Neonatal programming by immunological challenge: effects on ovarian function in the adult rat

Disruptions in Hypothalamic-Pituitary-Gonadal Axis Development and Their IgG Modulation after Prenatal Systemic Inflammation in Male Rats

The development of the neuroendocrine system, including the hypothalamic-pituitary-gonadal (HPG) axis, is sensitive to environmental impacts during critical developmental periods. Maternal immune system activation by bacterial or viral infection may be one of the negative impacts. This study focused on the effect of systemic inflammation induced by lipopolysaccharides (LPS E. coli) on the HPG axis development in male rat offspring, corrected by the anti-inflammatory action of polyclonal IgG and monoclonal anti-interleukin (IL)-6 receptor antibodies (IL-6RmAbs). A single LPS exposure on the 12th embryonic day (ED) led to a decrease in the number of afferent synaptic inputs on gonadotropin-releasing, hormone-producing neurons in adult male offspring. LPS exposure on ED18 did not lead to such disruptions. Moreover, after the LPS injections on ED12, circulating follicle-stimulating hormone and sex steroid levels were reduced, and the gonadal structure was disrupted. A prenatal IL-6R blockade with IL-6RmAbs and polyclonal IgG reduced the negative effects of inflammation on fetal HPG axis development. Overall, the data obtained confirm the morphogenetic effect of inflammation on fetal HPG development and IL-6 involvement in these processes.

Early programming of reproductive health and fertility: novel neuroendocrine mechanisms and implications in reproductive medicine

BACKGROUND

According to the Developmental Origins of Health and Disease (DOHaD) hypothesis, environmental changes taking place during early maturational periods may alter normal development and predispose to the occurrence of diverse pathologies later in life. Indeed, adverse conditions during these critical developmental windows of high plasticity have been reported to alter the offspring developmental trajectory, causing permanent functional and structural perturbations that in the long term may enhance disease susceptibility. However, while solid evidence has documented that fluctuations in environmental factors, ranging from nutrient availability to chemicals, in early developmental stages (including the peri-conceptional period) have discernible programming effects that increase vulnerability to develop metabolic perturbations, the impact and eventual mechanisms involved, of such developmental alterations on the reproductive phenotype of offspring have received less attention.

OBJECTIVE AND RATIONALE

This review will summarize recent advances in basic and clinical research that support the concept of DOHaD in the context of the impact of nutritional and hormonal perturbations, occurring during the periconceptional, fetal and early postnatal stages, on different aspects of reproductive function in both sexes. Special emphasis will be given to the effects of early nutritional stress on the timing of puberty and adult gonadotropic function, and to address the underlying neuroendocrine pathways, with particular attention to involvement of the Kiss1 system in these reproductive perturbations. The implications of such phenomena in terms of reproductive medicine will also be considered.

SEARCH METHODS

A comprehensive MEDLINE search, using PubMed as main interface, of research articles and reviews, published mainly between 2006 and 2021, has been carried out. Search was implemented using multiple terms, focusing on clinical and preclinical data from DOHaD studies, addressing periconceptional, gestational and perinatal programming of reproduction. Selected studies addressing early programming of metabolic function have also been considered, when relevant.

OUTCOMES

A solid body of evidence, from clinical and preclinical studies, has documented the impact of nutritional and hormonal fluctuations during the periconceptional, prenatal and early postnatal periods on pubertal maturation, as well as adult gonadotropic function and fertility. Furthermore, exposure to environmental chemicals, such as bisphenol A, and maternal stress has been shown to negatively influence pubertal development and gonadotropic function in adulthood. The underlying neuroendocrine pathways and mechanisms involved have been also addressed, mainly by preclinical studies, which have identified an, as yet incomplete, array of molecular and neurohormonal effectors. These include, prominently, epigenetic regulatory mechanisms and the hypothalamic Kiss1 system, which likely contribute to the generation of reproductive alterations in conditions of early nutritional and/or metabolic stress. In addition to the Kiss1 system, other major hypothalamic regulators of GnRH neurosecretion, such as γ-aminobutyric acid and glutamate, may be targets of developmental programming.

WIDER IMPLICATIONS

This review addresses an underdeveloped area of reproductive biology and medicine that may help to improve our understanding of human reproductive disorders and stresses the importance, and eventual pathogenic impact, of early determinants of puberty, adult reproductive function and fertility.

