Olfactory Dysfunction and Neurotransmitter Disturbance in Olfactory Bulb of Transgenic Mice Expressing Human A53T Mutant α-Synuclein

Parkinson disease is a multi-system neurodegenerative disease characterized by both motor and non-motor symptoms. Hyposmia is one of the early non-motor symptoms occurring in more than 90% of Parkinson disease cases, which can precede motor symptoms even several years. Up to now, the relationship between hyposmia and Parkinson disease remains elusive. Lack of proper animal models of hyposmia restricts the investigation. In this study we assessed olfactory function in Prp-A53T-α-synuclein transgenic (αSyn^A53T) mice which had been reported to show age-dependent motor impairments and intracytoplasmic inclusions. We also examined cholinergic and dopaminergic systems in olfactory bulb of αSyn^A53T mice by immunofluorescent staining, enzyme linked immunosorbent assay and western blot. We found that compared to wild type littermates, αSyn^A53T mice at 6 months or older displayed a deficit of odor discrimination and odor detection. No significant changes were found in olfactory memory and odor habituation. Furthermore compared to wildtype littermates, in olfactory bulb of αSyn^A53T mice at 10 months old we detected a marked decrease of cholinergic neurons in mitral cell layer and a decrease of acetylcholinesterase activity, while dopaminergic neurons were found increased in glomerular layer, accompanied with an increase of tyrosine hydroxylase protein. Our studies indicate that αSyn^A53T mice have olfactory dysfunction before motor deficits occur, and the cholinergic and dopaminergic disturbance might be responsible for the Parkinson disease-related olfactory dysfunction.     

Olfactory ensheathing glia and Schwann cells: two of a kind?

Prostatic carcinoma affects 1 in 11 men and targets bone with sclerotic metastases. The study of prostate carcinoma growth in bone has been hampered by the lack of suitable animal models. We have developed an in vivo model of prostate carcinoma growth in bone by inoculating three human prostate carcinoma cell lines (PC-3, DU-145, and LNCaP) into the tibia of congenitally athymic mice. Developing tumors were analyzed by radiographic, histologic, immunohistochemical, and in situ hybridization examination. Seven of the nine PC-3 inoculated mice and all (9/9) of the DU-145 inoculated mice developed tumors in the injected limb. In contrast, inoculation with LNCaP cells failed to produce tumors (0/9). Radiologically, the tumors had a mixed sclerotic/lytic appearance with extracortical extension. All the PC-3 tumors invaded the bone marrow cavity, cortical bone, and surrounding soft tissue. The DU-145 tumors were confined to the bone marrow cavity in 7/9 animals. CK18 and Ki67 localization identified the human tumor cells and their proliferative activity, respectively. The PC-3- and DU-145-induced tibial tumors expressed alpha(1)I procollagen and osteopontin mRNA, to varying degrees. All the tumors demonstrated an up-regulation of osteoclasts at the bone/tumor interface compared with the control limbs. Thus, this is a reliable and reproducible in vivo model of prostate carcinoma growth in bone enabling the study of the interactions that occur between prostate cancer cells and bone at an important part of the metastatic cascade, namely, growth and invasion at a distant site.     

Olfactory epithelium progenitors: insights from transgenic mice and in vitro biology

The rodent olfactory epithelium (OE) is capable of prolonged neurogenesis, beginning at E10 in the embryo and continuing throughout adulthood. Significant progress has been made over the last 10 years in revealing the signals that drive induction, differentiation and survival of its Olfactory Receptor Neurons (ORNs). Our understanding of the identity of specific progenitors or precursors that respond to these signals is, however, less well developed, and the search is still on for the elusive, definitive multipotent neuro-glial OE "Stem cell". Here, we review several lines of evidence that support the existence of a heterogeneous population of neural and glial progenitors in the olfactory mucosa, and highlight the differences in the identity and activity of progenitors found in the embryonic and adult OE. In particular, we show how recent advances in mouse transgenesis, and in the development of in vitro assays of progenitor activity, have helped to demonstrate the existence of multiple classes of olfactory mucosa-based progenitors.     

