Effects of total saponins of Panax notoginseng on immature neuroblasts in the adult olfactory bulb following global cerebral ischemia/reperfusion

The main active components extracted from Panax notoginseng are total saponins. They have been shown to inhibit platelet aggregation, increase cerebral blood flow, improve neurological behavior, decrease infarct volume and promote proliferation and differentiation of neural stem cells in the hippocampus and lateral ventricles. However, there is a lack of studies on whether total saponins of Panax notoginsertg have potential benefits on immature neuroblasts in the olfactory bulb following ischemia and reperfusion. This study established a rat model of global cerebral ischemia and reperfusion using four-vessel occlusion. Rats were administered total sa- ponins of Panax notoginseng at 75 mg/kg intraperitoneally 30 minutes after ischemia then once a day, for either 7 or 14 days. Total saponins of Panax notoginseng enhanced the number of dou- blecortin （DCX）＋ neural progenitor ceils and increased co-localization of DCX with neuronal nuclei and phosphorylated cAMP response element-binding/DCX＋ neural progenitor cells in the olfactory bulb at 7 and 14 days post ischemia. These findings indicate that following global brain ischemia/reperfusion, total saponins of Panax notoginseng promote differentiation of DCX＋ cells expressing immature neuroblasts in the olfactory bulb and the underlying mechanism is related to the activation of the signaling pathway of cyclic adenosine monophosphate response element binding protein.

Hyperhomocysteinemia induces injury in olfactory bulb neurons by downregulating Hes1 and Hes5 expression

Hyperhomocysteinemia has been shown to be associated with neurodegenerative diseases; however, lesions or histological changes and mechanisms underlying homocysteine-induced injury in olfactory bulb neurons remain unclear. In this study, hyperhomocysteinemia was induced in apolipoprotein E-deficient mice with 1.7% methionine. Pathological changes in the olfactory bulb were observed through hematoxylin-eosin and Pischingert staining. Cell apoptosis in the olfactory bulb was determined through terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling （TUNEL） staining. Transmission electron microscopy revealed an abnormal ultrastructure of neurons. Furthermore, immunoreactivity and expression of the hairy enhancer of the split 1 （Hesl） and Hess were measured using immunohistochemistry, immunofluorescence, and western blot assay. Our results revealed no significant structural abnormality in the ol- factory bulb of hyperhomocysteinemic mice. However, the number of TUNEL-positive cells increased in the olfactory bulb, lipofuscin and vacuolization were visible in mitochondria, and the expression of Hes1 and Hes5 decreased. These findings confirm that hyperhomocyste- inemia induces injury in olfactory bulb neurons by downregulating Hes1 and Hes5 expression.

Spontaneous firing in olfactory bulb neurons of Bufo bufo gargarizans in and after hibernation

Microelectrode technique was used to record the spontaneous electrical activities of the neurons in olfactory bulb of the Bufo bufo gargarizans, both in hibernation and after hibemation. This study investigated the electrophysiological characteristics of amphibian olfactory bulb in the period of hibernation and after hibernation and its effects on the start of hibernation and spontaneous awakening. The research showed four forms of spontaneous firings： single spontaneous firing, burst spontaneous firing, irregular spontaneous firing and consecutive single spontaneous firing. The single spontaneous firing includes slow depolarized spontaneous firing and fast depolarized spontaneous firing, and the slow depolarized spontaneous firing occurs only during the hibernation period. In hibernation, the low amplitude and low frequency firing with a longer duration may be relevant to maintaining the tonicity of the central nervous system in toads that are in hibernation, and this kind of firing may also provide an excited basis for their arousal from hibernation. After hibernation, the amplitude and frequency of firing increase, but the firing duration gets shorter. This form of short-term firing, which may be a phenomenon of sensory neurons fast adapting, is one of the neuronal mechanisms for the arousal of hibernating animals.

