Indices of dentate gyrus neurogenesis are unaffected immediately after or following withdrawal from morphine self-administration compared to saline self-administering control male rats

Opiates - including morphine - are powerful analgesics with high abuse potential. In rodents, chronic opiate exposure or self-administration negatively impacts hippocampal-dependent function, an effect perhaps due in part to the well-documented opiate-induced inhibition of dentate gyrus (DG) precursor proliferation and neurogenesis. Recently, however, intravenous (i.v.) morphine self-administration (MSA) was reported to enhance the survival of new rat DG neurons. To reconcile these disparate results, we used rat i.v. MSA to assess 1) whether a slightly-higher dose MSA paradigm also increases new DG neuron survival; 2) how MSA influences cells in different stages of DG neurogenesis, particularly maturation and survival; and 3) if MSA-induced changes in DG neurogenesis persist through a period of abstinence. To label basal levels of proliferation, rats received the S-phase marker bromodeoxyuridine (BrdU, i.p.) 24 -h prior to 21 days (D) of i.v. MSA or saline self-administration (SSA). Either immediately after SA (0-D) or after 4 weeks in the home cage (28-D withdrawal), stereology was used to quantify DG proliferating precursors (or cells in cell cycle; Ki67+ cells), neuroblast/immature neurons (DCX+ cells), and surviving DG granule cells (BrdU+ cells). Analysis revealed the number of DG cells immunopositive for these neurogenesis-relevant markers was similar between MSA and SSA rats at the 0-D or 28-D timepoints. These negative data highlight the impact experimental parameters, timepoint selection, and quantification approach have on neurogenesis results, and are discussed in the context of the large literature showing the negative impact of opiates on DG neurogenesis.

Prenatal exposure to oxcarbazepine increases hippocampal apoptosis in rat offspring

This study assessed apoptosis in the offspring of rats exposed to oxcarbazepine (OXC) from day 7 to 15 of gestation. Three groups of pregnant Wistar rats were used: 1) Control, treated with saline solution; 2) treated with 100 mg/kg OXC; 3) treated with 100 mg/kg of carbamazepine (CBZ, as a positive control for apoptosis); the route of administration was intragastric. Apoptosis was detected at three postnatal ages using the TUNEL technique in the CA1, and CA3 regions of the hippocampus and in the dentate gyrus (DG); neurogenesis was assessed in the DG using an antibody against doublecortin. The litter characteristics were recorded. OXC increased apoptosis in all regions (p < 0.01) at the three ages evaluated. Lamination disruption occurred in CA1 and CA3 due to the neuron absence and to ectopic neurons; there were also malformations in the dorsal lamina of the DG in 38% and 25% of the pups born from rats treated with OXC and CBZ respectively. CBZ also increased apoptosis. No clear effect on neurogenesis in the DG was observed. The size of the litter was smaller (p < 0.01) in the experimental groups. Nineteen-day OXC fetuses had low weight (p < 0.01), but 21 and 30 postnatal days old CBZ and OXC pups were overweight (p < 0.01). The results demonstrate that OXC administered during gestation is pro-apoptotic, alters the cytoarchitecture of the hippocampus, reduces litter size, and probably influences postnatal weight. We provide evidence of the proapoptotic effect of CBZ when administered early in gestation.

Differential effects of oxytocin on olfactory, hippocampal and hypothalamic neurogenesis in adult sheep

New neurons are continuously added in the dentate gyrus of the hippocampus, the olfactory bulb and the hypothalamus of mammalian brain. In sheep, while the control of adult neurogenesis by the social environment or the photoperiod has been the subject of several studies, its regulation by intrinsic factors, like hormones or neurotransmitters is less documented. We addressed this question by investigating the effects of central oxytocin administration on hippocampal, olfactory and hypothalamic neurogenesis. Endogenous markers, Ki67, Sox2 and DCX were used to assess cell proliferation, progenitor cells density and cell survival respectively in non-gestant ewes receiving a steroid treatment followed by intracerebroventricular injections of either oxytocin or saline. The results showed that oxytocin treatment significantly decreases the density of neuroblasts in the olfactory bulb, increases the density of neuroblasts in the ventromedian nucleus of the hypothalamus while no change is observed in both ventral and dorsal dentate gyrus. In addition, no change in the density of progenitor cells is found in the three neurogenic niches. These findings show for the first time that in females, oxytocin can regulate adult neurogenesis by acting on neuroblasts but not on progenitor cells and that this regulation is region specific.

Maturational phase of hippocampal neurogenesis and cognitive flexibility

INTRODUCTION

Pattern separation aids cognitive flexibility by reducing interference between closely related memories. Dentate gyrus (DG) neurogenesis may facilitate pattern separation by blocking memory retrieval via inhibition of non-neurogenic downstream CA3 neurons. We hypothesized that immature adult-born DG neurons would be associated with decreased CA3 activation and increased cognitive flexibility.

METHOD

Two groups of adult male rats were tested either on the place avoidance task (PAT) (unflipped condition) or a subtly altered-PAT (flipped condition). Four weeks prior, the rats were injected with the mitotic marker BrdU. Immature new neurons were detected by the microtubule protein doublecortin (DCX). Cells that took up BrdU and expressed NeuN were identified as relatively more mature neurons. Synaptic activation was determined by c-Fos expression. Adaptation to the flipped versus unflipped condition reflected a measure of cognitive flexibility.

