Nasal neuron PET imaging quantifies neuron generation and degeneration

Olfactory dysfunction is broadly associated with neurodevelopmental and neurodegenerative diseases and predicts increased mortality rates in healthy individuals. Conventional measurements of olfactory health assess odor processing pathways within the brain and provide a limited understanding of primary odor detection. Quantification of the olfactory sensory neurons (OSNs), which detect odors within the nasal cavity, would provide insight into the etiology of olfactory dysfunction associated with disease and mortality. Notably, OSNs are continually replenished by adult neurogenesis in mammals, including humans, so OSN measurements are primed to provide specialized insights into neurological disease. Here, we have evaluated a PET radiotracer, [¹¹C]GV1-57, that specifically binds mature OSNs and quantifies the mature OSN population in vivo. [¹¹C]GV1-57 monitored native OSN population dynamics in rodents, detecting OSN generation during postnatal development and aging-associated neurodegeneration. [¹¹C]GV1-57 additionally measured rates of neuron regeneration after acute injury and early-stage OSN deficits in a rodent tauopathy model of neurodegenerative disease. Preliminary assessment in nonhuman primates suggested maintained uptake and saturable binding of [¹⁸F]GV1-57 in primate nasal epithelium, supporting its translational potential. Future applications for GV1-57 include monitoring additional diseases or conditions associated with olfactory dysregulation, including cognitive decline, as well as monitoring effects of neuroregenerative or neuroprotective therapeutics.

[Effect of electro-acupuncture combined with olfactory ensheathing cell transplantation on spinal cord injury axonal regeneration and direction]

OBJECTIVE

To explore the impact and mechanism of electro-acupuncture (EA) on olfactory ensheathing cells (OECs) transplantation of spinal cord injury (SCI) axonal regeneration.

METHODS

In the experiment, 72 adult Sprague Dawley male rats weighted (220±20) g underwent contusion and transection method to cause the T9 model of spinal cord injury, were randomly divided into four groups involving model group, EA group,OECs group,and EA+OECs group. 5% fluorescein gold (FG) solution of 0.5 µl was injected into rats' spinal cord at 4 weeks and 8 weeks after SCI, a series of tests were performed including fluorescein gold(FG) retrograde tagging, BBB scores.

RESULTS

(1)The BBB scores level among four groups had no differences from the 1st day to the 1st week after the SCI (P>0.05). From the 3rd week after the SCI, the BBB scores level in EA+ OECs group were obviously higher than that of other groups (P<0.05). (2)The result of the fluorescein gold (FG) retrograde tagging showed at 4 weeks and 8 weeks after treatment FG positive nerve fibers were observed in SCI region. In EA+OECs group the number of FG positive nerve fibers was more than other three groups, and the fibers were more regularly arranged than other three groups.

CONCLUSION

The combination of electro-acupuncture and OECs transplantation can recover the pathway of nerve conduction and promote nerve fibers regeneration and hind limb function recovery for SCI rat, and can guide the trend of the axonal regeneration.

[The forgotten cranial nerve--clinical importance of olfaction]

Hyposmia is often undiagnosed despite the known negative effect on taste, appetite and life quality. However, a new focus on the first cranial nerve has emerged as a consequence of a discovered connection between neurodegenerative disorders and hyposmia. In Parkinson's disease and Alzheimer's disease hyposmia is not only one of the earliest clinical presentations, the degree of hyposmia also correlates with the later progression of these two conditions. Hyposmia should not be ignored nor accepted; instead it should be integrated in any neurological examination, especially in elderly patients.

Structural olfactory nerve changes in patients suffering from idiopathic intracranial hypertension

Background

Complications of idiopathic intracranial hypertension (IIH) are usually caused by elevated intracranial pressure (ICP). In a similar way as in the optic nerve, elevated ICP could also compromise the olfactory nerve system. On the other side, there is growing evidence that an extensive lymphatic network system around the olfactory nerves could be disturbed in cerebrospinal fluid disorders like IIH. The hypothesis that patients with IIH suffer from hyposmia has been suggested in the past. However, this has not been proven in clinical studies yet. This pilot study investigates whether structural changes of the olfactory nerve system can be detected in patients with IIH.

Methodology/Principal Findings

Twenty-three patients with IIH and 23 matched controls were included. Olfactory bulb volume (OBV) and sulcus olfactorius (OS) depth were calculated by magnetic resonance techniques. While mean values of total OBV (128.7±38.4 vs. 130.0±32.6 mm³, p=0.90) and mean OS depth (8.5±1.2 vs. 8.6±1.1 mm, p=0.91) were similar in both groups, Pearson correlation showed that patients with a shorter medical history IIH revealed a smaller OBV (r=0.53, p<0.01). In untreated symptomatic patients (n=7), the effect was greater (r=0.76, p<0.05). Patients who suffered from IIH for less than one year (n=8), total OBV was significantly smaller than in matched controls (116.6±24.3 vs. 149.3±22.2 mm³, p=0.01). IIH patients with visual disturbances (n=21) revealed a lower OS depth than patients without (8.3±0.9 vs. 10.8±1.0 mm, p<0.01).