Gene and protein expression profiles of olfactory ensheathing cells from olfactory bulb versus olfactory mucosa

Olfactory ensheathing cells(OECs) from the olfactory bulb(OB) and the olfactory mucosa(OM) have the capacity to repair nerve injury. However, the difference in the therapeutic effect between OB-derived OECs and OM-derived OECs remains unclear. In this study, we extracted OECs from OB and OM and compared the gene and protein expression profiles of the cells using transcriptomics and non-quantitative proteomics techniques. The results revealed that both OB-derived OECs and OM-derived OECs highly expressed genes and proteins that regulate cell growth, proliferation, apoptosis and vascular endothelial cell regeneration. The differentially expressed genes and proteins of OB-derived OECs play a key role in regulation of nerve regeneration and axon regeneration and extension, transmission of nerve impulses and response to axon injury. The differentially expressed genes and proteins of OM-derived OECs mainly participate in the positive regulation of inflammatory response, defense response, cytokine binding, cell migration and wound healing. These findings suggest that differentially expressed genes and proteins may explain why OB-derived OECs and OM-derived OECs exhibit different therapeutic roles. This study was approved by the Animal Ethics Committee of the General Hospital of Ningxia Medical University(approval No. 2017-073) on February 13, 2017.

Neurogenesis in the adult olfactory bulb

Neurogenesis is the process by which cells divide, migrate, and subsequently differentiate into a neuronal phenotype. Significant rates of neurogenesis persist into adulthood in two brain regions, the subgranular zone of the dentate gyrus and the subventricular zone of the lateral ventricles. Cells of the subventricular zone divide and migrate via the rostral migratory stream to the olfactory bulb where they differentiate into granule and pefiglomerular cells. With the discovery of large-sca^e neurogenesis in the adult brain, there have been significant efforts to identify the mechanisms that control this process as well as the role of these cells in neuronal functioning. Although many questions remain unanswered, new insights appear daily about adult neurogenesis, regulatory mechanisms, and the fates of the progeny. In this review we highlight the main studies investigating factors that regulate neurogenesis in the subventricular zone, neuronal migration to the olfactory bulb, neuronal integration into the existing bulbar network and shortly discuss the functional meaning of this process.

Magnetic Resonance Imaging Findings of Olfactory Bulb in Anosmic Patients with COVID-19: A Systematic Review

Background Anosmia is one of the symptoms in individuals with SARS-CoV-2 infection.In anosmic patients,SARS-CoV-2 temporarily alters the signaling process in olfactory nerve cells and olfactory bulb(OB),which eventually damages the structure of the olfactory epithelium,leading to a permanent disorder in the olfactory pathway that this damaged structure is showed in MRI imaging Method Two investigators independently searched four databases consisting of PubMed,ProQuest,Scopus,and Web of Science for relevant records as of November 11,2020 with no time,space,and language restrictions.Google Scholar was also searched for the related resources within the time limit of 2020.All the found articles were reviewed based on the PRISMA flow diagram.Qualitative studies,case reports,editorials,letters,and other non-original studies were excluded from this systematic analysis.Results Initial search yielded 434 records.After reviewing the titles and abstracts,we selected 74 articles;finally,8 articles were depicted to be investigated and read in full text.The obtained results showed an increase in the width and volume of the olfactory cleft(OC),complete or partial destruction of OC,and complete occlusion of OC in COVID-19 patients.Deformation and degeneration as well as a subtle asymmetry were evident in the OBs.Computed tomography(CT),meganetic resonance imaging(MRI),and positron emission tomography(PET)were used to detect the outcomes of anosmia in these studies.Conclusions The changes in OC are greater than those in OB in patients with COVID-19,mainly due to the inflammatory and immune responses in OC.However,fewer changes in OB are due to neurological or vascular disorders.Topical steroid therapy and topical saline can be helpful.

Odorant discrimination using functional near-infrared spectroscopy of the main olfactory bulb in rats

We characterize the hemodynamic response changes in the main olfactory bulb(MOB)of anesthetized rats with near-infrared spectroscopy(NIRS)during the presentation of three different odorants:(i)plain air as a reference(Blank),(ii) 2-heptanone(HEP),and(iii)isopropylbenzene(Ib).Odorants generate different changes in the concentrations of oxyhemoglobin.Our results suggest that NIRS technology might be useful in discriminating various odorants in a non-invasive manner using animals with a superb olfactory system.

