Sexual experience promotes adult neurogenesis in the hippocampus despite an initial elevation in stress hormones

Emotional vocalizations alter behaviors and neurochemical release into the amygdala

The basolateral amygdala (BLA), a brain center of emotional expression, contributes to acoustic communication by first interpreting the meaning of social sounds in the context of the listener's internal state, then organizing the appropriate behavioral responses. We propose that modulatory neurochemicals such as acetylcholine (ACh) and dopamine (DA) provide internal-state signals to the BLA while an animal listens to social vocalizations. We tested this in a vocal playback experiment utilizing highly affective vocal sequences associated with either mating or restraint, then sampled and analyzed fluids within the BLA for a broad range of neurochemicals and observed behavioral responses of adult male and female mice. In male mice, playback of restraint vocalizations increased ACh release and usually decreased DA release, while playback of mating sequences evoked the opposite neurochemical release patterns. In non-estrus female mice, patterns of ACh and DA release with mating playback were similar to males. Estrus females, however, showed increased ACh, associated with vigilance, as well as increased DA, associated with reward-seeking. Experimental groups that showed increased ACh release also showed the largest increases in an aversive behavior. These neurochemical release patterns and several behavioral responses depended on a single prior experience with the mating and restraint behaviors. Our results support a model in which ACh and DA provide contextual information to sound analyzing BLA neurons that modulate their output to downstream brain regions controlling behavioral responses to social vocalizations.

TERT mediates the U-shape of glucocorticoids effects in modulation of hippocampal neural stem cells and associated brain function

BACKGROUND

Glucocorticoids (GCs) are steroidal hormones produced by the adrenal cortex. A physiological-level GCs have a crucial function in maintaining many cognitive processes, like cognition, memory, and mood, however, both insufficient and excessive GCs impair these functions. Although this phenomenon could be explained by the U-shape of GC effects, the underlying mechanisms are still not clear. Therefore, understanding the underlying mechanisms of GCs may provide insight into the treatments for cognitive and mood-related disorders.

METHODS

Consecutive administration of corticosterone (CORT, 10 mg/kg, i.g.) proceeded for 28 days to mimic excessive GCs condition. Adrenalectomy (ADX) surgery was performed to ablate endogenous GCs in mice. Microinjection of 1 μL of Ad-mTERT-GFP virus into mouse hippocampus dentate gyrus (DG) and behavioral alterations in mice were observed 4 weeks later.

RESULTS

Different concentrations of GCs were shown to affect the cell growth and development of neural stem cells (NSCs) in a U-shaped manner. The physiological level of GCs (0.01 μM) promoted NSC proliferation in vitro, while the stress level of GCs (10 μM) inhibited it. The glucocorticoid synthesis blocker metyrapone (100 mg/kg, i.p.) and ADX surgery both decreased the quantity and morphological development of doublecortin (DCX)-positive immature cells in the DG. The physiological level of GCs activated mineralocorticoid receptor and then promoted the production of telomerase reverse transcriptase (TERT); in contrast, the stress level of GCs activated glucocorticoid receptor and then reduced the expression of TERT. Overexpression of TERT by AD-mTERT-GFP reversed both chronic stresses- and ADX-induced deficiency of TERT and the proliferation and development of NSCs, chronic stresses-associated depressive symptoms, and ADX-associated learning and memory impairment.

CONCLUSION

The bidirectional regulation of TERT by different GCs concentrations is a key mechanism mediating the U-shape of GC effects in modulation of hippocampal NSCs and associated brain function. Replenishment of TERT could be a common treatment strategy for GC dysfunction-associated diseases.

Increased proliferation and neuronal fate in prairie vole brain progenitor cells cultured in vitro: effects by social exposure and sexual dimorphism

BACKGROUND

The prairie vole (Microtus ochrogaster) is a socially monogamous rodent that establishes an enduring pair bond after cohabitation, with (6 h) or without (24 h) mating. Previously, we reported that social interaction and mating increased cell proliferation and differentiation to neuronal fate in neurogenic niches in male voles. We hypothesized that neurogenesis may be a neural plasticity mechanism involved in mating-induced pair bond formation. Here, we evaluated the differentiation potential of neural progenitor cells (NPCs) isolated from the subventricular zone (SVZ) of both female and male adult voles as a function of sociosexual experience. Animals were assigned to one of the following groups: (1) control (Co), sexually naive female and male voles that had no contact with another vole of the opposite sex; (2) social exposure (SE), males and females exposed to olfactory, auditory, and visual stimuli from a vole of the opposite sex, but without physical contact; and (3) social cohabitation with mating (SCM), male and female voles copulating to induce pair bonding formation. Subsequently, the NPCs were isolated from the SVZ, maintained, and supplemented with growth factors to form neurospheres in vitro.

RESULTS

Notably, we detected in SE and SCM voles, a higher proliferation of neurosphere-derived Nestin + cells, as well as an increase in mature neurons (MAP2 +) and a decrease in glial (GFAP +) differentiated cells with some sex differences. These data suggest that when voles are exposed to sociosexual experiences that induce pair bonding, undifferentiated cells of the SVZ acquire a commitment to a neuronal lineage, and the determined potential of the neurosphere is conserved despite adaptations under in vitro conditions. Finally, we repeated the culture to obtain neurospheres under treatments with different hormones and factors (brain-derived neurotrophic factor, estradiol, prolactin, oxytocin, and progesterone); the ability of SVZ-isolated cells to generate neurospheres and differentiate in vitro into neurons or glial lineages in response to hormones or factors is also dependent on sex and sociosexual context.

CONCLUSION

Social interactions that promote pair bonding in voles change the properties of cells isolated from the SVZ. Thus, SE or SCM induces a bias in the differentiation potential in both sexes, while SE is sufficient to promote proliferation in SVZ-isolated cells from male brains. In females, proliferation increases when mating is performed. The next question is whether the rise in proliferation and neurogenesis of cells from the SVZ are plastic processes essential for establishing, enhancing, maintaining, or accelerating pair bond formation. Highlights 1. Sociosexual experiences that promote pair bonding (social exposure and social cohabitation with mating) induce changes in the properties of neural stem/progenitor cells isolated from the SVZ in adult prairie voles. 2. Social interactions lead to increased proliferation and induce a bias in the differentiation potential of SVZ-isolated cells in both male and female voles. 3. The differentiation potential of SVZ-isolated cells is conserved under in vitro conditions, suggesting a commitment to a neuronal lineage under a sociosexual context. 4. Hormonal and growth factors treatments (brain-derived neurotrophic factor, estradiol, prolactin, oxytocin, and progesterone) affect the generation and differentiation of neurospheres, with dependencies on sex and sociosexual context. 5. Proliferation and neurogenesis in the SVZ may play a crucial role in establishing, enhancing, maintaining, or accelerating pair bond formation.