Conclusions/Significance

The results suggest that morphological changes of the olfactory nerve system could be present in IIH patients at an early stage of disease.

[Post-traumatic taste and smell disorders: forensic aspects]

The impact of anosmia or ageusia may be considerable for some occupations. Expert assessment shows how difficult it is to prove the diagnosis. A specialist is usually needed to demonstrate the asserted disorder. Damage compensation is based on the patient's occupation and coverage.

The olfactory nerve has a role in the body temperature and brain cytokine responses to influenza virus

Mouse-adapted human influenza virus is detectable in the olfactory bulbs of mice within hours after intranasal challenge and is associated with enhanced local cytokine mRNA and protein levels. To determine whether signals from the olfactory nerve influence the unfolding of the acute phase response (APR), we surgically transected the olfactory nerve in mice prior to influenza infection. We then compared the responses of olfactory-nerve-transected (ONT) mice to those recorded in sham-operated control mice using measurements of body temperature, food intake, body weight, locomotor activity and immunohistochemistry for cytokines and the viral antigen, H1N1. ONT did not change baseline body temperature (Tb); however, the onset of virus-induced hypothermia was delayed for about 13 h in the ONT mice. Locomotor activity, food intake and body weights of the two groups were similar. At 15 h post-challenge fewer viral antigen-immunoreactive (IR) cells were observed in the olfactory bulb (OB) of ONT mice compared to sham controls. The number of tumor necrosis factor alpha (TNFalpha)- and interleukin 1beta (IL1beta)-IR cells in ONT mice was also reduced in the OB and other interconnected regions in the brain compared to sham controls. These results suggest that the olfactory nerve pathway is important for the initial pathogenesis of the influenza-induced APR.

Usefulness and feasibility of psychophysical and electrophysiological olfactory testing in the rhinology clinic

TOPIC

Olfactory dysfunction may be assessed in the clinic with psychophysical testing and electrophysiological recording. Chemosensory event-related potentials (CSERPs) constitute an objective method to assess chemosensory function. Olfactory and trigeminal stimuli activate chemoreceptors from the olfactory neuroepithelium and from the nasal mucosa to evoke an electrophysiological response respectively called olfactory (OERPs) and trigeminal ERPs (TERPs). The purpose of this study is to assess the usefulness and feasibility of these diagnostic tools in the rhinology clinic and to correlate these results to the olfactory disorder aetiology.

MATERIALS AND METHODS

This study encompasses a cohort of 229 patients with a complaint of olfactory dysfunction from different origins. Orthonasal (Sniffing stick test with the treshold-discrimination-identification score: maximal score 48) and retronasal olfactory (maximal score 20) testing as well as CSERPs both after olfactory and trigeminal stimuli have been routinely performed. Olfactory dysfunction aetiologies were as follows: congenital (Cong.), chronic rhinosinusitis (CRS), idiopathic (Idiop.), post-medication (PM), neurologic (Neuro.), post-traumatic (PT) and post-infection (PI).

RESULTS

Mean orthonasal and retronasal scores were respectively: 11.8 and 10.1 for Cong., 18.5 and 13.1 for CRS, 15.6 and 10.4 for Idiop., 15.3 and 10.2 for PM, 17 and 10.6 for Neuro., 15 and 9.9 for PT and 18.3 and 12 for PI. Correlations between orthonasal and retronasal scores were present for all subgroups except congenital and chronic rhinosinusitis subgroups. Orthonasal and retronasal scores were different (p < 0.05) when comparing CRS vs Cong., CRS vs PT and PT vs PI. Technical problems (olfactometer or olfactory stimulation, EEG amplifier,...) and patients discomfort (anxiety, stress,...) did not allow to draw any conclusion in 2 patients. Three patients after olfactory stimulus and 6 patients after trigeminal stimulus demonstrated too much eye blinking or muscular artifacts that did not allow us to perform electrophysiological analysis and averaging as 60% of artifact-free recording was not achieved. Olfactory ERPs were recorded in 28% of the patients and trigeminal ERPs were obtained in almost every patient (95%). There was no statistical difference between each subgroup regarding the presence or absence of OERPs.

CONCLUSIONS

Psychophysical olfactory testing is a useful method to assess olfactory function in patients with olfactory loss and may help us to obtain a semi-objective and a basal evaluation of the olfactory performances. Feasibility and usefulness of CSERPs are also underlined in this study with only a limited number of patients who did not complete the examination. Psychophysical testing gives different results according to the aetiology of the olfactory disorder, which was not the case for electrophysiological recording. Olfactory acuity assessment should be based on psychophysical and CSERPs evaluation in a clinical setting.

Olfactory tau pathology in Alzheimer disease and mild cognitive impairment

OBJECTIVE

To examine the occurrence of tau pathology in the olfactory system in aged subjects and its relation to the severity of Alzheimer disease (AD) pathology.

MATERIAL AND METHODS

273 autopsy cases (167 female, 106 male, aged 61-102, mean 83.2+/-4.5 SD years) underwent a standard neuropathological assessment with immuno-histochemical study of tau and Abeta amyloid in the olfactory bulb and nerve, and diagnosis of AD using established consensus criteria including Braak staging of neuritic AD pathology.