Radial glia interact with primary olfactory axons to regulate development of the olfactory bulb

The developing olfactory system - merging of the periph- eral and central nervous systems： The olfactory system is responsible for the sense of smell and is comprised of a complex topographic map that regenerates throughout life. In rodents each olfactory sensory neuron expresses one of N 1,300 odorant receptors with the neurons being distributed mosaically within the epithelium. The axons of the sensory neurons do not maintain near-neighbour relationships and instead project to disparate topographic targets in the olfac- tory bulb within the central nervous system. The develop- ment of the targets relies on the intermingling of the sensory axons with the interneurons, glia and second order neurons of the olfactory bulb. Thus the formation of the olfactory system involves the coordinated integration of the axons of the peripheral olfactory sensory neurons with the cells of the olfactory bulb.

Combined VEGF/PDGF improves olfactory regeneration after unilateral bulbectomy in mice

The olfactory receptor neurons lining the nasal cavity have a remarkable capacity to regenerate throughout life. They are replenished continuously and their axons make new connections within the olfactory bulb. However, some factors such as head trauma and skull base surgery damage the olfactory nerve which lead to olfactory dysfunction. Losing the sense of smell has considerable effects on quality of life and life-expectancy. Therefore, there is a clear need to find a treatment for olfactory dysfunction. One such potential treatment is growth factor therapy which showed promising results in the spinal cord and brain injuries. The aim of the present study was to investigate whether combined delivery of two growth factors, vascular endothelial growth factor and platelet-derived growth factor treatment can improve the olfactory neurons regeneration in mice. The degeneration of the olfactory neurons was induced by unilateral bulbectomy. The treatment group received 1.5 μg of the combined growth factors intranasally, while the control injured group received saline. Growth factor treatment significantly increased the number of immature neurons at 5 and 7 days post injury and also the number of mature olfactory neurons at 10 and 14 days post bulbectomy. Regenerating axons extended over a larger volume in the operated cavity in the treatment group compared to control group at 14 days post bulbectomy. The growth factor treatment also significantly reduced astrocytic glia scar in the operated cavity. The results indicate that the combined delivery of the growth factors has the potential to improve olfactory dysfunction.

Plasticity of Sniffing Pattern and Neural Activity in the Olfactory Bulb of Behaving Mice During Odor Sampling,Anticipation,and Reward

The olfactory bulb(OB) is the first relay station in the olfactory system.In the OB,mitral/tufted cells(M/Ts),which are the main output neurons,play important roles in the processing and representation of odor information.Recent studies focusing on the function of M/Ts at the single-cell level in awake behaving mice have demonstrated that odor-evoked firing of single M/Ts displays transient/long-term plasticity during learning.Here,we tested whether the neural activity of M/Ts and sniffing patterns are dependent on anticipation and reward in awake behaving mice.We used an odor discrimination task combined with in vivo electrophysiological recordings in awake,head-fixed mice,and found that,while learning induced plasticity of spikes and beta oscillations during odor sampling,we also found plasticity of spikes,beta oscillation,sniffing pattern,and coherence between sniffing and theta oscillations during the periods of anticipation and/or reward.These results indicate that the activity of M/Ts plays important roles not only in odor representation but also in salience-related events such as anticipation and reward.

Reduction of Glucose Metabolism in Olfactory Bulb is an Earlier Alzheimer＇s Disease-related Biomarker in 5XFAD Mice

