Neurogenesis In Male Research Articles

Mating-induced prolactin surge is not required for subsequent neurogenesis in male mice.

Parenting involves major behavioral transitions that are supported by coordinated neuroendocrine and physiological changes to promote the onset of novel offspring-directed behaviors. In comparison to maternal care, however, the mechanisms underlying the transition to paternal care are less understood. Male laboratory mice are predominantly infanticidal as virgins but show paternal responses 2 weeks after mating. Interestingly, males show a mating-induced surge of prolactin, which we hypothesized may be involved in initiating this behavioral transition. During pregnancy, prolactin stimulates olfactory bulb neurogenesis, which is essential for maternal behavior. Mating induces olfactory bulb neurogenesis in males, but it is unknown whether this is driven by prolactin or is important for subsequent paternal care. New olfactory neurons are generated from cells in the subventricular zone (SVZ) and take about 2 weeks to migrate to the olfactory bulb, which may account for the delayed behavioral change in mated males. We investigated whether mating increases cell proliferation at the SVZ. Males were either mated, exposed to receptive female cues, or left alone (control) and injected with Bromodeoxyuridine (BrdU, a marker of cell division). Contrary to our hypothesis, we found that mating decreased cell proliferation in the caudal lateral portion of the SVZ. Next, we tested whether prolactin itself mediates cell proliferation in the SVZ and/or new cell survival in the olfactory bulb by administering bromocriptine (prolactin inhibitor), vehicle, or bromocriptine + prolactin prior to mating. While suppressing prolactin had no effect on cell proliferation in the SVZ, administering exogenous prolactin resulted in significantly higher BrdU-labeled cells in mated but not virgin male mice. No effects of prolactin were observed on new olfactory cell survival. Taken together, prolactin may have context-dependent effects on new cell division in the SVZ, while other unknown mechanisms may be driving the effects on new olfactory cell survival following mating.

Metformin Activates Resident Neural Stem and Progenitor Cells, Reduces Inflammation and Improves Functional Recovery Following Spinal Cord Injury

The mammalian spinal cord contains a population of neural stem and progenitor cells (NSPCs) located within the periventricular region lining the central canal. These cells are primarily quiescent under homeostatic conditions and are activated following injury, however, this response is not sufficient to support functional recovery in mammals. We propose that enhancing resident NSPC activation is a promising approach to promote neurorepair and improve functional outcomes following spinal cord injury (SCI). The FDA-approved drug metformin has demonstrated efficacy in promoting functional recovery following brain injury through pleiotropic effects including NSPC activation, increased neurogenesis and oligodendrogenesis and modulation of the injury microenvironment including the inflammatory response. We hypothesize that metformin administration will promote functional recovery following SCI concomitant with activation of NSPCs and reduced inflammation. In a first series of in vitro experiments, we found that metformin significantly increases the size of the NSPC pool in females, but not males; increases neurogenesis in males and enhances oligodendrogenesis in both sexes. We next examined the effect of metformin treatment following SCI. Metformin was delivered to mice for 14 days starting immediately following SCI or starting at 7 days after SCI. Mice were tested on a skilled walking test and using gait analysis at 1 and 2 weeks following the start of metformin treatment. Mice that received metformin starting at the time of injury recovered motor function by 2 weeks post-treatment however, delayed administration was not effective at improving functional outcomes. Interestingly, the functional outcomes observed in both treatment paradigms were correlated with metformin's effect on inflammation, as measured by the numbers of Iba1+ microglia/macrophages. In mice that received metformin immediately post-SCI, Iba1+ cells were significantly reduced compared to vehicle-treated SCI mice. Delayed metformin treatment did not lead to reduced inflammation relative to vehicle-treated SCI mice. Together, these results support metformin as a viable therapeutic strategy to expand and enhance NSPCs, decrease inflammation and enhance functional outcomes when administered in the acute phase following SCI.

Sex-specific acute and chronic neurotoxicity of acute diisopropylfluorophosphate (DFP)-intoxication in juvenile Sprague-Dawley rats

