The olfactory network of larval Xenopus laevis regenerates accurately after olfactory nerve transection.

Across vertebrate species, the olfactory epithelium (OE) exhibits the uncommon feature of lifelong neuronal turnover. Epithelial stem cells give rise to new neurons that can adequately replace dying olfactory receptor neurons (ORNs) during developmental and adult phases and after lesions. To relay olfactory information from the environment to the brain, the axons of the renewed ORNs must reconnect with the olfactory bulb (OB). In Xenopus laevis larvae, we have previously shown that this process occurs between 3 and 7 weeks after olfactory nerve (ON) transection. In the present study, we show that after 7 weeks of recovery from ON transection, two functionally and spatially distinct glomerular clusters are reformed in the OB, akin to those found in non-transected larvae. We also show that the same odourant response tuning profiles observed in the OB of non-transected larvae are again present after 7 weeks of recovery. Next, we show that characteristic odour-guided behaviour disappears after ON transection but recovers after 7-9 weeks of recovery. Together, our findings demonstrate that the olfactory system of larval X. laevis regenerates with high accuracy after ON transection, leading to the recovery of odour-guided behaviour.

High-dose IgG suppresses local inflammation and facilitates functional recovery after olfactory system injury.

OBJECTIVE: Head trauma can be a cause of refractory olfactory dysfunction due to olfactory nervous system injury. Anti-inflammatory treatment using steroids or anti-cytokine agents is known to contribute to functional recovery of the central and peripheral nervous systems in injury models, while there is a concern that they can induce adverse reactions. The present study examines if high-dose immunoglobulin G (IgG) can facilitate olfactory functional recovery following injury. METHODS: Olfactory nerve transection (NTx) was performed in OMP-tau-lacZ mice to establish injury models. High-dose IgG was intraperitoneally injected immediately after the NTx and histological assessment of recovery within the olfactory bulb was performed at 5, 14, 42, and 100 days after the drug injection. X-gal staining labeled degenerating and regenerating olfactory nerve fibers and immunohistochemical staining detected the presence of reactive astrocytes and macrophages/microglia. Olfactory function was assessed using an olfactory avoidance behavioral test. RESULTS: High-dose IgG-injected mice showed significantly smaller areas of injury-associated tissue, fewer astrocytes and macrophages/microglia, and an increase in regenerating nerve fibers. An olfactory avoidance behavioral test showed improved functional recovery in the IgG-injected mice. INTERPRETATION: These findings suggest that high-dose IgG could provide a new therapeutic strategy for the treatment of olfactory dysfunction following head injuries.

Neuroinvasive potential of SARS-CoV2 with neuroradiological and neuropathological findings: is the brain a target or a victim?

Coronaviridae family includes pathogen viruses for humans, that lead to clinical conditions with main respiratory involvement; many of these viruses have notoriously a neuroinvasive potential, as demonstrated by published data on SARS-CoV and MERS-CoV epidemics, as well by results obtained in experimental models. During pandemic of coronavirus disease 2019 (COVID-19), it is noticed that the central nervous system involvement represented a truly significant moment in the history of some COVID-19 patients; indeed, clinical and radiological features published in literature regarding COVID-19 disease are consistent with a neurological involvement. It is also known that histopathological data related to SARS-CoV2 infection have been published with considerable delay, which was even greater for neuropathological information. Moreover, many published data are incomplete, and often the lesions described are not directly related to the action of the virus. In this review, we collected the available radiological and neuropathological information, in order to delineate a more complete picture of the relationship between SARS-Cov2 and brain, focusing our attention on the two most important neuroinvasion routes for the virus. We also highlighted what we consider methodological mistakes both in the autopsy procedures and brain study in COVID-19 deaths. We emphasize the need for a complete study of all the organs in case of autopsy. It is important that through this experience, we no longer do the mistake of neglecting the brain.

[Using of ¹8F-FDG to evaluate the effect of traumatic olfactory nerve injury on drug delivery through the nasal-brain pathway: a PET-MRI pilot study].

