Imbalance in Unc80 RNA Editing Disrupts Dynamic Neuronal Activity and Olfactory Perception.

A-to-I RNA editing, catalyzed by the ADAR protein family, significantly contributes to the diversity and adaptability of mammalian RNA signatures, aligning with developmental and physiological needs. Yet, the functions of many editing sites are still to be defined. The Unc80 gene stands out in this context due to its brain-specific expression and the evolutionary conservation of its codon-altering editing event. The precise biological functions of Unc80 and its editing, however, are still largely undefined. In this study, we first demonstrated that Unc80 editing occurs in an ADAR2-dependent manner and is exclusive to the brain. By employing the CRISPR/Cas9 system to generate Unc80 knock-in mouse models that replicate the natural editing variations, our findings revealed that mice with the "gain-of-editing" variant (Unc80G/G) exhibit heightened basal neuronal activity in critical olfactory regions, compared to the "loss-of-editing" (Unc80S/S) counterparts. Moreover, an increase in glutamate levels was observed in the olfactory bulbs of Unc80G/G mice, indicating altered neurotransmitter dynamics. Behavioral analysis of odor detection revealed distinctive responses to novel odors-both Unc80 deficient (Unc80+/-) and Unc80S/S mice demonstrated prolonged exploration times and heightened dishabituation responses. Further elucidating the olfactory connection of Unc80 editing, transcriptomic analysis of the olfactory bulb identified significant alterations in gene expression that corroborate the behavioral and physiological findings. Collectively, our research advances the understanding of Unc80's neurophysiological functions and the impact of its editing on the olfactory sensory system, shedding light on the intricate molecular underpinnings of olfactory perception and neuronal activity.

HyperGCN: an effective deep representation learning framework for the integrative analysis of spatial transcriptomics data.

BACKGROUND: Advances of spatial transcriptomics technologies enabled simultaneously profiling gene expression and spatial locations of cells from the same tissue. Computational tools and approaches for integration of transcriptomics data and spatial context information are urgently needed to comprehensively explore the underlying structure patterns. In this manuscript, we propose HyperGCN for the integrative analysis of gene expression and spatial information profiled from the same tissue. HyperGCN enables data visualization and clustering, and facilitates downstream analysis, including domain segmentation, the characterization of marker genes for the specific domain structure and GO enrichment analysis. RESULTS: Extensive experiments are implemented on four real datasets from different tissues (including human dorsolateral prefrontal cortex, human positive breast tumors, mouse brain, mouse olfactory bulb tissue and Zabrafish melanoma) and technologies (including 10X visium, osmFISH, seqFISH+, 10X Xenium and Stereo-seq) with different spatial resolutions. The results show that HyperGCN achieves superior clustering performance and produces good domain segmentation effects while identifies biologically meaningful spatial expression patterns. This study provides a flexible framework to analyze spatial transcriptomics data with high geometric complexity. CONCLUSIONS: HyperGCN is an unsupervised method based on hypergraph induced graph convolutional network, where it assumes that there existed disjoint tissues with high geometric complexity, and models the semantic relationship of cells through hypergraph, which better tackles the high-order interactions of cells and levels of noise in spatial transcriptomics data.

Neuropathological assessment of the olfactory bulb and tract in individuals with COVID-19.

The majority of patients with Parkinson disease (PD) experience a loss in their sense of smell and accumulate insoluble α-synuclein aggregates in their olfactory bulbs (OB). Subjects affected by a SARS-CoV-2-linked illness (COVID-19) also frequently experience hyposmia. We previously postulated that microglial activation as well as α-synuclein and tau misprocessing can occur during host responses following microbial encounters. Using semiquantitative measurements of immunohistochemical signals, we examined OB and olfactory tract specimens collected serially at autopsies between 2020 and 2023. Deceased subjects comprised 50 adults, which included COVID19 + patients (n = 22), individuals with Lewy body disease (e.g., PD; dementia with Lewy bodies (n = 6)), Alzheimer disease (AD; n = 3), and other neurodegenerative disorders (e.g., progressive supranuclear palsy (n = 2); multisystem atrophy (n = 1)). Further, we included neurologically healthy controls (n = 9), and added subjects with an inflammation-rich brain disorder as neurological controls (NCO; n = 7). When probing for microglial and histiocytic reactivity in the anterior olfactory nuclei (AON) by anti-CD68 immunostaining, scores were consistently elevated in NCO and AD cases. In contrast, microglial signals on average were not significantly altered in COVID19 + patients relative to healthy controls, although anti-CD68 reactivity in their OB and tracts declined with progression in age. Mild-to-moderate increases in phospho-α-synuclein and phospho-tau signals were detected in the AON of tauopathy- and synucleinopathy-afflicted brains, respectively, consistent with mixed pathology, as described by others. Lastly, when both sides were available for comparison in our case series, we saw no asymmetry in the degree of pathology of the left versus right OB and tracts. We concluded from our autopsy series that after a fatal course of COVID-19, microscopic changes in the rostral, intracranial portion of the olfactory circuitry -when present- reflected neurodegenerative processes seen elsewhere in the brain. In general, microglial reactivity correlated best with the degree of Alzheimer's-linked tauopathy and declined with progression of age in COVID19 + patients.