Preclinical efforts to improve medical countermeasures against organophosphate (OP) chemical threat agents have largely focused on adult male models. However, age and sex have been shown to influence the neurotoxicity of repeated low-level OP exposure. Therefore, to determine the influence of sex and age on outcomes associated with acute OP intoxication, postnatal day 28 Sprague-Dawley male and female rats were exposed to the OP diisopropylfluorophosphate (DFP; 3.4 mg/kg, s.c.) or an equal volume of vehicle (∼80 µL saline, s.c.) followed by atropine sulfate (0.1 mg/kg, i.m.) and pralidoxime (2-PAM; 25 mg/kg, i.m.). Seizure activity was assessed during the first 4 h post-exposure using behavioral criteria and electroencephalographic (EEG) recordings. At 1 d post-exposure, acetylcholinesterase (AChE) activity was measured in cortical tissue, and at 1, 7, and 28 d post-exposure, brains were collected for neuropathologic analyses. At 1 month post-DFP, animals were analyzed for motor ability, learning and memory, and hippocampal neurogenesis. Acute DFP intoxication triggered more severe seizure behavior in males than females, which was supported by EEG recordings. DFP caused significant neurodegeneration and persistent microglial activation in numerous brain regions of both sexes, but astrogliosis occurred earlier and was more severe in males compared to females. DFP males and females exhibited pronounced memory deficits relative to sex-matched controls. In contrast, acute DFP intoxication altered hippocampal neurogenesis in males, but not females. These findings demonstrate that acute DFP intoxication triggers seizures in juvenile rats of both sexes, but the seizure severity varies by sex. Some, but not all, chronic neurotoxic outcomes also varied by sex. The spatiotemporal patterns of neurological damage suggest that microglial activation may be a more important factor than astrogliosis or altered neurogenesis in the pathogenesis of cognitive deficits in juvenile rats acutely intoxicated with OPs.

Probiotic treatment (Bifidobacterium longum subsp. longum 35624™) affects stress responsivity in male rats after chronic corticosterone exposure

Mounting evidence suggests that gut microbiota do not only regulate intestinal function and health, but that they also play a role in mental health via the gut-brain axis. Previous research further suggests that probiotics may have beneficial health effects, but more research is needed to confirm these beneficial effects and better understand the underlying mechanisms and potential sex differences in the response to probiotics. Therefore, the current study investigates the effects of chronic administration of the commercially available probiotic Bifidobacterium longum subsp. longum 35624™(B. 35624) to male and female rats under control or “stressed” conditions. For this, 24 male and 24 female Sprague-Dawley rats were either given daily corticosterone injections (40 mg/kg; to induce depressive-like behavior and a “stressed” condition) or oil injections (controls) together with oral administration of B.35624 or vehicle for 21 days (n = 5–7/group). Animals performed the Open Field Test (OFT) and Forced Swim Test (FST) and several blood samples were collected to investigate basal as well as stress-induced corticosterone levels. Rats were sacrificed on day 22 and their brains sliced and stained with doublecortin, a marker of immature neurons. Results showed that B.35624 was not able to rescue depressive-like behavior or induce changes in neurogenesis in males or females, but the probiotic impacted hypothalamic-pituitary-adrenal axis functioning in male animals and tended to reduce anxiolytic behavior in the OFT. More research is needed to further elucidate the potential health effects of probiotics especially in regard to possible sex differences.

Activating Resident Neural Precursor Cells in the Spinal Cord to Promote Neural Repair

Within the mammalian spinal cord there are two distinct populations of neural precursor cells: neural stem and progenitor cells (NSPCs) and oligodendrocyte progenitor cells (OPCs). NSPCs are located within the periventricular zone of the spinal cord and are relatively quiescent and non‐neurogenic under homeostatic conditions. OPCs are located throughout the grey and white matter of the spinal cord and give rise to new oligodendrocytes throughout life. Both of these populations are activated following injury, however, their response is not sufficient for functional recovery. We propose that enhancing resident precursor activation is a promising approach to improve structural and functional outcomes following SCI. The FDA‐approved drug metformin (MET) has demonstrated efficacy in promoting improved outcomes in the injured brain through pleiotropic effects including: decreased inflammation, enhanced precursor cell activation and increased neurogenesis and oligogenesis. Here, we seek to establish the influence of MET treatment on NSPC and OPC populations and explore whether MET can improve functional recovery following injury in the spinal cord. Our cellular data reveal that in uninjured animals, MET treatment significantly expands the NSPC pool in females, but not males; increases neurogenesis in males only and enhances oligogenesis across both sexes. Conversely, we observed no effect of MET treatment on the number of OPCs in uninjured mice, irrespective of sex. To test the efficacy of MET treatment following injury, we used two distinct models: (1) a dorsal column injury in the thoracic spinal cord (SCI), and (2), a model of multiple sclerosis (experimental autoimmune encephalomyelitis, EAE). In both models, MET was delivered to mice immediately following injury and for 14 days. Following SCI, mice were tested on a skilled walking test on post‐injury days (PID) 7 and 14. While all mice showed a significant deficit on PID7, by PID14, MET treated animals were not significantly impaired relative to pre‐injury performance and naive controls. In the EAE model, we evaluated the efficacy of MET treatment through both clinical scoring (based on degree of paralysis) and gait analysis. EAE resulted in significant clinical deficits 14 days following induction, which were mitigated in mice that received MET. Additionally, our gait analysis revealed improved metrics in MET treated mice. Across both injury models we observed significantly reduced inflammation. Taken together, our results support MET as a viable therapeutic strategy to expand and enhance NSPCs, improve the response of OPCs and support functional recovery following spinal cord injury.Support or Funding InformationCanadian Institute of Health ResearchMedicine by Design

Sex differences in the development of anxiodepressive-like behavior of mice subjected to sciatic nerve cuffing.