Early Life Painful Procedures: Long-Term Consequences and Implications for Farm Animal Welfare

Farm animals routinely undergo painful husbandry procedures early in life, including disbudding and castration in calves and goat kids, tail docking and castration in piglets and lambs, and beak trimming in chicks. In rodents, inflammatory events soon after birth, when physiological systems are developing and sensitive to perturbation, can profoundly alter phenotypic outcomes later in life. This review summarizes the current state of research on long-term phenotypic consequences of neonatal painful procedures in rodents and farm animals, and discusses the implications for farm animal welfare. Rodents exposed to early life inflammation show a hypo-/hyper-responsive profile to pain-, fear-, and anxiety-inducing stimuli, manifesting as an initial attenuation in responses that transitions into hyperresponsivity with increasing age or cumulative stress. Neonatal inflammation also predisposes rodents to cognitive, social, and reproductive deficits, and there is some evidence that adverse effects may be passed to offspring. The outcomes of neonatal inflammation are modulated by injury etiology, age at the time of injury and time of testing, sex, pain management, and rearing environment. Equivalent research examining long-term phenotypic consequences of early life painful procedures in farm animals is greatly lacking, despite obvious implications for welfare and performance. Improved understanding of how these procedures shape phenotypes will inform efforts to mitigate negative outcomes through reduction, replacement, and refinement of current practices.

Monocyte perturbation modulates the ovarian response to an immune challenge

Our recent findings indicate that an acute depletion of monocytes has no sustained effects on ovarian follicle health. Here, we utilised a Cx3cr1-Dtr transgenic Wistar rat model to transiently deplete monocytes and investigated the impact of an acute immune challenge by lipopolysaccharide (LPS) on ovarian follicle health and ovulatory capacity relative to wt once the monocytes had repopulated. Monocyte depletion and repopulation exacerbated the effects of LPS in several domains. As such, monocyte perturbation decreased the numbers of secondary follicles in those challenged with LPS. Monocyte perturbation was also associated with reduced antral follicle numbers and circulating luteinising hormone (LH) levels, as well as potential changes in ovarian sensitivity to LH, exacerbated by LPS. These data suggest that monocyte depletion and repopulation induce a transient suppression of ovulatory capacity in response to a subsequent immune challenge, but this is likely to be restored once the pro-inflammatory environment is resolved.

Effects of antiepileptic drugs on ovaries of female Wistar rats

Valproate (VPA) induced changes in ovarian morphology are observed in humans with epilepsy and in non-epileptic animals. The effects of lamotrigine (LTG) on female reproduction is not well known. We investigated whether LTG might be a safer drug for use with patients of reproductive age. Forty Wistar albino female rats were divided into five groups. The control group was injected with saline-vehicle solution. The low dose (LD)-VPA group was injected with 100 mg/kg VPA. The high dose (HD)-VPA group was injected with 500 mg/kg VPA. The LD-LTG group was injected with 10 mg/kg LTG. The HD-LTG group was injected with 50 mg/kg LTG. We evaluated histological and biochemical changes in the ovaries. The number of atretic and cystic follicles was increased in the HD-VPA and HD-LTG groups compared to the control group. A significant increase in malondialdehyde level was found in the VPA groups compared to the control and LTG groups. No significant differences in total glutathione levels or superoxide dismutase activity were found among study groups. Catalase activity was significantly higher in HD-VPA and HD-LTG groups compared to the control, LD-VPA and LD-LTG groups. Prevalence and intensity of caspase-3 immunoreactivity in the luteal cells were significantly greater in the HD-LTG group compared to the control group. VPA administration caused polycystic ovarian syndrome-like changes in the ovary. We found that LD-LTG, which reflects the dose for humans, might be a safer option for use during the reproductive age.