RESULTS

All cases of definite AD (Braak stages 5 and 6, n = 96) showed large numbers of neuropil threads and neurofibrillary tangles, with amyloid deposits in 50%, and neuritic plaques only in two cases. Braak stage 4 (n = 73) was associated with tau pathology in the olfactory system in 90.4 and amyloid deposits in 9%, Braak stage 3 (n = 56) with mainly mild to moderate olfactory tau lesions in 44.6 and Abeta deposits in 9%. Braak stage 2 (n = 22) showed olfactory tau pathology in 36.4% without amyloid deposits, whereas Braak stages 0 and 1 (n = 25) were all negative. Olfactory tau pathology showed highly significant correlation with neuritic Braak staging in the brain, while both scores showed significant but low correlation with age.

CONCLUSIONS

These data confirm previous studies demonstrating considerable tau pathology in the olfactory system in all definite AD cases, in more than 2/3 of limbic AD and in more than 1/3 of elderly individuals with or without mild cognitive impairment associated with Braak stage 2. Clinical dementia correlated with both Braak and olfactory tau scores, indicating that both are associated with a high risk of cognitive decline.

An updated review of clinical olfaction

PURPOSE OF REVIEW

Disorders of the sense of smell can result through hundreds of different processes, but most commonly occur from upper-respiratory-tract infections, trauma, and chronic rhinosinusitis.

RECENT DEVELOPMENTS

Research in the basic science of olfaction has progressed rapidly with powerful new molecular discoveries; however, our ability to treat these disorders remains limited. In clinical olfaction we are just realizing the broader existence of the sensory dysfunction in our population. We are discovering associations between neurodegenerative disorders and smell function that may allow us to identify these disorders earlier in the disease process. We are also challenging our previous categorization schemes and realizing that many etiologies cross the traditional conductive and neuro-sensory divisions.

SUMMARY

Currently, aside from the possible therapeutic potential of systemic steroids, we have no effective treatment for the most common causes of olfactory loss. Recent advances in the basic science of olfaction provides us with an opportunity to develop new and novel clinical studies in an attempt at improving the quality of life for many of these patients.

Olfactory Ability in the Healthy Population: Reassessing Presbyosmia

Age-associated loss of olfactory function, or presbyosmia, has been described in many studies of olfactory ability. Presbyosmia has been ascribed to idiopathic causes despite recognition that many neurodegenerative diseases also induce loss of olfactory function and increase in incidence in the aged population. Often this olfactory loss is unnoticed or unreported by affected individuals. More effective olfactory function in women compared with men is another common feature of many studies of olfactory function. Here we report on normative data from an Australian population study (n = 942) that has been divided into 2 subpopulations and reassessed as (included) a population of healthy, nonmedicated, nonsmokers with no history of nasal problems (n = 485) and (excluded) a population of participants who were either medicated, smokers or had a history of nasal problems (n = 457). The "included" data set shows a strong relationship between self-reporting of olfactory sensitivity and olfactory function score. The included data set shows a small but significant decline in olfactory ability after 65 years of age and better olfactory function in females compared with males. Data from the excluded population show a marked decline in olfactory ability after 65 years of age, no difference between males and females, and a weak relationship between self-reporting of olfactory function and actual olfactory function. The power of this approach is that it provides a normative data set against which many factors such as medication schedules and pathological conditions can be compared.

The enigmatic origin of subfrontal schwannomas: report of a case without hyposmia

Subfrontal schwannomas are rare intracranial tumors. Most of them are associated with hyposmia/anosmia. The source of origin of these tumors is still incompletely understood. We report a 23-year-old male who presented with recurrent focal motor seizures, but had no hyposmia. The tumor was completely removed by a subfrontal approach. Relevant literature has been reviewed.

[Olfactory acuity and improvement of olfaction after total laryngectomy]

OBJECTIVE

To test and evaluate the olfactory function of patient after total laryngectomy, seek to a practical method to ameliorate olfactory function and rise the qualitative character of these patients.

METHODS

Using the T&T olfactory examination to evaluate the olfactory function of 60 cases. Four cases olfactory mucosae were observed by electron microscope. Observing relation among the remains olfaction, the time after operation and whether or not undergone the voice reconstruction. And analyse the reasons of the above hyposomnia. Using the closing-mouth and nasal out-word airflow maneuver (CNOAM) as the intervention in the patients of tracheoesophageal fistula voice reconstruction after total laryngectomy to observe the amelioration after intervention.

RESULTS

It shows various degree of hyposmia and anosmia in the cases after total laryngectomy with or without tracheoesophageal fistula voice reconstruction, with significant deference (P < 0.01) compared to the normal person respectively. There are precisely correlation among the time after operation and whether or not undergone the voice reconstruction. The longer time leads to less remaining olfaction. The patients after total laryngectomy without tracheoesophageal fistula voice reconstruction have lost their olfaction thoroughly within 5 years. But for the patients after total laryngectomy with tracheoesophageal fistula voice reconstruction, they have a middle hyposmia within 5 years, with significant deference (P < 0.01) between the patients in 5 years and after 5 years. There were significant differences (P < 0.01) between the values of patients with and without tracheoesophageal fistula voice reconstruction. The ultrastructure of 4 cases of olfactory epithelium shows the apoptosis change. After the treatment of CNOAM, the remaining olfaction of most patients were improved, with significant deference (P < 0.01) compared to those before the treatment of CNOAM.