RESULTS

CA3 but not DG c-Fos was lower in the flipped versus unflipped condition [p = 0.002]. CA3 c-Fos correlated inversely with flipped task performance and immature (DCX) neurons with primary and secondary but not tertiary dendrites or more mature (BrdU + NeuN) new neurons. CA3 c-Fos was a significant predictor for the flipped versus unflipped condition specifically for DCX versus BrdU-NeuN neurons.

CONCLUSION

Immature new neurons (DCX+) without tertiary dendrites may be preferentially implicated in cognitive flexibility relative to more mature new neurons (BrdU-NeuN). In combination with decreased CA3 activation in the flipped PAT, the functional contribution of these immature DG neurons may involve the inhibition of postsynaptic CA3 neurons containing traces of previously salient conditioned memories.

Chronic aromatase inhibition increases ventral hippocampal neurogenesis in middle-aged female mice

Letrozole, a third-generation aromatase inhibitor, prevents the production of estrogens in the final step in conversion from androgens. Due to its efficacy at suppressing estrogens, letrozole has recently taken favor as a first-line adjuvant treatment for hormone-responsive breast cancer in middle-aged women. Though patient response to letrozole has generally been positive, there is conflicting evidence surrounding its effects on the development of depression. It is possible that the potential adverse effects of letrozole on mood are a result of the impact of hormonal fluctuations on neurogenesis in the hippocampus. Thus, to clarify the effects of letrozole on the hippocampus and behavior, we examined how chronic administration affects hippocampal neurogenesis and depressive-like behavior in middle-aged, intact female mice. Mice were given either letrozole (1 mg/kg) or vehicle by injection (i.p.) daily for 3 weeks. Depressive-like behavior was assessed during the last 3 days of treatment using the forced swim test, tail suspension test, and sucrose preference test. The production of new neurons was quantified using the immature neuronal marker doublecortin (DCX), and cell proliferation was quantified using the endogenous marker Ki67. We found that letrozole increased DCX and Ki67 expression and maturation in the dentate gyrus, but had no significant effect on depressive-like behavior. Our findings suggest that a reduction in estrogens in middle-aged females increases hippocampal neurogenesis without any adverse impact on depressive-like behavior; as such, this furthers our understanding of how estrogens modulate neurogenesis, and to the rationale for the utilization of letrozole in the clinical management of breast cancer.

Expression and clinical significance of doublecortin (DCX) in pituitary adenoma

PURPOSE

To date, no studies have investigated the expression of Doublecortin (DCX) in pituitary adenomas or evaluated the clinical value of DCX in the diagnosis of pituitary adenomas. This study aims to determine the expression levels of DCX in pituitary adenomas and to investigate its role in the staging of this condition.

METHODS

Forty-six patients with pituitary adenomas were recruited. The expression of DCX in tumor sections from pituitary adenomas was determined using immunohistochemistry and quantitative real-time polymerase chain reaction. Tumors were classified as either invasive or non-invasive on the basis of clinical stage and using the Knosp grading system. Differences in the expression of DCX and its association with clinical characteristics were investigated. The potential of the measurement of DCX levels for distinguishing between invasive and non-invasive tumors was estimated using receiver operating characteristic (ROC) analysis.

RESULTS

Expression of DCX were correlated with Knosp grade. No significant association was observed between DCX level and the clinical stage of the tumors. The expression of DCX was higher in tumors with Knosp 3 and lowest in Knosp 1, at both the mRNA and protein levels. Using DCX as a biomarker for the prediction of tumor invasiveness in pituitary adenoma patients, the area under the ROC curve was 0.829 (95% confidence interval, 0.6-28.1), which is higher than that obtained using Knosp grade.

CONCLUSIONS

The expression of DCX is related to the Knosp grade of pituitary adenoma. DCX levels can be used as a biomarker for tumor invasiveness prediction in pituitary adenoma patients.

Spared cognitive and behavioral functions prior to epilepsy onset in a rat model of subcortical band heterotopia

Subcortical band heterotopia (SBH), also known as doublecortex syndrome, is a malformation of cortical development resulting from mutations in the doublecortin gene (DCX). It is characterized by a lack of migration of cortical neurons that accumulate in the white matter forming a heterotopic band. Patients with SBH may present mild to moderate intellectual disability as well as epilepsy. The SBH condition can be modeled in rats by in utero knockdown (KD) of Dcx. The affected cells form an SBH reminiscent of that observed in human patients and the animals develop a chronic epileptic condition in adulthood. Here, we investigated if the presence of a SBH is sufficient to induce cognitive impairment in juvenile Dcx-KD rats, before the onset of epilepsy. Using a wide range of behavioral tests, we found that the presence of SBH did not appear to affect motor control or somatosensory processing. In addition, cognitive abilities such as learning, short-term and long-term memory, were normal in pre-epileptic Dcx-KD rats. We suggest that the SBH presence is not sufficient to impair these behavioral functions.

