[Prognostic value of olfactory bulb volume in patients with post-viral olfactory dysfunction].
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Objective:The purpose of this study was to compare the olfactory function examination results of patients with post-viral olfactory dysfunction（PVOD） in different prognostic groups and analyze prognostic factors, especially the influence of olfactory bulb volume（OBV） on prognosis, so as to provide objective basis for clinical diagnosis and treatment. Methods:After approval by the hospital ethics committee, the patients with PVOD admitted to Beijing Anzhen Hospital's outpatient department from January 2019 to December 2019 were followed up for at least 1 year. These patients completed the Sniffin' Sticks test and MRI examination of the olfactory pathway before treatment. According to the results of the Sniffin' Sticks test after 1 year follow-up（threshold-discrimination-identification（TDI） score of the patients was increased at least 6 points）, the patients were divided into two groups as the improvement group and the non-improvement group. The prognostic factors of PVOD patients were preliminarily determined by comparing the differences of various factors and the results of olfactory function examination between the two groups. Results:In this study, 47 patients with PVOD were included, with the smell improvement rate was 53.2%. Compared with the improvement group, the patients in the non-improvement group had longer duration, poorer initial olfactory function, higher olfactory threshold, and poorer olfactory discrimination and recognition ability（All P<0.01）. There was no statistical difference in terms of gender, age, allergic rhinitis and smoking between the two groups（All P>0.05）.The OBV of the non-improvement group was （59.48±23.92） mm³, which was significantly lower than that in the improvement group（[92.77±14.35]mm³, P<0.001）. Multiple logistic regression analysis showed that prognostic factors included course of disease（OR 0.677, 95%CI 0.461-0.993, P=0.046）, initial T value（OR 263.806, 95%CI 1.028-67 675.884, P=0.049） and OBV（OR 1.160, 95%CI 1.002-1.343, P=0.047）. The area under the receiver operating characteristic curve（ROC curve） of OBV was 0.888（0.797-0.979, P<0.001）. The correct diagnostic index of OBV≥78.50 mm³was used to determine the prognosis of olfactory function, with a specificity of 0.818 and a sensitivity of 0.840. The ROC curve analysis showed that the area under the ROC curve of duration was 0.822（0.703-0.940, P<0.001）. The correct diagnostic index of the duration ≤6 months was used to determine the prognosis of olfactory function, with a specificity of 0.727 and a sensitivity of 0.800. The area of T score was 0.793（0.662-0.924, P=0.001）. T score ≥1.25 was used as the correct diagnostic index to determine the prognosis of olfactory function. The specificity and sensitivity were 0.818 and 0.680, respectively. Conclusion:The prognosis of olfactory function in PVOD patients is related to the course of disease, the degree of olfactory loss and OBV. Those with no improvement in olfactory function have a longer disease course, aggravated olfactory damage and reduced OBV than those with improved olfactory function. The factors of Duration ≤6 months, T value ≥1.25 and OBV≥78.50 mm³suggested better prognosis, and the results of objective olfactory examination have greater value in evaluating the prognosis of olfactory function.目的：比较上呼吸道感染后嗅觉障碍（PVOD）患者不同预后组间的嗅觉功能检查结果，分析预后相关因素，尤其嗅球体积（OBV）对预后的影响，为临床诊疗提供客观依据。 方法：对2019年1月—2019年12月于北京安贞医院门诊就诊的PVOD患者进行≥1年的随访，这些患者在治疗前完成Sniffin'Sticks嗅觉测试、嗅通路MRI检查。根据1年随访期后Sniffin'Sticks嗅觉测试结果总分提高≥6分，将患者分为嗅觉功能改善组和嗅觉功能无改善组。比较两组间各因素和嗅觉功能检查结果的差异，初步确定影响PVOD患者的预后因素。 结果：共纳入47例PVOD患者，Sniffin'Sticks嗅觉测试复查结果显示嗅觉改善率为53.2%。与嗅觉功能改善组相比，嗅觉功能无改善组患者病程长，初始嗅觉功能差，嗅觉阈值高，嗅觉辨别和识别能力差（均P<0.01）。两组在性别、年龄、变应性鼻炎和吸烟方面差异均无统计学意义（均P>0.05）。