CONCLUSIONS

The proceed hypofunction of olfaction may be influenced by the reform of respiratory air, the extinction of air velocity bypass the nasal cavity and the apoptosis of epithelial cells in the patients after total laryngectomy. But if we give an early intervention study such as tracheoesophageal fistula voice reconstruction and CNOAM, the olfactory function may be maintenance. During the intervention, the ending of olfactory nerves may be get uninterrupt stimulation. This may help the patients keep a better existing quality than those fail to accept the interventions.

Dauerhafter Erhalt der Riechnervenfunktion nach bifrontaler Kraniotomie bei Läsionen der vorderen und mittleren Schädelgrube

OBJECTIVE

The preservation of the olfactory tract during bifrontal approach for lesions located in the frontal skull base and the supra- and parasellar region has not previously been investigated.

METHODS

In our study 12 patients underwent surgery for various lesions via the basal subfrontal route. All patients were observed prospectively, olfaction testing was performed pre- and postoperatively by an independent otorhinolaryngologist.

RESULTS

We obtained complete preservation of the olfactory tracts and normal postoperative olfaction in all 12 cases.

CONCLUSION

The bifrontal approach allowed a bilateral, wide operative field with excellent orientation and views of important structures. The shortcoming of this method, damage of the olfactory tracts and postoperative anosmia can be overcome.

[Olfactory disorders]

Smell and taste problems are of major importance to those who suffer from olfactory disorders. The inability to determine the presence of odors in the home and the markedly reduced capacity or incapacity to appreciate food flavors are key reasons given for limited social interaction. Patients experiencing distorted smells and tastes may avoid food, which results in weight loss and possible malnutrition. We present an overview of smell disorders, based on physiological considerations, with specific attention to clinical characteristics of conditions most commonly causing smell disorders.

Olfactory event-related potentials in normal subjects and patients with smell disorders

We developed a device to record olfactory event-related potentials (OERP) from the human scalp. Methyl-cyclopentenolone was used as the odorant element. A total of 50 stimuli were delivered. Each stimulus lasted 0.5 sec and was delivered once every three inspirations. Normal OERPs were obtained with this device. The positive peak latencies were approximately 350 msec (P1) and 700 msec (P2), respectively. OERPs were also recorded in 40 patients with smell disorders. A positive response at about 300-400 msec was recorded in 7 patients (all females, 15-59 years old). The other 33 patients showed no response. The high potential area of this positive peak was located in the centro-occipital region of the scalp. The latency and the high potential area of this peak were similar to P1 recorded in normal subjects. The source of this peak was considered identical to that of P1. This may be a response to the trigeminal nerve during odor administration. P2 was not recorded in the patients with smell disorders. P2 may therefore be a response to the olfactory nerve.

Does Intranasal Application of Zinc Sulfate Produce Anosmia in the Mouse? An Olfactometric and Anatomical Study

Mice pre-trained in an olfactometer were tested daily on odor detection and discrimination tasks after irrigation of their olfactory epithelium in each naris with 50 microl of 5% zinc sulfate or saline. Anterograde transport of a wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) conjugate from the epithelium to the olfactory bulb was used to assess anatomical connectivity in these and in mice that were used only for histological analyses. One day after treatment, saline controls performed at high levels of accuracy in detecting vapor from solutions of 5-0.01% ethyl acetate and in an odor discrimination task but most ZnSO4-treated mice performed at chance for 5-30 days before showing recovery. Although dense WGA-HRP reaction product was found in the accessory olfactory bulb, there was little or no evidence for axonal transport to glomeruli of the main olfactory bulb in the first 4-8 days after treatment. These results demonstrate that intranasal application of ZnSO4 to mice produces a brief but essentially total disruption of functional connections from the olfactory epithelium to the main olfactory bulb and a corresponding transient anosmia.

[Do blind persons have a better sense of smell than normal sighted people?]

Functional disorders of sense organs may intensify the remaining senses. It is presumed that blind persons do not only hear better and have an intensified tactile sense but also have a stronger sense of smell. Better hearing ability was demonstrated by auditory evoked potentials. We investigated the sense of smell of blind persons by subjective tests (Sniffin' sticks: threshold, discrimination and identification) and for the first time also by objective tests (olfactory evoked potentials and trigeminal evoked potentials) and compared the results with the smelling ability of normal sighted persons by pair matching. Moreover, the investigated persons judged their performance via a questionnaire. The subjective test showed neither differences in the peripheral function nor in the central function between both groups. The amplitudes and latencies of the evoked potentials of vanillin, carbon dioxide and hydrogen sulfide were also not different. Blind persons tried unasked to identify the smell given in the discrimination test and thought themselves to be better in smelling. For the first time the smelling ability of blind people was compared with normal sighted people by objective test methods. Neither with subjective nor with objective methods differences were found.