Genetic reprogramming of somatic cells into neuroblasts through a co-induction of the doublecortin gene along the Yamanaka factors: A promising approach to model neuroregenerative disorders

Neural stem cell (NSC) mediated adult neurogenesis represents the regenerative plasticity of the brain. The functionality of the neurogenic process appears to be operated by neuroblasts, the multipotent immature neuronal population of the adult brain. While neuroblasts have been realized to play a major role in synaptic remodeling and immunogenicity, neurodegenerative disorders have been characterized by failure in the terminal differentiation, maturation, integration and survival of newborn neuroblasts. Advancement in understanding the impaired neuroregenerative process along the neuropathological conditions has currently been limited by lack of an appropriate experimental model of neuroblasts. The genetic reprogramming of somatic cells into pluripotent state offers a potential strategy for the experimental modeling of brain disorders. Thus, the induced pluripotent stem cell (iPSC) based direct reprogramming of somatic cells into neuroblasts would represent a potential tool to understand the regenerative biology of the adult brain. Therefore, this concise article discusses the significance of iPSCs, the functional roles of neuroblasts in the adult brain and provides a research hypothesis for the direct reprogramming of somatic cells into neuroblasts through the co-induction of a potential proneurogenic marker, the doublecortin (DCX) gene along with the Yamanaka factors. The proposed cellular model of adult neurogenesis may provide us with further insights into neuropathogenesis of many neurodegenerative disorders and will provide a potential experimental platform for diagnostic, drug discovery and regenerative therapeutic strategies.

Quantitative analysis of age and life-history stage related changes in DCX expression in the male Japanese quail (Cortunix japonica) telencephalon

Most avian neurogenesis studies focused on the song control system and little attention has been given to non-song birds such as the Japanese quail. However, the only few neurogenesis studies in quails mainly focused on the sex steroid sensitive areas of the brain such as the medial preoptic and lateral septal nuclei. Despite the important role the quail telencephalon plays in filial imprinting and passive avoidance learning, neurogenesis in this structure has been completely overlooked. The aim of this study was therefore to quantitatively determine how DCX expression in the Japanese quail telencephalon changes with post hatching age (3-12 weeks) and life history stage. In this study, DCX was used as a proxy for neuronal incorporation. Bipolar and multipolar DCX immunoreactive cells were observed in the entire telencephalon except for the entopallium and arcopallium. In addition, DCX expression in all the eight telencephalic areas quantified was strongly negatively correlated with post-hatching age. Furthermore, numbers of bipolar and multipolar DCX immunoreactive cells were higher in the juvenile compared to subadult and adult quails. In conclusion, neuronal incorporation in the quail telencephalon is widespread but it declines with post hatching age. In addition, the most dramatic decline in neuronal incorporation in the telencephalic areas quantified takes place just after the birds have attained sexual maturity.

Doublecortin X (DCX) serine 28 phosphorylation is a regulatory switch, modulating association of DCX with microtubules and actin filaments

Doublecortin X (DCX) plays essential roles in neuronal development via its regulation of cytoskeleton dynamics. This is mediated through direct interactions between its doublecortin (DC) domains (DC1 and DC2) with microtubules (MTs) and indirect association with actin filaments (F-ACT). While the regulatory role of the DCX C-terminus following DC2 (i.e. DCX residues 275-366) has been established, less is known of the possible contributions made by the DCX N-terminus preceding DC1 (i.e. DCX residues 1-44). Here, we assessed the influence of DCX Ser28 within the DCX N-terminus, on the association of DCX with MTs and F-ACT. We compared the cytoskeletal interactions of the DCX S28E phosphomimetic and DCX S28A phospho-resistant mutants and wild-type DCX. Immunoprecipitation and colocalisation analyses indicated increased association of DCX S28E with F-ACT but decreased interaction with MTs, and conversely enhanced DCX S28A association with MTs but decreased association with F-ACT. To evaluate the impact of DCX mutants on cytoskeletal filaments we performed fluorescence recovery after photobleaching (FRAP) studies on SiR-tubulin and β-actin-mCherry and observed comparable tubulin and actin exchange rates in the presence of DCX WT and DCX S28A. However, we observed faster tubulin exchange rates but slower actin exchange rates in the presence of DCX S28E. Moreover, DCX S28E enhanced the association with the actin-binding protein spinophilin (Spn) suggesting the shift to favour association with both F-ACT and Spn in the presence of DCX S28E. Taken together, our results highlight a new role for DCX S28 as a regulatory switch for cytoskeletal organisation.

Conditioned media from AICAR-treated skeletal muscle cells increases neuronal differentiation of adult neural progenitor cells

Exercise has profound benefits for brain function in animals and humans. In rodents, voluntary wheel running increases the production of new neurons and upregulates neurotrophin levels in the hippocampus, as well as improving synaptic plasticity, memory function and mood. The underlying cellular mechanisms, however, remain unresolved. Recent research indicates that peripheral organs such as skeletal muscle, liver and adipose tissue secrete factors during physical activity that may influence neuronal function. Here we used an in vitro cell assay and proteomic analysis to investigate the effects of proteins secreted from skeletal muscle cells on adult hippocampal neural progenitor cell (aNPC) differentiation. We also sought to identify the relevant molecules driving these effects. Specifically, we treated rat L6 skeletal muscle cells with the AMP-kinase (AMPK) agonist 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) or vehicle (distilled water). We then collected the conditioned media (CM) and fractionated it using high-performance liquid chromatography (HPLC). Treatment of aNPCs with a specific fraction of the AICAR-CM upregulated expression of doublecortin (DCX) and Tuj1, markers of immature neurons. Proteomic analysis of this fraction identified proteins known to be involved in energy metabolism, cell migration, adhesion and neurogenesis. Culturing differentiating aNPCs in the presence of one of the factors, glycolytic enzyme glucose-6-phosphate isomerase (GPI), or AICAR-CM, increased the proportion of neuronal (Tuj1⁺) and astrocytic, glial fibrillary acidic protein (GFAP⁺) cells. Our study provides further evidence that proteins secreted from skeletal muscle cells may serve as a critical communication link to the brain through factors that enhance neural differentiation.