Objective:This study evaluated the effect of traumatic olfactory nerve injury on drug delivery through the nasal-brain pathway via the instillation of ¹8F-FDG at the olfactory cleft. Method:Seven healthy volunteers and 5 patients with traumatic dysosmia were enrolled in the study. Subjects were all instilled with ¹8F-FDG on each side of the olfactory cleft under endoscopy. After 12 hours, a PET/MR scan was performed to track the metabolism pathway of ¹8F-FDG. Then, we compared the diameter of the olfactory bulb and the olfactory bulb intake between normal volunteers and patients with traumatic olfactory disorders. Result:In healthy volunteers, there was a significant difference in ¹8F-FDG uptake between the regions of interest in which ¹8F-FDG was or was not in contact with the cribriform plate（P=0.012 7）; this difference also existed in patients with traumatic olfactory disorders（P=0.038 1）. Patients with traumatic olfactory disorders did not exhibit significant differences in ¹8F-FDG uptake in the region of interest compared with healthy volunteers（P=0.937 2）. Conclusion:The olfactory bulb is obviously atrophied in patients with traumatic olfactory dysfunction, and the uptake of ¹8F-FDG in the olfactory bulb region of interest is also reduced. The administration of ¹8F-FDG via olfactory fissure area can enter olfactory bulb and parafrontal tissues through the nasal brain pathway,¹8F-FDG can enter the central nervous system through the nasal-brain pathway, which is not affected by olfactory nerve transection injury.

Anti-high mobility group box 1 antibody suppresses local inflammatory reaction and facilitates olfactory nerve recovery following injury.

BACKGROUND: Refractory olfactory dysfunction is a common finding in head trauma due to olfactory nerve injury. Anti-inflammatory treatment using steroids is known to contribute to functional recovery of the central and peripheral nervous systems in injury models, while there is a concern that steroids can induce side effects. The present study examines if the inhibition of proinflammatory cytokine, high mobility group box 1 (HMGB1), can facilitate olfactory functional recovery following injury. METHODS: Olfactory nerve transection (NTx) was performed in OMP-tau-lacZ mice to establish injury models. We measured HMGB1 gene expression in the olfactory bulb using semi-quantitative polymerase chain reaction (PCR) assays and examined HMGB1 protein localization in the olfactory bulb using immunohistochemical staining. Anti-HMGB1 antibody was intraperitoneally injected immediately after the NTx and histological assessment of recovery within the olfactory bulb was performed at 5, 14, 42, and 100 days after the drug injection. X-gal staining labeled OMP in the degenerating and regenerating olfactory nerve fibers, and immunohistochemical staining detected the presence of reactive astrocytes and macrophages/microglia. Olfactory function was assessed using both an olfactory avoidance behavioral test and evoked potential recording. RESULTS: HMGB1 gene and protein were significantly expressed in the olfactory bulb 12 h after NTx. Anti-HMGB1 antibody-injected mice showed significantly smaller areas of injury-associated tissue, fewer astrocytes and macrophages/microglia and an increase in regenerating nerve fibers. Both an olfactory avoidance behavioral test and evoked potential recordings showed improved functional recovery in the anti-HMGB1 antibody-injected mice. CONCLUSIONS: These findings suggest that inhibition of HMGB1 could provide a new therapeutic strategy for the treatment of olfactory dysfunction following head injuries.

A Time Limit for Initiating Anti-Inflammatory Treatment for Improved Olfactory Function after Head Injury.

We previously reported that treatment with an anti-inflammatory drug, specifically a steroid, is effective in improving recovery during the acute phase of head injury. Clinically, however, patients with head injury usually become aware of their olfactory loss several weeks or months after the injury, which may be a critical factor in poor recovery from olfactory dysfunction. This raises an important question: When should steroid administration begin in order to achieve optimum improvement of olfactory dysfunction? The present study was designed to reveal the time limit for starting anti-inflammatory treatment for better improvement of post-traumatic olfactory dysfunction. Olfactory nerve transection (NTx) was performed in olfactory marker protein (OMP)-tau-lacZ mice and subcutaneous injections of dexamethasone sodium phosphate for 5 consecutive days was started at 7, 14, 28, and 42 days after the NTx (7-, 14-, 28-, and 42-day time-points). Histological assessment of olfactory nerve recovery in the olfactory bulb was made at 5, 14, and 42 days after the start of drug treatment. Olfactory function assessments using both an olfactory avoidance behavioral test and evoked potential testing also were performed. Animals treated at 7 days post-injury had less injury-associated tissue with fewer astrocytes and macrophages and better histological and functional nerve recovery, compared with control mice. However, those treated at 14, 28, or 42 days post-injury did not show significant histological or functional differences between saline control and treatment groups. These findings suggest that an anti-inflammatory treatment using steroids for traumatic olfactory dysfunction may be effective if started at least by 7 days, but may be ineffective at 14 days or later after head injury.