Topographic Mapping��The Olfactory System

Sensory systems must map accurate representations of the external world in the brain. Although the physical senses of touch and vision build topographic representations of the spatial coordinates of the body and the field of view, the chemical sense of olfaction maps discontinuous features of chemical space, comprising an extremely large number of possible odor stimuli. In both mammals and insects, olfactory circuits are wired according to the convergence of axons from sensory neurons expressing the same odorant receptor. Synapses are organized into distinctive spherical neuropils—the olfactory glomeruli—that connect sensory input with output neurons and local modulatory interneurons. Although there is a strong conservation of form in the olfactory maps of mammals and insects, they arise using divergent mechanisms. Olfactory glomeruli provide a unique solution to the problem of mapping discontinuous chemical space onto the brain.The olfactory system detects airborne organic and inorganic chemicals that originate from plant and animal metabolites and environmental and industrial sources. Odors mediate both innate and learned behaviors such as attraction and aversion, governing decisions to eat, mate, attack or flee from aggressors and predators. A remarkable feature of the olfactory system is the extraordinary diversity of possible odor molecules that exist. Although accurate measurements can be made of the detection range of visual wavelengths or auditory frequencies in humans, there are no reliable estimates of the number of odorous molecules that exist on earth or those that can be detected by a given animal species (Gilbert 2008). Nevertheless, the number of possible odorants is thought to be high, in the range of many thousands. Beyond odor detection lies the problem of odor discrimination: how can chemicals with slightly different physical properties be discriminated and associated with distinct odor percepts?Experiments investigating the molecular logic of olfaction over the last 20 years have led to major insights into how animals solve the problem of detecting and discriminating a vast number of different odor stimuli (Axel 1995). Four organizational principles have emerged from this work. First, large numbers of distinct odorant receptor (OR) genes are dedicated to olfaction: ∼1000 in mammals and ∼100 in insects. Second, each olfactory sensory neuron (OSN) typically expresses only a single receptor out of this large repertoire. Each OR has a distinct odor ligand profile, such that there are ∼1000 types of OSNs in the mouse and ∼100 types in the typical insect. Third, OSNs expressing the same receptor extend axons that converge on the same glomerulus in the brain, forming a map of ORs in the brain. Fourth, each odor is encoded in a combinatorial manner: One odor can activate multiple ORs, and each OR can respond to multiple odors (Malnic et al. 1999; Hallem and Carlson 2006). As a result, odor information is spatially encoded in the first relay station of the brain (reviewed in Mori et al. 2006). Strikingly, these four principles along with the anatomical organization of the olfactory system are quite similar in mammals and insects, suggesting a mechanism of convergent evolution (Hildebrand and Shepherd 1997).Recent studies in two genetic model organisms, the mouse and the fly, Drosophila melanogaster, have elucidated mechanisms governing how the topographic yet discrete olfactory map is established in the brain (see Luo and Flanagan 2007 for an excellent recent review). Although mice and flies have multiple olfactory subsystems and additional classes of chemosensory receptors (reviewed in Brennan and Zufall 2006; Touhara and Vosshall 2009), this article will focus on comparative mechanisms used to map ORs and OSNs from the main olfactory epithelium in the mouse and adult chemosensory structures in the fly to glomerular targets in the brain.     

Are Olfactory Receptors Really Olfactive?

Any living organism interacts with and responds specifically to environmental molecules by expressing specific olfactory receptors. In this paper, this specificity will be first examined in causal terms with particular emphasis on the mechanisms controlling olfactory gene expression, cell-to-cell interactions and odor-decoding processes. However, this type of explanation does not entirely justify the role olfactory receptors have played during evolution, since they are also expressed ectopically in different organs and/or tissues. Homologous olfactory genes have in fact been found in such diverse cells and/or organs as spermatozoa, testis and kidney where they are assumed to act as chemotactic sensors or renin modulators. To justify their functional diversity, homologous olfactory receptors are assumed to share the same basic role: that of conferring a self-identity to cells or tissues under varying environmental conditions. By adopting this standpoint, the functional attribution as olfactory or chemotactic sensors to these receptors should not be seen either as a cause conditioning receptor gene expression, or as a final effect resulting from genetically predetermined programs, but as a direct consequence of the environmental conditions olfactory receptor genes have explored during evolution. The association of odorant patterns with specific environmental or contextual situations makes their relationship semiotically triadic, due to the emergence of an interpretant capable of perceiving odorants as meaningful signs out of a noisy background. This perspective highlights the importance of odorant-receptor relationships as respect to the properties of the interacting partners. It is our contention that only when taken together can these different explanatory strategies provide a realistic account of how olfactory receptor genes have been structurally and functionally modified during evolution.     