A conserved molecular logic for neurogenesis to gliogenesis switch in the cerebral cortex.

During development, neural stem cells in the cerebral cortex, also known as radial glial cells (RGCs), generate excitatory neurons, followed by production of cortical macroglia and inhibitory neurons that migrate to the olfactory bulb (OB). Understanding the mechanisms for this lineage switch is fundamental for unraveling how proper numbers of diverse neuronal and glial cell types are controlled. We and others recently showed that Sonic Hedgehog (Shh) signaling promotes the cortical RGC lineage switch to generate cortical oligodendrocytes and OB interneurons. During this process, cortical RGCs generate intermediate progenitor cells that express critical gliogenesis genes Ascl1, Egfr, and Olig2. The increased Ascl1 expression and appearance of Egfr+ and Olig2+ cortical progenitors are concurrent with the switch from excitatory neurogenesis to gliogenesis and OB interneuron neurogenesis in the cortex. While Shh signaling promotes Olig2 expression in the developing spinal cord, the exact mechanism for this transcriptional regulation is not known. Furthermore, the transcriptional regulation of Olig2 and Egfr has not been explored. Here, we show that in cortical progenitor cells, multiple regulatory programs, including Pax6 and Gli3, prevent precocious expression of Olig2, a gene essential for production of cortical oligodendrocytes and astrocytes. We identify multiple enhancers that control Olig2 expression in cortical progenitors and show that the mechanisms for regulating Olig2 expression are conserved between the mouse and human. Our study reveals evolutionarily conserved regulatory logic controlling the lineage switch of cortical neural stem cells.

Influence of age on nicotinic cholinergic regulation of blood flow in rat's olfactory bulb and neocortex.

The olfactory bulb receives cholinergic basal forebrain inputs as does the neocortex. With a focus on nicotinic acetylcholine receptors (nAChRs), this review article provides an overview and discussion of the following findings: (1) the nAChRs-mediated regulation of regional blood flow in the neocortex and olfactory bulb, (2) the nAChR subtypes that mediate their responses, and (3) their activity in old rats. The activation of the α4ß2-like subtype of nAChRs produces vasodilation in the neocortex, and potentiates olfactory bulb vasodilation induced by olfactory stimulation. The nAChR activity producing neocortical vasodilation was similarly maintained in 2-year-old rats as in adult rats, but was clearly reduced in 3-year-old rats. In contrast, nAChR activity in the olfactory bulb was reduced already in 2-year-old rats. Thus, age-related impairment of α4ß2-like nAChR function may occur earlier in the olfactory bulb than in the neocortex. Given the findings, the vasodilation induced by α4ß2-like nAChR activation may be beneficial for neuroprotection in the neocortex and the olfactory bulb.

IL-6 mediates olfactory dysfunction in a mouse model of allergic rhinitis.

