BDNF signaling during olfactory bulb neurogenesis

The olfactory bulb: A neuroendocrine spotlight on feeding and metabolism

Olfaction is the most ancient sense and is needed for food-seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour-specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.

A protein-coding gene expression atlas from the brain of pregnant and non-pregnant goats

Background: The brain is an extraordinarily complex organ with multiple anatomical structures involved in highly specialized functions related with behavior and physiological homeostasis. Our goal was to build an atlas of protein-coding gene expression in the goat brain by sequencing the transcriptomes of 12 brain regions in seven female Murciano-Granadina goats, from which three of them were 1-month pregnant. Results: Between 14,889 (cerebellar hemisphere) and 15,592 (pineal gland) protein-coding genes were expressed in goat brain regions, and most of them displayed ubiquitous or broad patterns of expression across tissues. Principal component analysis and hierarchical clustering based on the patterns of mRNA expression revealed that samples from certain brain regions tend to group according to their position in the anterior-posterior axis of the neural tube, i.e., hindbrain (pons and medulla oblongata), midbrain (rostral colliculus) and forebrain (frontal neocortex, olfactory bulb, hypothalamus, and hippocampus). Exceptions to this observation were cerebellum and glandular tissues (pineal gland and hypophysis), which showed highly divergent mRNA expression profiles. Differential expression analysis between pregnant and non-pregnant goats revealed moderate changes of mRNA expression in the frontal neocortex, hippocampus, adenohypophysis and pons, and very dramatic changes in the olfactory bulb. Many genes showing differential expression in this organ are related to olfactory function and behavior in humans. Conclusion: With the exception of cerebellum and glandular tissues, there is a relationship between the cellular origin of sampled regions along the anterior-posterior axis of the neural tube and their mRNA expression patterns in the goat adult brain. Gestation induces substantial changes in the mRNA expression of the olfactory bulb, a finding consistent with the key role of this anatomical structure on the development of maternal behavior.

BDNF/TrkB Is a Crucial Regulator in the Inflammation-Mediated Odontoblastic Differentiation of Dental Pulp Stem Cells

The odontoblastic differentiation of dental pulp stem cells (DPSCs) associated with caries injury happens in an inflammatory context. We recently demonstrated that there is a link between inflammation and dental tissue regeneration, identified via enhanced DPSC-mediated dentinogenesis in vitro. Brain-derived neurotrophic factor (BDNF) is a nerve growth factor-related gene family molecule which functions through tropomyosin receptor kinase B (TrkB). While the roles of BDNF in neural tissue repair and other regeneration processes are well identified, its role in dentinogenesis has not been explored. Furthermore, the role of BDNF receptor-TrkB in inflammation-induced dentinogenesis remains unknown. The role of BDNF/TrkB was examined during a 17-day odontogenic differentiation of DPSCs. Human DPSCs were subjected to odontogenic differentiation in dentinogenic media treated with inflammation inducers (LTA or TNFα), BDNF, and a TrkB agonist (LM22A-4) and/or antagonist (CTX-B). Our data show that BDNF and TrkB receptors affect the early and late stages of the odontogenic differentiation of DPSCs. Immunofluorescent data confirmed the expression of BDNF and TrkB in DPSCs. Our ELISA and qPCR data demonstrate that TrkB agonist treatment increased the expression of dentin matrix protein-1 (DMP-1) during early DPSC odontoblastic differentiation. Coherently, the expression levels of runt-related transcription factor 2 (RUNX-2) and osteocalcin (OCN) were increased. TNFα, which is responsible for a diverse range of inflammation signaling, increased the levels of expression of dentin sialophosphoprotein (DSPP) and DMP1. Furthermore, BDNF significantly potentiated its effect. The application of CTX-B reversed this effect, suggesting TrkB`s critical role in TNFα-mediated dentinogenesis. Our studies provide novel findings on the role of BDNF-TrkB in the inflammation-induced odontoblastic differentiation of DPSCs. This finding will address a novel regulatory pathway and a therapeutic approach in dentin tissue engineering using DPSCs.

