psychosocial stress differentially affects apoptosis in hippocampal subregions and cortex of the adult tree shrew

We studied the effect of chronic psychosocial stress on cell death and volume changes in the tree shrew hippocampus. In situ end labelling (ISEL) identified low frequent but convincing apoptosis in many hippocampal subregions. Also in entorhinal cortex, apoptosis was found, generally at higher frequencies. After 28 days of chronic stress, apoptosis was significantly reduced in the CA1 stratum radiatum, whereas an increase was observed in the hilus (P < 0.04). With all subregions taken together, the hippocampus showed a decrease, whereas in the cortex, an increase in apoptosis was found after stress (P < 0.04). In a parallel and similar chronic stress study, post mortem morphometry of the same brain regions was performed, revealing mild decreases (7.6%) in entire hippocampal volume. We conclude that (i) low frequent apoptosis occurs throughout the adult tree shrew brain, and (ii) 28 days of chronic stress differentially affects its occurrence in distinct hippocampal subregions and entorhinal cortex. As previous stereological investigations failed to detect any loss in the principal neuronal layers, psychosocial stress, therefore, must affect other (structural) parameters like dendritic tree, interneurons, neurogenesis, or glia.

At the roots of a never-ending cycle

Recent studies have yielded a number of important insights into the mechanisms of hair follicle development and cycling and have highlighted the particularly important roles played by stem cells and Wnt signaling pathways.

How to use the optical fractionator: an example based on the estimation of neurons in the hippocampal CA1 and CA3 regions of tree shrews

Until recently, exposure of the hippocampus to prolonged elevated glucocorticoid levels was thought to result in damage and loss of pyramidal neurons. Most of the earlier studies were based on measures of neuronal density and used assumptions-based counting methods. Using a stereological technique, the optical fractionator, which eliminates potential biases inherent in the assumption-based techniques, we were able to demonstrate that chronic psychosocial stress in tree shrews has no effect on neuronal number in the hippocampal CA1 and CA3 regions. The present report will focus on the practical aspects of the optical fractionator, by describing in detail how to estimate the total number of neurons in the hippocampal CA1 and CA3 regions of tree shrews. In this example the group sizes have been increased over those used in the earlier study. The present study supports our previous conclusion that stress does not affect the number of hippocampal neurons in the CA1 and CA3 areas as suggested by other authors. The results obtained with the optical fractionator can be used to estimate the precision of the data.

Gender-specific alterations of cerebral metabolites with aging and cortisol treatment

Excess availability of the adrenocortical glucocorticoid hormone cortisol has been correlated with structural brain changes and a decline of cognitive functions during aging. Pertinent studies need to consider gender as a potential confound because of sexual dimorphism in the regulation of hypothalamus-pituitary-adrenal axis activity. In vivo localized proton magnetic resonance spectroscopy of male and female tree shrews revealed similar concentrations of cerebral metabolites in young adult animals but gender-specific alterations with aging as well as in response to cortisol treatment. In comparison with adult tree shrews, aged males had reduced concentrations of N-acetylaspartate (-33%; P<0.01) and total creatine (-34%; P< 0.01). These findings are in line with the occurrence of neuronal loss. In contrast, aged females exhibited increased concentrations of choline-containing compounds (+27%; P<0.05) which--together with a tendency for increased creatine (+24%) and myo-inositol (+14%)--is indicative of glial proliferation. After chronic administration of cortisol (4 mg/day for 28 days), male but not female tree shrews showed a specific reduction of the choline-containing compounds (-29%; P< 0.05). The observed sex differences with age are likely to result from differences in the regulation of stress-related hormones which is further supported by the gender-specific responses to cortisol.