BACKGROUND: Immune-inflammatory response is a key element in the occurrence and development of olfactory dysfunction (OD) in patients with allergic rhinitis (AR). As one of the core factors in immune-inflammatory responses, interleukin (IL)-6 is closely related to the pathogenesis of allergic diseases. It may also play an important role in OD induced by diseases, such as Sjögren's syndrome and coronavirus disease 2019. However, there is no study has reported its role in OD in AR. Thus, this study aimed to investigate the role of IL-6 in AR-related OD, in an attempt to discover a new target for the prevention and treatment of OD in patients with AR. METHODS: Differential expression analysis was performed using the public datasets GSE52804 and GSE140454 for AR, and differentially expressed genes (DEGs) were obtained by obtaining the intersection points between these two datasets. IL-6, a common differential factor, was obtained by intersecting the DEGs with the General Olfactory Sensitivity Database (GOSdb) again. A model of AR mice with OD was developed by sensitizing with ovalbumin (OVA) to verify the reliability of IL-6 as a key factor of OD in AR and explore the potential mechanisms. Furthermore, a supernatant and microglia co-culture model of nasal mucosa epithelial cells stimulated by the allergen house dust mite extract Derp1 was established to identify the cellular and molecular mechanisms of IL-6-mediated OD in AR. RESULTS: The level of IL-6 in the nasal mucosa and olfactory bulb of AR mice with OD significantly increased and showed a positive correlation with the expression of olfactory bulb microglia marker Iba-1 and the severity of OD. In-vitro experiments showed that the level of IL-6 significantly increased in the supernatant after the nasal mucosa epithelial cells were stimulated by Derp1, along with significantly decreased barrier function of the nasal mucosa. The expression levels of neuroinflammatory markers IL-1ß and INOS increased after a conditioned culture of microglia with the supernatant including IL-6. Then knockdown (KD) of IL-6R by small interfering RNA (siRNA), the expression of IL-1ß and INOS significantly diminished. CONCLUSION: IL-6 plays a key role in the occurrence and development of OD in AR, which may be related to its effect on olfactory bulb microglia-mediated neuroinflammation.

Illuminating the terminal nerve: Uncovering the link between GnRH-1 neuron and olfactory development.

During embryonic development, the olfactory placode (OP) generates migratory neurons, including olfactory pioneer neurons, cells of the terminal nerve (TN), gonadotropin-releasing hormone-1 (GnRH-1) neurons, and other uncharacterized neurons. Pioneer neurons from the OP induce olfactory bulb (OB) morphogenesis. In mice, GnRH-1 neurons appear in the olfactory system around mid-gestation and migrate via the TN axons to different brain regions. The GnRH-1 neurons are crucial in controlling the hypothalamic-pituitary-gonadal axis. Kallmann syndrome is characterized by impaired olfactory system development, defective OBs, secretion of GnRH-1, and infertility. The precise mechanistic link between the olfactory system and GnRH-1 development remains unclear. Studies in humans and mice highlight the importance of the prokineticin-2/prokineticin-receptor-2 (Prokr2) signaling pathway in OB morphogenesis and GnRH-1 neuronal migration. Prokr2 loss-of-function mutations can cause Kallmann syndrome (KS), and hence the Prokr2 signaling pathway represents a unique model to decipher the olfactory/GnRH-1 connection. We discovered that Prokr2 is expressed in the TN neurons during the critical period of GnRH-1 neuron formation, migration, and induction of OB morphogenesis. Single-cell RNA sequencing identified that the TN is formed by neurons distinct from the olfactory neurons. The TN neurons express multiple genes associated with KS. Our study suggests that the aberrant development of pioneer/TN neurons might cause the KS spectrum.

A2A adenosine receptor-driven cAMP signaling in olfactory bulb astrocytes is unaffected in experimental autoimmune encephalomyelitis.

Introduction: The cyclic nucleotide cyclic adenosine monophosphate (cAMP) is a ubiquitous second messenger, which is known to play an important anti-inflammatory role. Astrocytes in the central nervous system (CNS) can modulate inflammation but little is known about the significance of cAMP in their function. Methods: We investigated cAMP dynamics in mouse olfactory bulb astrocytes in brain slices prepared from healthy and experimental autoimmune encephalomyelitis (EAE) mice. Results: The purinergic receptor ligands adenosine and adenosine triphosphate (ATP) both induced transient increases in cAMP in astrocytes expressing the genetically encoded cAMP sensor Flamindo2. The A2A receptor antagonist ZM241385 inhibited the responses. Similar transient increases in astrocytic cAMP occurred when olfactory receptor neurons were stimulated electrically, resulting in ATP release from the stimulated axons that increased cAMP, again via A2A receptors. Notably, A2A-mediated responses to ATP and adenosine were not different in EAE mice as compared to healthy mice. Discussion: Our results indicate that ATP, synaptically released by afferent axons in the olfactory bulb, is degraded to adenosine that acts on A2A receptors in astrocytes, thereby increasing the cytosolic cAMP concentration. However, this pathway is not altered in the olfactory bulb of EAE mice.