Tight temporal coupling between synaptic rewiring of olfactory glomeruli and the emergence of odor-guided behavior in Xenopus tadpoles.

Olfactory sensory neurons (OSNs) are chemoreceptors that establish excitatory synapses within glomeruli of the olfactory bulb. OSNs undergo continuous turnover throughout life, causing the constant replacement of their synaptic contacts. Using Xenopus tadpoles as an experimental system to investigate rewiring of glomerular connectivity, we show that novel OSN synapses can transfer information immediately after formation, mediating olfactory-guided behavior. Tadpoles recover the ability to detect amino acids 4 days after bilateral olfactory nerve transection. Restoration of olfactory-guided behavior depends on the efficient reinsertion of OSNs to the olfactory bulb. Presynaptic terminals of incipient synaptic contacts generate calcium transients in response to odors, triggering long lasting depolarization of olfactory glomeruli. The functionality of reconnected terminals relies on well-defined readily releasable and cytoplasmic vesicle pools. The continuous growth of non-compartmentalized axonal processes provides a vesicle reservoir to nascent release sites, which contrasts to the gradual development of cytoplasmic vesicle pools in conventional excitatory synapses. The immediate availability of fully functional synapses upon formation supports an age-independent contribution of OSNs to the generation of odor maps.

Neuronal degeneration and regeneration induced by axotomy in the olfactory epithelium of Xenopus laevis.

The olfactory epithelium (OE) has the remarkable capability to constantly replace olfactory receptor neurons (ORNs) due to the presence of neural stem cells (NSCs). For this reason, the OE provides an excellent model to study neurogenesis and neuronal differentiation. In the present work, we induced neuronal degeneration in the OE of Xenopus laevis larvae by bilateral axotomy of the olfactory nerves. We found that axotomy induces specific- neuronal death through apoptosis between 24 and 48h post-injury. In concordance, there was a progressive decrease of the mature-ORN marker OMP until it was completely absent 72h post-injury. On the other hand, neurogenesis was evident 48h post-injury by an increase in the number of proliferating basal cells as well as NCAM-180- GAP-43+ immature neurons. Mature ORNs were replenished 21 days post-injury and the olfactory function was partially recovered, indicating that new ORNs were integrated into the olfactory bulb glomeruli. Throughout the regenerative process no changes in the expression pattern of the neurotrophin Brain Derivate Neurotrophic Factor were observed. Taken together, this work provides a sequential analysis of the neurodegenerative and subsequent regenerative processes that take place in the OE following axotomy. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1308-1320, 2017.

Tumor necrosis factor-α antagonist suppresses local inflammatory reaction and facilitates olfactory nerve recovery following injury.

OBJECTIVE: Olfactory dysfunction is a common finding in head trauma due to injury to the olfactory nerve. We previously reported that anti-inflammatory treatment with steroids improves recovery outcome in olfactory nerve injury models. Clinically, however, steroid administration is not recommended in the acute phase of head injury cases because of concerns regarding its side effects. Tumor necrosis factor (TNF-α) is known to play a key role in inflammatory response to injury. The present study examines if the inhibition of TNF-α can facilitate functional recovery in the olfactory system following injury. MATERIALS AND METHODS: Olfactory nerve transection (NTx) was performed in olfactory marker protein (OMP-tau-lacZ) mice to establish injury models. We measured TNF-α gene expression in the olfactory bulb using semi-quantitative and real time polymerase chain reaction (PCR) assays and found that they increase within hours after NTx injury. A TNF-α antagonist (etanercept) was intraperitoneally injected immediately after the NTx and histological assessment of recovery within the olfactory bulb was performed at 5-70 days. X-gal staining labeled OMP in the degenerating and regenerating olfactory nerve fibers, and immunohistochemical staining detected the presence of reactive astrocytes and macrophages/microglia. RESULTS: Etanercept-injected mice showed significantly smaller areas of injury-associated tissue, fewer astrocytes and macrophages/microglia, and an increase in regenerating nerve fibers. Olfactory function assessments using both an olfactory avoidance behavioral test and evoked potential recordings showed improved functional recovery in etanercept-injected animals. CONCLUSION: These findings suggest that inhibition of TNF-α could provide a new therapeutic strategy for the treatment of olfactory dysfunction following head injuries.