Neurocognitive effects of stress: a metaparadigm perspective

Stressful experiences, both physical and psychological, that are overwhelming (i.e., inescapable and unpredictable), can measurably affect subsequent neuronal properties and cognitive functioning of the hippocampus. At the cellular level, stress has been shown to alter hippocampal synaptic plasticity, spike and local field potential activity, dendritic morphology, neurogenesis, and neurodegeneration. At the behavioral level, stress has been found to impair learning and memory for declarative (or explicit) tasks that are based on cognition, such as verbal recall memory in humans and spatial memory in rodents, while facilitating those that are based on emotion, such as differential fear conditioning in humans and contextual fear conditioning in rodents. These vertically related alterations in the hippocampus, procedurally observed after subjects have undergone stress, are generally believed to be mediated by recurrently elevated circulating hypothalamic-pituitary-adrenal (HPA) axis effector hormones, glucocorticoids, directly acting on hippocampal neurons densely populated with corticosteroid receptors. The main purposes of this review are to (i) provide a synopsis of the neurocognitive effects of stress in a historical context that led to the contemporary HPA axis dogma of basic and translational stress research, (ii) critically reappraise the necessity and sufficiency of the glucocorticoid hypothesis of stress, and (iii) suggest an alternative metaparadigm approach to monitor and manipulate the progression of stress effects at the neural coding level. Real-time analyses can reveal neural activity markers of stress in the hippocampus that can be used to extrapolate neurocognitive effects across a range of stress paradigms (i.e., resolve scaling and dichotomous memory effects issues) and understand individual differences, thereby providing a novel neurophysiological scaffold for advancing future stress research.

Cell proliferation and cell death levels in the dentate gyrus correlate with home range size among adult male meadow voles

Neurogenesis occurs throughout adulthood within the dentate gyrus, and evidence indicates that these new neurons play a critical role in both spatial and social memory. However, a vast majority of past research on adult neurogenesis has involved experiments with captive mice and rats, making the generalizability of results to natural settings questionable. We assessed the connection between adult neurogenesis and memory by measuring the home range size of wild-caught, free-ranging meadow voles (Microtus pennsylvanicus). Adult male voles (n = 18) were captured, fitted with radio collars, and released back into their natural habitat, where each vole's home range was assessed using 40 radio-telemetry fixes over the course of 5 evenings. Voles were then recaptured, and brain tissue was collected. Cellular markers of cell proliferation (pHisH3, Ki67), neurogenesis (DCX), and pyknosis were labeled on histological sections and then quantified using either fluorescent or light microscopy. Voles with larger home ranges had significantly higher pHisH3+ cell densities within the granule cell layer and subgranular zone (GCL+SGZ) of the dentate gyrus and higher Ki67+ cell densities in the dorsal GCL+SGZ. Voles with larger ranges also had significantly higher pyknotic cell densities in the entire GCL+SGZ and in the dorsal GCL+SGZ. These results support the hypothesis that cell proliferation and cell death within the hippocampus are involved with spatial memory formation. However, a marker of neurogenesis (DCX+) was not correlated with range size, suggesting that there may be selective cellular turnover in the dentate gyrus when a vole is ranging through its environment.

Social Enhancement of Adult Neurogenesis in Zebrafish is Not Regulated by Cortisol

In Mammals adult neurogenesis is influenced by environmental conditions, and the glucocorticoid hormones (GC) play a major role in this regulation. In contrast in fish, the study of the effects of cortisol on the regulation of environmental driven adult neurogenesis has produced conflicting results. While in some species elevated cortisol levels impair cell proliferation, in others, it promotes cell proliferation and differentiation. This lack of consistency may be explained by methodological differences across studies, namely in the stimuli and/or cortisol treatments used. Here, we tested the effects of the social environment on adult neurogenesis, considering a positive and a negative social context, and different durations of cortisol exposure. We hypothesise that there is an interaction between the valence of the social environment and cortisol, such that elevated acute cortisol experienced during social interactions only have a detrimental effect on neurogenesis in negative social contexts. Therefore, fish were exposed to a positive (conspecific shoal) or negative (predator) social experience, and the interaction between the valence of the social context and cortisol exposure (acute and chronic) was tested. Our results indicate that adult neurogenesis is modulated by the social environment, with the number of newly generated cells being dependent on the valence of the social information (positive > negative). These effects were independent of cortisol, either for acute or chronic exposure, highlighting the social environment as a key factor in the modulation of cell proliferation in the adult zebrafish brain, and rejecting a role for cortisol in this modulation.

Adult newborn granule cells confer emotional state-dependent adaptability in memory retrieval

Achieving optimal behavior requires animals to flexibly retrieve prior knowledge. Here, we show that adult newborn granule cells (anbGCs) mediate emotional state-dependent adaptability of memory retrieval. We find that acute social reward (aSR) enhances memory retrieval by increasing the reactivation of engram cells, while acute social stress (aSS) weakens retrieval and reduces the reactivation. Such bidirectional regulation relies on the activation of distinct populations of anbGCs by aSR and aSS, triggering opposing modifications of dDG activity, which is sufficient to regulate and predict the performance of memory retrieval. Concordantly, in emotional disorder models, aSR-dependent memory adaptability is impaired, while the effect of aSS remains intact. Together, our data revealed that anbGCs mediate adaptability of memory retrieval, allowing animals to flexibly retrieve memory according to the current emotional state, and suggested the essential roles of anbGCs in translating emotional information to the regulation of memory expression.

Pair-bonding and social experience modulate new neurons survival in adult male and female prairie voles (Microtus ochrogaster)

Prairie voles are a socially monogamous species that, after cohabitation with mating, form enduring pair bonds. The plastic mechanisms involved in this social behavior are not well-understood. Neurogenesis in adult rodents is a plastic neural process induced in specific brain areas like the olfactory bulbs (OB) and dentate gyrus (DG) of the hippocampus. However, it is unknown how cell survival is modulated by social or sexual experience in prairie voles. This study aimed to evaluate if cohabitation with mating and/or social exposure to a vole of the opposite sex increased the survival of the new cells in the main and accessory OB and DG. To identify the new cells and evaluate their survival, voles were injected with the DNA synthesis marker 5-bromo-2’-deoxyuridine (BrdU) and were randomly distributed into one of the following groups: (A) Control (C), voles that did not receive any sexual stimulation and were placed alone during the behavioral test. (B) Social exposure (SE), voles were individually placed in a cage equally divided into two compartments by an acrylic screen with small holes. One male and one female were placed in opposite compartments. (C) Social cohabitation with mating (SCM), animals mated freely. Our findings demonstrated that SCM females had increases in the number of new cells (BrdU-positive cells) in the main olfactory bulb and new mature neurons (BrdU/NeuN-positive cells) in the glomerular layer (GlL). In contrast, these new cells decrease in males in the SE and SCM conditions. In the granular cell layer (GrL), SCM females had more new cells and neurons than the SE group. In the accessory olfactory bulb, in the anterior GlL, SCM decreased the number of new cells and neurons in females. On the other hand, in the DG, SCM and SE increase the number of new cells in the suprapyramidal blade in female voles. Males from SCM express more new cells and neurons in the infrapyramidal blade compared with SE group. Comparison between male and females showed that new cells/neurons survival was sex dependent. These results suggest that social interaction and sexual behavior modulate cell survival and influence the neuronal fate in a sex-dependent manner, in the OB and DG. This study will contribute to understand neural mechanisms of complex social and pair bond behaviors in the prairie voles; supporting adult neurogenesis as a plastic mechanism potentially involved in social monogamous strategy.