Olfactory Bulbs in Arthritis Model Mouse Persistently Express Interleukin-6 before the Onset of Arthritis: Relationship to Food Intake.

INTRODUCTION: Rheumatoid arthritis (RA) can be comorbid with psychiatric symptoms. Brain abnormalities in RA patients and in arthritis models have been reported. However, it remains unclear when these abnormalities occur and where they are distributed. In this study, we analyzed spatiotemporal changes in gene expression in the brains of mice with collagen-induced arthritis (CIA). METHODS: Mice were divided into three groups: (i) CIA (all mice developed arthritis on day 35): complete Freund's adjuvant (CFA) and type II collagen at initial immunization, and incomplete Freund's adjuvant (IFA) and type II collagen at booster immunization; (ii) C(+/-) (50% mice developed arthritis on day 35): only IFA at booster immunization; and (iii) C(-/-) (no arthritis): only CFA at initial immunization and only IFA at booster immunization. Whole brains were collected at ten stages of arthritis and divided into six sections. Real-time polymerase chain reaction was performed using RNA extracted from the brain, and the expression of proinflammatory cytokines and glial markers was semi-quantified. Arthritis score, body weight, and food and water intakes were recorded and analyzed for correlations with brain gene expression. We also investigated the effect of interleukin-6 (IL-6) injection in the olfactory bulbs (OBs) on the food intake. RESULTS: After booster immunization, a transient increase in Integrin subunit α-M and IL-1ß was observed in multiple areas in CIA. IL-6 is persistently expressed in the OB before the onset of arthritis, which is correlated with body weight loss and decreased food intake. This change in the OB was observed in the C(+/-) but not in the C(-/-) groups. In the C(+/-) group, non-arthritic mice showed the same changes in the OB as the arthritic mice. This elevation in IL-6 levels persisted throughout the chronic phase until day 84. In addition, IL-6 injection into the OB reduced food intake. CONCLUSION: Persistent elevation of IL-6 in the OB from the early stage of arthritis may be an important finding that might explain the neuropsychiatric pathophysiology of RA, including appetite loss, which is present in the early stages of the disease and manifests as a variety of symptoms over time.

Effects of estradiol on dopaminergic synapse formation in the mouse olfactory bulb.

Olfactory glomeruli are the sites of initial synaptic integration in olfactory information processing. They are surrounded by juxtaglomerular (JG) cells, which include periglomerular, superficial short axon, and external tufted cells. A subpopulation of JG cells expresses the dopamine synthetic enzymes, tyrosine hydroxylase (TH), and aromatic l-amino acid decarboxylase (AADC). TH cells corelease γ-aminobutyric acid (GABA) and their processes extend to multiple glomeruli forming intra- and interglomerular circuits. It is well established that 17ß-estradiol (E2) exerts wide ranging effects in the central nervous system. However, participation of E2 in the modulation of neurotransmission and synaptic plasticity of TH cells in olfactory glomeruli is unknown. To address this, we subcutaneously implanted a 60-day release pellet of E2 or placebo into intact male mice and compared glomerular TH, AADC, and vesicular γ-aminobutyric acid transporter (VGAT) immunoreactivity between them. High-voltage electron microscopy (HVEM) and ultra-HVEM using immunogold revealed significantly increased immunoreactive intensity at the cellular level for TH and AADC after E2 treatment and for VGAT in TH cells. These results indicate that E2 may affect the interplay between dopaminergic and GABAergic systems. Moreover, random-section electron microscopy analysis showed a significant increase in the number of symmetrical synapses from TH cell to mitral/tufted cell dendrites after E2 treatment. This result was supported by quantitative immunofluorescence staining with synapse markers. Together, these data indicate that E2 may regulate inhibition between TH cells and olfactory bulb neurons within the glomerulus via interaction between dopaminergic and GABAergic systems, thereby contributing to neuromodulation of odor information processing.