Early life stress accelerates age-induced effects on neurogenesis, depression, and metabolic risk

Early life stress (ELS) affects hippocampal neurogenesis, increases depressive-like behavior, and causes mild metabolic imbalance in early adulthood (2 months). However, whether these effects worsen in mid life remains unclear. To test whether age-dependent effects of ELS on hippocampal neurogenesis are related to deficient hypothalamic-pituitary-adrenal (HPA) axis feedback that causes increased comorbidity of depression and metabolic risk, we evaluated the effects of periodic maternal separation (MS180) in young (4-months-old) and middle-aged (10-months-old) adult rats. MS180 caused more severe depressive-like behavior in middle-aged adults than in young animals. There were no behavioral phenotypic differences between young MS180 and control middle-aged groups. MS180 similarly affected glucose tolerance, increased fasting corticosterone, insulin, and the quantitative insulin sensitivity check index (QUICKI) at both ages. However, middle-aged adult MS180 rats showed more severe age-induced obesity (>40% BW) than controls (>22% BW). MS180 differentially affected dorsal and ventral neurogenesis. In young adults, MS180 animals only showed a decrease in dorsal hippocampal neurogenesis as compared to their age-matched counterparts. In contrast, at 10 months of age, MS180 caused a similar decrease in both dorsal and ventral hippocampal neurogenesis as compared to age-matched controls, and a more severe decrease as compared to young animals. Taken together, our data indicate that MS180 animals show an early onset of age-induced alterations on depression and metabolic risk, and these effects relate to alterations in hippocampal neurogenesis.

Doublecortin-expressing cell types in temporal lobe epilepsy

Doublecortin (DCX) is widely regarded as a marker of immature and migrating neurons during development. While DCX expression persists in adults, particularly in the temporal lobe and neurogenic regions, it is unknown how seizures influence its expression. The aim of the present study was to explore the distribution and characteristics of DCX-expressing cells in surgical and postmortem samples from 40 adult and paediatric patients, with epilepsy and with or without hippocampal sclerosis (HS), compared to post mortem controls. The hippocampus (pes and body), parahippocampal gyrus, amygdala, temporal pole and temporal cortex were examined with DCX immunohistochemistry using four commercially-available DCX antibodies, labelled cells were quantified in different regions of interest as well as their co-expression with cell type specific markers (CD68, Iba1, GFAP, GFAP∂, nestin, SOX2, CD34, OLIG2, PDGFRβ, NeuN) and cell cycle marker (MCM2). Histological findings were compared with clinical data, as well as gene expression data obtained from the temporal cortex of 83 temporal lobe epilepsy cases with HS. DCX immunohistochemistry identified immature (Nestin⁻/NeuN⁻) neurons in layer II of the temporal neocortex in patients with and without epilepsy. Their number declined significantly with age but was not associated with the presence of hippocampal sclerosis, seizure semiology or memory dysfunction. DCX⁺ cells were prominent in the paralaminar nuclei and periamygdalar cortex and these declined with age but were not significantly associated with epilepsy history. DCX expressing cells with ramified processes were prominent in all regions, particularly in the hippocampal subgranular zone, where significantly increased numbers were observed in epilepsy samples compared to controls. DCX ramified cells co-expressed Iba1, CD68 and PDGFRβ, and less frequently MCM2, OLIG2 and SOX2, but no co-localization was observed with CD34, nestin or GFAP/GFAP ∂. Gene expression data from neocortical samples in patients with TLE and HS supported ongoing DCX expression in adults. We conclude that DCX identifies a range of morphological cell types in temporal lobe epilepsy, including immature populations, glial and microglial cell types. Their clinical relevance and biological function requires further study but we show some evidence for alteration with age and in epilepsy.

Clusters of DCX+ cells "trapped" in the subcortical white matter of early postnatal Cetartiodactyla (Tursiops truncatus, Stenella coeruloalba and Ovis aries)

The cytoskeletal protein doublecortin (DCX) is a marker for neuronal cells retaining high potential for structural plasticity, originating from both embryonic and adult neurogenic processes. Some of these cells have been described in the subcortical white matter of neonatal and postnatal mammals. In mice and humans it has been shown they are young neurons migrating through the white matter after birth, reaching the cortex in a sort of protracted neurogenesis. Here we show that DCX+ cells in the white matter of neonatal and young Cetartiodactyla (dolphin and sheep) form large clusters which are not newly generated (in sheep, and likely neither in dolphins) and do not reach the cortical layers, rather appearing "trapped" in the white matter tissue. No direct contact or continuity can be observed between the subventricular zone region and the DCX+ clusters, thus indicating their independence from any neurogenic source (in dolphins further confirmed by the recent demonstration that periventricular neurogenesis is inactive since birth). Cetartiodactyla include two orders of large-brained, relatively long-living mammals (cetaceans and artiodactyls) which were recognized as two separate monophyletic clades until recently, yet, despite the evident morphological distinctions, they are monophyletic in origin. The brain of Cetartiodactyla is characterized by an advanced stage of development at birth, a feature that might explain the occurrence of "static" cell clusters confined within their white matter. These results further confirm the existence of high heterogeneity in the occurrence, distribution and types of structural plasticity among mammals, supporting the emerging view that multiple populations of DCX+, non-newly generated cells can be abundant in large-brained, long-living species.