Background：Early diagnosis assumes a vital role in an effective treatment of Alzheimer＇s disease （AD）.Most of the current studies can only make anAD diagnosis after the manifestation of typical clinical symptoms.The present study aimed to investigate typical and other biomarkers of AD to find a possible early biomarker.Methods：A total of 14 5XFAD mice （at 3 and 6 months old）,with 14 age-matched wild-type （WT） mice as control,were enrolled in this case-control study.Morris water maze test was performed to evaluate the cognitive function;buried food pellet test and olfactory maze test were employed to investigate the olfactory function;immunofluorescence to detect amyloid deposition and positron emission tomography to examine 2-deoxy-2-（18F） fluoro-D-glucose （[18F]-FDG） uptake in the hippocampus and cerebral cortex.Results：With the increasing age,cognitive performance （P =0.0262） and olfactory function were significantly deteriorated （day 1 P =0.0012,day 2 P =0.0031,day 3 P =0.0160,respectively） and the （18F）-FDG uptake was markedly decreased in multi-cerebral regions including the olfactory bulb （P 〈 0.0001）,hippocampus （P =0.0121）,and cerebral cortex （P 〈 0.0001）.Of note,in 3-month-old 5XFAD mice,a significant decline of （18F）-FDG uptake in the olfactory bulb was found when compared with that of age-matched WT mice （P =0.023） while no significant difference was present when the uptakes in other cerebral regions were compared.Conclusions：The decline of （18F）-FDG uptake in the olfactory bulb occurs earlier than other incidents,serving as an earlier in vivo biological marker of AD in 5XFAD mice and making early diagnosis of AD possibly.

Effects of Pinealectomy and Gonadectomy on Olfactory Bulb Dopaminergic Neurons in Rats

Background： Olfactory disorder is an early manifestation of Parkinson＆#39;s disease （PD）, likely to be associated with abnormalities of the dopaminergic neurons in the olfactory bulb （OB）; however, the causes of olfactory disorder in PD are not entirely clear. Some studies showed that melatonin （MT） and androgens （mainly testosterone, T） might participate in the pathogenesis of PD. The research aimed to investigate effects of MT or T deficiency on OB dopaminergic neurons in rats. Methods： One hundred and twenty normal male Wistar rats were randomly divided into the control, sham operation pinealectomy （PX）, sham operation gonadectomy （GDX）, PX, GDX, and PX ＋ GDX groups. After 60 days, glial cell hyperplasia and neuronal apoptosis were examined with hematoxylin and eosin and the TUNEL method; the expression levels of tyrosine hydroxylase （TH）, Bax, and Bcl-2 were measured using immunohistochemistry （IH） by the streptavidin peroxidase conjugated method. Comparison among multiple sets used analysis of variance and LSD method or Kruskal-Wallis test and Nemenyi method. Results： There were no significant differences between the sham operation groups and the control group; thus, they were merged into Group A. There was no significant glial cell hyperplasia （P 〉 0.05） or change in shape in any of the groups after PX or GDX. The number of apoptotic cells in Groups A （1.41 ± 0.56）, PX （12.31 ± 4.68）, GDX （20.52 ± 5.13）, and PX ＋ GDX （30.23 ± 5.25） successively significantly increased （P 〈 0.05）. The number of TH （＋） cells in Groups A （42.62 ± 5.63）, PX （37.31 ± 4.32）, GDX （31.07 ± 4.21）, and PX ＋ GDX （25.22 ± 3.66） was successively significantly decreased （P 〈 0.05）. The gray value of TH （＋） cells and fibers in Groups A （98.51 ± 10.36）, PX （108.96 ± 13.01）, GDX （119.02 ± 12.98）, and PX ＋ GDX （128.99 ± 13.39） was successively significantly increased （P 〈 0.05）. The results of Bax staining were as follows： Group A＋, Group PX＋＋, Group GDX＋＋, and Group PX＋ GDX＋＋＋, the results of Bcl-2 in all groups were ＋. Conclusions： PX or GDX could lead to OB neurotoxicity in the following groups of rats in the following order： PX 〈 GDX 〈 PX ＋ GDX. PX or GDX increased the ratio of Bax/Bcl-2. The effect of PX and GDX was equal, but both were less than that of PX ＋ GDX. Neurotoxicity as a result of PX or GDX was not related to inflammation.