Development of a novel peptide to prevent entry of SARS-CoV-2 into lung and olfactory bulb cells of hACE2 expressing mice.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus that has caused a global pandemic Coronavirus Disease 2019 (COVID-19). Currently, there are no effective treatments specifically for COVID-19 infection. The initial step in SARS-CoV-2 infection is attachment to the angiotensin-converting enzyme 2 (ACE2) on the cell surface. We have developed a protein peptide that effectively disrupts the binding between the SARS-CoV-2 spike protein and ACE2. When delivered by nasal spray, our peptide prevents SARS-CoV-2 spike protein from entering lung and olfactory bulb cells of mice expressing human ACE2. Our peptide represents a potential novel treatment and prophylaxis against COVID-19.

Olfactory Bulb Amyloid-ß Correlates With Brain Thal Amyloid Phase and Severity of Cognitive Impairment.

The Alzheimer disease (AD) neuropathological hallmarks amyloid ß (Aß) and tau neurofibrillary (NF) pathology have been reported in the olfactory bulb (OB) in aging and in different neurodegenerative diseases, which coincides with frequently reported olfactory dysfunction in these conditions. To better understand when the OB is affected in relation to the hierarchical progression of Aß throughout the brain and whether OB pathology might be an indicator of AD severity, we assessed the presence of OB Aß and tau NF pathology in an autopsy cohort of 158 non demented control and 173 AD dementia cases. OB Aß was found in less than 5% of cases in lower Thal phases 0 and 1, in 20% of cases in phase 2, in 60% of cases in phase 3 and in more than 80% of cases in higher Thal phases 4 and 5. OB Aß and tau pathology significantly predicted a Thal phase greater than 3, a Braak NF stage greater than 4, and an MMSE score lower than 24. While OB tau pathology is almost universal in the elderly and therefore is not a good predictor of AD severity, OB Aß pathology coincides with clinically-manifest AD and might prove to be a useful biomarker of the extent of brain spread of both amyloid and tau pathology.

The oxygen initial dip in the brain of anesthetized and awake mice.

An ongoing controversy in brain metabolism is whether increases in neural activity cause a local and rapid decrease in oxygen concentration (i.e., the "initial dip") preceding functional hyperemia. This initial dip has been suggested to cause a transient increase in vascular deoxyhemoglobin with several imaging techniques and stimulation paradigms, but not consistently. Here, we investigate contributors to this initial dip in a distinct neuronal network, an olfactory bulb (OB) glomerulus most sensitive to a specific odorant (ethyl tiglate [ET]) and a site of strong activation and energy consumption upon ET stimulation. Combining two-photon fluorescence and phosphorescence lifetime microscopy, and calcium, blood flow, and pO2 measurements, we characterized this initial dip in pO2 in mice chronically implanted with a glass cranial window, during both awake and anesthetized conditions. In anesthetized mice, a transient dip in vascular pO2 was detected in this glomerulus when functional hyperemia was slightly delayed, but its amplitude was minute (0.3 SD of resting baseline). This vascular pO2 dip was not observed in other glomeruli responding nonspecifically to ET, and it was poorly influenced by resting pO2. In awake mice, the dip in pO2 was absent in capillaries as well as, surprisingly, in the neuropil. These high-resolution pO2 measurements demonstrate that in awake mice recovered from brain surgery, neurovascular coupling was too fast and efficient to reveal an initial dip in pO2.

Antidepressant effects of Enterococcus faecalis 2001 through the regulation of prefrontal cortical myelination via the enhancement of CREB/BDNF and NF-κB p65/LIF/STAT3 pathways in olfactory bulbectomized mice.