Bioluminescence imaging visualizes osteopontin-induced neurogenesis and neuroblast migration in the mouse brain after stroke

Background

Osteopontin (OPN), an acidic phosphoglycoprotein, is upregulated in the brain after cerebral ischemia. We previously reported that OPN supports migration, survival, and proliferation of neural stem cells (NSC) in primary cell culture, as well as their differentiation into neurons. We here analyzed the effects of OPN on neuroblasts in vivo in the context of cerebral ischemia.

Methods

Transgenic mice expressing luciferase under the control of the neuroblast-specific doublecortin (DCX)-promoter, allowing visualization of neuroblasts in vivo using bioluminescence imaging (BLI), were injected with OPN intracerebroventricularly while control mice were injected with vehicle buffer. To assess the effects of OPN after ischemia, additional mice were subjected to photothrombosis and injected with either OPN or vehicle.

Results

OPN enhanced the migration of neuroblasts both in the healthy brain and after ischemia, as quantified by BLI in vivo. Moreover, the number of neural progenitors was increased following OPN treatment, with the maximum effect on the second day after OPN injection into the healthy brain, and 14 days after OPN injection following ischemia. After ischemia, OPN quantitatively promoted the endogenous, ischemia-induced neuroblast expansion, and additionally recruited progenitors from the contralateral hemisphere.

Conclusions

Our results strongly suggest that OPN constitutes a promising substance for the targeted activation of neurogenesis in ischemic stroke.

Granulocyte-macrophage colony-stimulating factor neuroprotective activities in Alzheimer's disease mice

We investigated the effects of granulocyte-macrophage colony stimulating factor (GM-CSF) on behavioral and pathological outcomes in Alzheimer's disease (AD) and non-transgenic mice. GM-CSF treatment in AD mice reduced brain amyloidosis, increased plasma Aβ, and rescued cognitive impairment with increased hippocampal expression of calbindin and synaptophysin and increased levels of doublecortin-positive cells in the dentate gyrus. These data extend GM-CSF pleiotropic neuroprotection mechanisms in AD and include regulatory T cell-mediated immunomodulation of microglial function, Aβ clearance, maintenance of synaptic integrity, and induction of neurogenesis. Together these data support further development of GM-CSF as a neuroprotective agent for AD.

[Effect of Moxibustion on Delayed Memory and Expression of Hippocampal Nestin and Doublecortin Proteins in Dementia Rats]

OBJECTIVE

To observe the effect of "Huayu Tongluo"(Blood-stasis Dispersing and Meridian-collateral Dredging) moxibustion on the delayed memory and expression of Nestin and Doublecortin (DCX) proteins in the hippocampus in vascular dementia (VD) rats in the view of neurogenesis produced by intracerebral transplantation of neural stem cells (NSCs) and endothelial progenitor cells (EPCs).

METHODS

Healthy male Wistar rats were randomized into control group, VD model group,NSCs＋EPCs group and NSCs＋EPCs moxibustion group. The VD model was established by using a modified 2-vessels occlusion method, and neurogenesis was produced by transplantation of NSCs＋EPCs (2×10⁶cell/10 µL) into the lateral ventricle for rats of the NSCs＋EPCs groups 3 days after successful VD-modeling. Moxibustion was applied to "Dazhui" (GV 14), "Baihui" (GV 20) and "Shenting" (GV 24) once daily for 21 days with an interval of one day between every two 7 days. The Morris Water Maze was used to test the rat's delayed memory ability before and 24 h after the treatment. The expression of Nestin and DCX proteins in the hippocampus tissues was detected using double-labeled immunofluorescence technique.

RESULTS

Following modeling, Morris Water Maze tests showed that the average escape latency of location navigation task was significantly prolonged in VD rats(P<0.008)and the times of target platform crossing (spatial probing task) within 120 s were remarkably reduced in VD rats (P<0.008). Compared with pre-treatment in the same one group, the escape latency of NSCs＋EPCs and NSCs＋EPCs moxibustion groups were considerably reduced (P<0.05), and the average times of target platform crossing of the NSCs＋EPCs moxibustion group were markedly increased(P<0.05). The effect of NSCs＋EPCs moxibustion was evidently superior to that of simple NSCs＋EPCs in shortening the escape latency (P<0.008). The expression levels of Nestin protein were significantly higher in the NSCs＋EPCs moxibustion group after 1 and 3 period treatment than those in the NSCs＋EPCs group (P<0.05)．.

CONCLUSION

Moxibustion intervention is able to improve the delayed memory in VD rats, which may be related to its effect in up-regulating the expression of hippocampal Nestin and DCX proteins within 15 days via accelerating neurogenesis.