Neuroplastic changes in c-Fos, ΔFosB, BDNF, trkB, and Arc expression in the hippocampus of male Roman rats: differential effects of sexual activity

Sexual activity causes differential changes in the expression of markers of neural activation (c‐Fos and ΔFosB) and neural plasticity (Arc and BDNF/trkB), as determined either by Western Blot (BDNF, trkB, Arc, and ΔFosB) or immunohistochemistry (BDNF, trkB, Arc, and c‐Fos), in the hippocampus of male Roman high (RHA) and low avoidance (RLA) rats, two psychogenetically selected rat lines that display marked differences in sexual behavior (RHA rats exhibit higher sexual motivation and better copulatory performance than RLA rats). Both methods showed (with some differences) that sexual activity modifies the expression levels of these markers in the hippocampus of Roman rats depending on: (i) the level of sexual experience, that is, changes were usually more evident in sexually naïve than in experienced rats; (ii) the hippocampal partition, that is, BDNF and Arc increased in the dorsal but tended to decrease in the ventral hippocampus; (iii) the marker considered, that is, in sexually experienced animals BDNF, c‐Fos, and Arc levels were similar to those of controls, while ΔFosB levels increased; and (iv) the rat line, that is, changes were usually larger in RHA than RLA rats. These findings resemble those of early studies in RHA and RLA rats showing that sexual activity influences the expression of these markers in the nucleus accumbens, medial prefrontal cortex, and ventral tegmental area, and show for the first time that also in the hippocampus sexual activity induces neural activation and plasticity, events that occur mainly during the first phase of the acquisition of sexual experience and depend on the genotypic/phenotypic characteristics of the animals.

Variation in the sexual behavior and blood count parameters induced by sleep deprivation in male rats

BACKGROUND

Sleep is a fundamental biological requirement, and lack of sleep has increasingly been recognized to cause metabolic consequences and adversely affect immune function. Recent articles have pointed to how sleep and sexual functions may be interlinked, involving inflammation, vascular alterations, tissue damage, and endothelial dysfunction.

OBJECTIVES

We examined the effect of paradoxical sleep deprivation (PSD) on sexual behavior and hemogram parameters in male rats. In addition, we also explored whether 7 days of recovery sleep is sufficient to offset these detriments.

MATERIALS AND METHODS

 Male rats were given sexual experience through training. At the 5th test, the sexually vigorous males were randomly separated into 3 experimental groups: PSD (rats submitted to 96 hours of PSD, n = 6), RS (recovery sleep 7 days after PSD, n = 6), and control (n = 10). We evaluated the sexual behaviors of three groups. Blood samples were collected to analysis hemogram parameters.

RESULTS

In this study, we recognized that repeated copulatory tests can lead to changes in sexual behavior over time. We found that 96 hours of acute sleep deprivation impaired the sexual behavior of male rats. Our results demonstrated that 96 hours of PSD also increased levels of white blood cell (WBC) subpopulations, in particular neutrophils. Recovery sleep after sleep deprivation has a certain reversal effect on WBC subgroups and impairment of sexual behavior, with some signs that not all levels were back to baseline even after 7 days of recovery.

CONCLUSION

In general, we found that 96 hours of PSD impaired the sexual behavior of male rats. Our results demonstrated that PSD can cause systemic inflammation by affecting WBC subpopulations, in particular neutrophils. 7 days of recovery sleep after sleep deprivation has a certain reversal effect to these impairments. This article is protected by copyright. All rights reserved.

Hippocampal cytogenesis abrogation impairs inter-regional communication between the hippocampus and prefrontal cortex and promotes the time-dependent manifestation of emotional and cognitive deficits

Impaired ability to generate new cells in the adult brain has been linked to deficits in multiple emotional and cognitive behavioral domains. However, the mechanisms by which abrogation of adult neural stem cells (NSCs) impacts on brain function remains controversial. We used a transgenic rat line, the GFAP-Tk, to selectively eliminate NSCs and assess repercussions on different behavioral domains. To assess the functional importance of newborn cells in specific developmental stages, two parallel experimental timeframes were adopted: a short- and a long-term timeline, 1 and 4 weeks after the abrogation protocol, respectively. We conducted in vivo electrophysiology to assess the effects of cytogenesis abrogation on the functional properties of the hippocampus and prefrontal cortex, and on their intercommunication. Adult brain cytogenesis abrogation promoted a time-specific installation of behavioral deficits. While the lack of newborn immature hippocampal neuronal and glial cells elicited a behavioral phenotype restricted to hyperanxiety and cognitive rigidity, specific abrogation of mature new neuronal and glial cells promoted the long-term manifestation of a more complex behavioral profile encompassing alterations in anxiety and hedonic behaviors, along with deficits in multiple cognitive modalities. More so, abrogation of 4 to 7-week-old cells resulted in impaired electrophysiological synchrony of neural theta oscillations between the dorsal hippocampus and the medial prefrontal cortex, which are likely to contribute to the described long-term cognitive alterations. Hence, this work provides insight on how newborn neurons and astrocytes display different functional roles throughout different maturation stages, and establishes common ground to reconcile contrasting results that have marked this field.

Hypothalamic cellular and molecular plasticity linked to sexual experience in male rats and mice

Male sexual behavior is subject to learning, resulting in increased efficiency of experienced males compared to naive ones. The improvement in behavioral parameters is underpinned by cellular and molecular changes in the neural circuit controlling sexual behavior, particularly in the hypothalamic medial preoptic area. This review provides an update on the mechanisms related to the sexual experience in male rodents, emphasizing the differences between rats and mice.

Distinct regulation of hippocampal neuroplasticity and ciliary genes by corticosteroid receptors

Glucocorticoid hormones (GCs) — acting through hippocampal mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) — are critical to physiological regulation and behavioural adaptation. We conducted genome-wide MR and GR ChIP-seq and Ribo-Zero RNA-seq studies on rat hippocampus to elucidate MR- and GR-regulated genes under circadian variation or acute stress. In a subset of genes, these physiological conditions resulted in enhanced MR and/or GR binding to DNA sequences and associated transcriptional changes. Binding of MR at a substantial number of sites however remained unchanged. MR and GR binding occur at overlapping as well as distinct loci. Moreover, although the GC response element (GRE) was the predominant motif, the transcription factor recognition site composition within MR and GR binding peaks show marked differences. Pathway analysis uncovered that MR and GR regulate a substantial number of genes involved in synaptic/neuro-plasticity, cell morphology and development, behavior, and neuropsychiatric disorders. We find that MR, not GR, is the predominant receptor binding to >50 ciliary genes; and that MR function is linked to neuronal differentiation and ciliogenesis in human fetal neuronal progenitor cells. These results show that hippocampal MRs and GRs constitutively and dynamically regulate genomic activities underpinning neuronal plasticity and behavioral adaptation to changing environments.

Glucocorticoid hormones (GCs) are of critical importance for maintaining brain health, but their involvement in mental disorders is poorly understood. Here the authors show how GCs act through hippocampal mineralocorticoid and glucocorticoid receptors to impact the gene regulatory programs underpinning neuronal plasticity, ciliogenesis and behavioral adaptation.