A therapeutic strategy through the gut-brain axis has been proven to be effective in treatment for depression. In our previous study, we demonstrated that Enterococcus faecalis 2001 (EF-2001) prevents colitis-induced depressive-like behavior through the gut-brain axis in mice. More recently, we found that demyelination in the prefrontal cortex (PFC) was associated with depressive-like behavior in an animal model of major depressive disorder, olfactory bulbectomized (OBX) mice. The present study investigated the effects of EF-2001 on depressive-like behaviors in OBX mice and the underlying molecular mechanisms from the perspective of myelination in the PFC. OBX mice exhibited depressive-like behaviors in the tail-suspension, splash, and sucrose preference tests, and decreased myelin and paranodal proteins along with mature oligodendrocytes in the PFC. These behavioral and biochemical changes were all prevented by treatment with EF-2001. Further, EF-2001 treatment increased brain-derived neurotrophic factor (BDNF) and leukemia inhibitory factor (LIF) in the PFC. Interestingly, an immunohistochemical analysis revealed enhanced phospho (p) -cAMP-responsive element binding protein (CREB) expression in neurons, p-nuclear factor-kappa B (NFκB) p65 (Ser536) expression in astrocytes, and p-signal transducer and activator of transcription 3 (STAT3) (Ty705) expression in mature oligodendrocytes in the PFC of OBX mice. From these results, we suggest that EF-2001 administration prevents depressive-like behaviors by regulating prefrontal cortical myelination via the enhancement of CREB/BDNF and NFκB p65/LIF/STAT3 pathways. Our findings strongly support the idea that a therapeutic strategy involving the gut microbiota may be a promising alternative treatment for alleviating symptoms of depression.

Immunological status of the olfactory bulb in a murine model of Toll-like receptor 3-mediated upper respiratory tract inflammation.

BACKGROUND: Postviral olfactory dysfunction (PVOD) following a viral upper respiratory tract infection (URI) is one of the most common causes of olfactory disorders, often lasting for over a year. To date, the molecular pathology of PVOD has not been elucidated. METHODS: A murine model of Toll-like receptor 3 (TLR3)-mediated upper respiratory tract inflammation was used to investigate the impact of URIs on the olfactory system. Inflammation was induced via the intranasal administration of polyinosinic-polycytidylic acid (poly(I:C), a TLR3 ligand) to the right nostril for 3 days. Peripheral olfactory sensory neurons (OSNs), immune cells in the olfactory mucosa, and glial cells in the olfactory bulb (OB) were analyzed histologically. Proinflammatory cytokines in the nasal tissue and OB were evaluated using the quantitative real-time polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA). RESULTS: In the treated mice, OSNs were markedly reduced in the olfactory mucosa, and T cell and neutrophil infiltration therein was observed 1 day after the end of poly(I:C) administration. Moreover, there was a considerable increase in microglial cells and slight increase in activated astrocytes in the OB. In addition, qPCR and ELISA revealed the elevated expression of interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha, and interferon-gamma both in the OB and nasal tissue. CONCLUSIONS: Taken together, the decreased peripheral OSNs, OB microgliosis, and elevated proinflammatory cytokines suggest that immunological changes in the OB may be involved in the pathogenesis of PVOD.

Function of Oncogene Mycn in Adult Neurogenesis and Oligodendrogenesis.

Human MYCN is an oncogene amplified in neuroblastoma and many other tumors. Both human MYCN and mouse Mycn genes are important in embryonic brain development, but their functions in adult healthy nerve system are completely unknown. Here, with Mycn-eGFP mice and quantitative RT-PCR, we found that Mycn was expressed in specific brain regions of young adult mice, including subventricular zone (SVZ), subgranular zone (SGZ), olfactory bulb (OB), subcallosal zone (SCZ), and corpus callosum (CC). With immunohistochemistry (IHC), we found that many Mycn-expressing cells expressed neuroblast marker doublecortin (DCX) and proliferation marker Ki67. With Dcx-creER and Mki67-creER mouse lines, we fate mapped Dcx-expressing neuroblasts and Mki67-expressing proliferation cells, along with deleting Mycn from these cells in adult mice. We found that knocking out Mycn from adult neuroblasts or proliferating cells significantly reduced cells in proliferation in SVZ, SGZ, OB, SCZ, and CC. We also demonstrated that the Mycn-deficient neuroblasts in SGZ matured quicker than wild-type neuroblasts, and that Mycn-deficient proliferating cells were more likely to survive in SVZ, SGZ, OB, SCZ, and CC compared to wild type. Thus, our results demonstrate that, in addition to causing tumors in the nervous system, oncogene Mycn has a crucial function in neurogenesis and oligodendrogenesis in adult healthy brain.

A sex-specific feedback projection from aromatase-expressing neurons in the medial amygdala to the accessory olfactory bulb.