Antidepressant-Like Effects of Chronic Guanosine in the Olfactory Bulbectomy Mouse Model

Major depressive disorder (MDD) leads to pervasive changes in the health of afflicted patients. Despite advances in the understanding of MDD and its treatment, profound innovation is needed to develop fast-onset antidepressants with higher effectiveness. When acutely administered, the endogenous nucleoside guanosine (GUO) shows fast-onset antidepressant-like effects in several mouse models, including the olfactory bulbectomy (OBX) rodent model. OBX is advocated to possess translational value and be suitable to assess the time course of depressive-like behavior in rodents. This study aimed at investigating the long-term behavioral and neurochemical effects of GUO in a mouse model of depression induced by bilateral bulbectomy (OBX). Mice were submitted to OBX and, after 14 days of recovery, received daily (ip) administration of 7.5 mg/kg GUO or 40 mg/kg imipramine (IMI) for 45 days. GUO and IMI reversed the OBX-induced hyperlocomotion and recognition memory impairment, hippocampal BDNF increase, and redox imbalance (ROS, NO, and GSH levels). GUO also mitigated the OBX-induced hippocampal neuroinflammation (IL-1, IL-6, TNF-α, INF-γ, and IL-10). Brain microPET imaging ([¹⁸F]FDG) shows that GUO also prevented the OBX-induced increase in hippocampal FDG metabolism. These results provide additional evidence for GUO antidepressant-like effects, associated with beneficial neurochemical outcomes relevant to counteract depression.

The effects of rotenone on TH, BDNF and BDNF-related proteins in the brain and periphery: Relevance to early Parkinson's disease

Loss of dopaminergic neurons in the substantia nigra (SN) is one of the pathological hallmarks in Parkinson's disease (PD). This neuron loss is accompanied by reduced protein and activity levels of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis. Reduced nigral brain-derived neurotrophic factor (BDNF) has been postulated to contribute to the loss of nigral dopaminergic neurons in PD by causing a lack of trophic support. Prior to this nigral cell loss many patients develop non-motor symptoms such as hyposmia, constipation and orthostatic hypotension. We investigated how TH, BDNF and BDNF related receptors are altered in the SN, olfactory bulb, adrenal glands and colon (which are known to be affected in PD) using rotenone-treated rats. Rotenone was administered to Sprague-Dawley rats at a dose of 2.75 mg/kg, 5 days/week for 4 weeks, via intraperitoneal injections. Rats underwent behavioural testing, and tissues were collected for western blot and ELISA analysis. This rotenone treatment induced reduced rears and distance travelled in the rearing and open field test, respectively but caused no impairments in forced movement (rotarod test). The SN had changes consistent with a pro-apoptotic state, such as increased proBDNF but no change in TH; whereas, the colon had significantly reduced TH and increased sortilin. Thus, our results indicate further investigation is warranted for this rotenone-dosing paradigm's capacity for reproducing the early stage of PD, as we observed impairments in voluntary movement and pathology in the colon without overt motor symptoms or nigral dopaminergic loss.

Prep1 Deficiency Affects Olfactory Perception and Feeding Behavior by Impairing BDNF-TrkB Mediated Neurotrophic Signaling

Prep1 is a homeodomain transcription factor which has an important role in hindbrain development. Prep1 expression is also kept in adult mouse brain and in particular within the olfactory bulbs. Moreover, many Prep1 neurons co-localize with Calbindin-positive periglomerular interneurons in olfactory glomerular layer. However, Prep1 function in this brain region is still unknown. In this study, we show that Prep1 hypomorphic heterozygous (Prep1^i/+) mice express low levels of protein and feature a 30% reduction of olfactory bulb area, compared to WT mice. In addition, Prep1^i/+ mice olfactory bulb histological analysis indicated a 20% lower cytochrome C oxidase activity within the glomerular layer, accompanied by a reduced number of periglomerular interneurons, compared to the WT littermates. Consistently, olfactory perception test highlighted that Prep1 hypomorphic heterozygous mice display a scant ability to distinguish odors, which significantly impacts on feeding behavior, as Prep1^i/+ mice revealed a reduced preference for high-fat food. Analysis of BDNF signaling, which represents the main molecular mediator of olfactory plasticity, showed that Prep1^i/+ mouse olfactory bulbs feature a 30% reduction of TrkB receptor levels and a decreased activation of ERK1/2. Similarly, overexpression of Prep1 in mouse neuronal cells (N2A) caused an increase of TrkB expression levels, BDNF-induced ERK phosphorylation, and cell viability, compared to control cells. We conclude that Prep1 deficiency alters olfactory morpho-functional integrity and olfaction-mediated eating behavior by affecting BDNF-TrkB signaling. Prep1 could, therefore, play a crucial role in behavioral dysfunctions associated to impaired responsiveness to BDNF.