Effects of FTY720 on brain neurogenic niches in vitro and after kainic acid-induced injury

Background

FTY720 (fingolimod, Gilenya™) is an oral, blood-brain barrier (BBB)-passing drug approved as immunomodulatory treatment for relapsing-remitting form of the multiple sclerosis (MS). In addition, FTY720 exerts several effects in the central nervous system (CNS), ranging from neuroprotection to reduction of neuroinflammation. However, the neurogenic and oligodendrogenic potential of FTY720 has been poorly investigated. In this study, we assessed the effect of FTY720 on the production of new neurons and oligodendrocytes from neural stem/precursor cells both in vitro and in vivo.

Methods

Neural stem cells (NSCs) derived from the young rat subventricular zone (SVZ) were exposed to FTY720 (10, 100 nM), and their differentiation into neurons and oligodendrocytes was measured using immunofluorescence for anti-β-III tubulin or CNPase (2′,3′-cyclic nucleotide 3′-phosphodiesterase) as markers of mature neurons or oligodendrocytes, respectively. In addition, intracerebroventricular (icv) administration of kainic acid (KA; 0.5 μg/2 μl) in Sprague-Dawley rats was used as an in vivo model of neuronal death and inflammation. FTY720 was applied icv (1 μg/2 μl), together with KA, plus intraperitoneally (ip; 1 mg/kg) 24 h before, and daily, until sacrifice 8 days after KA injection. To visualize cell proliferation in the hippocampus and in white matter regions, rats were administered 5-bromo-2-deoxyuridine (BrdU) 100 mg/kg, ip injected every 2 days. Immunohistochemical analyses were performed on rat brain slices to measure the production of new neuronal precursors (doublecortin/DCX⁺ cells) and new oligodendrocytes precursors (proteoglycan/NG2⁺ cells).

Results

In this study, we observed that FTY720 increased postnatal NSCs differentiation into both neurons and oligodendrocytes in vitro. In turn, in adult animals, FTY720 enhanced the percentage of BrdU⁺ cells coexpressing DCX marker, both in basal (FTY720 alone) and in neurodegenerative (FTY720 + KA) conditions. However, FTY720 had only a partial effect on proliferation and differentiation of oligodendrocyte progenitor cell (OPC) population in vivo.

Conclusions

FTY720 promotes neurogenesis and oligodendrogenesis in vitro under basal conditions. In addition, it increases the generation of neuroblasts and oligodendrocytes after excitotoxic brain injury. This suggests that FTY720 has the potential to activate the neurogenic niche and thus favour tissue repair after lesion.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0922-6) contains supplementary material, which is available to authorized users.

Sex-dependent effects of maternal corticosterone and SSRI treatment on hippocampal neurogenesis across development

Background

Postpartum depression affects approximately 15% of mothers and represents a form of early life adversity for developing offspring. Postpartum depression can be treated with prescription antidepressants like fluoxetine (FLX). However, FLX can remain active in breast milk, raising concerns about the consequences of neonatal FLX exposure. The hippocampus is highly sensitive to developmental stress, and males and females respond differently to stress at many endpoints, including hippocampal plasticity. However, it is unclear how developmental exposure to FLX alters the trajectory of hippocampal development. The goal of this study was to examine the long-term effects of maternal postpartum corticosterone (CORT, a model of postpartum depression) and concurrent FLX on hippocampal neurogenesis in male and female offspring.

Methods

Female Sprague-Dawley rat dams were treated daily with either CORT or oil and FLX or saline from postpartum days 2–23. Offspring were perfused on postnatal day 31 (pre-adolescent), postnatal day 42 (adolescent), and postnatal day 69 (adult). Tissue was processed for doublecortin (DCX), an endogenous marker of immature neurons, in the dorsal and ventral hippocampus.

Results

Maternal postpartum CORT reduced density of DCX-expressing cells in the dorsal hippocampus of pre-adolescent males and increased it in adolescent males, suggesting that postpartum CORT exposure disrupted the typical progression of the density of DCX-expressing cells. Further, among offspring of oil-treated dams, pre-adolescent males had greater density of DCX-expressing cells than pre-adolescent females, and maternal postpartum CORT prevented this sex difference. In pre-adolescent females, maternal postpartum FLX decreased the density of DCX-expressing cells in the dorsal hippocampus compared to saline. As expected, maternal CORT reduced the density of DCX-expressing cells in adult female, but not male, offspring. The combination of maternal postpartum CORT/FLX diminished density of DCX-expressing cells in dorsal hippocampus regardless of sex or age.

Conclusions

These findings reveal how modeling treatment of postpartum depression with FLX alters hippocampal neurogenesis in developing offspring differently depending on sex, predominantly in the dorsal dentate gyrus and earlier in life.