The accessory olfactory bulb (AOB) plays a critical role in classifying pheromonal signals. Here we identify two previously undescribed sources of aromatase signaling in the AOB: (1) a population of aromatase-expressing neurons in the AOB itself; (2) a tract of aromatase-expressing axons which originate in the ventral medial amygdala (MEA) and terminate in the AOB. Using a retrograde tracer in conjunction with a transgenic strategy to label aromatase-expressing neurons throughout the brain, we found that a single contiguous population of neurons in the ventral MEA provides the only significant feedback by aromatase-expressing neurons to the AOB. This population expresses the estrogen receptor alpha (ERα) and displayed anatomical sex differences in the number of neurons (higher in male mice) and the size of cell bodies (larger in females). Given the previously established relationship between aromatase expression, estrogen signaling, and the function of sexually dimorphic circuits, we suggest that this feedback population is well-positioned to provide neuroendocrine feedback to modulate sensory processing of social stimuli in the AOB.

Gestational stress alters maternal behavior and inflammatory markers in the olfactory bulb of lactating mice.

Inflammatory markers represent important candidates responsible for the altered behavior and physiology observed after stressful experiences. In the maternal brain, the olfactory bulb (OB) is a key constituent of the neural circuit that mediates the reciprocal interaction between mother and infant. This study aimed to investigate the effects of stress during pregnancy on maternal behavior and inflammatory changes in the olfactory bulb of lactating mice. Female Balb/c mice were divided into two groups: control (CT) and restraint stress (RS). Maternal behavior was performed during the first 8 days of life of the offspring. On the 10th day after parturition, corticosterone, gene, and protein expression were assessed. Stress during pregnancy decreased the maternal index at postnatal day 4 and the nuclear factor-κB 1 (NFκB1) gene expression in the OB. Moreover, females from the RS group showed increased interleukin (IL-1ß) protein expression. In contrast, stressed females exhibited a decreased tumor necrosis factor (TNF-α) protein expression in the OB. In conclusion, exposure to stress during pregnancy was able to induce specific postnatal effects on maternal behavior and balance of inflammatory mediators in the OB.

Adenosine A2A receptor neurons in the olfactory bulb mediate odor-guided behaviors in mice.

Depression, rapid eye movement (REM) sleep behavior disorder, and altered olfaction are often present in Parkinson's disease. Our previous studies demonstrated the role of the olfactory bulb (OB) in causing REM sleep disturbances in depression. Furthermore, adenosine A2A receptors (A2AR) which are richly expressed in the OB, play an important role in the regulation of REM sleep. Caffeine, an adenosine A1 receptors and A2AR antagonist, and other A2AR antagonists were reported to improve olfactory function and restore age-related olfactory deficits. Therefore, we hypothesized that the A2AR neurons in the OB may regulate olfaction or odor-guided behaviors in mice. In the present study, we employed chemogenetics to specifically activate or inhibit neuronal activity. Then, buried food test and olfactory habituation/dishabituation test were performed to measure the changes in the mice's olfactory ability. We demonstrated that activation of OB neurons or OB A2AR neurons shortened the latency of buried food test and enhanced olfactory habituation to the same odors and dishabituation to different odors; inhibition of these neurons showed the opposite effects. Photostimulation of ChR2-expressing OB A2AR neuron terminals evoked inward current in the olfactory tubercle (OT) and the piriform cortex (Pir), which was blocked by glutamate receptor antagonists 2-amino-5-phosphonopentanoic acid and 6-cyano-7nitroquinoxaline-2,3-dione. Collectively, these results suggest that the OB mediates olfaction via A2AR neurons in mice. Moreover, the excitatory glutamatergic release from OB neurons to the OT and the Pir were found responsible for the olfaction-mediated effects of OB A2AR neurons.

SPARK-X: non-parametric modeling enables scalable and robust detection of spatial expression patterns for large spatial transcriptomic studies.

Spatial transcriptomic studies are becoming increasingly common and large, posing important statistical and computational challenges for many analytic tasks. Here, we present SPARK-X, a non-parametric method for rapid and effective detection of spatially expressed genes in large spatial transcriptomic studies. SPARK-X not only produces effective type I error control and high power but also brings orders of magnitude computational savings. We apply SPARK-X to analyze three large datasets, one of which is only analyzable by SPARK-X. In these data, SPARK-X identifies many spatially expressed genes including those that are spatially expressed within the same cell type, revealing new biological insights.