A single-cell atlas of mouse olfactory bulb chromatin accessibility

Olfaction,the sense of smell,is a fundamental trait crucial to many species.The olfactory bulb(OB)plays pivotal roles in processing and transmitting odor information from the environment to the brain.The cellular heterogeneity of the mouse OB has been studied using single-cell RNA sequencing.However,the epigenetic landscape of the m OB remains mostly unexplored.Herein,we apply single-cell assay for transposaseaccessible chromatin sequencing to profile the genome-wide chromatin accessibility of 9,549 single cells from the m OB.Based on single-cell epigenetic signatures,m OB cells are classified into 21 clusters corresponding to 11 cell types.We identify distinct sets of putative regulatory elements specific to each cell cluster from which putative target genes and enriched potential functions are inferred.In addition,the transcription factor motifs enriched in each cell cluster are determined to indicate the developmental fate of each cell lineage.Our study provides a valuable epigenetic data set for the m OB at single-cell resolution,and the results can enhance our understanding of regulatory circuits and the therapeutic capacity of the OB at the single-cell level.

Distinct Characteristics of Odor-evoked Calcium and Electrophysiological Signals in Mitral/Tufted Cells in the Mouse Olfactory Bulb

Fiber photometry is a recently-developed method that indirectly measures neural activity by monitoring Ca^(2+)signals in genetically-identified neuronal populations.Although fiber photometry is widely used in neuroscience research,the relationship between the recorded Ca^(2+)signals and direct electrophysiological measurements of neural activity remains elusive.Here,we simultaneously recorded odor-evoked Ca^(2+)and electrophysiological signals[single-unit spikes and local field potentials(LFPs)]from mitral/tufted cells in the olfactory bulb of awake,head-fixed mice.Odors evoked responses in all types of signal but the response characteristics(e.g.,type of response and time course)differed.The Ca^(2+)signal was correlated most closely with power in theβ-band of the LFP.The Ca^(2+)signal performed slightly better at odor classification than high-γoscillations,worse than single-unit spikes,and similarly toβoscillations.These results provide new information to help researchers select an appropriate method for monitoring neural activity under specific conditions.

Effects of rhidosin on expression of fibroblast growth factor onolfactory bulb in rats and its relation with senile hyposmia

Objectives To determine the expression of fibroblast growth factor (FGF) on olfactory bulb in rats and its relation with senile hyposmia, and to discuss the effects of rhidosin on expression of FGF on olfactory bulb in senile rats and its significance Methods Four groups of rats, ie, young group, senile group, rhidosin group, and physiological saline control group were used in this study After the removal of the heads of these rats, olfactory mucosa and olfactory bulbs were immediately fixed with neutral formalin, followed with paraffin embedding, serial sectioning, immunohistochemical staining and light microscopic observation Results The positive expression rate of FGF on olfactory bulb in young group was significantly higher than that in senile group (P<0 01) The positive expression rate of FGF on olfactory bulb in rhidosin group was significantly higher than that in physiological saline control group (P<0 01) No positive expression of FGF on olfactory mucosa was observed in these four groups Conclusion These results suggest that the expression of FGF on olfactory bulb gradually decline with aging The decrease of expression of FGF on olfactory bulb may play a key role in the occurrence of senile hyposmia Rhidosin can increase the expression of FGF on olfactory bulbs in senile rats and this may be one of the mechanisms by which rhidosin promotes the growth of olfactory cells and inhibits aging effects on the olfactory system

APPL2 Negatively Regulates Olfactory Functions by Switching Fate Commitments of Neural Stem Cells in Adult Olfactory Bulb via Interaction with Notch1 Signaling

Adult olfactory neurogenesis plays critical roles in maintaining olfactory functions.Newly-generated neurons in the subventricular zone migrate to the olfactory bulb(OB) and determine olfactory discrimination,but the mechanisms underlying the regulation of olfactory neurogenesis remain unclear.Our previous study indicated the potential of APPL2(adaptor protein,phosphotyrosine interacting with PH domain and leucine zipper 2) as a modulating factor for neurogenesis in the adult olfactory system.In the present study,we report how APPL2 affects neurogenesis in the OB and thereby mediates olfactory discrimination by using both in vitro neural stem cells(NSCs) and an in vivo animal model-APPL2 transgenic(Tg) mice.In the in vitro study,we found that APPL2 overexpression resulted in NSCs switching from neuronal differentiation to gliogenesis while APPL2 knockdown promoted neurogenesis.In the in vivo study,APPL2 Tg mice had a higher population of glial cells and dampened neuronal production in the olfactory system,including the corpus callosum,OB,and rostral migratory stream.Adult APPL2 Tg mice displayed impaired performance in olfactory discrimination tests compared with wild-type mice.Furthermore,we found that an interaction of APPL2 with Notch1 contributed to the roles of APPL2 in modulating the neurogenic lineage-switching and olfactory behaviors.In conclusion,APPL2 controls olfactory discrimination by switching the fate choice of NSCs via interaction with Notch1 signaling.