Influence of innate immune activation on endocrine and metabolic pathways in infancy

Prematurity is the leading cause of neonatal morbidity and mortality worldwide. Premature infants often require extended hospital stays, with increased risk of developing infection compared with term infants. A picture is emerging of wide-ranging deleterious consequences resulting from innate immune system activation in the newborn infant. Those who survive infection have been exposed to a stimulus that can impose long-lasting alterations into later life. In this review, we discuss sepsis-driven alterations in integrated neuroendocrine and metabolic pathways and highlight current knowledge gaps in respect of neonatal sepsis. We review established biomarkers for sepsis and extend the discussion to examine emerging findings from human and animal models of neonatal sepsis that propose novel biomarkers for early identification of sepsis. Future research in this area is required to establish a greater understanding of the distinct neonatal signature of early and late-stage infection, to improve diagnosis, curtail inappropriate antibiotic use, and promote precision medicine through a biomarker-guided empirical and adjunctive treatment approach for neonatal sepsis. There is an unmet clinical need to decrease sepsis-induced morbidity in neonates, to limit and prevent adverse consequences in later life and decrease mortality.

Mechanisms of Reciprocal Regulation of Gonadotropin-Releasing Hormone (GnRH)-Producing and Immune Systems: The Role of GnRH, Cytokines and Their Receptors in Early Ontogenesis in Normal and Pathological Conditions

Different aspects of the reciprocal regulatory influence on the development of gonadotropin-releasing hormone (GnRH)-producing- and immune systems in the perinatal ontogenesis and their functioning in adults in normal and pathological conditions are discussed. The influence of GnRH on the development of the immune system, on the one hand, and the influence of proinflammatory cytokines on the development of the hypothalamic-pituitary-gonadal system, on the other hand, and their functioning in adult offspring are analyzed. We have focused on the effects of GnRH on the formation and functional activity of the thymus, as the central organ of the immune system, in the perinatal period. The main mechanisms of reciprocal regulation of these systems are discussed. The reproductive health of an individual is programmed by the establishment and development of physiological systems during critical periods. Regulatory epigenetic mechanisms of development are not strictly genetically controlled. These processes are characterized by a high sensitivity to various regulatory factors, which provides possible corrections for disorders.

The reduction in sexual behavior of adult female rats exposed to immune stress in the neonatal period is associated with reduced hypothalamic progesterone receptor expression

PURPOSE

We examined the mechanism by which neonatal immune stress reduces the sexual behavior of female rats in adulthood.

METHODS

Neonatal female rats were randomly divided into 3 groups: control (n = 11), postnatal day 10 lipopolysaccharide (PND10LPS) (n = 23), and PND25LPS (n = 11) groups, which received intraperitoneal injections of LPS (100 μg/kg) or saline on PND10 and 25. Daily inspections of the vaginal opening (VO) were performed from PND27 to PND37. Thereafter, the frequency of estrus was assessed for 15 days. Female rats (at 11-12 weeks of age) were placed in a cage with male rats, and their sexual behavior was monitored for 30 min. The hypothalamic mRNA expression levels of factors related to sexual behavior were examined via real-time PCR.

RESULTS

VO occurred later and the frequency of estrus was lower in the PND10LPS group compared to the control group. The number of lordosis behaviors and the total number of mounts performed by male partners were lower in the PND10LPS and PND25LPS groups than in the control group. Acceptability: The lordosis quotient and lordosis rating were lower in the PND10LPS group than in the control group. Proceptive behavior: the number of ear wiggling events was lower in the PND10LPS group than in the other groups, and the number of hops/darts was lower in the PND10LPS group than in the control group. The hypothalamic mRNA expression level of progesterone receptors (PR)A + B was lower in the PND10LPS group than in the control group, and the hypothalamic PRB mRNA expression level was lower in the PND10LPS and PND25LPS groups than in the control group.

CONCLUSION

Neonatal immune stress impeded sexual behavior and hypothalamic PR mRNA expression in female rats. Decreased progesterone activity in the hypothalamus might explain the reduction in sexual behavior seen in these rats.

Gonadotropin-Releasing Hormone in Regulation of Thymic Development in Rats: Profile of Thymic Cytokines