Chronic tinnitus and unipolar brush cell alterations in the cerebellum and dorsal cochlear nucleus

Animal model research has shown that the central features of tinnitus, the perception of sound without an acoustic correlate, include elevated spontaneous and stimulus-driven activity, enhanced burst-mode firing, decreased variance of inter-spike intervals, and distortion of tonotopic frequency representation. Less well documented are cell-specific correlates of tinnitus. Unipolar brush cell (UBC) alterations in animals with psychophysical evidence of tinnitus has recently been reported. UBCs are glutamatergic interneurons that appear to function as local-circuit signal amplifiers. UBCs are abundant in the dorsal cochlear nucleus (DCN) and very abundant in the flocculus (FL) and paraflocculus (PFL) of the cerebellum. In the present research, two indicators of UBC structure and function were examined: Doublecortin (DCX) and epidermal growth factor receptor substrate 8 (Eps8). DCX is a protein that binds to microtubules where it can modify their assembly and growth. Eps8 is a cell-surface tyrosine kinase receptor mediating the response to epidermal growth factor; it appears to have a role in actin polymerization as well as cytoskeletal protein interactions. Both functions could contribute to synaptic remodeling. In the present research UBC Eps8 and DCX immunoreactivity (IR) were determined in 4 groups of rats distinguished by their exposure to high-level sound and psychophysical performance: Unexposed, exposed to high-level sound with behavioral evidence of tinnitus, and two exposed groups without behavioral evidence of tinnitus. Compared to unexposed controls, exposed animals with tinnitus had Eps8 IR elevated in their PFL; other structures were not affected, nor was DCX IR affected. This was interpreted as UBC upregulation in animals with tinnitus. Exposure that failed to produce tinnitus did not increase either Eps8 or DCX IR. Rather Eps8 IR was decreased in the FL and DCN of one subgroup (Least-Tinnitus), while DCX IR decreased in the FL of the other subgroup (No-Tinnitus). Neuron degeneration was also documented in the cochlear nucleus and PFL of exposed animals, both with and without tinnitus. Degeneration was not found in unexposed animals. Implications for tinnitus neuropathy are discussed in the context of synaptic remodeling and cerebellar sensory modulation.

Quantitative assessment of fibroblast growth factor receptor 1 expression in neurons and glia

Background

Fibroblast growth factors (FGFs) and their receptors (FGFRs) have numerous functions in the developing and adult central nervous system (CNS). For example, the FGFR1 receptor is important for proliferation and fate specification of radial glial cells in the cortex and hippocampus, oligodendrocyte proliferation and regeneration, midline glia morphology and soma translocation, Bergmann glia morphology, and cerebellar morphogenesis. In addition, FGFR1 signaling in astrocytes is required for postnatal maturation of interneurons expressing parvalbumin (PV). FGFR1 is implicated in synapse formation in the hippocampus, and alterations in the expression of Fgfr1 and its ligand, Fgf2 accompany major depression. Understanding which cell types express Fgfr1 during development may elucidate its roles in normal development of the brain as well as illuminate possible causes of certain neuropsychiatric disorders.

Methods

Here, we used a BAC transgenic reporter line to trace Fgfr1 expression in the developing postnatal murine CNS. The specific transgenic line employed was created by the GENSAT project, tgFGFR1-EGFPGP338Gsat, and includes a gene encoding enhanced green fluorescent protein (EGFP) under the regulation of the Fgfr1 promoter, to trace Fgfr1 expression in the developing CNS. Unbiased stereological counts were performed for several cell types in the cortex and hippocampus.

Results

This model reveals that Fgfr1 is primarily expressed in glial cells, in both astrocytes and oligodendrocytes, along with some neurons. Dual labeling experiments indicate that the proportion of GFP+ (Fgfr1+) cells that are also GFAP+ increases from postnatal day 7 (P7) to 1 month, illuminating dynamic changes in Fgfr1 expression during postnatal development of the cortex. In postnatal neurogenic areas, GFP expression was also observed in SOX2, doublecortin (DCX), and brain lipid-binding protein (BLBP) expressing cells. Fgfr1 is also highly expressed in DCX positive cells of the dentate gyrus (DG), but not in the rostral migratory stream. Fgfr1 driven GFP was also observed in tanycytes and GFAP+ cells of the hypothalamus, as well as in Bergmann glia and astrocytes of the cerebellum.

Conclusions

The tgFGFR1-EGFPGP338Gsat mouse model expresses GFP that is congruent with known functions of FGFR1, including hippocampal development, glial cell development, and stem cell proliferation. Understanding which cell types express Fgfr1 may elucidate its role in neuropsychiatric disorders and brain development.

Effect of skilled reaching training and enriched environment on generation of oligodendrocytes in the adult sensorimotor cortex and corpus callosum

Background

Increased motor activity or social interactions through enriched environment are strong stimulators of grey and white matter plasticity in the adult rodent brain. In the present study we evaluated whether specific reaching training of the dominant forelimb (RT) and stimulation of unspecific motor activity through enriched environment (EE) influence the generation of distinct oligodendrocyte subpopulations in the sensorimotor cortex and corpus callosum of the adult rat brain. Animals were placed in three different housing conditions: one group was transferred to an EE, a second group received daily RT, whereas a third group remained in the standard cage. Bromodeoxyuridine (BrdU) was applied at days 2–6 after start of experiments and animals were allowed to survive for 10 and 42 days.

Results

Enriched environment and daily reaching training of the dominant forelimb significantly increased the number of newly differentiated GSTπ⁺ oligodendrocytes at day 10 and newly differentiated CNPase⁺ oligodendrocytes in the sensorimotor cortex at day 42. The myelin level as measured by CNPase expression was increased in the frontal cortex at day 42. Distribution of newly differentiated NG2⁺ subpopulations changed between 10 and 42 days with an increase of GSTπ⁺ subtypes and a decrease of NG2⁺ cells in the sensorimotor cortex and corpus callosum. Analysis of neuronal marker doublecortin (DCX) showed that more than half of NG2⁺ cells express DCX in the cortex. The number of new DCX⁺NG2⁺ cells was reduced by EE at day 10.