The effects of desipramine, fluoxetine, or tianeptine on changes in bulbar BDNF levels induced by chronic social instability stress and inflammation

BACKGROUND

Stress is a major predisposing factor in the development of psychiatric disorders and potential source of augmented inflammatory processes in the brain. Increasing body of evidence shows an important role of alterations in the olfactory bulbs (OBs) function in stress-related disorders. The aim of the present study was to investigate the impact of antidepressants on the alterations of brain-derived neurotrophic factor (BDNF) induced by lipopolysaccharide (LPS) in female rats subjected to chronic social instability stress (CSIS).

METHODS

9 weeks old female rats were subjected to CSIS and injected ip once daily with desipramine (10 mg/kg), fluoxetine (5 mg/kg), or tianeptine (10 mg/kg) for 4 weeks. On the last day of the experiment, rats being at the estrus phase of cycle were injected ip with LPS (1 mg/kg) or saline.

RESULTS

The BDNF mRNA and protein levels were evaluated in the olfactory bulbs. and the BDNF protein levels were measured in plasma. A single LPS administration in the stressed rats resulted in significant decrease in the bulbar BDNF mRNA, but not in the protein level. Chronic administration of desipramine, fluoxetine, or tianeptine increased the BDNF mRNA expression and protein levels in the LPS-injected stressed rats. There was no effect of the studied antidepressants on the reduction of the plasma BDNF protein level induced by CSIS and LPS.

CONCLUSIONS

These results suggest that studied antidepressants were effective in inhibiting the impact of LPS on BDNF expression in the stressed rats what may be significant for beneficial action of this drugs.

Huatuo Zaizao pill promotes functional recovery and neurogenesis after cerebral ischemia-reperfusion in rats

Background

Ischemic stroke is the third leading cause of death in adults worldwide and is the first leading cause of long-term disability. Neurogenesis plays an important role in promoting behavioral recovery after stroke. Huatuo Zaizao pill (HT), a traditional Chinese medicine, has been used clinically in China to promote the rehabilitation after stroke, but the underlying mechanism of action was still unclear. This study is to investigate the effects of HT on the functional recovery in a rat model of cerebral ischemia-reperfusion (I/R) injury, and the potential molecular mechanisms.

Methods

Rats were randomly divided into sham, model with cerebral I/R injury, or HT-treated groups, then administered orally with vehicle (for the sham and model group) or HT (0.5, 1.0, or 2.0 mg/kg) respectively, for 3 or 7 days. Functional recovery was assessed by cylinder test, beam walking test, and adhesive test. Neurogenesis was investigated by double immunofluorescence staining for 5-ethynyl-2-deoxyuridine (EdU) and neuronal nuclear protein (NeuN). The proteins of kinase A (PKA), cAMP response element-binding protein (CREB), and brain-derived neurotrophic factor (BDNF) were assayed by western blotting. The level of BDNF mRNA was evaluated by RT-PCR.

Results

Compared with the model group, treatment with HT significantly promoted functional recovery in I/R injured rats (p < 0.05 or p < 0.01). The generation of new neurons was increased in the HT groups. HT treatment for 3 days increased the level of BDNF mRNA in I/R injured rats. Expression of PKA, phosphorylated CREB, and BDNF were significantly (p < 0.05) increased with the 7-day HT treatment.

Conclusions

These results indicated that HT treatment could promote functional recovery after stroke. HT enhanced the expression of BDNF and increased the level of neurogenesis in cerebral I/R animal, which might be associated with the functional recovery.

Adult Neurogenesis in the Female Mouse Hypothalamus: Estradiol and High-Fat Diet Alter the Generation of Newborn Neurons Expressing Estrogen Receptor α

Estrogens and leptins act in the hypothalamus to maintain reproduction and energy homeostasis. Neurogenesis in the adult mammalian hypothalamus has been implicated in the regulation of energy homeostasis. Recently, high-fat diet (HFD) and estradiol (E2) have been shown to alter cell proliferation and the number of newborn leptin-responsive neurons in the hypothalamus of adult female mice. The current study tested the hypothesis that new cells expressing estrogen receptor α (ERα) are generated in the arcuate nucleus (ARC) and the ventromedial nucleus of the hypothalamus (VMH) of the adult female mouse, hypothalamic regions that are critical in energy homeostasis. Adult mice were ovariectomized and implanted with capsules containing E2 or oil. Within each hormone group, mice were fed an HFD or standard chow for 6 weeks and treated with BrdU to label new cells. Newborn cells that respond to estrogens were identified in the ARC and VMH, of which a subpopulation was leptin sensitive, indicating that the subpopulation consists of neurons. Moreover, there was an interaction between diet and hormone with an effect on the number of these newborn ERα-expressing neurons that respond to leptin. Regardless of hormone treatment, HFD increased the number of ERα-expressing cells in the ARC and VMH. E2 decreased hypothalamic fibroblast growth factor 10 (Fgf10) gene expression in HFD mice, suggesting a role for Fgf10 in E2 effects on neurogenesis. These findings of newly created estrogen-responsive neurons in the adult brain provide a novel mechanism by which estrogens can act in the hypothalamus to regulate energy homeostasis in females.