We investigated the contribution of nucleus locus ceruleus (LC) to the development of pain-associated affective behavior. Mice of both sexes were subjected to sciatic nerve cuffing, a model of peripheral nerve injury, and monitored for 45 days. Although the thermal and mechanical thresholds were equally decreased in both males and females, only the male mice developed anxiodepressive-like behavior, which was complemented by suppressed hippocampal neurogenesis. Furthermore, the LC activity was lower in males when compared with females subjected to sciatic cuffing. Next, we used a chemogenetic approach to modulate the activity of LC projections to the dentate gyrus of the hippocampus in females without cuffs and in males with sciatic cuffs. Sustained inhibition of the LC projections to the dentate gyrus for 15 days induced anxiodepressive-like behavior and reduced the hippocampal neurogenesis in females. Activation of the LC projections to the dentate gyrus for 15 days prevented the development of anxiodepressive-like behavior and increased the hippocampal neurogenesis in males with cuffs. In sum, we demonstrated that the LC projections to the hippocampus link the sensory to the affective component of neuropathic injury and that the female mice are able to dissociate the nociception from affect by maintaining robust LC activity. The work provides evidence that sex differences in LC response to pain determine the sex differences in the development of pain phenotype.

High-Fat Diet-Induced Obesity Causes Sex-Specific Deficits in Adult Hippocampal Neurogenesis in Mice.

Adult hippocampal neurogenesis (AHN) is suppressed by high-fat (HF) diet and metabolic disease, including obesity and type 2 diabetes. Deficits in AHN may contribute to cognitive decline and increased risk of dementia and mood disorders, which have higher prevalence in women. However, sex differences in the effects of HF diet/metabolic disease on AHN have yet to be thoroughly investigated. Herein, male and female C57BL/6J mice were fed an HF or control (CON) diet from ∼2 to 6 months of age. After 3 months on the diet, mice were injected with 5-ethynyl-2′-deoxyuridine (EdU) then killed 4 weeks later. Cell proliferation, differentiation/maturation, and survival of new neurons in the dentate gyrus were assessed with immunofluorescence for EdU, Ki67, doublecortin (DCX), and NeuN. CON females had more proliferating cells (Ki67+) and neuroblasts/immature neurons (DCX+) compared with CON males; however, HF diet reduced these cells in females to the levels of males. Diet did not affect neurogenesis in males. Further, the numbers of proliferating cells and immature neurons were inversely correlated with both weight gain and glucose intolerance in females only. These effects were robust in the dorsal hippocampus, which supports cognitive processes. Assessment of microglia in the dentate gyrus using immunofluorescence for Iba1 and CD68 uncovered sex-specific effects of diet, which may contribute to observed differences in neurogenesis. These findings demonstrate sex-specific effects of HF diet/metabolic disease on AHN, and highlight the potential for targeting neurogenic deficits to treat cognitive decline and reduce the risk of dementia associated with these conditions, particularly in females.

Sex hormones and adult hippocampal neurogenesis: Regulation, implications, and potential mechanisms.

Neurogenesis within the adult hippocampus is modulated by endogenous and exogenous factors. Here, we review the role of sex hormones in the regulation of adult hippocampal neurogenesis in males and females. The review is framed around the potential functional implications of sex hormone regulation of adult hippocampal neurogenesis, with a focus on cognitive function and mood regulation, which may be related to sex differences in incidence and severity of dementia and depression. We present findings from preclinical studies of endogenous fluctuations in sex hormones relating to reproductive function and ageing, and from studies of exogenous hormone manipulations. In addition, we discuss the modulating roles of sex, age, and reproductive history on the relationship between sex hormones and neurogenesis. Because sex hormones have diverse targets in the central nervous system, we overview potential mechanisms through which sex hormones may influence hippocampal neurogenesis. Lastly, we advocate for a more systematic consideration of sex and sex hormones in studying the functional implications of adult hippocampal neurogenesis.