Regeneration and rewiring of rodent olfactory sensory neurons.

The olfactory sensory neurons are the only neurons in the mammalian nervous system that not only regenerate naturally and in response to injury, but also project to specific targets in the brain. The stem cells in the olfactory epithelium commit to both neuronal and non-neuronal lineages depending on the environmental conditions. They provide a continuous supply of new neurons. A newly generated neuron must express a specific odorant receptor gene and project to a central target consist of axons expressing the same receptor type. Recent studies have provided insights into this highly regulated, complex process. However, the molecular mechanisms that determine the regenerative capacity of stem cells, and the ability of newly generated neurons in directing their axons toward specific targets, remain elusive. Here we review progresses and controversies in the field and offer testable models.

Posttraumatic olfactory dysfunction.

Impairment of smell may occur following injury to any portion of the olfactory tract, from nasal cavity to brain. A thorough understanding of the anatomy and pathophysiology combined with comprehensively obtained history, physical exam, olfactory testing, and neuroimaging may help to identify the mechanism of dysfunction and suggest possible treatments. Although most olfactory deficits are neuronal mediated and therefore currently unable to be corrected, promising technology may provide novel treatment options for those most affected. Until that day, patient counseling with compensatory strategies and reassurance is essential for the maintenance of safety and QoL in this unique and challenging patient population.

Olfactory preservation during anterior interhemispheric approach for anterior skull base lesions: technical note.

Anosmia is not a rare complication of surgeries that employ the anterior interhemispheric approach. Here, we present a fibrin-gelatin fixation method that provides reinforcement and moisture to help preserve the olfactory nerve when using the anterior interhemispheric approach and describe the results and outcomes of this technique. We analyze the outcomes with this technique in 45 patients who undergo surgery for aneurysms, brain tumors, or other pathologies via the anterior interhemispheric approach. Anosmia occurred in 4 patients (8.8%); it was transient in 2 (4.4%) and permanent in the remaining 2 (4.4%). Brain tumors clearly attached to the olfactory nerve were resected in the patients with permanent anosmia. We found a significant difference in the presence of anosmia between patients with or without lesions that were attaching the olfactory nerve (p = 0.011). Our results suggested that fibrin-gelatin fixation method can reduce the reported risk of anosmia. However, the possibility of olfactory nerve damage is relatively high when operating on brain tumors attaching olfactory nerve.

Mechanisms Involved in Guiding the Preference for Fat Emulsion Differ Depending on the Concentration.

High-fat foods tend to be palatable and can cause addiction in mice via a reinforcing effect. However, mice showed preference for low fat concentrations that do not elicit a reinforcing effect in a two-bottle choice test with water as the alternative. This behavior indicates the possibility that the mechanism underlying fat palatability may differ depending on the dietary fat content. To address this issue, we examined the influences of the opioid system and olfactory and gustatory transductions on the intake and reinforcing effects of various concentrations of a dietary fat emulsion (Intralipid). We found that the intake and reinforcing effects of fat emulsion were reduced by the administration of an opioid receptor antagonist (naltrexone). Furthermore, the action of naltrexone was only observed at higher concentrations of fat emulsion. The intake and the reinforcing effects of fat emulsion were also reduced by olfactory and glossopharyngeal nerve transections (designated ONX and GLX, respectively). In contrast to naltrexone, the effects of ONX and GLX were mainly observed at lower concentrations of fat emulsion. These results imply that the opioid system seems to have a greater role in determining the palatability of high-fat foods unlike the contribution of olfactory and glossopharyngeal nerves.