Intranasally administered mesenchymal stem cells promote a regenerative niche for repair of neonatal ischemic brain injury

Previous work from our group has shown that intranasal MSC-treatment decreases lesion volume and improves motor and cognitive behavior after hypoxic-ischemic (HI) brain damage in neonatal mice. Our aim was to determine the kinetics of MSC migration after intranasal administration, and the early effects of MSCs on neurogenic processes and gliosis at the lesion site. HI brain injury was induced in 9-day-old mice and MSCs were administered intranasally at 10days post-HI. The kinetics of MSC migration were investigated by immunofluorescence and MRI analysis. BDNF and NGF gene expression was determined by qPCR analysis following MSC co-culture with HI brain extract. Nestin, Doublecortin, NeuN, GFAP, Iba-1 and M1/M2 phenotypic expression was assessed over time. MRI and immunohistochemistry analyses showed that MSCs reach the lesion site already within 2h after intranasal administration. At 12h after administration the number of MSCs at the lesion site peaks and decreases significantly at 72h. The number of DCX(+) cells increased 1 to 3days after MSC administration in the SVZ. At the lesion, GFAP(+)/nestin(+) and DCX(+) expression increased 3 to 5days after MSC-treatment. The number of NeuN(+) cells increased within 5days, leading to a dramatic regeneration of the somatosensory cortex and hippocampus at 18days after intranasal MSC administration. Interestingly, MSCs expressed significantly more BDNF gene when exposed to HI brain extract in vitro. Furthermore, MSC-treatment resulted in the resolution of the glial scar surrounding the lesion, represented by a decrease in reactive astrocytes and microglia and polarization of microglia towards the M2 phenotype. In view of the current lack of therapeutic strategies, we propose that intranasal MSC administration is a powerful therapeutic option through its functional repair of the lesion represented by regeneration of the cortical and hippocampal structure and decrease of gliosis.

Involvement of miR-9/MCPIP1 axis in PDGF-BB-mediated neurogenesis in neuronal progenitor cells

Highly conserved microRNA-9 (miR-9) has a critical role in various cellular processes including neurogenesis. However, its regulation by neurotropins that are known to mediate neurogenesis remains poorly defined. In this study, we identify platelet-derived growth factor-BB (PDGF-BB)-mediated upregulation of miR-9, which in turn downregulates its target gene monocyte chemotactic protein-induced protein 1 (MCPIP1), as a key player in modulating proliferation, neuronal differentiation as well as migration of neuronal progenitor cells (NPCs). Results indicate that miR-9-mediated NPC proliferation and neuronal differentiation involves signaling via the nuclear factor-kappa B (NF-κB) and cAMP response element-binding protein (CREB) pathways, and that NPC migration involves CREB but not the NF-κB signaling. These findings thus suggest that miR-9-mediated downregulation of MCPIP1 acts as a molecular switch regulation of neurogenesis.

Effects of infrasound on hippocampus-dependent learning and memory in rats and some underlying mechanisms

To investigate the effect of infrasound on the hippocampus-dependent spatial learning and memory as well as its underlying mechanisms, we measured the changes of cognitive abilities, brain-derived neurotrophic factor (BDNF)-tyrosine kinase receptor B (TrkB) signal transduction pathway and neurogenesis in the hippocampus of rats. The results showed that rats exposed to infrasound of 16 Hz at 130 dB for 14 days exhibited longer escape latency from day 2 and shortened time staying in the quadrant P in Morris water maze (MWM). It was found that mRNA and protein expression levels of hippocampal BDNF and TrkB were significantly decreased in real-time PCR and Western blot, and the number of BrdU-labeled cells in hippocampus was also reduced when compared to control. These results provided novel evidences that the infrasound of a certain exposure parameter can impair hippocampus-dependent learning and memory, in which the downregulation of the neuronal plasticity-related BDNF-TrkB signal pathway and less neurogenesis in hippocampus might be involved.