An increasing body of recent experimental data confirms the impact of neurohormones on fetal development and function of different body systems. The synthesis of many neurohormones starts in fetal tissues before the hypothalamic–pituitary–adrenal and hypothalamic–pituitary–gonadal systems are formed, and their high levels are detected in the bloodstream. Here, we studied the role of gonadotropin-releasing hormone (GnRH) in rat thymus development and tried to reveal possible mechanisms underlying the GnRH effects in early development. Western blotting and reverse transcription-polymerase chain reaction allowed us to identify receptor for GnRH in the fetal thymus with peak expression on embryonic days 17–18 (ED17–18). Blocking the receptors in utero on ED17 by a GnRH antagonist suppressed the concanavalin A-induced proliferative response of T cells in adults. GnRH (10⁻⁷ M) increased mRNA expression of interleukin (IL)-4, IL-10, IL-1β, interferon γ (IFNγ), and tumor necrosis factor α (TNFα) in the thymus of 18-day fetuses after an ex vivo culture for 24 h. The increased mRNA levels of the cytokines in the thymus were accompanied by increased numbers of CD4+ T helpers. Overall, the data obtained confirm the regulatory or morphogenetic effect of GnRH on fetal thymus development mediated by synthesis of thymic cytokines.

Maternal high-fat diet impairs follicular development of offspring through intraovarian kisspeptin/GPR54 system

BACKGROUND

Excessive gestational weight gain (GWG), which is associated with adverse long-term effects on the health of the offspring, has become a major clinical problem. Accumulating evidence indicates that the ovary kisspeptin/GPR54 system directly participates in a series of physiological activities. We used a model of high-fat diet (HFD) during gestational to investigate offspring's ovarian function and whether kisspeptin/GPR54 system is involved.

METHODS

After introducing the male and confirmation of mating by checking a vaginal sperm plug, female rats were randomized into two groups: control diet called NCD group and high-fat diet called HFD group. After birth, all rats were changed into a control diet and litter size was adjusted to 12 pups per litter. Ovaries were collected for assessment at postnatal day (PND) 4 and PND 30. The timing of vaginal opening was recorded, and the estrous cyclicity was monitored for 2 consecutive weeks immediately. Primary granulosa cells and ovaries which were taken from PND 4 were collected for determination of the direct effect of kisspeptin-10 (kp-10) in vitro.

RESULTS

Neonatal rats exposed to HFD during gestation had a lower number of secondary follicles in the ovary. The expression of follicle-stimulating hormone receptor (FSHR) and kisspeptin was not altered. At prepuberty, the number of antral follicles and preovulatory follicles was elevated with decreased type III follicles in the HFD group. While the expression of ovulation-related genes was decreased, the expression levels of follicular growth-related genes and steroidogenesis synthesis related genes were elevated. A significant increase in kiss1 mRNA and kisspeptin protein was detected without changes in kiss1r mRNA and GPR54. Maternal high-fat diet during gestation resulted in a significant advanced puberty onset and an irregular estrous cycle in offspring rats. In addition, the administration of kp-10 produced an increase in viability of primary granulosa cells and enlarged the size of oocytes.

CONCLUSIONS

HFD exposure during maternal gestation had a long-term effect on reproductive function in the offspring and the increased ovarian kisspeptin/GPR54 system might be involved.

Neonatal immune activation depletes the ovarian follicle reserve and alters ovarian acute inflammatory mediators in neonatal rats

Normal ovarian development is crucial for female reproductive success and longevity. Interruptions to the delicate process of initial folliculogenesis may lead to ovarian dysfunction. We have previously demonstrated that an early life immune challenge in the rat, induced by administration of lipopolysaccharide (LPS) on postnatal day (PND) 3 and 5, depletes ovarian follicle reserve long term. Here, we hypothesized that this neonatal immune challenge leads to an increase in peripheral and ovarian inflammatory signaling, contributing to an acute depletion of ovarian follicles. Morphological analysis of neonatal ovaries indicated that LPS administration significantly depleted PND 5 primordial follicle populations and accelerated follicle maturation. LPS exposure upregulated circulating interleukin 6, tumor necrosis factor alpha (TNFa), and C-reactive protein on PND 5, and upregulated ovarian mRNA expression of Tnfa, mitogen-activated protein kinase 8 (Mapk8/Jnk1), and growth differentiation factor 9 (Gdf9) (P < 0.05). Mass spectrometry and cell signaling pathway analysis indicated upregulation of cellular pathways associated with acute phase signaling, and cellular survival and assembly. Apoptosis assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling indicated significantly increased positive staining in the ovaries of LPS-treated neonates. These findings suggest that increased proinflammatory signaling within the neonatal ovary may be responsible for the LPS-induced depletion of the primordial follicle pool. These findings also have implications for female reproductive health, as the ovarian reserve is a major determinate of female reproductive longevity.