[Objective test of smell with cognitive potentials]

BACKGROUND

An objective smelling test is indicated for a reliable assessment of olfactory disorders. Usually olfactory evoked potentials (OEP) are registered. But the technique of this measurement is complicated and the generation of the OEP depends on the respiration of the subject. Alternatively, the contingent negative variation (CNV) can be used in the diagnosis of anosmia and parosmia, requiring only a simple olfactory stimulator.

SUBJECTS AND METHOD

OEP and CNV were derived from 25 adults with normal smelling and from 16 patients with anosmia after head injury. First, the "direct" CNV was registered when the subjects expected a tone following a smell stimulus after 1.5 s. Using two different odors in a random order, the tone only followed one of them, so the "selective" CNV was scored.

RESULTS

In both tests a distinct CNV was found in 21 and 23 normal smelling subjects, respectively. OEPs were absent in 4.3 % of this control group. No patient with anosmia showed an OEP or a CNV. The amplitudes of the "selective" CNV are significantly higher than those of the "direct" CNV. No gender dependency was found.

CONCLUSION

The results show that an objective olfactometry can be realized by registration of CNV. Contrary to the measurement of OEP which depend on the physical parameters of olfactory stimuli, CNV correlates well with the cognitive identification of odor.

Phantom smelling

A case of phantom smelling (phantosmia) is described in a 28-yr.-old man who developed permanent bilateral anosmia after a serious injury to olfaction-related brain structures at the age of 25 years. The findings indicate that, even years after loss of input from olfactory receptors, the neural representation of olfactory perception can still recreate olfactory sensations without any conscious recall of them. This indicates that the neural representation of olfactory sensations remains functional and implies that neuronal activity in the olfactory organ or in other brain structures gives rise to olfactory experiences perceived as originating from the perception of original odor substances. The report suggests the intriguing possibility that the olfactory perception is not a passive process that merely reflects its normal input from the olfactory system but is continuously generated by a neural representation in the olfactory organ or in other olfaction-related brain structures, based on both genetic and sensory determinants. To the author's knowledge this is the first reported case of its kind.

Neural regeneration and the peripheral olfactory system

The peripheral olfactory system is able to recover after injury, i.e., the olfactory epithelium reconstitutes, the olfactory nerve regenerates, and the olfactory bulb is reinnervated, with a facility that is unique within the mammalian nervous system. Cell renewal in the epithelium is directed to replace neurons when they die in normal animals and does so at an accelerated pace after damage to the olfactory nerve. Neurogenesis persists because neuron-competent progenitor cells, including transit amplifying and immediate neuronal precursors, are maintained within the population of globose basal cells. Notwithstanding events in the neuron-depleted epithelium, the death of both non-neuronal cells and neurons directs multipotent globose basal cell progenitors, to give rise individually to sustentacular cells and horizontal basal cells as well as neurons. Multiple growth factors, including TGF-alpha, FGF2, BMPs, and TGF-betas, are likely to be central in regulating choice points in epitheliopoiesis. Reinnervation of the bulb is rapid and robust. When the nerve is left undisturbed, i.e., by lesioning the epithelium directly, the projection of the reconstituted epithelium onto the bulb is restored to near-normal with respect to rhinotopy and in the targeting of odorant receptor-defined neuronal classes to small clusters of glomeruli in the bulb. However, at its ultimate level, i.e., the convergence of axons expressing the same odorant receptor onto one or a few glomeruli, specificity is not restored unless a substantial number of fibers of the same type are spared. Rather, odorant receptor-defined subclasses of neurons innervate an excessive number of glomeruli in the rough vicinity of their original glomerular targets.

Hyposmia following laryngectomy: experimental model

Hyposmia following laryngectomy is a well-known clinical observation, yet the causes have been controversial for many years. In an attempt to resolve this issue, an animal model was constructed. Eighteen dogs were divided into three equal groups: control dogs, dogs that underwent tracheostomy, and dogs that underwent tracheostomy and denervation of the larynx, simulating total laryngectomy. Four to 6 months following these operations, biopsies from olfactory mucosa were taken. The results showed marked changes in the olfactory mucosa of the two test groups: cystic degeneration of secretory glands in the olfactory mucosa of the first group and involution of the olfactory mucosa, substituted by dense connective tissue and "ballooning" of olfactory nerve fibres in the second group. These findings suggest that the changes in olfactory mucosa are not only caused by a loss of nasal airway but also the existence of a neurologic connecting network between the vagus nerve and the olfactory cortex.

Olfactory dysfunction discriminates Alzheimer's dementia from major depression

This study tested the hypothesis that olfactory dysfunction could discriminate between groups of patients with Alzheimer's disease and major depression. Forty patients meeting DSM-IV criteria for Alzheimer's disease and for major depression (20 per group) underwent assessment with the Pocket Smell Test (PST), a three-item screening measure of cranial nerve I function. A PST score of < or = 1 (1 or 0 correct) discriminated between the groups with a hit rate of 90% (sensitivity = 80%, specificity = 100%). Olfactory assessment may be a useful adjunctive screening measure in differentiating Alzheimer's disease from depression in elderly patients.