Plasticity of the paternal brain: Effects of fatherhood on neural structure and function

Care of infants is a hallmark of mammals. Whereas parental care by mothers is obligatory for offspring survival in virtually all mammals, fathers provide care for their offspring in only an estimated 5%-10% of genera. In these species, the transition into fatherhood is often accompanied by pronounced changes in males' behavioral responses to young, including a reduction in aggression toward infants and an increase in nurturant behavior. The onset of fatherhood can also be associated with sensory, affective, and cognitive changes. The neuroplasticity that mediates these changes is not well understood; however, fatherhood can alter the production and survival of new neurons; function and structure of existing neurons; morphology of brain structures; and neuroendocrine signaling systems. Although these changes are thought to promote infant care by fathers, very little evidence exists to support this hypothesis; in most cases, neither the mechanisms underlying neuroplasticity in fathers nor its functional significance is known. In this paper, we review the available data on the neuroplasticity that occurs during the transition into fatherhood. We highlight gaps in our knowledge and future directions that will provide key insights into how and why fatherhood alters the structure and functioning of the male brain.

Glucocorticoid-mediated mechanisms of hippocampal damage: Contribution of subgranular neurogenesis

A comprehensive overview of the interplay between glucocorticoids (GCs) and adult hippocampal neurogenesis (AHN) is presented, particularly, in the context of a diseased brain. The effectors of GCs in the dentate gyrus neurogenic niche of the hippocampal are reviewed, and the consequences of the GC signaling on the generation and integration of new neurons are discussed. Recent findings demonstrating how GC signaling mediates impairments of the AHN in various brain pathologies are overviewed. GC-mediated effects on the generation and integration of adult-born neurons in the hippocampal dentate gyrus depend on the nature, severity, and duration of the acting stress factor. GCs realize their effects on the AHN primarily via specific glucocorticoid and mineralocorticoid receptors. Disruption of the reciprocal regulation between the hypothalamic-pituitary-adrenal (HPA) axis and the generation of the adult-born granular neurons is currently considered to be a key mechanism implicating the AHN into the pathogenesis of numerous brain diseases, including those without a direct hippocampal damage. These alterations vary from reduced proliferation of stem and progenitor cells to increased cell death and abnormalities in morphology, connectivity, and localization of young neurons. Although the involvement of the mutual regulation between the HPA axis and the AHN in the pathogenesis of cognitive deficits and mood impairments is evident, several unresolved critical issues are stated. Understanding the details of GC-mediated mechanisms involved in the alterations in AHN could enable the identification of molecular targets for ameliorating pathology-induced imbalance in the HPA axis/AHN mutual regulation to conquer cognitive and psychiatric disturbances.

Appetitive olfactory conditioning in the neonatal male rat facilitates subsequent sexual partner preference

Pairing a neutral odor with a male rat's initial sexual experiences to ejaculation produces a subsequent conditioned ejaculatory preference (CEP) in which males ejaculate preferentially with receptive females that bear the odor relative to unscented receptive females. In 1986, Fillion and Blass reported that neonatal male rats exposed to a neutral lemon odor (citral) painted on their mother's ventrum while nursing ejaculated faster as adults with sexually receptive, citral-scented females compared to unscented receptive females. The present study examined whether the same odor paired with tactile reward in neonatal male rats would alter the subsequent expression of a CEP. Newborn Long-Evans male rats were separated from their mothers each day beginning on Postnatal Day 1 and placed into a Plexiglas cage that contained either unscented or citral-scented bedding (N = 8/group). During each trial, rats were stroked from head to toe with a soft, narrow paintbrush, after which they were returned to their mothers. Males were weaned at 21 days of age and housed in same-treatment pairs for an intervening 50 days. Following habituation to a large open field, males were presented with two sexually receptive Long-Evans females, one scented with citral, and the other unscented, for a 30-min test of copulation. Males in the Paired group copulated and ejaculated preferentially with the scented female whereas males in the Unpaired group showed no preference. Pairing a neutral odor with a reward state in infancy generates a preference in male rats to ejaculate with sexually receptive females bearing the same odor in adulthood.

Effects of Mating and Social Exposure on Cell Proliferation in the Adult Male Prairie Vole (Microtus ochrogaster)

Microtus ochrogaster is a rodent with a monogamous reproductive strategy characterized by strong pair bond formation after 6 h of mating. Here, we determine whether mating-induced pair bonding increases cell proliferation in the subventricular zone (SVZ), rostral migratory stream (RMS), and dentate gyrus (DG) of the hippocampus in male voles. Males were assigned to one of the four groups: (1) control: males were placed alone in a clean cage; (2) social exposure to a female (SE m/f): males that could see, hear, and smell a sexually receptive female but where physical contact was not possible, because the animals were separated by an acrylic screen with small holes; (3) social exposure to a male (SE m/m): same as group 2 but males were exposed to another male without physical contact; and (4) social cohabitation with mating (SCM): males that mated freely with a receptive female for 6 h. This procedure leads to pair bond formation. Groups 2 and 3 were controls for social interaction. Male prairie voles were injected with 5-bromo-2′-deoxyuridine (BrdU) during the behavioral tests and were sacrificed 48 h later. Brains were processed to identify the new cells (BrdU-positive) and neuron precursor cells (neuroblasts). Our principal findings are that in the dorsal region of the SVZ, SCM and SE m/f and m/m increase the percentage of neuron precursor cells. In the anterior region of the RMS, SE m/f decreases the percentage of neuron precursor cells, and in the medial region SE m/f and m/m decrease the number of new cells and neuron precursor cells. In the infrapyramidal blade of the subgranular zone of the DG, SE m/m and SCM increase the number of new neuron precursor cells and SE m/m increases the percentage of these neurons. Our data suggests that social interaction, as well as sexual stimulation, leads to pair bonding in male voles modulating cell proliferation and differentiation to neuronal precursor cells at the SVZ, RMS, and DG.

II. Antidepressants and sexual behavior: Acute fluoxetine, but not ketamine, disrupts paced mating behavior in sexually experienced female rats

Female sexual dysfunction is both a symptom of depression and exacerbated by treatments for depression. Ketamine, a novel treatment for depression, has been shown to enhance, whereas fluoxetine has been shown to impair sexual motivation. Sexual experience leads to more robust partner preference and paced mating behavior in female rats. Whether acute ketamine and fluoxetine similarly affect sexual motivation and mating behavior in sexually experienced female rats is unknown. Sexually experienced female rats received 10 mg/kg i.p. of ketamine or saline vehicle (Experiment 1) or 10 mg/kg i.p. of fluoxetine or water vehicle (Experiment 2) 30 min before a 10-min no-contact partner preference test followed immediately by a 15-intromission paced mating test. Partner preference and paced mating behavior did not differ between ketamine- and saline-treated rats. In contrast, rats treated with fluoxetine spent significantly less time with either stimulus animal and were less active during the partner preference test than water-treated rats. Additionally, contact-return latency to ejaculation was significantly longer in fluoxetine-treated rats and they spent less time with the male during paced mating in comparison to water-treated rats. Thus, even with sexual experience, fluoxetine disrupts sexual function whereas ketamine has no detrimental effects on sexual behavior in female rats. A growing body of evidence suggests that ketamine is an encouraging new approach to treat depression particularly because it is not associated with sexual dysfunction.