The strategy of olfactory signal processing in the olfactory bulb

In mammals, olfactory sensory neurons expressing common odorant receptor (OR)

Combined Transplantation of Neural Stem Cells and Olfactory Ensheathing Cells Improves the Motor Function of Rats with Intracerebral Hemorrhage

Objective To investigate the effects of combined transplantation of neural stem cells （NSC） and olfactory ensheathing cells （OEC） on the motor function of rats with intracerebral hemorrhage. Methods In three days after a rat model of caudate nucleus hemorrhage was established, NSCs and OEC, NSC, OEC （from embryos of Wistar rats） or normal saline were injected into bematomas of rats in combined transplantation group, NSC group, OEC group, and control group, respectively. Damage of neural function was scored before and in 3, 7, 14, 30 days after operation. Tissue after transplantation was observed by immunocytochemistry staining. Results The scores for the NSC, OEC and co-transplantation groups were significantly lower in 14 and 30 days after operation than in 3 days after operation （P〈0.05）. The scores for the NSC and OEC groups were significantly lower than those for the control group only in 30 days after operation （P〈0.05）, while the difference for the NSC-OEC group was significant in 14 days after operation （P〈0.05）. Immunocytochemistry staining revealed that the transplanted OEC and NSC could survive, migrate and differentiate into neurons, astrocytes, and oligodendrocytes. The number of neural precursor cells was greater in the NSC and combined transplantation groups than in the control group. The number of neurons differentiated from NSC was significantly greater in the co-transplantation group than in the NSC group. Conclusion Co-transplantation of NSC and OEC can promote the repair of injured tissue and improve the motor fimction of rats with intracerebral hemorrhage.

Simplified methods to isolate,culture and purify olfactory ensheathing cells

Conventional methods for harvesting, culturing and purifying olfactory ensheathing cells are complicated, time-consuming, and poorly reproducible. Olfactory bulbs were detached from adult Sprague Dawley rats and olfactory ensheathing cells were isolated using shearing, dispersion processes. After the primary cultures reached confluence, the cells were purified using a three-step process. The olfactory ensheathing cells attached and grew rapidly. The purity of the olfactory ensheathing cells increased following the three purification steps, eventually exceeding 95%. These cells could be maintained for an extended period time in culture. This simple, inexpensive, reproducible method of harvesting, culturing and purifying olfactory ensheathing cells shortens the culture cycle and provides sufficient olfactory ensheathing cells of controllable purity.

Special function of nestin^+ neurons in the medial septum-diagonal band of Broca in adult rats

Nestin＋ neurons have been shown to express choline acetyltransferase （CHAT） in the medial septum-diagonal band of Broca in adult rats. This study explored the projection of nestin＋ neu-rons to the olfactory bulb and the time course of nestin＋ neurons in the medial septum-diagonal band of Broca in adult rats during injury recovery after olfactory nerve transection. This study observed that all nestin＋ neurons were double-labeled with ChAT in the medial septum-diagonal band of Broca. Approximately 53.6% of nestin~ neurons were projected to the olfactory bulb and co-labeled with fast blue. A large number of nestin~ neurons were not present in each region of the medial septum-diagonal band of Broca. Nestin＋ neurons in the medial septum and vertical limb of the diagonal band of Broca showed obvious compensatory function. The number of nestin＋ neurons decreased to a minimum later than nestin/CHAT＋ neurons in the medial sep- turn-diagonal band of Broca. The results suggest that nestin＋ cholinergic neurons may have a closer connection to olfactory bulb neurons. Nestin＋ cholinergic neurons may have a stronger tolerance to injury than Nestin/CHAT＋ neurons. The difference between nestin＋ and nestin-/ ChAT＋ neurons during the recovery process requires further investigations.