Androgens Increase Survival of Adult-Born Neurons in the Dentate Gyrus by an Androgen Receptor-Dependent Mechanism in Male Rats

Gonadal steroids are potent regulators of adult neurogenesis. We previously reported that androgens, such as testosterone (T) and dihydrotestosterone (DHT), but not estradiol, increased the survival of new neurons in the dentate gyrus of the male rat. These results suggest androgens regulate hippocampal neurogenesis via the androgen receptor (AR). To test this supposition, we examined the role of ARs in hippocampal neurogenesis using 2 different approaches. In experiment 1, we examined neurogenesis in male rats insensitive to androgens due to a naturally occurring mutation in the gene encoding the AR (termed testicular feminization mutation) compared with wild-type males. In experiment 2, we injected the AR antagonist, flutamide, into castrated male rats and compared neurogenesis levels in the dentate gyrus of DHT and oil-treated controls. In experiment 1, chronic T increased hippocampal neurogenesis in wild-type males but not in androgen-insensitive testicular feminization mutation males. In experiment 2, DHT increased hippocampal neurogenesis via cell survival, an effect that was blocked by concurrent treatment with flutamide. DHT, however, did not affect cell proliferation. Interestingly, cells expressing doublecortin, a marker of immature neurons, did not colabel with ARs in the dentate gyrus, but ARs were robustly expressed in other regions of the hippocampus. Together these studies provide complementary evidence that androgens regulate adult neurogenesis in the hippocampus via the AR but at a site other than the dentate gyrus. Understanding where in the brain androgens act to increase the survival of new neurons in the adult brain may have implications for neurodegenerative disorders.

Sex differences in neurogenesis and activation of new neurons in response to spatial learning and memory

Adult hippocampal neurogenesis is often associated with hippocampus-dependent learning and memory. Throughout a new neuron's development, it is differentially sensitive to factors that can influence its survival and functionality. Previous research shows that spatial training that occurred 6-10 days after an injection of the DNA synthesis marker, bromodeoxyuridine (BrdU), increased cell survival in male rats. Because sex differences in spatial cognition and hippocampal neurogenesis have been reported, it is unclear whether spatial training would influence hippocampal neurogenesis in the same way in males and females. Therefore, this study examined sex differences in hippocampal neurogenesis following training in a spatial task. Male and female rats were trained in the spatial or cued version of the Morris water maze 6-10 days after one injection of BrdU (200mg/kg). Twenty days following BrdU injection, all animals were given a probe trial and perfused. Males performed better in the spatial, but not cue, task than females. Spatial training increased BrdU-labeled cells relative to cue training only in males, but both males and females showed greater activation of new cells (BrdU co-labeled with immediate early gene product zif268) after spatial training compared to cue training. Furthermore, performance during spatial training was positively correlated with cell activation in females but not males. This study shows that while spatial training differentially regulates hippocampal neurogenesis in males and females, the activity of new neurons in response to spatial memory retrieval is similar. These findings highlight the importance of sex on neural plasticity and cognition.

Postnatal day 7 ethanol treatment causes persistent reductions in adult mouse brain volume and cortical neurons with sex specific effects on neurogenesis

Ethanol treatment on postnatal day seven (P7) causes robust brain cell death and is a model of late gestational alcohol exposure (Ikonomidou et al., 2000). To investigate the long-term effects of P7 ethanol treatment on adult brain, mice received either two doses of saline or ethanol on P7 (2.5 g/kg, s.c., 2 h apart) and were assessed as adults (P82) for brain volume (using postmortem MRI) and cellular architecture (using immunohistochemistry). Adult mice that received P7 ethanol had reduced MRI total brain volume (4%) with multiple brain regions being reduced in both males and females. Immunohistochemistry indicated reduced frontal cortical parvalbumin immunoreactive (PV + IR) interneurons (18–33%) and reduced Cux1+IR layer II pyramidal neurons (15%) in both sexes. Interestingly, markers of adult hippocampal neurogenesis differed between sexes, with only ethanol treated males showing increased doublecortin and Ki67 expression (52 and 57% respectively) in the dentate gyrus, consistent with increased neurogenesis compared to controls. These findings suggest that P7 ethanol treatment causes persistent reductions in adult brain volume and frontal cortical neurons in both males and females. Increased adult neurogenesis in males, but not females, is consistent with differential adaptive responses to P7 ethanol toxicity between the sexes. One day of ethanol exposure, e.g. P7, causes persistent adult brain dysmorphology.

Automated simultaneous determination of total protein and albumin in serum

Neurogenesis within the adult hippocampus is modulated by endogenous and exogenous factors. Here, we review the role of sex hormones in the regulation of adult hippocampal neurogenesis in males and females. The review is framed around the potential functional implications of sex hormone regulation of adult hippocampal neurogenesis, with a focus on cognitive function and mood regulation, which may be related to sex differences in incidence and severity of dementia and depression. We present findings from preclinical studies of endogenous fluctuations in sex hormones relating to reproductive function and ageing, and from studies of exogenous hormone manipulations. In addition, we discuss the modulating roles of sex, age, and reproductive history on the relationship between sex hormones and neurogenesis. Because sex hormones have diverse targets in the central nervous system, we overview potential mechanisms through which sex hormones may influence hippocampal neurogenesis. Lastly, we advocate for a more systematic consideration of sex and sex hormones in studying the functional implications of adult hippocampal neurogenesis.