Inducible and Conditional Stimulation of Adult Hippocampal Neurogenesis Rescues Cadmium-Induced Impairments of Adult Hippocampal Neurogenesis and Hippocampus-Dependent Memory in Mice

Cadmium (Cd) is a heavy metal and an environmental pollutant. However, the full spectrum of its neurotoxicity and the underlying mechanisms are not completely understood. Our previous studies demonstrated that Cd exposure impairs adult hippocampal neurogenesis and hippocampus-dependent memory in mice. This study aims to determine if these adverse effects of Cd exposure can be mitigated by genetically and conditionally enhancing adult neurogenesis. To address this issue, we utilized the transgenic constitutive active MEK5 (caMEK5) mouse strain we previously developed and characterized. This mouse strain enables us to genetically and conditionally activate adult neurogenesis by administering tamoxifen to induce expression of a caMEK5 in adult neural stem/progenitor cells, which stimulates adult neurogenesis through activation of the endogenous extracellular signal-regulated kinase 5 mitogen-activated protein kinase pathway. The caMEK5 mice were exposed to 0.6 mg/l Cd through drinking water for 38 weeks. Once impairment of memory was confirmed, tamoxifen was administered to induce caMEK5 expression and to activate adult neurogenesis. Behavior tests were conducted at various time points to monitor hippocampus-dependent memory. Upon completion of the behavior tests, brain tissues were collected for cellular studies of adult hippocampal neurogenesis. We report here that Cd impaired hippocampus-dependent spatial memory and contextual fear memory in mice. These deficits were rescued by the tamoxifen induction of caMEK5 expression. Furthermore, Cd inhibition of adult hippocampal neurogenesis was also reversed. This rescue experiment provides strong evidence for a direct link between Cd-induced impairments of adult hippocampal neurogenesis and hippocampus-dependent memory.

Hormonal Regulation of Mammalian Adult Neurogenesis: A Multifaceted Mechanism

Adult neurogenesis—resulting in adult-generated functioning, integrated neurons—is still one of the most captivating research areas of neuroplasticity. The addition of new neurons in adulthood follows a seemingly consistent multi-step process. These neurogenic stages include proliferation, differentiation, migration, maturation/survival, and integration of new neurons into the existing neuronal network. Most studies assessing the impact of exogenous (e.g., restraint stress) or endogenous (e.g., neurotrophins) factors on adult neurogenesis have focused on proliferation, survival, and neuronal differentiation. This review will discuss the multifaceted impact of hormones on these various stages of adult neurogenesis. Specifically, we will review the evidence for hormonal facilitation (via gonadal hormones), inhibition (via glucocorticoids), and neuroprotection (via recruitment of other neurochemicals such as neurotrophin and neuromodulators) on newly adult-generated neurons in the mammalian brain.

Adult Neurogenesis, Glia, and the Extracellular Matrix

In the adult mammalian hippocampus, new neurons arise from stem and progenitor cell division, in a process known as adult neurogenesis. Adult-generated neurons are sensitive to experience and may participate in hippocampal functions, including learning and memory, anxiety and stress regulation, and social behavior. Increasing evidence emphasizes the importance of new neuron connectivity within hippocampal circuitry for understanding the impact of adult neurogenesis on brain function. In this Review, we discuss how the functional consequences of new neurons arise from the collective interactions of presynaptic and postsynaptic neurons, glial cells, and the extracellular matrix, which together form the "tetrapartite synapse."

Chronic sleep deprivation prolongs the reduction of sexual behaviour associated with daily sexual encounter in male rats

Chronic sleep deprivation (CSD) is common in many societies. Consecutive sleep loss increases allostatic load, which is known to negatively affect health outcomes. We investigated the impact of CSD on male sexual behaviour. Sexually-experienced male Long-Evans rats (singly housed under 14:10 light:dark) were either subjected to CSD or no CSD for 7 days, followed by a 7-day sleep recovery (SR) period. Their sexual behaviours were tested daily during both periods. CSD was performed by a 'gentle-handling' protocol for 4 hours per day, at the end of the light phase. Daily sexual behaviour tests led to a change in sexual behaviour over time. Intromission and ejaculation frequencies declined with repeated testing, but the reduction in these behaviours lasted for a longer period in rats that were previously subjected to CSD. Ejaculation latency was significantly longer towards the end of the recovery period in rats that had undergone CSD, but not in the control group. Post-ejaculatory interval increased and mounting behaviour did not change with daily mating tests, regardless of sleep deprivation protocol. CSD prolongs the decline in sexual behaviours associated with daily sexual encounters in male rats, and thus the return to baseline for these parameters requires days.

Altered Sexual Behavior in Dopamine Transporter (DAT) Knockout Male Rats: A Behavioral, Neurochemical and Intracerebral Microdialysis Study

Central dopamine plays a key role in sexual behavior. Recently, a Dopamine Transporter knockout (DAT KO) rat has been developed, which displays several behavioral dysfunctions that have been related to increased extracellular dopamine levels and altered dopamine turnover secondary to DAT gene silencing. This prompted us to characterize the sexual behavior of these DAT KO rats and their heterozygote (HET) and wild type (WT) counterparts in classical copulatory tests with a sexually receptive female rat and to verify if and how the acquisition of sexual experience changes along five copulatory tests in these rat lines. Extracellular dopamine and glutamic acid concentrations were also measured in the dialysate obtained by intracerebral microdialysis from the nucleus accumbens (Acb) shell of DAT KO, HET and WT rats, which underwent five copulatory tests, when put in the presence of an inaccessible sexually receptive female rat and when copulation was allowed. Markers of neurotropism (BDNF, trkB), neural activation (Δ-FosB), functional (Arc and PSA-NCAM) and structural synaptic plasticity (synaptophysin, syntaxin-3, PSD-95) were also measured in the ventral tegmental area (VTA), Acb (shell and core) and medial prefrontal cortex (mPFC) by Western Blot assays. The results indicate that the sexual behavior of DAT KO vs. HET and WT rats shows peculiar differences, mainly due to a more rapid acquisition of stable sexual activity levels and to higher levels of sexual motivation and activity. These differences occurred with differential changes in dopamine and glutamic acid concentrations in Acb dialysates during sexual behavior, with lower increases of dopamine and glutamic acid in DAT KO vs. WT and HET rats, and a lower expression of the markers investigated, mainly in the mPFC, in DAT KO vs. WT rats. Together these findings confirm a key role of dopamine in sexual behavior and provide evidence that the permanently high levels of dopamine triggered by DAT gene silencing cause alterations in both the frontocortical glutamatergic neurons projecting to the Acb and VTA and in the mesolimbic dopaminergic neurons, leading to specific brain regional changes in trophic support and neuroplastic processes, which may have a role in the sexual behavior differences found among the three rat genotypes.