Olfactory learning and behaviour are ‘insulated’ against visual processing in larval Drosophila

We investigate the organization of behaviour across sensory modalities, using larval Drosophila melanogaster. We ask whether olfactory learning and behaviour are affected by visual processing. We find that: (1) Visual choice does not affect concomitant odour choice. (2) Visual context does not influence odour learning, nor do changes of visual context between training and test affect retrieval of odour memory. (3) Larvae cannot solve a biconditional discrimination task, despite generally permissive conditions. In this task, larvae are required to establish conditional associations: in light, one odour is rewarded and the other one is not, whereas in dark the opposite contingency is established. After such training, choice between the two odours is equal under light and dark testing conditions, suggesting that larvae do not establish odour memories specifically for one visual context only. Together, these data suggest that, in larval Drosophila, olfactory learning and behaviour are ‘insulated’ against visual processing.     

Cell Type- and Isotype-Specific Expression and Regulation of β-Tubulins in Primary Olfactory Ensheathing Cells and Schwann Cells In Vitro

Olfactory ensheathing cells (OECs) and Schwann cells (SCs) are closely-related cell types with regeneration-promoting properties. Comparative gene expression analysis is particularly relevant since it may explain cell type-specific effects and guide the use of each cell type into special clinical applications. In the present study, we focused on β-tubulin isotype expression in primary adult canine glia as a translational large animal model. β-tubulins so far have been studied mainly in non-neuronal tumors and implied in tumorigenic growth. We show here that primary OECs and SCs expressed βII–V isotype mRNA. Interestingly, βIII-tubulin mRNA and protein expression was high in OECs and low in SCs, while fibroblast growth factor-2 (FGF-2) induced its down-regulation in both cell types to the same extent. This was in contrast to βV-tubulin mRNA which was similarly expressed in both cell types and unaltered by FGF-2. Immunocytochemical analysis revealed that OEC cultures contained a higher percentage of βIII-tubulin-positive cells compared to SC cultures. Addition of FGF-2 reduced the number of βIII-tubulin-positive cells in both cultures and significantly increased the percentage of cells with a multipolar morphology. Taken together, we demonstrate cell type-specific expression (βIII) and isotype-specific regulation (βIII, βV) of β-tubulin isotypes in OECs and SCs. While differential expression of βIII-tubulin in primary glial cell types with identical proliferative behaviour argues for novel functions unrelated to tumorigenic growth, strong βIII-tubulin expression in OECs may help to explain the specific properties of this glial cell type.     

Olfactory discrimination: when vision matters?

Many previous studies have attempted to investigate the effect of visual cues on olfactory perception in humans. The majority of this research has only looked at the modulatory effect of color, which has typically been explained in terms of multisensory perceptual interactions. However, such crossmodal effects may equally well relate to interactions taking place at a higher level of information processing as well. In fact, it is well-known that semantic knowledge can have a substantial effect on people's olfactory perception. In the present study, we therefore investigated the influence of visual cues, consisting of color patches and/or shapes, on people's olfactory discrimination performance. Participants had to make speeded odor discrimination responses (lemon vs. strawberry) while viewing a red or yellow color patch, an outline drawing of a strawberry or lemon, or a combination of these color and shape cues. Even though participants were instructed to ignore the visual stimuli, our results demonstrate that the accuracy of their odor discrimination responses was influenced by visual distractors. This result shows that both color and shape information are taken into account during speeded olfactory discrimination, even when such information is completely task irrelevant, hinting at the automaticity of such higher level visual-olfactory crossmodal interactions.     