嗅觉功能无改善组的OBV为（59.48±23.92） mm³，明显小于嗅觉功能改善组[（92.77±14.35） mm³]。经多元logistic回归分析预后相关因素包括病程（OR 0.677，95%CI 0.461~0.993，P=0.046），初始T值（OR 263.806，95%CI 1.028~67 675.884，P=0.049）和OBV（OR 1.160，95%CI 1.002~1.343，P=0.047）。ROC曲线分析结果显示，OBV在ROC曲线下面积为0.888（0.797~0.979，P<0.001），以OBV≥78.50 mm³ 正确诊断指数判断嗅觉功能预后良好，其特异性为0.818，敏感性为0.840；病程因素ROC曲线下面积为0.822（0.703~0.940，P<0.001），以病程≤6个月为正确诊断指数判断嗅觉功能预后良好，其特异性为0.727，敏感性为0.800；T值ROC曲线下面积为0.793（0.662~0.924，P=0.001），以T值≥1.25为正确诊断指数判断嗅觉功能预后较好，其特异性为0.818，敏感性为0.680。 结论：PVOD患者嗅觉功能预后与病程、嗅觉损伤程度和OBV有关。嗅觉功能无改善者较嗅觉功能改善者病程延长，嗅觉损伤程度加重和OBV减小。病程≤6个月，T值≥1.25和OBV≥78.50 mm³均提示预后良好，且客观嗅觉检查结果对嗅觉功能预后的评估价值更大。.Lateral inhibition
Bulb
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The olfactory bulb is an outgrowth of the forebrain, specialized for processing the molecular signals that give rise to the sense of smell. It receives sensory input from the olfactory sensory neurons and sends its output directly to the olfactory cortex. This chapter focuses on the principles of synaptic organization underlying a critical function of the olfactory system: the ability to discriminate between different odor molecules.
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Olfactory memory
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Olfactory ensheathing glia
Olfactory nerve
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Olfactory sensory neurons detect a large variety of odor molecules and send information through their axons to the olfactory bulb, the first site for the processing of olfactory information in the brain. The axonal connection is precisely organized so that signals from 1000 different types of odorant receptors are sorted out in 1800 glomeruli in the mouse olfactory bulb. Individual glomerular modules presumably represent a single type of receptor and are thus tuned to specific molecular features of odorants. Local neuronal circuits in the bulb mediate lateral inhibition among glomerular modules to sharpen the tuning specificity of output neurons. They also mediate synchronized oscillatory discharges among specific combinations of output neurons and may contribute to the integration of signals from distinct odorant receptors in the olfactory cortex.
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Abstract The structure of neuronal connectivity often provides insights into the relevant stimulus features, such as spatial location, orientation, sound frequency, etc 1–6 . The olfactory system, however, appears to lack structured connectivity as suggested by reports of broad and distributed connections both from the olfactory bulb to the piriform cortex 7–22 and within the cortex 23–25 . These studies have inspired computational models of circuit function that rely on random connectivity 26–33 . It remains, nonetheless, unclear whether the olfactory connectivity contains spatial structure. Here, we use high throughput anatomical methods (MAPseq and BARseq) 34–38 to analyze the projections of 5,309 bulb and 30,433 piriform cortex output neurons in the mouse at single-cell resolution. We identify previously unrecognized spatial organization in connectivity along the anterior-posterior axis (A-P) of the piriform cortex. We find that both the bulb projections to the cortex and the cortical outputs are not random, but rather form gradients along the A-P axis. Strikingly, these gradients are matched : bulb neurons targeting a given location within the piriform cortex co-innervate extra-piriform regions that receive strong inputs from neurons within that piriform locus. We also identify signatures of local connectivity in the piriform cortex. Our findings suggest an organizing principle of matched direct and indirect olfactory pathways that innervate extra-piriform targets in a coordinated manner, thus supporting models of information processing that rely on structured connectivity within the olfactory system.