Maternal restraint stress during pregnancy negatively affects behaviors and antioxidant capacity of offspring rats (Rattus norvegicus)

This study evaluated the effect of maternal restraint stress during the gestation period on behaviors, biochemical parameters, and antioxidant capacities of offspring rats (Rattus norvegicus (Berkenhout,1769)) at weaning age. Behaviors, plasma biochemical indices, and antioxidant ability of the liver, soleus muscle, and gastrocnemius muscle of mother and (or) offspring rats were analyzed. Significant increases were found in the immobility and swinging behavior frequencies of offspring male rats; no difference was found in behaviors of female rats. The antioxidant indices including superoxide dismutase, nitric oxide synthase, and total antioxidant capacity in the soleus muscle of offspring male rats were significantly decreased in the restraint group. Female offspring rats showed significant lower glutathione and higher malondialdehyde levels in the gastrocnemius muscle and liver, respectively. No difference was found in the productive performance and plasma biochemical indices of maternal rats, nor in the biochemical parameters of the two groups of weaning rats. The results suggested that maternal chronic stresses negatively affected the behaviors and antioxidant abilities of offspring rats, and that these effects possibly have a greater impact on offspring male rats than on female rats.

Disruptions in the hypothalamic-pituitary-gonadal axis in rat offspring following prenatal maternal exposure to lipopolysaccharide

Postnatal treatment with bacterial endotoxin lipopolysaccharide (LPS) changes the activity of the hypothalamic-pituitary-gonadal (HPG) axis and the gonadotropin-releasing hormone (GnRH) surge in rats. Exposure to an immune challenge in the critical periods of development has profound and long-lasting effects on the stress response, immune, metabolic, and reproductive functions. Prenatal LPS treatment delays the migration of GnRH neurons associated with increased cytokine release in maternal and fetal compartments. We investigated the effects of a single maternal exposure to LPS (18 μg/kg, i.p.) on day 12 (embryonic day (E)12) of pregnancy on reproductive parameters in rat offspring. Hypothalamic GnRH content, plasma luteinizing hormone (LH), testosterone, and estradiol concentrations were measured in both male and female offsprings at different stages of postnatal development by RIA and ELISA (n = 10 each per group). Body weight and in females day of vaginal opening (VO) were recorded. In offspring exposed to LPS prenatally, compared with controls, body weight was decreased in both sexes at P5 and P30; in females, VO was delayed; hypothalamic GnRH content was decreased at postnatal days 30-60 (P30-P60) in both sexes; plasma LH concentration was decreased at P14-P60 in females; plasma concentrations of testosterone/estradiol were increased at P14 in females, and plasma estradiol was increased at P14 in males. Hence activation of the maternal immune system by LPS treatment at a prenatal critical period leads to decreased GnRH and LH levels in pre- and postpubertal life and sex steroid imbalance in the prepubertal period, and delayed sexual maturation of female offspring.

Endotoxin exposure and puberty in female rats: the role of nitric oxide and caspase-1 inhibition in neonates

Bacterial toxins are widespread in the environment as well as in the digestive system of humans and animals. Toxin from Gram-negative bacteria (endotoxin or lipopolysaccharide; LPS) has a life-long programming effect on reproduction in rats, but the mediators have not been well-documented, so we investigated the effects of LPS on the timing of puberty in female rats. Because the levels of nitric oxide (NO) and interleukin 1β (IL-1β) increase following injection of LPS, we injected neonates (post-natal day (pnd) 7) with LPS, with or without NO or IL-1β inhibitors. Half of the prepubescent (pnd 30) animals received an additional LPS injection. Vaginal opening, number of ovarian follicles, and serum anti-LPS antibodies were determined. A single LPS injection was sufficient to reduce the primordial follicle pool, but puberty was delayed when rats received 2 LPS injections (at pnd 7 and 30). NO or IL-1β inhibitors improved both of these parameters, suggesting that the early detrimental effects of LPS on puberty and primordial follicle pool are mediated by NO and IL-1β.

