The subjective experience of stress leads to reproductive dysfunction in many species, including rodents and humans. Stress effects on reproduction result from multilevel interactions between the hormonal stress response system, i.e., the hypothalamic-pituitary-adrenal (HPA) axis, and the hormonal reproductive system, i.e., the hypothalamic-pituitary-gonadal (HPG) axis. A novel negative regulator of the HPG axis known as gonadotropin-inhibitory hormone (GnIH) was recently discovered in quail, and orthologous neuropeptides known as RFamide-related peptides (RFRPs) have also been identified in rodents and primates. It is currently unknown, however, whether GnIH/RFRPs influence HPG axis activity in response to stress. We show here that both acute and chronic immobilization stress lead to an up-regulation of RFRP expression in the dorsomedial hypothalamus (DMH) of adult male rats and that this increase in RFRP is associated with inhibition of downstream HPG activity. We also show that adrenalectomy blocks the stress-induced increase in RFRP expression. Immunohistochemistry revealed that 53% of RFRP cells express receptors for glucocorticoids (GCs), indicating that adrenal GCs can mediate the stress effect through direct action on RFRP cells. It is thought that stress effects on central control of reproduction are largely mediated by direct or indirect effects on GnRH-secreting neurons. Our data show that stress-induced increases in adrenal GCs cause an increase in RFRP that contributes to hypothalamic suppression of reproductive function. This novel insight into HPA-HPG interaction provides a paradigm shift for work on stress-related reproductive dysfunction and infertility, and indicates that future work on stress and reproductive system interactions must include investigation of the role of GnIH/RFRP.GnIH ͉ reproduction ͉ RFRP S tress has acute and chronic effects on many aspects of vertebrate physiology and behavior. Reproduction is a key life-history component that is often adversely affected by physical and psychological stressors. The negative impact of stress occurs at several levels of the vertebrate hypothalamic-pituitary-gonadal (HPG) axis. Centrally, it leads to activation of the hypothalamic-pituitaryadrenal (HPA) axis, which in turn leads to suppression of HPG activity through inhibition of gonadotropin-releasing hormone (GnRH) secretion (1, 2). Downstream of GnRH, the functional effects of stress on reproduction can be seen with suppression of luteinizing hormone (LH) release from the pituitary (3, 4) and suppression of sexual behavior (5, 6). The stress effect on HPG function appears to be mediated by the adrenal stress hormones glucocorticoids (GCs). In male mammals, systemic GC administration inhibits circulating gonadotropin levels (7), decreases seminal vesicle weight, and results in fewer implantation sites and viable fetuses in female mates (8). However, hypothalamic corticotropinreleasing hormone (CRH) has also been strongly implicated in stress effects on reproduction (2, 9, 10).Gonadotropin i...

Stress can exert long-lasting changes on the brain that contribute to vulnerability to mental illness, yet mechanisms underlying this long-term vulnerability are not well understood. We hypothesized that stress may alter the production of oligodendrocytes in the adult brain, providing a cellular and structural basis for stress-related disorders. We found that immobilization stress decreased neurogenesis and increased oligodendrogenesis in the dentate gyrus (DG) of the adult rat hippocampus, and that injections of the rat glucocorticoid stress hormone corticosterone (cort) were sufficient to replicate this effect. The DG contains a unique population of multipotent neural stem cells (NSCs) that give rise to adult newborn neurons, but oligodendrogenic potential has not been demonstrated in vivo. We used a nestin-CreER/YFP transgenic mouse line for lineage tracing and found that cort induces oligodendrogenesis from nestin-expressing NSCs in vivo. Using hippocampal NSCs cultured in vitro, we further showed that exposure to cort induced a pro-oligodendrogenic transcriptional program and resulted in an increase in oligodendrogenesis and decrease in neurogenesis, which was prevented by genetic blockade of glucocorticoid receptor (GR). Together, these results suggest a novel model in which stress may alter hippocampal function by promoting oligodendrogenesis, thereby altering the cellular composition and white matter structure.

Increased dietary intake of choline early in life improves performance of adult rats on memory tasks and prevents their age-related memory decline. Because neurogenesis in the adult hippocampus also declines with age, we investigated whether prenatal choline availability affects hippocampal neurogenesis in adult Sprague-Dawley rats and modifies their neurogenic response to environmental stimulation. On embryonic days (ED) 12−17, pregnant rats ate a choline-supplemented (SUP-5 g/ kg), choline sufficient (SFF-1.1 g/kg), or choline-free (DEF) semisynthetic diet. Adult offspring either remained in standard housing or were given 21 daily visits to explore a maze. On the last ten exploration days, all rats received daily injections of 5-bromo-2-deoxyuridine (BrdU, 100 mg/kg). The number of BrdU+ cells was significantly greater in the dentate gyrus in SUP rats compared to SFF or DEF rats. While maze experience increased the number of BrdU+ cells in SFF rats to the level seen in the SUP rats, this enriching experience did not alter cell proliferation in DEF rats. Similar patterns of cell proliferation were obtained with immunohistochemical staining for neuronal marker doublecortin, confirming that diet and exploration affected hippocampal neurogenesis. Moreover, hippocampal levels of the brain-derived neurotrophic factor (BDNF) were increased in SUP rats as compared to SFF and DEF animals. We conclude that prenatal choline intake has enduring effects on adult hippocampal neurogenesis, possibly via up-regulation of BDNF levels, and suggest that these alterations of neurogenesis may contribute to the mechanism of life-long changes in cognitive function governed by the availability of choline during gestation.