Changes in Olfactory Bulb Volume in Parkinson’s Disease: A Systematic Review and Meta-Analysis

Objective

The changes in olfactory bulb (OB) volume in Parkinson’s disease (PD) patients have not yet been comprehensively evaluated. The purpose of this meta-analysis was to explore whether the OB volume was significantly different between PD patients and healthy controls.

Methods

PubMed and Embase were searched up to March 6, 2015 with no language restrictions. Two independent reviewers screened eligible studies and extracted data on study characteristics and OB volume. Additionally, a systematic review and meta-analysis using a random-effects model were conducted. Publication bias was determined by using funnel plots and Begg’s and Egger’s tests. Subgroup analyses were performed to assess possible sources of heterogeneity.

Results

Six original case-control studies of 216 PD patients and 175 healthy controls were analyzed. The pooled weighted mean difference (WMD) in the OB volume between the PD patients and the healthy participants was -8.071 for the right OB and -10.124 for the left OB; these values indicated a significant difference among PD patients compared with healthy controls. In addition, a significant difference in the lateralized OB volume was observed in PD patients, with a pooled WMD of 1.618; these results indicated a larger right OB volume than left OB volume in PD patients. In contrast, no difference in the lateralized OB volume was found in healthy controls. No statistical evidence of publication bias among studies was found based on Egger’s or Begg’s tests. Sensitivity analyses revealed that the results were consistent and robust.

Conclusions

Overall, both the left and the right OB volume were significantly smaller in PD patients than in healthy controls. However, significant heterogeneity and an insufficient number of studies underscore the need for further observational research.     

Olfactory morphology of carcharhinid and sphyrnid sharks: Does the cephalofoil confer a sensory advantage?

Many hypotheses have been advanced to explain the adaptive significance of the sphyrnid cephalofoil, including potential advantages of spacing the olfactory organs at the distal tips of the broad surface. We employed comparative morphology to test whether the sphyrnid cephalofoil provides better stereo-olfaction, increases olfactory acuity, and samples a greater volume of the medium compared to the situation in carcharhiniform sharks. The broadly spaced nares provide sphyrnid species with a significantly greater separation between the olfactory rosettes, which could lead to an enhanced ability to resolve odor gradients. In addition, most sphyrnid species possess prenarial grooves that greatly increase the volume of water sampled by the nares and thus increase the probability of odorant encounter. However, despite a much greater head width, and a significantly greater number of olfactory lamellae, scalloped hammerhead sharks do not possess a greater amount of olfactory epithelial surface area than the carcharhiniform sandbar sharks. Therefore, sphyrnid sharks might not possess any greater olfactory acuity than carcharhinids. Despite this, there are clear olfactory advantages to the cephalofoil head morphology that could have led to its evolution, persistence, and diversification. persistence, and diversification.     

Conditioned Medium of Wnt/β-Catenin Signaling-Activated Olfactory Ensheathing Cells Promotes Synaptogenesis and Neurite Growth In Vitro

Olfactory ensheathing cells (OECs), the major glia cells in the olfactory system, have been extensively studied because of their ability to promote axonal growth and regeneration. Whether it could facilitate synaptogenesis is an important, but remains as yet an unanswered question. We have identified a subgroup of Wnt signaling-activated OECs, spatiotemporal distribution of which in the olfactory bulb suggests a role for these cells in both axonal growth and synaptogenesis. In the present study, we explored this possibility in vitro. OECs were primarily cultured, in which Wnt signaling was activated by overexpressing β-catenin, and inhibited by dominant negative TCF4. Neurite growth and synaptogenesis were assessed by co-culturing neurons with conditioned medium from control OECs (cOECs CM), Wnt/β-catenin signaling-activated OECs (wOECs CM), or Wnt signaling-inhibited OECs (wiOECs). The results showed that although cOECs CM enhances axonal growth, wOECs CM exhibited a stronger axonal growth-promoting effect, than cOECs CM. More importantly, wOECs CM stimulates synatpogenesis, demonstrated by the expression of Synaptophysin and whole-cell patch clamp recording. In contrast, both cOECs CM and wiOECs CM do not affect synaptogenesis. Our data, for the first time, demonstrated that, in comparison with regularly cultured OECs, wOECs CM are more effective in enhancing axonal growth, and can promote synaptogenesis, probably by secreting factors. These results suggest a potential application of wOECs for treating spinal cord injury.     