Tcf3 and Lef1 regulate lineage differentiation of multipotent stem cells in skin

In skin, multipotent stem cells generate the keratinocytes of the epidermis, sebaceous gland, and hair follicles. In this paper, we show that Tcf3 and Lef1 control these differentiation lineages. In contrast to Lef1, which requires Wnt signaling and stabilized beta-catenin to express the hair-specific keratin genes and control hair differentiation, Tcf3 can act independently of its beta-catenin interacting domain to suppress features of epidermal terminal differentiation, in which Tcf3 is normally shut off, and promote features of the follicle outer root sheath (ORS) and multipotent stem cells (bulge), the compartments which naturally express Tcf3. These aspects of Tcf3's action are dependent on its DNA binding and Groucho repressor-binding domains. In the absence of its beta-catenin interacting domain, Lef1's behavior (Delta NLef1) seems to be markedly distinct from that of Delta NTcf3. Delta NLef1 does not suppress epidermal differentiation and promote ORS/bulge differentiation, but rather suppresses hair differentiation and gives rise to sebocyte differentiation. Taken together, these findings provide powerful evidence that the status of Tcf3/Lef complexes has a key role in controlling cell fate lineages in multipotent skin stem cells.

Chronic subordination stress in male tree shrews: replacement of testosterone affects behavior and central alpha(2)-adrenoceptors

Subordination stress induced by social defeat in male animals is known to inhibit gonadal functions and it has been discussed whether the resulting deficit in testosterone might play a role in subordination behavior. One of the major transmitter systems involved in regulation of behavior is the noradrenergic system. To analyze whether a testosterone replacement can alter subordination behavior and whether this might be related to changes in the brain noradrenergic system, we quantified alpha(2)-adrenoceptors (alpha(2)-ARs) in the central nervous system of male tree shrews. Animals were submitted to chronic subordination stress and received testosterone at the same time. Behavior was monitored during all phases of the experiment: the control period of 10 days, the period of social stress lasting 10 days when subordinates were confronted daily with a dominant male, and, subsequently, the stress and treatment period of 18 days when in parallel to the stress, animals received either injections of testosterone or vehicle. Brain alpha(2)-ARs were quantified by in vitro receptor autoradiography using the antagonist ligand (3)H-RX821002. Locomotor activity decreased significantly during the stress period and was not re-normalized by testosterone. In contrast, testosterone re-normalized scent marking behavior and autogrooming, parameters that had both been reduced due to the subordination stress. Vehicle injections improved none of these behaviors. In 8 of 10 brain regions that were analyzed, numbers of alpha(2)-adrenergic binding sites were increased in stressed animals that received vehicle injections, but a difference between testosterone and vehicle injected animals was only observed in five regions. These brain regions are all known to be involved in emotional behavior (anterior hypothalamus, medial nucleus of the amygdala, cingulate cortex) or autonomic regulation, respectively (solitary tract nucleus, dorsal motor nucleus of vagus). Therefore, our data show that testosterone influences behavior of male subordinates and modulates alpha(2)-AR expression in their brains. Androgen-mediated alterations in receptors occur in brain regions that are known to be involved in emotionality, e.g., in the anterior hypothalamus which regulates aggressive behavior. One can therefore conclude that alpha(2)-ARs contribute to neuronal functions that are responsible for subordination of stress behavior, and that testosterone-induced receptor changes are related to the partial restoration of normal behavior.

Psychosocial stress, glucocorticoids, and structural alterations in the tree shrew hippocampus

Animal models for chronic stress represent an indispensable preclinical approach to human pathology since clinical data point to a major role of psychological stress experiences, acute and/or chronic, to the development of behavioral and physiological disturbances. Chronic emotional arousal is a consequence of various types of social interactions, and one major neurohumoral accompaniment is the activation of the classic stress circuit, the limbic--hypothalamic--pituitary--adrenocortical (LHPA) axis. The adrenocortical glucocorticoid hormones cortisol and corticosterone are principal effectors within this circuit since they affect neurotransmission and neuroendocrine control, thus having profound effects on mood and behavior. Using the experimental paradigm of chronic psychosocial stress in tree shrews, we investigated the impact of aversive chronic social encounters on hippocampal structure and function. In chronically stressed animals, we observed dendritic atrophy of hippocampal pyramidal neurons and an impairment of neurogenesis in the dentate gyrus. However, a stress-induced loss of hippocampal neurons was not observed in this animal model. This review summarizes our recent results on structural changes occurring during chronic stress in neurons of the hippocampus and their potential influence on learning and memory. We discuss whether these changes are reversible and to what extent glucocorticoids might be responsible for the stress-induced effects.