Repeated Paced Mating Increases the Survival of New Neurons in the Accessory Olfactory Bulb

In female rats, the first sexual experience under paced mating conditions increases the number of newborn cells that migrate into the granular layer of the accessory olfactory bulb (AOB). Repeated paced mating has a potentiating effect on the number of new neurons that migrate to the AOB compared with a single session 15 days after paced mating. On the other hand, one paced mating session does no increases the survival of new cells 45 days after mating. In the present study, we evaluated if four paced mating sessions could increase the survival of new neurons in the AOB and main olfactory bulb (MOB) 45 days after females mated. Sexually naive female rats were ovariectomized, hormonally supplemented and randomly assigned to one of five groups: (1) Control, no sexual contact (C); (2) Four sessions in which females were exposed, without mating, to a sexually experience male rat (SE); (3) One session of paced mating (PM1); (4) Four sessions of paced mating (PM4); and (5) Four sessions of non-paced mating (NPM4). In the first behavioral test, females received the DNA synthesis marker 5-bromo-2'deoxyuridine and were euthanized 45 days later. Our data showed that the number of new cells that survived in the mitral cell layer of the AOB decreased when females were exposed to a sexually active male, in comparison to females that mated once pacing the sexual interaction. Repeated sexual behavior in pacing conditions did not increase the survival of new cells in other layers of the MOB and AOB. However, a significant increase in the percentage of new neurons in the granular and glomerular layers of the AOB and granular layer of the MOB was observed in females that mated in four sessions pacing the sexual interaction. In the group that paced the sexual interaction for one session, a significant increase in the percentage of neurons was observed in the glomerular layer of the AOB. Our data suggest that repeated paced mating increases the percentage of new neurons that survive in the olfactory bulb of female rats.

Sexual behavior in rodents: Where do we go from here?

Hormones and Behavior was first published 50 years ago including some articles related to the hormonal regulation of sexual behavior in different species. Since then, this research field has produced outstanding discoveries that have contributed to our understanding of the control of sexual behavior. The refinement of classical techniques and the development of new experimental tools has opened the door to a new era of research that will allow us to understand different aspects of sexual behavior. It would also expand the possible extrapolation from animal models to understand human sexuality and its dysfunctions. In this review, we summarize some of the most recent findings about sexual behavior in both sexes including the refinement of classical methods of study with new approaches and questions as well as the development of new methods trying to explain mechanisms of action on motivational and consummatory elements of mating behavior. We also reviewed other aspects that modulate sexual behavior such as attractivity, olfactory signals and learning which model mate selection. Additionally, we described studies demonstrating that sexual behavior induces permanent brain modifications in neuronal circuits. Finally, we briefly describe recent contributions on animal models of human sexuality dysfunctions which, although with their own limitations, are under continuous refining.

Sexual Behavior and Synaptic Plasticity

Although sex drive is present in many animal species, sexual behavior is not static and, like many other behaviors, can be modified by experience. This modification relies on synaptic plasticity, a sophisticated mechanism through which neurons change how they process a given stimulus, and the neurophysiological basis of learning. This review addresses the main plastic effects of steroid sex hormones in the central nervous system (CNS) and the effects of sexual experience on the CNS, including effects on neurogenesis, intracellular signaling, gene expression, and changes in dendritic spines, as well as behavioral changes.

Regulation of adult hippocampal neurogenesis exerted by sexual, cognitive and physical activity: An update

In 1962, Joseph Altman described that the brain generates neurons after the postnatal period, and this continues throughout your life (Altman, 1962). This was a breakthrough in the neuroscience field because before this the accepted paradigm was that the brain only generated neurons during the embryonal development. This discovery has been controversial ever since, especially since one of the areas of the brain with neurogenic properties is the hippocampus, which is the area involved in memory storage and neurodegenerative processes. The adult hippocampal neurogenesis modulates in response to different environmental factors. In this article, we review how exercise and cognitive and sexual activity can regulate the generation of new neurons in the hippocampal in an adult brain and the impact of these new neurons in the brain circuitry.

Validation of hippocampal biomarkers of cumulative affective experience

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Recent knowledge on hippocampal structural plasticity is reviewed.

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This knowledge is harnessed to develop biomarkers of cumulative experience.

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Hippocampal plasticity is shown to have construct, content and criterion validity in mammals.

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The biomarkers require further validation to be used in birds and fish.

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We discuss some practical considerations to implement the biomarkers.

Progress in improving the welfare of captive animals has been hindered by a lack of objective indicators to assess the quality of lifetime experience, often called cumulative affective experience. Recent developments in stress biology and psychiatry have shed new light on the role of the mammalian hippocampus in affective processes. Here we review these findings and argue that structural hippocampal biomarkers demonstrate criterion, construct and content validity as indicators of cumulative affective experience in mammals. We also briefly review emerging findings in birds and fish, which have promising implications for applying the hippocampal approach to these taxa, but require further validation. We hope that this review will motivate welfare researchers and neuroscientists to explore the potential of hippocampal biomarkers of cumulative affective experience.

Adult mammalian neurogenesis and motivated behaviors

Adult neurogenesis continues to captivate the curiosity of the scientific community; and researchers seem to have a particular interest in identifying the functional implications of such plasticity. While the majority of research focuses on the association between adult neurogenesis and learning and memory (including spatial learning associated with hippocampal neurogenesis and olfactory discrimination associated with neurogenesis in the olfactory system), the following review will explore the link to motivated behaviors. In particular, goal-directed behaviors such as sociosexual, parental, aggressive, as well as depression- and anxiety-like behaviors and their reciprocal association to adult neurogenesis will be evaluated. The review will detail research in humans and other mammalian species. Furthermore, the potential mechanisms underlying these neurogenic alterations will be highlighted. Lastly, the review will conclude with a discussion on the functional significance of these newly generated cells in mediating goal-directed behaviors.

Neuroendocrine Mechanisms Involved in Male Sexual and Emotional Behavior

OBJECTIVE

The aim of this narrative review was to analyze the role played by brain areas, neurohormones and neurotransmitters in the regulation of emotional and sexual behavior in the male.

METHODS

We analyzed the currently available literature dealing with brain structures, neurotransmitters and neurohormones involved in the regulation of emotional and sexual behavior in the male.

RESULTS

A common brain pathway is involved in these two aspects. The Hippocampus seems to control the signals coming from the external environment, while the amygdala and the hypothalamus control the response to social stimuli. Stimulation of amygdala in the animal models increases sexual performance, while it triggers violent emotional responses. Stimulation of the hypothalamus causes reactions of violent anger and increases sexual activity. Catecholaminergic stimulation of the amygdala and hypothalamus increases emotional and sexual behavior, while serotonin plays an inhibitory role. Cholinergic inhibition leads to a suppression of copulatory activity, while the animal becomes hyperemotive. Opioids, such as β-endorphin and met-enkephalin, reduce copulatory activity and induce impotence. Gonadal steroid hormones, such as estrogen in female and testosterone in male, which play a major role in the control of sexual behavior and gender difference have been highlighted in this review. Vasopressin, oxytocin and their receptors are expressed in high density in the "social behavior neural network" and play a role as signal system controlling social behavior. Finally, the neuropeptide kisspeptin and its receptors, located in the limbic structures, mediate olfactory control of the gonadotropic axis.

CONCLUSION

Further studies are needed to evaluate possible implications in the treatment of psychosexual and reproductive disorders.