Stress is a potent modulator of the mammalian brain. The highly conserved stress hormone response influences many brain regions, particularly the hippocampus, a region important for memory function. The effect of acute stress on the unique population of adult neural stem/progenitor cells (NPCs) that resides in the adult hippocampus is unclear. We found that acute stress increased hippocampal cell proliferation and astrocytic fibroblast growth factor 2 (FGF2) expression. The effect of acute stress occurred independent of basolateral amygdala neural input and was mimicked by treating isolated NPCs with conditioned media from corticosterone-treated primary astrocytes. Neutralization of FGF2 revealed that astrocyte-secreted FGF2 mediated stress-hormone-induced NPC proliferation. 2 weeks, but not 2 days, after acute stress, rats also showed enhanced fear extinction memory coincident with enhanced activation of newborn neurons. Our findings suggest a beneficial role for brief stress on the hippocampus and improve understanding of the adaptive capacity of the brain.DOI: http://dx.doi.org/10.7554/eLife.00362.001

Ethologically relevant behavioral testing is a critical component of any study that uses mouse models to study the cognitive effects of various physiological or pathological changes. The object location task (OLT) and the novel object recognition task (NORT) are two effective behavioral tasks commonly used to reveal the function and relative health of specific brain regions involved in memory. While both of these tests exploit the inherent preference of mice for the novelty to reveal memory for previously encountered objects, the OLT primarily evaluates spatial learning, which relies heavily on hippocampal activity. The NORT, in contrast, evaluates non-spatial learning of object identity, which relies on multiple brain regions. Both tasks require an open-field-testing arena, objects with equivalent intrinsic value to mice, appropriate environmental cues, and video recording equipment and the software. Commercially available systems, while convenient, can be costly. This manuscript details a simple, cost-effective method for building the arenas and setting up the equipment necessary to perform the OLT and NORT. Furthermore, the manuscript describes an efficient testing protocol that incorporates both OLT and NORT and provides typical methods for data acquisition and analysis, as well as representative results. Successful completion of these tests can provide valuable insight into the memory function of various mouse model systems and appraise the underlying neural regions that support these functions.

The adult hippocampus hosts a population of neural stem and progenitor cells (NSPCs) that proliferates throughout the mammalian life span. To date, the new neurons derived from NSPCs have been the primary measure of their functional relevance. However, recent studies show that undifferentiated cells may shape their environment through secreted growth factors. Whether endogenous adult NSPCs secrete functionally relevant growth factors remains unclear. We show that adult hippocampal NSPCs secrete surprisingly large quantities of the essential growth factor VEGF in vitro and in vivo. This self-derived VEGF is functionally relevant for maintaining the neurogenic niche as inducible, NSPC-specific loss of VEGF results in impaired stem cell maintenance despite the presence of VEGF produced from other niche cell types. These findings reveal adult hippocampal NSPCs as an unanticipated source of an essential growth factor and imply an exciting functional role for adult brain NSPCs as secretory cells.adult neurogenesis | vascular endothelial growth factor | stem cell | hippocampus | neural precursor

Supplemental choline in the maternal diet produces a lasting enhancement in memory in offspring that resists age-related decline and is accompanied by neuroanatomical, neurophysiological and neurochemical changes in the hippocampus. The present study was designed to examine: 1) if prenatal choline supplementation alters behaviors that contribute to risk or resilience in cognitive aging, and 2) whether, at old age (25 months), prenatally choline supplemented rats show evidence of preserved hippocampal plasticity. A longitudinal design was used to look at exploration of an open field, with and without objects, at 1 and 24 months of age in male and female rats whose mothers were fed a diet supplemented with choline (SUP; 5 mg/kg choline chloride) or not supplemented (CON; 1.1 mg/kg choline chloride) on embryonic days 12-17. Aging caused a significant decline in open field exploration that was more pronounced in males but interest in novel objects was maintained in both sexes. Prenatal choline supplementation attenuated, but did not prevent age-related decline in exploration in males and increased object exploration in young females. Following behavioral assessment, rats were euthanized to assess markers of hippocampal plasticity. Aged SUP males and females had more newly proliferated cells in the hippocampal dentate gyrus and protein levels of vascular-endothelial growth factor (VEGF) and neurotrophin-3 (NT-3) were significantly elevated in female SUP rats in comparison to all other groups. Taken together, these findings provide the first evidence that prenatal cholinesupplementation causes changes in exploratory behaviors over the lifespan and preserves some features of hippocampal plasticity that can be seen even at 2 years of age.

Impaired regulation of emotional memory is a feature of several affective disorders, including depression, anxiety and post-traumatic stress disorder. Such regulation occurs, in part, by interactions between the hippocampus and the basolateral amygdala (BLA). Recent studies have indicated that within the adult hippocampus, newborn neurons may contribute to support of emotional memory, and that regulation of hippocampal neurogenesis is implicated in depressive disorders. How emotional information impacts newborn neurons in adults is not clear. Given the role of the BLA in hippocampus-dependent emotional memory, we investigated whether hippocampal neurogenesis was sensitive to emotional stimuli from the BLA. We show that BLA lesions suppress adult neurogenesis, while lesions of the central nucleus of the amygdala do not. Similarly, we show that reducing BLA activity through viral vector-mediated overexpression of an outwardly rectifying potassium channel suppresses neurogenesis. We also show that BLA lesions prevent selective activation of immature newborn neurons in response to a fear conditioning task. These results demonstrate that BLA activity regulates adult hippocampal neurogenesis and the fear context-specific activation of newborn neurons. Together, these findings denote functional implications for proliferation and recruitment of new neurons into emotional memory circuits.