Carbon Dioxide and Fruit Odor Transduction in Drosophila Olfactory Neurons. What Controls their Dynamic Properties?

We measured frequency response functions between odorants and action potentials in two types of neurons in Drosophila antennal basiconic sensilla. CO₂ was used to stimulate ab1C neurons, and the fruit odor ethyl butyrate was used to stimulate ab3A neurons. We also measured frequency response functions for light-induced action potential responses from transgenic flies expressing H134R-channelrhodopsin-2 (ChR2) in the ab1C and ab3A neurons. Frequency response functions for all stimulation methods were well-fitted by a band-pass filter function with two time constants that determined the lower and upper frequency limits of the response. Low frequency time constants were the same in each type of neuron, independent of stimulus method, but varied between neuron types. High frequency time constants were significantly slower with ethyl butyrate stimulation than light or CO₂ stimulation. In spite of these quantitative differences, there were strong similarities in the form and frequency ranges of all responses. Since light-activated ChR2 depolarizes neurons directly, rather than through a chemoreceptor mechanism, these data suggest that low frequency dynamic properties of Drosophila olfactory sensilla are dominated by neuron-specific ionic processes during action potential production. In contrast, high frequency dynamics are limited by processes associated with earlier steps in odor transduction, and CO₂ is detected more rapidly than fruit odor.     

Olfactory axon pathfinding: who is the pied piper?

Mammalian olfactory sensory neurons that express a particular odorant receptor (OR) project axons to the same few glomeruli in the olfactory bulb. In this issue of Neuron, Vassalli et al. use OR minigenes that coexpress histochemical markers and show that the determinants in the sensory neurons required to generate the stereotyped olfactory bulb map are the same as those needed for appropriate expression of the OR.     

Are Pheromones Detected Through the Main Olfactory Epithelium?

A major sensory organ for the detection of pheromones by animals is the vomeronasal organ (VNO). Although pheromones control the behaviors of various species, the effect of pheromones on human behavior has been controversial because the VNO is not functional in adults. However, recent genetic, biochemical, and electrophysiological data suggest that some pheromone-based behaviors, including male sexual behavior in mice, are mediated through the main olfactory epithelium (MOE) and are coupled to the type 3 adenylyl cyclase (AC3) and a cyclic nucleotide-gated (CNG) ion channel. These recent discoveries suggest the provocative hypothesis that human pheromones may signal through the MOE.     

It’s Not Easy Being Blue: Are There Olfactory and Visual Trade-Offs in Plant Signalling?

Understanding the signals used by plants to attract seed disperses is a pervasive quest in evolutionary and sensory biology. Fruit size, colour, and odour variation have long been discussed in the controversial context of dispersal syndromes targeting olfactory-oriented versus visually-oriented foragers. Trade-offs in signal investment could impose important physiological constraints on plants, yet have been largely ignored. Here, we measure the reflectance and volatile organic compounds of a community of Malagasy plants and our results indicate that extant plant signals may represent a trade-off between olfactory and chromatic signals. Blue pigments are the most visually-effective – blue is a colour that is visually salient to all known seed dispersing animals within the study system. Additionally, plants with blue-reflecting fruits are less odiferous than plants that reflect primarily in other regions of the colour spectrum.     