Sexual experience confers resilience to restraint stress in female rats

During paced mating, sexually experienced female rats spend more time with the male, return to the male more quickly after intromission, and exhibit shorter interintromission intervals as compared to sexually naïve rats. Factors that trigger the shift in paced mating behavior are unknown. The present study used the elevated plus maze to test whether anxiety-like behavior differs as a function of sexual experience. Ovariectomized, Long-Evans female rats were primed with estradiol benzoate plus progesterone (EB + P) and then either received four, twice weekly, paced mating treatments to gain sexual experience (Experienced) or remained sexually naïve (Naïve) but were exposed to an empty mating apparatus. In Experiment 1, anxiety-like behavior was compared between Experienced or Naïve female rats that were primed with either EB + P or oil. Significantly more time was spent in open arms under EB + P vs. oil, independent of sexual history. To test whether exposure to an acute stressor before elevated plus maze testing affected anxiety-like behavior, EB + P treated, Experienced or Naïve rats received paced mating (Experiment 2) or restraint (Experiment 3) immediately prior to the elevated plus maze task. Restraint, but not mating, led to less anxiety-like behaviors for Experienced rats compared to Naïve rats. Collectively, our data shows that one component of the shift in paced mating behavior that occurs with sexual experience appears to be altered stress responsiveness. We propose that mating is a beneficial stressor that, when repeated, increases the ability to cope with anxiety-producing events such as aversive components of mating or non-voluntary stressors.

Repeated restraint stress promotes hippocampal neuronal cell ciliogenesis and proliferation in mice

Stress severely disturbs physiological and mental homeostasis which includes adult neurogenesis in hippocampus. Neurogenesis in hippocampus is a key feature to adapt to environmental changes and highly regulated by multiple cellular signaling pathways. The primary cilium is a cellular organelle, which acts as a signaling center during development and neurogenesis in adult mice. However, it is not clear how the primary cilia are involved in the process of restraint (RST) stress response. Using a mouse model, we examined the role of primary cilia in repeated and acute RST stress response. Interestingly, RST stress increased the number of ciliated cells in the adult hippocampal dentate gyrus (DG). In our RST model, cell proliferation in the DG also increased in a time-dependent manner. Moreover, the analysis of ciliated cells in the hippocampal DG with cell type markers indicated that cells that were ciliated in response to acute RST stress are neurons. Taken together, these findings suggest that RST stress response is closely associated with an increase in the number of ciliated neurons and leads to an increase in cell proliferation.

Sexual activity modulates neuroinflammatory responses in male rats

Immune activity influences reproduction, however, the extent to which mating experience may inversely alter immune pathways is poorly understood. A few studies in humans suggest that mating triggers a circulating immune and hypothalamic-pituitary-adrenal axis response. In male rats, mating experience enhances neuroplasticity and improves cognitive function and affective-like behavior, independent of the physical activity component. Yet, the extent to which mating experience may influence immune responses in the brain remain unexplored. Here, we hypothesized that recent mating experience in male rats increases neuroinflammatory signaling (via lipopolysaccharide [LPS] stimulation, i.p.) and associated sickness behaviors (i.e., food intake, weight loss) relative to sexually-naïve controls. Virgin male rats were exposed to a sexually non-receptive (control) or sexually-receptive female for 30 min for six consecutive days. Immediately following the last mating experience, rats were administered a saline or LPS injection and euthanized four hours later. Mating increased Tnfα responses to LPS in the brain, which positively correlated with LPS-induced weight loss. Mating also increased peripheral corticosterone among saline-treated rats, but this corticosterone response was attenuated in the most proficient copulators (e.g., shortest latencies). Thus, recent mating experience may be a unique modulator of select stimulated inflammatory signals that are relevant to adaptive neuroimmune responses and behavior.

The First Mating Experience Induces New Neurons in the Olfactory Bulb in Male Mice

In rodents, neurogenesis in the olfactory bulbs (OBs) is enhanced by exposure to olfactory enriched environments including sexually relevant odors. In the present study we evaluated whether sexual stimulation in male mice increases the number of newly generated cells that reach the OB and whether these cells differentiate into neurons. To this end, we used sexually naive male C57BL mice randomly assigned to one of three groups: (1) control, in which animals were left alone in their home cages; (2) exposure, in which animals were exposed to a receptive female precluding any physical contact; and (3) mating, in which males copulated with females. Males were given three injections of the DNA synthesis marker 5-bromo-2'-deoxyuridine (BrdU) 2 h before, at the end and 2 h after the test. Fifteen days after BrdU administration, brains were removed and processed to identify new cells and evaluate if they had differentiated into neurons in the granular (GR), mitral (MI) and glomerular (GL) cell layers of the main and accessory OB (MOB and AOB, respectively). We found an increase in the percentage of new cells that differentiate into neurons in the GL cell layer of the MOB of males from the mating group compared with those from the exposure and control groups. No differences were found in the number of new cells or percentage of new neurons in the rest of the analyzed regions. In male mice, the first sexual experience increases the percentage of new cells that differentiate into neurons in the GL cell layer of the MOB.

Sexually experienced, but not naïve, female rats show a conditioned object preference (COP) for mating after a single training trial

Female rats with mating experience spend more time with the male rat, exhibit shorter contact-return latency to intromission, and display more proceptive behaviors in the male rat's compartment than during the first mating experience. The present study tested 1) whether mating induced conditioned object preference (COP) is possible with a single conditioning trial and 2) whether a preference is induced for an object associated with the first mating encounter or the fifth mating encounter in female rats. Ovariectomized, Long-Evans female rats were primed with estradiol benzoate + progesterone and either exposed to an empty paced mating chamber for 15 min (Naïve) or received a 15 intromission test of paced mating behavior (Experienced) on four separate occasions before undergoing the COP procedure. Experienced, but not Naïve, female rats developed a COP for a single mating bout, indicating that mating is highly rewarding for sexually experienced female rats. The findings raise questions about the effect of sexual experience on reward regions in the brain, the responsiveness of genital tissue, and learning mechanisms.

Neurogenesis and sexual behavior

Different conditions induce proliferation, migration and integration of new neurons in the adult brain. This process of neurogenesis is a clear example of long lasting plastic changes in the brain of different species. Sexual behavior is a motivated behavior that is crucial for the survival of the species, but an individual can spend all his life without displaying sexual behavior. In the present review, we briefly describe some of the effects of pheromones on neurogenesis. We review in detail studies describing the effects of sexual behavior in both males and females on proliferation, migration and integration of new cells and neurons. It will become evident that most of the studies have been done in rodents, assessing the effects of this behavior on neurogenesis within the dentate gyrus of the hippocampus and in the subventricular zone - rostral migratory stream - olfactory bulb system.

Sexual Activity and Cognitive Decline in Older Adults

This prospective study tested whether sexual activity and emotional closeness during partnered sexual activity relate to cognitive decline (episodic memory performance) in older adulthood. In total, 6016 adults aged 50 and over (2672 men, 3344 women; M age = 66.0 ± 8.8 years) completed an episodic memory task and self-report questions related to health, sexual activity, and emotional closeness. Two years later, participants again completed the episodic memory task. After controlling for demographic and health-related lifestyle factors, more frequent sexual activity and greater emotional closeness during partnered sexual activity were associated with better memory performance. The association between sexual activity and memory performance was stronger among older participants in the sample. Memory performance worsened over 2 years, but change in memory performance was unrelated to sexual activity or emotional closeness during partnered sexual activity. These findings build on experimental research that has found sexual activity enhances episodic memory in non-human animals. Further research using longer timeframes and alternative measures of cognitive decline is recommended.