Factors in Early-Life Programming of Reproductive Fitness

Fertility rates have been declining worldwide, with a growing number of young women suffering from infertility. Infectious and inflammatory diseases are important causes of infertility, and recent evidence points to the critical role of the early-life microbial environment in developmental programming of adult reproductive fitness. Our laboratory and others have demonstrated that acute exposure to an immunological challenge early in life has a profound and prolonged impact on male and female reproductive development. This review presents evidence that perinatal exposure to immunological challenge by a bacterial endotoxin, lipopolysaccharide, acts at all levels of the hypothalamic-pituitary-gonadal axis, resulting in long-lasting changes in reproductive function, suggesting that disposition to infertility may begin early in life.

Lipopolysaccharide-induced maternal inflammation affects the gonadotropin-releasing hormone neuron development in fetal mice

Recent studies provide evidence that prenatal immunological stress may affect the programming of reproductive health and sexual behavior in adult animals. The aim of this study was to investigate the influence of maternal inflammation, induced by an intraperitoneal (i.p.) injection of lipopolysaccharide (LPS, 45 µg/kg) on embryonic day 11.5 (E 11.5), on the development of the gonadotropin-releasing hormone (GnRH) system in mouse fetuses as well as on the proinflammatory cytokine level in pregnant mice and their fetuses. In the fetuses, the GnRH neuron migration from the olfactory pit to the forebrain was estimated on embryonic days 14.5 and 18.5. The levels of the proinflammatory cytokines interleukin (IL)-6, monocyte chemotactic protein (MCP)-1, tumor necrosis factor (TNF)-α and leukemia inhibitory factor (LIF) were measured with the cytometric bead and ELISA array method in the maternal and fetal blood, amniotic fluid and fetal cerebrospinal fluid (CSF). According to our data, activation of the immune system by LPS treatment on embryonic day 11.5 leads to an increased quantity of neurons in the nasal and olfactory bulb areas and a decreased quantity in the forebrain area on embryonic day 14.5. There was a slight decrease in the total number of neurons in the forebrain area on embryonic day 18.5. The levels of proinflammatory cytokines were significantly increased within 3 h after LPS treatment in the maternal and fetal blood, amniotic fluid and fetal CSF. IL-6-receptor immunoreactivity was detected on olfactory/vomeronasal axons. Thus, prenatal immunological stress delays the GnRH neuron migration in the nasal compartment of mouse fetuses, which may be mediated by the regulation of IL-6, MCP-1 and LIF secretion in the maternal-fetal system.

High-fat diet decreases the expression of Kiss1 mRNA and kisspeptin in the ovary, and increases ovulatory dysfunction in postpubertal female rats

BACKGROUND

Female reproductive health is noticeably compromised by obesity. The underlying mechanisms remain to be elucidated. Accumulating evidence indicates that the expression level of ovarian Kiss1 peaks in the afternoon during prooestrus, suggesting local regulatory roles for Kiss1 in the ovulatory process. We used a diet-induced model of obesity to evaluate whether the ovarian Kiss1 system is affected by obesity, and, to investigate the association of the Kiss1 system with ovulatory disorders in female rats.

METHODS

Post-weaning, female, Sprague-Dawley rats were randomly fed either a high-fat diet (HFD) or a normal chow diet (NCD) until they reached postnatal day 30 (PND 30), PND 42, or PND 70. The timing of vaginal opening was recorded, and oestrous cyclicity was monitored for 2 consecutive weeks immediately post puberty and again at 8-9 weeks of age. Tissues from the left ovary were collected for determination of the levels of Kiss1 and G protein-coupled receptor 54 (GPR54) mRNA, and tissues from the right ovary were collected for assessment of the immunoreactivity (IR) of the corresponding protein products, kisspeptin and GPR54.

RESULTS

The high-fat diet resulted in a significantly higher body weight and an earlier puberty onset. Oestrous cyclicity was disrupted by the HFD with significant reductions in the expression of ovulation-related genes. A marked suppression of ovarian Kiss1 mRNA levels was observed during prooestrus and oestrus at PND 42, and, during prooestrus, oestrus, and metoestrus at PND 70 in the HFD rats compared with the NCD controls. In the HFD group, the immunoreactivity of kisspeptin was significantly lower in theca cells from antral follicles during prooestrus and oestrus at PND 42, and, during prooestrus, oestrus at PND 70. At the prooestrus stage, in the HFD group the immunoreactivity of kisspeptin was also lower in the theca cells of preovulatory follicles at both PND 42 and PND 70.