In vitro activities of six quinolones and mechanisms of resistance in Staphylococcus aureus and coagulase-negative staphylococci

Of 94 clinical isolates of Staphylococcus aureus (n = 51) and coagulase-negative staphylococci (CNS) (n = 43), mutations in the quinolone resistance-determining region of topoisomerases GrlA, GrlB, GyrA, and GyrB together with MICs of six quinolones were analyzed. Amino acid substitutions at identical residues (GrlA residues 80 and 84; GyrA residues 84 and 88) were found in S. aureus and CNS. Active efflux, as suggested by blocking by reserpine, contributed substantially to the resistance phenotype in some strains. Among ciprofloxacin, clinafloxacin, levofloxacin, nalidixic acid, trovafloxacin, and sparfloxacin, a 0.5-microg/ml concentration of sparfloxacin discriminated best between strains with two or three mutations and those with no mutations.

Rescuing desmoplakin function in extra-embryonic ectoderm reveals the importance of this protein in embryonic heart, neuroepithelium, skin and vasculature

Desmosomes mediate intercellular adhesion through desmosomal cadherins, which interface with plakoglobin (PG) and desmoplakin (DP) to associate with the intermediate filament (IF) cytoskeleton. Desmosomes first assemble in the E3.5 mouse trophectoderm, concomitant with establishment of epithelial polarity and appearance of a blastocoel cavity. Increasing in size and number, desmosomes continue their prominence in extra-embryonic tissues, but as development proceeds, they also become abundant in a number of embryonic tissues, including heart muscle, epidermis and neuroepithelium. Previously, we explored the functional importance of desmosomes by ablating the Dsp gene. Homozygous Dsp mutant embryos progressed through implantation, but did not survive beyond E6.5, owing to a loss or instability of desmosomes and tissue integrity. We have now rescued the extra-embryonic tissues by aggregation of tetraploid (wild-type) and diploid (Dsp mutant) morulae. These animals survive several days longer, but die shortly after gastrulation, with major defects in the heart muscle, neuroepithelium and skin epithelium, all of which possess desmosomes, as well as the microvasculature, which does not. Interestingly, although wild-type endothelial cells of capillaries do not form desmosomes, they possess unusual intercellular junctions composed of DP, PG and VE-cadherin. The severity in phenotype and the breadth of defects in the Dsp mutant embryo is greater than PG mutant embryos, substantiating redundancy between PG and other armadillo proteins (e.g. beta-catenin). The timing of lethality is similar to that of the VE-cadherin null embryo, suggesting that a participating cause of death may be a defect in vasculature, not reported for PG null embryos.

Social isolation after a single defeat reduces striatal dopamine transporter binding in rats

A single social defeat in male rats has long lasting physiological and behavioural consequences, which are similar to those seen in depressive patients. In addition, the housing conditions after social defeat appear to be crucial for the development of depression-like symptoms. Because the dopaminergic system is thought to be altered in depressive illness, we investigated the impact of individual and group housing on the temporal development of changes of dopamine transporter (DAT) binding in male rats after a single social defeat. The number of striatal DAT binding sites was reduced in animals that remained isolated after being defeated. The isolation length after social defeat amplified this effect, indicating a temporal development of the changes on the striatal DAT. In animals which returned to the familiar group after social defeat the density of striatal DAT binding sites was not affected. We conclude that social isolation after a single defeat reduces the number of DAT binding sites. In contrast, a familiar environment after a single social defeat appears to prevent the stress-induced alterations on the dopaminergic system. This finding suggests that housing conditions are critical when investigating the central nervous effects of social defeat in male rats.