Adult Hippocampal Neurogenesis: Regulation and Possible Functional and Clinical Correlates

The formation of new neurons in the adult central nervous system (CNS) has been recognized as one of the major findings in neuroanatomical research. The hippocampal formation (HF), one of the main targets of these investigations, holds a neurogenic niche widely recognized among several mammalian species and whose existence in the human brain has sparked controversy and extensive debate. Many cellular features from this region emphasize that hippocampal neurogenesis suffers changes with normal aging and, among regulatory factors, physical exercise and chronic stress provoke opposite effects on cell proliferation, maturation and survival. Considering the numerous functions attributable to the HF, increasing or decreasing the integration of new neurons in the delicate neuronal network might be significant for modulation of cognition and emotion. The role that immature and mature adult-born neurons play in this circuitry is still mostly unknown but it could prove fundamental to understand hippocampal-dependent cognitive processes, the pathophysiology of depression, and the therapeutic effects of antidepressant medication in modulating behavior and mental health.

The short-term stress response - Mother nature's mechanism for enhancing protection and performance under conditions of threat, challenge, and opportunity

Our group has proposed that in contrast to chronic stress that can have harmful effects, the short-term (fight-or-flight) stress response (lasting for minutes to hours) is nature's fundamental survival mechanism that enhances protection and performance under conditions involving threat/challenge/opportunity. Short-term stress enhances innate/primary, adaptive/secondary, vaccine-induced, and anti-tumor immune responses, and post-surgical recovery. Mechanisms and mediators include stress hormones, dendritic cell, neutrophil, macrophage, and lymphocyte trafficking/function and local/systemic chemokine and cytokine production. Short-term stress may also enhance mental/cognitive and physical performance through effects on brain, musculo-skeletal, and cardiovascular function, reappraisal of threat/anxiety, and training-induced stress-optimization. Therefore, short-term stress psychology/physiology could be harnessed to enhance immuno-protection, as well as mental and physical performance. This review aims to provide a conceptual framework and targets for further investigation of mechanisms and conditions under which the protective/adaptive aspects of short-term stress/exercise can be optimized/harnessed, and for developing pharmacological/biobehavioral interventions to enhance health/healing, and mental/cognitive/physical performance.

Neurogenesis in the olfactory bulb induced by paced mating in the female rat is opioid dependent

The possibility to control the rate of sexual stimulation that the female rat receives during a mating encounter (pacing) increases the number of newborn neurons that reach the granular layer of the accessory olfactory bulb (AOB). If females mate repeatedly, the increase in the number of neurons is observed in other regions of the AOB and in the main olfactory bulb (MOB). It has also been shown that paced mating induces a reward state mediated by opioids. There is also evidence that opioids modulate neurogenesis. In the present study, we evaluated whether the opioid receptor antagonist naloxone (NX) could reduce the increase in neurogenesis in the AOB induced by paced mating. Ovariectomized female rats were randomly divided in 5 different groups: 1) Control (not mated) treated with saline, 2) control (not mated) treated with naloxone, 3) females that mated without controlling the sexual interaction (no-pacing), 4) females injected with saline before pacing the sexual interaction and 5) females injected with NX before a paced mating session. We found, as previously described, that paced mating induced a higher number of new cells in the granular layer of the AOB. The administration of NX before paced mating, blocked the increase in the number of newborn cells and prevented these cells from differentiating into neurons. These data suggest that opioid peptides play a fundamental role in the neurogenesis induced by paced mating in female rats.

Endocannabinoids: Effectors of glucocorticoid signaling

For decades, there has been speculation regarding the interaction of cannabinoids with glucocorticoid systems. Given the functional redundancy between many of the physiological effects of glucocorticoids and cannabinoids, it was originally speculated that the biological mechanisms of cannabinoids were mediated by direct interactions with glucocorticoid systems. With the discovery of the endocannabinoid system, additional research demonstrated that it was actually the opposite; glucocorticoids recruit endocannabinoid signaling, and that the engagement of endocannabinoid signaling mediated many of the neurobiological and physiological effects of glucocorticoids. With the development of advances in pharmacology and genetics, significant advances in this area have been made, and it is now clear that functional interactions between these systems are critical for a wide array of physiological processes. The current review acts a comprehensive summary of the contemporary state of knowledge regarding the biological interactions between glucocorticoids and endocannabinoids, and their potential role in health and disease.

The effect of hypertension on adult hippocampal neurogenesis in young adult spontaneously hypertensive rats and Dahl rats

The dentate gyrus of the hippocampus is one of the few places in the brain where neurogenesis occurs in adulthood. Nowadays, an increasing number of children and young adults are affected by hypertension, one of the factors in the development of cerebrovascular diseases and age-related cognitive deficits. Since these cognitive deficits are often hippocampus-dependent, it is possible that hypertension exerts this effect via decreasing adult neurogenesis which has been shown to be essential for a range of cognitive tasks. We used spontaneously hypertensive rats, which develop hypertension in the first weeks of life. Half of them were treated with the antihypertensive drug captopril. We found that the drug-induced lowering of blood pressure in this period did not affect the rate of adult neurogenesis. In a second experiment, we used another animal model of hypertension - salt-sensitive and salt-resistant strains of Dahl rats. A high-salt diet induces hypertension in the salt-sensitive strain, but not in the salt-resistant strain. The high-salt diet led to salt-induced hypertension, but did not affect the level of adult neurogenesis in the dentate gyrus of the hippocampus. We conclude that hypertension does not significantly affect the rate of hippocampal neurogenesis in young adult rats.

Adult neurogenesis reduction by a cytostatic treatment improves spatial reversal learning in rats

Adult neurogenesis in the dentate gyrus adds a substantial number of new functional neurons to the hippocampus network in rodents. To date, however, the function of these new granule cells remains unclear. We conducted an experiment to assess the contribution of adult neurogenesis in the dentate gyrus to acquisition and reversal learning in a task that predominantly requires generalization of a rule. Young adult male Long-Evans rats were repeatedly administered either a cytostatic temozolomide or saline for a period of four weeks (3 injections per week). Post treatment, animals were injected with bromodeoxyuridine to quantify adult neurogenesis in the dentate gyrus. For behavioral assessment we used hippocampus-dependent active place avoidance with reversal in a Carousel maze. Animals first learned to avoid a 60° sector on the rotating arena. Afterwards, sector was relocated to the opposite side of the rotating arena (reversal). The administration of temozolomide significantly improved the reversal performance compared to saline-treated rats. Our results suggest a significant, level-dependent, improvement of reversal learning in animals with reduced adult neurogenesis in hippocampus.

Integrative medicine: Breaking down silos of knowledge and practice an epigenetic approach

The future of medicine is discussed in the context of epigenetic influences during the entire life course and the lived experiences of each person, avoiding as much as possible the "medicalization" of the individual and taking a more humanistic view. The reciprocal communication between brain and body via the neuroendocrine, autonomic, metabolic and immune systems and the plasticity of brain architecture provide the basis for devising better "top down" interventions that engage the whole person in working towards his or her welfare. The life course perspective emphasizes the importance of intervening early in life to prevent adverse early life experiences, including the effects of poverty, that can have lifelong consequences, referred to as "biological embedding". In the spirit of integrative, humanistic medicine, treatments that "open windows of plasticity" allow targeted behavioral interventions to redirect brain and body functions and behavior in healthier directions. Policies of government and the private sector, particularly at the local, community level, can create a supporting environment for such interventions. See "Common Ground for Health: Personalized, Precision and Social Medicine McEwen & Getz - https://www.youtube.com/watch?v=IRy_uUWyrEw.