Conclusions

Our results indicate for the first time that specific and unspecific motor training conditions differentially alter the process of differentiation from oligodendrocyte subpopulations, in particular NG2⁺DCX⁺ cells, in the sensorimotor cortex and corpus callosum.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-017-0347-2) contains supplementary material, which is available to authorized users.

In vivo bioluminescence imaging of neurogenesis - the role of the blood brain barrier in an experimental model of Parkinson's disease

Bioluminescence imaging in transgenic mice expressing firefly luciferase in Doublecortin⁺ (Dcx) neuroblasts might serve as a powerful tool to study the role of neurogenesis in models of brain injury and neurodegeneration using non-invasive, longitudinal in vivo imaging. Therefore, we aimed to use BLI in B6(Cg)-Tyrc-2J/J Dcx-Luc (Doublecortin-Luciferase, Dcx-Luc) mice to investigate its suitability to assess neurogenesis in a unilateral injection model of Parkinson's disease. We further aimed to assess the blood brain barrier leakage associated with the intranigral 6-OHDA injection to evaluate its impact on substrate delivery and bioluminescence signal intensity. Two weeks after lesion, we observed an increase in bioluminescence signal in the ipsilateral hippocampal region in both, 6-OHDA and vehicle injected Dcx-Luc mice. At the same time, no corresponding increase in Dcx⁺ neuroblast numbers could be observed in the dentate gyrus of C57Bl6 mice. Blood brain barrier leakage was observed in the hippocampal region and in the degenerating substantia nigra of C57Bl6 mice in vivo using T1 weighted Magnetic Resonance Imaging with Gadovist^® and ex vivo using Evans Blue Fluorescence Reflectance Imaging and mouse Immunoglobulin G staining. Our data suggests a BLI signal dependency on blood brain barrier permeability, underlining a major pitfall of substrate/tracer dependent imaging in invasive disease models.

Non-neurogenic SVZ-like niche in dolphins, mammals devoid of olfaction

Adult neurogenesis has been implicated in brain plasticity and brain repair. In mammals, it is mostly restricted to specific brain regions and specific physiological functions. The function and evolutionary history of mammalian adult neurogenesis has been elusive so far. The largest neurogenic site in mammals (subventricular zone, SVZ) generates neurons destined to populate the olfactory bulb. The SVZ neurogenic activity appears to be related to the dependence of the species on olfaction since it occurs at high rates throughout life in animals strongly dependent on this function for their survival. Indeed, it dramatically decreases in humans, who do not depend so much on it. This study investigates whether the SVZ neurogenic site exists in mammals devoid of olfaction and olfactory brain structures, such as dolphins. Our results demonstate that a small SVZ-like region persists in these aquatic mammals. However, this region seems to have lost its neurogenic capabilities since neonatal stages. In addition, instead of the typical newly generated neuroblasts, some mature neurons were observed in the dolphin SVZ. Since cetaceans evolved from terrestrial ancestors, non-neurogenic SVZ may indicate extinction of adult neurogenesis in the absence of olfactory function, with the retention of an SVZ-like anatomical region either vestigial or of still unknown role.

Noradrenergic regulation of plasticity marker expression in the adult rodent piriform cortex

The adult rodent piriform cortex has been reported to harbor immature neurons that express markers associated with neurodevelopment and plasticity, namely polysialylated neural cell adhesion molecule (PSA-NCAM) and doublecortin (DCX). We characterized the expression of PSA-NCAM and DCX across the rostrocaudal axis of the rat piriform cortex and observed higher numbers of PSA-NCAM and DCX positive cells in the posterior subdivision. As observed in the rat piriform cortex, Nestin-GFP reporter mice also revealed a similar gradient of GFP-positive cells with an increasing rostro-caudal gradient of expression. Given the extensive noradrenergic innervation of the piriform cortex and its role in regulating piriform cortex function and synaptic plasticity, we addressed the influence of norepinephrine (NE) on piriform cortex plasticity marker expression. Depletion of NE by treatment with the noradrenergic neurotoxin DSP-4 significantly increased the number of DCX and PSA-NCAM immunopositive cells in the piriform cortex of adult rats. Similarly, DSP-4 treated Nestin-GFP reporter mice revealed a robust induction of GFP-positive cells within the piriform cortex following NE depletion. Genetic loss of NE in dopamine β-hydroxylase knockout (Dbh -/-) mice phenocopied the effects of DSP-4, with an increase noted in PSA-NCAM and DCX positive cells in the piriform cortex. Further, chronic α₂-adrenergic receptor stimulation with the agonist guanabenz increased PSA-NCAM and DCX positive cells in the piriform cortex of adult rats and GFP-positive cells in the piriform cortex of Nestin-GFP mice. By contrast, chronic α₂-adrenergic receptor blockade with the antagonist yohimbine reduced PSA-NCAM and DCX positive cells in the piriform cortex of adult rats. Our results provide novel evidence for a role of NE in regulating the expression of plasticity markers, including PSA-NCAM, DCX, and nestin, within the adult mouse and rat piriform cortex.