Beauty is skin deep: the fascinating biology of the epidermis and its appendages

A number of fascinating questions remain unaddressed in the realm of skin biology. We still know very little about the mechanisms that set up the patterning of hair follicles over the surface ectoderm, or about the precise signalling pathways involved in mesenchymal-epithelial interactions during hair development and differentiation. Studies over the past 10 years have implicated both the notch and sonic hedgehog pathways in these processes (Chen et al., 1997; Chiang et al., 1999; Crowe et al., 1998; Kopan and Weintraub, 1993; Nohno et al., 1995; Oro and Scott, 1998; Powell et al., 1998; St. Jacques et al., 1998). Furthermore, we know that members of the fibroblast growth factor and bone morphogenic protein families are also involved in mesenchymal-epithelial cues required for follicle morphogenesis, hair cycling, and/or follicle differentiation (Hebert et al., 1994; Jung et al., 1998; Kratochwil et al., 1996; Noramly and Morgan, 1998; Rosenquist and Martin, 1996; Song et al., 1996). However, it is not clear precisely how these pathways and factors are involved and how they might also interact with the wnt pathway in regulating hair follicle patterning and morphogenesis. These areas are currently centers of activity in the field, and answers will undoubtedly emerge with the flurry of new experiments presently being conducted. Another important issue is the residence of stem cells within the skin. While it is clear that the epidermis contains a population of cells with extraordinary proliferative capacity (Jones and Watt, 1993; Jones et al., 1995), their precise location in most body regions of the skin remains unclear. Similarly, while the bulge hypothesis has received considerable attention and support as the residence of the hair follicle stem cells (Cotsarelis et al., 1989; Lavker et al., 1993), the outer root sheath and the matrix of the follicle have also been postulated as potential homes for these critical cells (Oliver and Jahoda, 1988; Rochat et al., 1994). An equally challenging issue for the future is the extent to which skin stem cells might retain pluripotency, able to choose between an epidermal or hair follicle cell fate. Our recent studies implicating a Wnt pathway provide a starting point for exploration. I have discussed a number of recent insights that have surfaced concerning transcriptional regulation in the epidermis. Additionally, besides Lef1/beta-catenin, there are a number of transcription factors that have been identified that are likely to regulate key aspects of hair follicle differentiation and gene expression. The most interesting of these include a member, Whn, of the winged-helix transcription factors, recently been shown to be the defect underlying the nude mouse phenotype (Nehls et al., 1994; Segre et al., 1995) and the zinc finger transcription factor responsible for the hairless phenotype in mice and in humans (Ahmad et al., 1998; Cachon-Gonzalez et al., 1994). A major area for future study will be to elucidate the upstream and/or downstream targets of Lef1/beta-catenin, hairless, and whn. Let me close by returning to the issues of structure and function in the skin and to the underlying genetic basis of skin disorders. It is surprising that despite nearly 20 years of molecular genetics and its application to skin biology, we still know very little about the molecules and pathways involved in the acquisition of the epidermal barrier, the very purpose of the epidermis. Biochemical studies have given us clues as to the most important lipids involved (for review, see Proksch et al., 1993), and recent studies suggest that barrier function may in part be regulated through action of the steroid hormone superfamily of receptors (Attar et al., 1997; Hardman et al., 1998). A major research effort is now needed to begin to decipher the transcriptional regulation and the complex pathways involved in lipid synthesis and packaging. (ABSTRACT TRUNCATED)

Identification and dissection of an enhancer controlling epithelial gene expression in skin

Keratins 14 and 5 are the structural hallmarks of the basal keratinocytes of the epidermis and outer root sheath (ORS) of the hair follicle. Their genes are controlled in a tissue-specific manner and thus serve as useful tools to elucidate the regulatory mechanisms involved in keratinocyte-specific transcription. Previously we identified several keratinocyte-specific DNase I hypersensitive sites (HSs) in the 5' regulatory sequences of the K14 gene and showed that a 700-bp regulatory domain encompassing HSs II and III can confer epidermal and ORS-specific gene expression in transgenic mice in vivo. Although HS II harbored much of the transactivation activity in vitro, it was not sufficient to restrict expression to keratinocytes in vivo. We now explore the HS III regulatory element. Surprisingly, this element on its own confers gene expression to the keratinocytes of the inner root sheath (IRS) of the hair follicle, whereas a 275-bp DNA fragment containing both HSs II and III shifts the expression from the IRS to the basal keratinocytes and ORS in vivo. Electrophoretic mobility-shift assays and mutational studies of HSs III reveal a role for CACCC-box binding proteins, Sp1 family members, and other factors adding to the list of previously described factors that are involved in keratinocyte-specific gene expression. These studies highlight a cooperative interaction of the two HSs domains and strengthen the importance of combinatorial play of transcription factors that govern keratinocyte-specific gene regulation.