Retinoic acid enhances the rate of olfactory recovery after olfactory nerve transection

In the olfactory system, retinoic acid (RA) plays an important role in development and may affect growth in the adult animal. To explore the potential effects of RA on recovery after injuries, adult mice were trained in a buried food paradigm and were given a single oral supplement of RA after olfactory nerve transection. Results demonstrate that RA accelerates the recovery of olfactory functions after injury.

Olfactory and trigeminal event-related potentials in migraine

BACKGROUND

Trigeminal/neuronal hyperexcitability and spreading depression activating the trigemino-vascular system are discussed in migraine-pathophysiology. This study investigated trigeminal and olfactory event-related potentials in migraineurs.

METHODS

Nasal chemosensitivity was assessed in 19 female migraineurs with or without aura > 72 h before or after an attack and in 19 healthy females employing event-related cortical potentials (ERPs) after specific trigeminal stimulation of nasal nociceptors with short pulses of CO2, and specific olfactory stimulation with H2S. Odour thresholds and odour identification performance were also tested.

RESULTS

Migraineurs exhibited greater responses to trigeminal stimulation, indicated by significantly larger ERP amplitudes N1. In contrast, olfactory ERP amplitudes P1N1 were significantly smaller in migraineurs. A leave-one-out classification procedure on the basis of these two parameters assigned 76.3% cases correctly. The olfactory ERP amplitude discriminated better between groups than trigeminal ERPs (71.1 vs. 68.4% correct classification).

CONCLUSIONS

Our data suggest trigeminal hyperexcitability in migraineurs. A general increase of nasal chemosensitivity is not supported because of smaller olfactory ERP amplitudes in migraineurs. Olfactory ERPs discriminate better than trigeminal ERPs between migraineurs and controls, emphasizing the significance of the olfactory system in migraine.

Chemosensory function and response in idiopathic environmental intolerance

This chapter reviews the current literature on the possible role of olfactory and trigeminal chemosensory function in idiopathic environmental intolerances (IEI). Two general points emerge from the review. First, studies of chemosensory function in IEI patients indicate that, despite their self-reported "heightened sensitivity" and enhanced responsivity to environmental odors, when compared to healthy controls they generally are found to be equally or even less sensitive to odors as measured by objective psychophysical and electrophysiological measures of olfactory function. These studies point towards alterations in the cognitive processing of olfactory information as the major characteristic of IEI. Second, studies of the role of sensitivity and bias in olfactory and trigeminal chemosensory functioning indicate that nonsensory factors (e.g., attention, bias, personality) can dramatically alter the self-reported impact of exposure to volatile chemicals. Together, these general points suggest a perspective on IEI that views many symptoms of the disorder to primarily reflect the influence of nonsensory, cognitive processes on responses to environmental odors.

Assessing olfactory function in laryngectomees using the Sniffin'Sticks test battery and chemosensory evoked potentials

OBJECTIVES/HYPOTHESIS

Laryngectomees are often considered to be completely anosmic. The aim of this study was to determine whether anosmia in laryngectomees reflects diminished transport of odorants to the olfactory epithelium or olfactory epithelial damage.

STUDY DESIGN

Twenty-five laryngectomees were examined psychophysically using the Sniffin'Sticks test battery. All patients rated the degree of their subjectively perceived deficit on a rating scale. Chemosensory evoked potentials were also recorded in 11 of 25 patients.

RESULTS

Sixteen patients complained very little about their smell deficit, even though the psychophysical testing found 18 patients to be anosmic and 7 hyposmic. Olfactory potentials could be recorded in only 7 of the 11 patients who received this evaluation, despite the fact that all 11 perceived, at least vaguely, the olfactory stimulus, H2S, during the recording sessions. No meaningful correlation between the psychophysical and electrophysiological data was observed.

CONCLUSIONS

The psychophysical data revealed the laryngectomees to be either functionally anosmic or hyposmic. The olfactory evoked potential data suggested that at least in two thirds of the laryngectomized patients the olfactory system had some function, even up to 22 years after surgery. Because patients in everyday situations find ways to bring odorants to the olfactory mucosa, the low number of complaints about subjectively perceived deficits is reasonable.