CONCLUSIONS

Exposure of female rats to an post-weaning, high-fat diet has long-term deleterious effects on ovulation, that may involve down-regulation of ovarian Kiss1 mRNA and kisspeptin.

Modulation of adult hippocampal neurogenesis by early-life environmental challenges triggering immune activation

The immune system plays an important role in the communication between the human body and the environment, in early development as well as in adulthood. Per se, research has shown that factors such as maternal stress and nutrition as well as maternal infections can activate the immune system in the infant. A rising number of research studies have shown that activation of the immune system in early life can augment the risk of some psychiatric disorders in adulthood, such as schizophrenia and depression. The mechanisms of such a developmental programming effect are unknown; however some preliminary evidence is emerging in the literature, which suggests that adult hippocampal neurogenesis may be involved. A growing number of studies have shown that pre- and postnatal exposure to an inflammatory stimulus can modulate the number of proliferating and differentiating neural progenitors in the adult hippocampus, and this can have an effect on behaviours of relevance to psychiatric disorders. This review provides a summary of these studies and highlights the evidence supporting a neurogenic hypothesis of immune developmental programming.

Immune regulation of ovarian development: programming by neonatal immune challenge

Neonatal immune challenge by administration of lipopolysaccharide (LPS) produces enduring alterations in the development and activity of neuroendocrine, immune and other physiological systems. We have recently reported that neonatal exposure to an immune challenge by administration of LPS results in altered reproductive development in the female Wistar rat. Specifically, LPS-treated animals exhibited diminished ovarian reserve and altered reproductive lifespan. In the current study, we examined the cellular mechanisms that lead to the previously documented impaired ovulation and reduced follicular pool. Rats were administered intraperitoneally either 0.05 mg/kg of LPS (Salmonella Enteritidis) or an equivalent volume of non-pyrogenic saline on postnatal days (PNDs) 3 and 5, and ovaries were obtained on PND 7. Microarray analysis revealed a significant upregulation in transcript expression (2-fold change; p < 0.05) for a substantial number of genes in the ovaries of LPS-treated animals, implicated in immune cell signaling, inflammatory responses, reproductive system development and disease. Several canonical pathways involved in immune recognition were affected by LPS treatment, such as nuclear factor-κB (NF-κB) activation and LPS-stimulated mitogen-activated protein kinase (MAPK) signaling. Quantitative Real-time PCR analysis supported the microarray results. Protein expression analysis of several components of the MAPK signaling pathway revealed a significant upregulation in the expression of Toll-like receptor 4 (TLR4) in the neonatal ovary of LPS-treated animals. These results indicate that neonatal immune challenge by administration of LPS has a direct effect on the ovary during the sensitive period of follicular formation. Given the pivotal role of inflammatory processes in the regulation of reproductive health, our findings suggest that early life immune activation via TLR signaling may have significant implications for the programming of ovarian development and fertility.

Impacts of early intervention with fluoxetine following early neonatal immune activation on depression-like behaviors and body weight in mice

Several reports have suggested that early neonatal immune activation adversely influences the hypothalamic-pituitary-adrenal (HPA) axis development in humans and animal models. In addition, there have been several studies indicating that early intervention with fluoxetine (FLX) can alter HPA axis development and function, and prevent occurrence of behavioral abnormalities induced by common early-life insults. The present study aims to investigate the effects of early intervention with FLX following early neonatal immune activation on depression-like behaviors and body weight in mice. Neonatal mice in their postnatal days (PNDs) 3 and 5 received either lipopolysaccharide (LPS; 50 μg/kg, s.c.) or saline treatment, then male and female mice of both neonatal intervention groups received oral administration of FLX (5 and 10 mg/kg/day) or water via regular drinking bottles during the periadolescent period (PNDs 35-65). The results showed that neonatal LPS exposure elevated depression-like behaviors accompanied by increasing corticosterone levels in adulthood and decreasing body weight during neonatal and adolescent periods. Furthermore, the periadolescent FLX treatment inhibited the depression-like behaviors induced by neonatal infection in both sexes. This study obtained some experimental evidence indicating the potential adverse impacts of the FLX on normal behavioral development in male control animals. In conclusion, our findings suggest that an early pharmacological intervention with FLX may prevent emergence of depression-like behaviors induced by neonatal immune challenge without any detrimental effect on health in a sex- and dose-dependent manner in mice.