Hyperproliferation and defects in epithelial polarity upon conditional ablation of alpha-catenin in skin

When surface epithelium was conditionally targeted for ablation of alpha-catenin, hair follicle development was blocked and epidermal morphogenesis was dramatically affected, with defects in adherens junction formation, intercellular adhesion, and epithelial polarity. Differentiation occurred, but epidermis displayed hyperproliferation, suprabasal mitoses, and multinucleated cells. In vitro, alpha-catenin null keratinocytes were poorly contact inhibited and grew rapidly. These differences were not dependent upon intercellular adhesion and were in marked contrast to keratinocytes conditionally null for another essential intercellular adhesion protein, desmoplakin (DP). KO keratinocytes exhibited sustained activation of the Ras-MAPK cascade due to aberrations in growth factor responses. Thus, remarkably, features of precancerous lesions often attributed to defects in cell cycle regulatory genes can be generated by compromising the function of alpha-catenin.

Actin dynamics and cell-cell adhesion in epithelia

Recent advances in the field of intercellular adhesion highlight the importance of adherens junction association with the underlying actin cytoskeleton. In skin epithelial cells a dynamic feature of adherens junction formation involves filopodia, which physically project into the membrane of adjacent cells, catalyzing the clustering of adherens junction protein complexes at their tips. In turn, actin polymerization is stimulated at the cytoplasmic interface of these complexes. Although the mechanism remains unclear, the VASP/Mena family of proteins seems to be involved in organizing actin polymerization at these sites. In vivo, adherens junction formation appears to rely upon filopodia in processes where epithelial sheets must be physically moved closer to form stable intercellular connections, for example, in ventral closure in embryonic development or wound healing in the postnatal animal.

Capillary changes in hippocampal CA1 and CA3 areas of the aging rhesus monkey

The rhesus monkey is considered a useful animal model for studying human aging, because non-human primates show many of the neurobiological alterations that have been reported in aging humans. Cognitive impairment that accompanies normal aging may, at least partially, originate from capillary changes in the hippocampus, known to be involved in learning and memory. Age-related effects on the cerebral capillaries in the non-human primate hippocampus have not yet been studied. Therefore, we investigated age-related microvascular changes in the hippocampus of the aged non-human primate. We examined by electron microscopy the microvascular ultrastructure in the CAI and CA3 areas of 14 male rhesus monkeys (Macaca mulatta), ranging from 1 to 31 years of age. The percentages of capillaries showing basement membrane thickening and deposits of collagen in the basement membrane were determined semiquantitatively in 4 young (1-6 years), 6 middle-aged (17-24 years), and 4 aged (29-31 years) monkeys. Aberrations in the basement membrane are few in young subjects (28 +/- 6% of capillaries), and occur with increasing frequency during the aging process in rhesus monkeys (aged animals: 71 +/- 5% of capillaries). This could be ascribed to an aging-associated increasing number of capillaries showing depositions of collagen fibrils, rather than local thickenings of the basement membrane. The observed changes in microvascular integrity are very similar to those seen in humans, supporting the view of rhesus monkeys as a model for human aging. The slow but steady progression of these changes could be detrimental for an efficient nutrient supply of the neuropil, and might therefore contribute to decreased cognitive functioning during normal aging.

Large-scale N-ethyl-N-nitrosourea mutagenesis of mice--from phenotypes to genes

The most important tool for obtaining insight into the function of genes is the use of mutant model organisms. Homologous recombination in embryonic stem cells allows the systematic production of mouse mutants for any gene that has been cloned. Gene trap strategies have been designed to interrupt even unknown genes which are tagged by the inserted vector and can be characterised structurally and functionally. Complementary to such 'gene-driven' approaches, 'phenotype-driven' approaches are necessary to identify new genes or gene products through a search for mutants with specific defects, uncovering the function of genetic pathways in physiological and pathological processes. Mutagenesis using the alkylating agent N-ethyl-N-nitrosourea (ENU) is a powerful approach for the production of such mouse mutants. Since ENU induces mainly point mutations in premeiotic spermatogonia, this strategy allows the production of multiple alleles of a particular gene, which is pivotal for a fine tuned analysis of its function.