Olfactory disorders induced by cadmium exposure: a clinical study

The evaluation of olfaction is not only widely applied and undeniably valuable in clinical diagnostics but it is also of interest to industrial medicine. It should be borne in mind that in certain workplaces, particularly in the chemical industry, the olfactory receptor has to act as an organ which warns the worker against threatening intoxication, and this is possible only when it functions properly. Cadmium, as a highly toxic metal, found widely in industry and in the environment, is frequently included in the list of chemicals known to cause olfactory impairment. The purpose of this study was to evaluate olfaction in workers occupationally exposed to cadmium. The correlation between olfaction and concentrations of cadmium in urine, blood and in the workplace air as well as employment duration was examined in workers of the "CENTRA" S.A., an electrochemical plant in Poznań. In this plant cadmium-nickel batteries are produced, and there is chronic occupational exposure to cadmium in quantities exceeding maximum allowable concentration (MAC). A group of 73 workers aged 20 to 60 years (42.0 +/- 18.0), employed from 4 to 24 years (12.5 +/- 8.5) were examined. Of the 73 workers who completed the evaluation, 53 people (72.7%) were smokers (10-40 cigarettes per day). In addition to medical history, medical and ENT examinations, blood and urine tests were taken and olfactometry performed. Olfactometry was performed according to Elsberg and Levy's method, modified by Pruszewicz, in which natural coffee as well as aniseed, lemon and mint oils were used. The quantitative and qualitative olfactory disorders were evaluated on the basis of the established odor detection threshold (ODT) and odor identification threshold (OIT). The examinations revealed numerous cases of hyposmia (26.0%) and parosmia (17.8%) and one case of anosmia (1.4%). In the majority of people with olfactory disorders, hypertrophic changes in the nasal mucosa, dependent on the duration of employment, were identified. Statistically significant relationship between olfactory impairment and cadmium concentration in blood, urine and the workplace air was observed. However, such a relationship was not found in regard to the duration of employment. The study indicated the need to carry out routine olfactometries. The results of these examinations could be the ground to perform certain preventive and therapeutic procedures.

Olfactory and intranasal trigeminal event-related potentials in anosmic patients

The aim of this study was to investigate the usefulness of chemosensory event-related potentials (CSERPs) in response to both olfactory and intranasal trigeminal stimulation in the diagnosis of anosmia. Forty-four patients participated. Gaseous CO2 was used for trigeminal stimulation, vanillin and H2S were used as olfactory stimulants. Event-related potentials to olfactory stimuli could not be obtained in any of the anosmic patients, indicating the complete loss of the sense of smell. However, all patients responded to stimulation of the trigeminal nerve with CO2. These data clearly demonstrate the clinical significance of CSERPs in the assessment of anosmia.

Rapid clinical evaluation of anosmia. The alcohol sniff test

BACKGROUND

Smell impairment affects 1% to 2% of Americans and leads to frequent physician visits. Olfactory testing is available in chemosensory centers, but not as part of a routine cranial nerve examination. The alcohol sniff test (AST), which uses the standard 70% isopropyl alcohol pad, was developed as a quick, reliable measure of olfactory function.

METHODS

Sixty-four patients and 36 healthy control subjects (N = 100) were tested with the AST and with a standard butanol threshold test.

RESULTS

The AST reliably, consistently, and correctly measured olfactory function.

CONCLUSIONS

The AST is a rapid, reliable olfactory test that can be used for screening olfactory function and should be incorporated in the routine cranial nerve examination.

Postoperative anosmia after anterior communicating artery aneurysms surgery by the pterional approach

Damage to the olfactory nerve during the pterional approach to the anterior communicating artery aneurysms has not previously been investigated in a quantified manner. In this retrospective study, 100 patients with anterior communicating artery aneurysms, for whom the pterional approach was employed, were observed from the point of view of postoperative olfactory nerve function. In the postoperative period only three cases suffered from the impaired sense of smell ipsilateral to the side of surgery. 15 patients objectively showed olfactory nerve distinctions. The functions of olfactory nerve could be preserved at a relatively high rate of 85 per cent. This high rate resulted from the microtechnique employed as well as the relatively cautious frontal lobe retraction which was less than 1.5 cm.

Intranasal chemoreception in patients with multiple chemical sensitivities: a double-blind investigation

Multiple chemical sensitivities (MCS) has become an increasingly frequent diagnosis assigned to patients with symptoms associated with exposures to environmental chemicals. Since the characteristic symptoms of MCS are triggered by very low concentrations of chemicals, in the range of olfactory thresholds, it is widely believed that the intranasal chemoreceptive senses are involved in the pathophysiology of MCS. Thus, the present study addressed both the olfactory and trigeminal systems: using a double-blind approach we investigated whether MCS patients show differences in responses after exposure to either room air or low concentrations of a widely used chemical agent (2-propanol). A total of 23 patients participated in the experiments (mean age 47 years; 13 female, 10 male). MCS was diagnosed according to Cullen's criteria Performance of the nasal chemical senses was established by means of chemosensory event-related potentials (CSERP) and subjective measures of olfactory function (odor discrimination, phenylethyl alcohol odor thresholds). CSERP were recorded in response to olfactory (H2S), and trigeminal (CO2) stimuli. The study provided three major results: (1) Approximately 20% of patients diagnosed with MCS presented symptoms regardless of the type of challenge, suggesting the susceptibility of MCS patients to unspecific experimental manipulations. (2) Changes in CSERP latencies indicated a change in the processing of both olfactory and trigeminal stimuli. (3) While odor threshold remained unchanged, the patients' ability to discriminate odors decreased after exposure to room air. In contrast, this decrease was less pronounced after exposure to 2-prop. Summarily, MCS patients respond to challenge with 2-prop with changes of chemosensory perception which might increase their susceptibility to environmentally volatile chemicals. Changes in the pattern of event-related potentials are interpreted as the possible change of the orientation of cortical generators, i.e., neuronal populations that were involved in the processing of chemosensory information. However, investigations in healthy controls are needed in order to draw further conclusions.