Lesões olfatórias pós-traumáticas / Post traumatic olfactory lesions

OBJETIVO: Documentar a incidência de lesões traumáticas do nervo olfatório, assim como a etiologia traumática; correlacionar as lesões do nervo olfatório com achados radiológicos (lesões cranianas e intracranianas) e estudar lesões múltiplas de nervos cranianos. MÉTODOS: Vinte e quatro pacientes admitidos no Serviço de Emergência da Santa Casa de Misericórdia de São Paulo com lesão traumática do nervo olfatório foram incluídos. Os pacientes foram divididos em três grupos, de acordo com o escore da escala de coma de Glasgow (ECG): trauma leve (ECG de 13 a 15), moderado (ECG de 9 a 12) e grave (ECG de 3 a 8), assim como em diferentes graus de lesão do olfatório, como hiposmia, anosmia e parosmia, distribuição quanto a gênero, presença de fraturas, lesões intracranianas, fístulas liquóricas e mecanismo de trauma. RESULTADOS: Dos 24 casos, 15 lesões ocorreram em conjunto com outros nervos cranianos e em nove casos houve lesão exclusiva do nervo olfatório. O atropelamento foi a causa mais comum de lesão do nervo olfatório de forma isolada, assim como nas lesões de múltiplos nervos. Hematomas extradurais foram as lesões intracranianas mais frequentes e a ausência de fraturas predominou nos indivíduos estudados. CONCLUSÃO: Neuropatia traumática do olfatório deve ser pesquisada na admissão do paciente (quando possível), sobretudo quando houver evidência de traumas frontais ou occipitais.

OBJECTIVE: To register the incidence of the traumatic lesions to the cranial nerves and its etiology; to correlate the lesions to the radiological ndings (cranial and intracranial) and study multiple cranial nerve lesions. METHODS: Fifty-four patients admitted to the Emergency Service of Santa Casa de Misericórdia de São Paulo Hospital have been studied and lesions to the different cranial nerves were described. All patients were submitted do radiographic exams, computed tomography, and, when necessary, magnetic resonance imaging. The patients were divided into 3 groups according to the Glasgow Coma Scale (GCS) in: mild trauma (GCS: 13 to 15), moderate (GCS: 9 to 12) and severe (GCS: 3 to 8). RESULTS: Posttraumatic single nerve lesion was more frequent seen on olfactory, facial and oculomotor nerves.Running over was the main cause of these lesions (single nerve and multiple nerves). Contusions and extradural hematomas were the most frequent intracranial lesions. CONCLUSION: Traumatic cranial neuropathy occurs frequently and must be searched on the patient admission, because it can surgical decompression may necessary, such as decompression of the optic or facial nerves.

Blockade of interleukin-6 receptor suppresses inflammatory reaction and facilitates functional recovery following olfactory system injury.

We previously reported that anti-inflammatory treatment with steroids improves recovery outcome in an olfactory nerve injury model. Clinically, however, steroid administration is not recommended in the acute phase of head injury because of concerns regarding side effects and no evidence of its efficacy. Recently, it has been reported that interleukin-6 (IL-6) plays an important role in the inflammatory reaction. The present study investigates if anti-IL-6 receptor (IL-6R) antibody can facilitate functional recovery in the olfactory system following injury. Rat anti-mouse IL-6R antibody (MR16-1) was intraperitoneally injected to severe olfactory nerve injury model mice immediately after the nerve transection (NTx). Histological assessment of recovery within the olfactory bulb was made at 5-70 days. X-gal staining labeled the degenerating and regenerating olfactory nerve fibers and immunohistochemical staining detected the presence of reactive astrocytes and macrophages/microglia. MR16-1-injected animals showed significantly smaller areas of injury-associated tissue, fewer astrocytes and macrophages/microglia, and an increase in regenerating nerve fibers. Olfactory function assessments using both an olfactory avoidance behavioral test and evoked potential testing showed improved functional recovery in MR16-1-injected mice. These findings suggest that blockade of IL-6R could provide a new therapeutic strategy for the treatment of olfactory dysfunction following head injuries.

[Clinical diagnosis of the olfactory nerve transport function].