Usefulness of Cardiac MIBG Scintigraphy,Olfactory Testing and Substantia Nigra Hyperechogenicity as Additional Diagnostic Markers for Distinguishing between Parkinson’s Disease and Atypical Parkinsonian Syndromes

BackgroundWe aimed to evaluate the utility of the combined use of cardiac ¹²³I-metaiodobenzylguanidine (MIBG) scintigraphy, olfactory testing, and substantia nigra (SN) hyperechogenicity on transcranial sonography (TCS) in differentiating Parkinson’s disease (PD) from atypical parkinsonian syndromes (APSs), such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP).MethodsCardiac MIBG scintigraphy, card-type odor identification testing (Open Essence (OE), Wako, Japan), and TCS were performed with 101 patients with PD and 38 patients with APSs (MSA and PSP). Receiver operating characteristic (ROC) curve analysis was used to assess the sensitivity and specificity of these batteries for diagnosing PD from APSs. The diagnostic accuracy of the three tests was also assessed among patients at the early disease stage (drug-naïve patients with a disease duration of 3 years or less).ResultsIn differentiating PD from APSs, the area under the ROC curve was 0.74 (95% CI, 0.65–0.83), 0.8 (95% CI, 0.73–0.87), and 0.75 (95% CI, 0.67–0.82) for TCS, cardiac MIBG scintigraphy, and olfactory testing, respectively. The diagnostic sensitivity and specificity were 53.1% and 91.7%, respectively, for TCS, 70.3% and 86.8%, respectively, for cardiac MIBG scintigraphy, 58.4% and 76.3%, respectively, for OE. Among early-stage patients, sensitivity and specificity were 50.0% and 93.8%, respectively, for TCS, 57.1% and 87.5%, respectively, for cardiac MIBG scintigraphy, and 54.8% and 79.2%, respectively, for OE. At least one positive result from 3 tests improved sensitivity (86.1%) but decreased specificity (63.2%). In contrast, at least 2 positive results from 3 tests had good discrimination for both early-stage patients (50.0% sensitivity and 93.8% specificity) and patients overall (57.8% sensitivity and 95.8% specificity). Positive results for all 3 tests yielded 100% specificity but low sensitivity (25%).ConclusionsAt least 2 positive results from among TCS, cardiac MIBG scintigraphy, and olfactory testing can support clinical diagnosis in distinguishing PD from APSs.     

Olfactory Deficits in an Alpha-Synuclein Fly Model of Parkinson’s Disease

Parkinson’s disease (PD) is the most common motor neurodegenerative disorder. Olfactory dysfunction is a prevalent feature of PD. It often precedes motor symptoms by several years and is used in assisting PD diagnosis. However, the cellular and molecular bases of olfactory dysfunction in PD are not known. The fruit fly Drosophila melanogaster, expressing human alpha-synuclein protein or its mutant, A30P, captures several hallmarks of PD and has been successfully used to model PD in numerous studies. First, we report olfactory deficits in fly expressing A30P (A30P), showing deficits in two out of three olfactory modalities, tested – olfactory acuity and odor discrimination. The remaining third modality is odor identification/naming. Second, oxidative stress is an important environmental risk factor of PD. We show that oxidative stress exacerbated the two affected olfactory modalities in younger A30P flies. Third, different olfactory receptor neurons are activated differentially by different odors in flies. In a separate experiment, we show that the odor discrimination deficit in A30P flies is general and not restricted to a specific class of chemical structure. Lastly, by restricting A30P expression to dopamine, serotonin or olfactory receptor neurons, we show that A30P expression in dopamine neurons is necessary for development of both acuity and discrimination deficits, while serotonin and olfactory receptor neurons appeared not involved. Our data demonstrate olfactory deficits in a synuclein fly PD model for exploring olfactory pathology and physiology, and for monitoring PD progression and treatment.     

Olfactory Bulb Excitotoxicity as a Gap-Filling Mechanism Underlying the Link Between Traumatic Brain Injury-Induced Secondary Neuronal Degeneration and Parkinson’s Disease-Like Pathology

Neurochemical Research - There is increasing preclinical and clinical data supporting a potential association between Traumatic Brain Injury (TBI) and Parkinson’s disease (PD). It has been...     

Olfactory ensheathing cells - another miracle cure for spinal cord injury?

Several recent publications describe remarkably promising effects of transplanting olfactory ensheathing cells as a potential future method to repair human spinal cord injuries. But why were cells from the nose transplanted into the spinal cord? What are olfactory ensheathing cells, and how might they produce these beneficial effects? And more generally, what do we mean by spinal cord injury? To what extent can we compare repair in an animal to repair in a human?