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Stimulus (psychology)
Anterior olfactory nucleus
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Levels of the proposed neurotransmitter amino acids glutamate, aspartate, gamma-aminobutyric acid (GABA), and glycine were measured within the layered structures of the olfactory bulb and olfactory cortex following unilateral transections of the lateral olfactory tract or of virtually all fiber tracts of the olfactory peduncle. Distributions of the amino acids on both lesion and control sides were examined and compared by means of a mapping procedure. The results suggest: 1) Glutamate and aspartate are specifically associated with mitral (and presumably also tufted) cell axons and terminals in the piriform cortex. The distribution of aspartate in the olfactory bulb is further suggestive of a specific association of aspartate with mitral cell dendrites and somata. 2) Glutamate might be specifically associated with some centrifugal fibers traveling to the olfactory bulb in or near the anterior commissure. 3) GABA might be specifically related to some certrifugal fibers to the olfactory bulb in addition to its prominent association with granule cells of the bulb. 4) Glycine is unlikely to play a prominent neurotransmitter role in either the olfactory bulb or olfactory cortex.
Piriform cortex
Anterior olfactory nucleus
Rhinencephalon
Granule cell
Olfactory ensheathing glia
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Pregnant rats received 2-[ 14 C]deoxy-D-glucose (2DG) intravenously on the last day of gestation, and their fetuses were delivered 1 hour later by cesarean section. Fetal brains showed high 2DG uptake spread throughout the accessory olfactory bulb and little or no differential uptake in the main olfactory bulb. These findings demonstrate that functional activity occurs in the accessory olfactory bulb in utero and suggest that the accessory olfactory system may be the pathway by which fetal rats detect the odor quality of their intrauterine milieu.
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Rhinencephalon
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Piriform cortex
Olfactory ensheathing glia
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The mammalian olfactory system has incredible ability to detect and discriminate a large number of volatile chemicals. Recent molecular and physiological studies have revealed the genetic basis of odor detection and wiring of the olfactory system. The olfactory sensing is accomplished by～1000 odorant receptor genes expressed by olfactory sensory neurons in the nose. Olfactory sensory neurons expressing the same odorant receptor gene project to one or a few glomeruli in the olfactory bulb,thus forming an intricate two-dimensional olfactory map. Understanding how the incoming olfactory signals are processed in the olfactory bulb is central to information coding in the olfactory system. This review summarizes current progresses concerning different strategies used by the olfactory bulb to process olfactory information.
Olfactory memory
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Objective
To analyze the changes of olfactory function, olfactory bulb volume, depth of olfactory sulcus in patients with Parkinson’s disease (PD) and their diagnostic values in PD.
Methods
Thirty-four PD patients, 20 patients with other neurological diseases and 25 healthy controls, collected in our hospital from January 2014 to October 2015, were enrolled. The olfactory detection threshold (DT) and identification threshold (IT) of these three groups were determined by usingfive odors olfactory detection arrays. Olfactory bulb volume and depth of olfactory sulcus were assessed with MR imaging. The olfactory function, olfactory bulb volume, depth of olfactory sulcus in the three groups, and PD patients of different disease courses and H-Y grading were compared. The relation of olfactory function with olfactory bulb volume was analyzed, and the sensibility and specificity of their combination in PD detection.
Results
Olfactory testing revealed that PD patients (DT=0.59±0.46, IT=2.01±0.48) had higher scores of DT and IT than group of other neurological diseases (DT=-0.33±0.40, IT=1.13±0.45) and healthy controls (DT=-0.22±0.41, IT=1.06±0.38), with significant differences (P<0.05). Average olfactory bulb volume in PD group (31.71±3.23 mm3) was smaller than that in group of other neurological diseases (39.52±4.47 mm3) and healthy controls (41.60±4.24 mm3), with significant differences (P<0.05). The olfactory bulb volume in PD patients of disease courses ≥4 years was significantly smaller than that in PD patients of disease courses <4 years (P<0.05). The olfactory bulb volume in PD patients of H-Y grading II and III was significantly smaller than that in PD patients of H-Y grading I (P<0.05). Olfactory threshold was negatively correlated with average olfactory bulb volume in PD patients (DT: r=-0.607, P=0.000; IT: r=-0.898, P=0.000). The sensitivity in PD diagnosis was 64.7% by olfactory bulb volume only; the sensitivity and specificity in PD diagnosis increased to 67.7% and 100.0%, respectively, by combining the olfactory IT and olfactory bulb volume.
Conclusion
Olfactory dysfunction and decreased olfactory bulb volume are noted in PD patients; the olfactory bulb volume is positively correlated with olfactory function; olfactory function combined MR imaging examination might play an important role in the diagnosis of PD.
Key words:
Parkinson’s disease; Olfaction function; Olfactory bulb volume; Olfactory sulcus depth; Diagnosis
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