Physiological control of smooth muscle-specific gene expression through regulated nuclear translocation of serum response factor

Prolonged serum deprivation induces a structurally and functionally contractile phenotype in about 1/6 of cultured airway myocytes, which exhibit morphological elongation and accumulate abundant contractile apparatus-associated proteins. We tested the hypothesis that transcriptional activation of genes encoding these proteins accounts for their accumulation during this phenotypic transition by measuring the transcriptional activities of the murine SM22 and human smooth muscle myosin heavy chain promoters during transient transfection in subconfluent, serum fed or 7 day serum-deprived cultured canine tracheal smooth muscle cells. Contrary to our expectation, SM22 and smooth muscle myosin heavy chain promoter activities (but not viral murine sarcoma virus-long terminal repeat promoter activity) were decreased in long term serum-deprived myocytes by at least 8-fold. Because serum response factor (SRF) is a required transcriptional activator of these and other smooth muscle-specific promoters, we evaluated the expression and function of SRF in subconfluent and long term serum-deprived cells. Whole cell SRF mRNA and protein were maintained at high levels in serum-deprived myocytes, but SRF transcription-promoting activity, nuclear SRF binding to consensus CArG sequences, and nuclear SRF protein were reduced. Furthermore, immunocytochemistry revealed extranuclear redistribution of SRF in serum-deprived myocytes; nuclear localization of SRF was restored after serum refeeding. These results uncover a novel mechanism for physiological control of smooth muscle-specific gene expression through extranuclear redistribution of SRF and consequent down-regulation of its transcription-promoting activity.

Anterograde tracing of retinal afferents to the tree shrew hypothalamus and raphe

The anterograde neuronal transport of Cholera toxin B subunit (CTB) was used in this study to label the termination of retinal afferents in the hypothalamus of the tree shrew Tupaia belangeri. Upon pressure-injection of the substance into the vitreous body of one eye, a major projection of the retinohypothalamic tract (RHT) was found to the hypothalamic suprachiasmatic nuclei (SCN). Although the innervation pattern was bilateral, the ipsilateral SCN received a somewhat stronger projection. Labeling was also found in the supraoptic nucleus and its perinuclear zone, respectively, mainly ipsilaterally as well as in the bilateral para- and periventricular hypothalamic regions without lateral predominance. In the raphe region, scattered fibers and terminals were seen in the dorsal and median raphe nuclei. CTB-immunoreactive structures were observed neither in the locus ceruleus nor in vagal nuclei. Our results, partly in contradiction to earlier studies using different tracing techniques in another tree shrew species (Tupaia glis), reveal that hypothalamic nuclei, in particular the SCN, are contacted by retino-afferent fibers which are thought to mediate the effects of light to the endogenous 'clock' and to parts of the neuroendocrine system.

Genome-wide, large-scale production of mutant mice by ENU mutagenesis

In the post-genome era, the mouse will have a major role as a model system for functional genome analysis. This requires a large number of mutants similar to the collections available from other model organisms such as Drosophila melanogaster and Caenorhabditis elegans. Here we report on a systematic, genome-wide, mutagenesis screen in mice. As part of the German Human Genome Project, we have undertaken a large-scale ENU-mutagenesis screen for dominant mutations and a limited screen for recessive mutations. In screening over 14,000 mice for a large number of clinically relevant parameters, we recovered 182 mouse mutants for a variety of phenotypes. In addition, 247 variant mouse mutants are currently in genetic confirmation testing and will result in additional new mutant lines. This mutagenesis screen, along with the screen described in the accompanying paper, leads to a significant increase in the number of mouse models available to the scientific community. Our mutant lines are freely accessible to non-commercial users (for information, see http://www.gsf.de/ieg/groups/enu-mouse.html).