Nasal administration of macromolecular drugs (peptides, nanoparticles) has a possibility to enable a drug delivery system beyond the blood brain barrier via olfactory nerve transport. Basic research on nasal drug delivery to the brain has been well studied. However, evaluation of the olfactory nerve transport function in patients with olfactory disorders has yet to be done, although such an evaluation is important in selecting candidates for clinical trials. Current olfactory function tests are useful for the analysis of olfactory thresholds in olfaction-impaired patients. However, the usefulness of using the increase in olfactory thresholds in patients as an index for evaluating olfactory nerve damage has not been confirmed because of the difficulty in directly evaluating the viability of the peripheral olfactory nerves. Nasally administered thallium-201 migrates to the olfactory bulb, as has been shown in healthy volunteers. Furthermore, transection of olfactory nerve fibers in mice significantly decreases migration of nasally administered thallium-201 to the olfactory bulb. The migration of thallium-201 to the olfactory bulb is reduced in patients with impaired olfaction due to head trauma, upper respiratory tract infections, and chronic rhinosinusitis, relative to the values in healthy volunteers. Nasally administrating thallium-201 followed by single photon emission computed tomography, X-ray computed tomography and magnetic resonance imaging might be useful in choosing candidates for clinical trials of nasal drug delivery methods to the brain.

Intranasal trigeminal chemosensitivity in patients with postviral and post-traumatic olfactory dysfunction.

CONCLUSIONS: The olfactory and intranasal trigeminal systems are closely connected. With regard to intranasal trigeminal event-related potential (ERP), patients with olfactory dysfunction (OD) showed longer latency and lower amplitude, which indicated decreased trigeminal sensitivity. Different age, etiology, and olfactory status also affect trigeminal sensitivity differently. OBJECTIVE: OD is a common symptom in the rhinology clinic. ERP is considered an important method to evaluate chemosensitivity. The aim of this study was to investigate changes of intranasal trigeminal sense in patients with postviral OD (PVOD) and post-traumatic OD (PTOD). METHODS: A total of 96 participants (30 healthy adults and 66 patients with OD) aged 20-65 years were investigated. The T&T olfactometer, the Sniffin' Sticks olfactory test, and trigeminal ERPs (tERPs) were used. We evaluated trigeminal sensitivity influenced by different factors (age, etiology, and olfactory status) in healthy subjects with normal olfactory function and in patients with PVOD and PTOD. RESULTS: Patients with OD showed higher trigeminal thresholds than normal controls. Compared with controls, N1/P2 latencies of tERPs increased and amplitudes decreased in patients with OD. Older subjects showed longer latencies and lower amplitudes than young subjects in both controls and the OD group. Patients with PTOD exhibited worse psychophysical olfactory function and decreased trigeminal sensitivity.

Strength testing of the human olfactory nerve at the frontal skull base.

Olfactory dysfunction may influence the quality of life tremendously. This study investigated the strength of the human olfactory nerve at the frontal skull base using cadavers. A total of 180 olfactory nerves were examined in 90 human cadaveric heads. The cut edges of the olfactory nerves were pulled until they were pulled out from the skull base. In the first set of 30 cases, each right olfactory nerve was pulled 0° laterally and 0° upward, and each left olfactory nerve was pulled 0° laterally and 15° upward. In the second set of 30 cases, each right olfactory nerve was pulled 0° laterally and 15° upward, and each left olfactory nerve was pulled 15° laterally and 15° upward. In the third set of 30 cases, each right olfactory nerve was pulled 15° laterally and 15° upward, and each left olfactory nerve was pulled 30° laterally and 15° upward. The strength of the olfactory nerve was measured when pulled in each direction. There was no significant difference in the strength of the olfactory nerves when pulling them in the postero-upward direction between 0° and 15° upward. The strengths of the olfactory nerves when pulling them in the postero-lateral direction 0° and 15° laterally were 3.14±1.87 and 4.05±1.70 g (mean ± standard deviation [SD]), respectively; the difference was almost significant. The olfactory nerve could be pulled more laterally than posteriorly because the retraction force is absorbed by the lateral wall of the olfactory fossa.

Matrix metalloproteinase-9 is associated with acute inflammation after olfactory injury.

We previously reported an increase in matrix metalloproteinase-9 (MMP-9) levels in the olfactory bulb immediately after nerve transection; however, its role remains unknown. In this study, we determined the source of MMP-9 by monitoring the infiltration of inflammatory leukocytes in the olfactory bulb after nerve transection. We used myeloperoxidase to identify neutrophils and CD68 to identify macrophages at days 1, 7, and 10. MMP-9 colocalized with neutrophils at all three time points but was not contained in macrophages. This is the first study to demonstrate that MMP-9 is associated with early inflammatory response after olfactory injury, and provides insight into mechanisms underlying olfactory injury and recovery processes.