Neonatal immune challenge exacerbates seizure-induced hippocampus-dependent memory impairment in adult rats

Our aim was to examine whether neonatal lipopolysaccharide (LPS) exposure is associated with changes in microglia and whether these alternations could influence later seizure-induced neurobehavioral outcomes. Male pups were first injected intraperitoneally with either LPS or saline on postnatal day 3 (P3) and postnatal day 5 (P5). Immunohistochemical analysis showed that LPS-treated animals exhibited increased microglia activation that persisted into adolescence. At P45, seizures were induced in rats by intraperitoneal injection of kainic acid (KA). Rats treated with LPS neonatally showed significantly greater proinflammatory responses and performed significantly worse in the Y-maze, Morris water maze, and inhibitory avoidance tasks after KA insult. Treatment with minocycline at the time of neonatal LPS exposure to block LPS-induced microglia alternation attenuated the exaggerated neuroinflammatory responses and alleviated memory impairment associated with the KA insult. Our findings suggest that neonatal immune activation can predispose the brain to exacerbated behavioral deficits following seizures in adulthood, possibly by priming microglia.

Stress regulation of kisspeptin in the modulation of reproductive function

Stressful stimuli abound in modern society and have shaped evolution through altering reproductive development, behavior, and physiology. The recent identification of kisspeptin as an important component of the hypothalamic regulatory circuits involved in reproductive homeostasis sparked a great deal of research interest that subsequently implicated kisspeptin signaling in the relay of metabolic, environmental, and physiological cues to the hypothalamo-pituitary-gonadal axis. However, although it is widely recognized that exposure to stress profoundly impacts on reproductive function, the roles of kisspeptin within the complex mechanisms underlying stress regulation of reproduction remain poorly understood. We and others have recently demonstrated that a variety of experimental stress paradigms downregulate the expression of kisspeptin ligand and receptor within the reproductive brain. Coincidently, these stressors also inhibit gonadotropin secretion and delay pubertal onset-processes that rely on kisspeptin signaling. However, a modest literature is inconsistent with an exclusively suppressive influence of stress on the reproductive axis and suggests that complicated neural interactions and signaling mechanisms translate the stress response into reproductive perturbations. The purpose of this chapter is to review the evidence for a novel role of kisspeptin signaling in the modulation of reproductive function by stress and to broaden the understanding of this timely phenomenon.

Neonatal immune challenge alters reproductive development in the female rat

Neonatal lipopolysaccharide (LPS) exposure alters neuroendocrine, immune and behavioural responses in adult rats. Recent findings indicate that neonatal LPS treatment may have a more pronounced effect on the mating behaviours of females compared to males. The current study further explored the impact of neonatal inflammation on reproductive development in the female rat. Wistar rats were administered LPS (0.05 mg/kg, i.p.) or saline (equivolume) on postnatal days (PNDs) 3 and 5. The immediate effect of treatment was assessed on plasma corticosterone and tyrosine hydroxylase (TH) phosphorylation in the adrenal medulla. Weight gain and vaginal opening were recorded, and oestrous cyclicity was monitored post-puberty and in late adulthood. Blood and ovaries were collected throughout development to assess HPA and HPG hormones and to examine ovarian morphology. Reproductive success in the first (F1) generation and reproductive development in the second (F2) generation were also assessed. Neonatal LPS exposure resulted in increased TH phosphorylation in the neonatal adrenals. LPS treatment increased the corticosterone concentrations of females as juveniles, adolescents and adults, and reduced FSH in adolescence. Increased catch-up growth was evident in LPS-treated females, prompting earlier onset of puberty. Diminished follicular reserve was observed in neonatally LPS-treated females along with the advanced reproductive senescence. While fertility rates were not compromised, higher mortality and morbidity were observed in litters born to LPS-treated mothers. Female offspring of LPS-treated mothers displayed increased corticosterone on PND 14, increased catch-up growth and delayed emergence of the first oestrous cycle. No differences in any of the parameters assessed were observed in F2 males. These data suggest that neonatal immunological challenge has a profound impact on the female reproductive development, via the alteration of metabolic and neuroendocrine factors which regulate sexual maturation. Evidence of altered development in the female, but not male offspring of LPS-treated dams suggests increased susceptibility of females to the deleterious effects of neonatal immunological stress and its possible transferability to a subsequent generation.