Loss of olfactory function leads to a decrease of trigeminal sensitivity

Healthy controls were compared to patients with decreased olfactory sensitivity (n = 32) to investigate interactions between the olfactory and trigeminal systems. Amplitudes of chemo-somatosensory event-related potentials in response to suprathreshold trigeminal stimuli (CO2) were found to be smaller in patients (P < 0.05) indicating a decrease of trigeminally mediated sensations.

Posttraumatic olfactory dysfunction: MR and clinical evaluation

PURPOSE

To evaluate the sites of injury in patients with posttraumatic olfactory deficits and to compare damage with findings on clinical olfactory tests.

METHODS

Twenty-five patients with posttraumatic olfactory dysfunction were examined by means of olfactory testing, endoscopy, and MR imaging. MR surface-coil scans through the olfactory bulbs and tracts and head-coil scans of the temporal lobes were evaluated. Quantitative and qualitative gradings of damage to the olfactory bulbs, tracts, subfrontal region, hippocampus, and temporal lobes were compared with results on tests of odor identification, detection, memory, and discrimination.

RESULTS

Twelve patients were anosmic, eight had severe impairment, and five were mildly impaired. Injuries to the olfactory bulbs and tracts (88% of patients), subfrontal region (60%), and temporal lobes (32%) were found, but these did not correlate well with individual olfactory test scores. Volumetric analysis showed that patients without smell function had greater volume loss in olfactory bulbs and tracts than did those posttraumatic patients who retained some sense of smell. Qualitative and quantitative assessments of damage showed few significant correlations with olfactory tests, probably because of multifocal injuries, primary olfactory nerve damage, and the constraints of a small sample size on the detection of clinically significant differences.

CONCLUSION

MR imaging shows abnormalities in patients with posttraumatic olfactory dysfunction at a very high rate (88%), predominantly in the olfactory bulbs and tracts and the inferior frontal lobes.

[Posturographic registration of body sway after odor stimulation]

The methods of "reflex olfactometry" are rarely able to detect simulated anosmia because of the lack of reproducible correlations between stimulus and intensity of reaction. Interactions between the olfactory and vestibulospinal systems have not yet been investigated. Thirty persons with normosmia and 21 patients with anosmia were studied using a posturographic platform. Only in subjects with normosmia were body sway increases statistically significant in an anterior-posterior direction after the application of an olfactory nerve stimulant. Stimulations of the trigeminal nerve cause both in subjects with normosmia, and anosmia an increase in body sway occurred in a sagittal and lateral direction. The recording of vestibulospinal reactions during platform posturography after application of an olfactory stimulations enables quantification of body sway. These responses can also be useful in differentiating real from stimulated anosmia.

Olfactory dysfunction in diabetes mellitus

Olfactory dysfunction has been reported in individuals with diabetes mellitus, but the etiology is unknown. Diabetes is often complicated by serious medical conditions which could be related to the development of decreased olfactory ability. Overall, our 111 subjects with diabetes showed deficiencies in their ability to identify odorants measured with the Odorant Confusion Matrix (mean = 67.8% correct). The presence of macrovascular disease was found to be associated with olfactory dysfunction. Glycemic control as well as the type and duration of diabetes were not related to olfactory ability. Also, there was no distinct association with the presence of neuropathy, retinopathy, nephropathy, hypertension, or impotence. Consistent with previous studies utilizing measures of odorant identification, performance decreased with increased age, females were somewhat superior to males, and smoking had a deleterious effect. Other nondiabetes-related medical conditions and medications had no apparent effect on the olfactory ability of our subjects. These results suggest that the sequelae associated with macrovascular disease, such as perhaps, ischemia, to the olfactory area, impact negatively on olfactory ability.

[Clinical observations on parosmia]

We reviewed the clinical records of 15 patients with parosmia examined in our department from April 1987 to September 1990. Seven (29.2%) of 24 patients with olfactory disturbance caused by traumatic injury complained of parosmia. Eight (23.2%) of 34 patients with olfactory disturbance caused by influenza also showed parosmia. The incidence of parosmia between two groups was not statistically significant (p greater than 0.05). Parosmia was observed in none of 42 patients with olfactory disturbance caused by nasal-paranasal diseases. All patients (n:15) always perceived odors as unpleasent. Twelve of them had spontaneous parosmia, and three patients recognized the unpleasant smell when an odor came. In comparison with the auditory system, we speculated that spontaneous parosmia resembles tinnitus. The cause of tinnitus is recognized as a disturbance of the auditory nerve (the first order neuron). Tinnitus is rare in patients with conductive hearing loss, and cases of olfactory disturbance of the "respiratory dysosmia" did not complain of parosmia. Post-traumatic olfactory disturbance is caused by transection of the fila olfactoria, which is part of an olfactory neuron, while post-inflammatory olfactory disturbance is caused by damage to olfactory receptor cells. Furthermore, the fact that the incidence of parosmia between the two groups was not statistically significant suggests the same etiological mechanism in receptor cells. We consider that parosmia is caused by damage to olfactory sensory neurons.

Olfactory impairment in motor neuron disease: a pilot study

The ability to identify smells was tested in nine males and six females with motor neuron disease (MND) of varying severity, using the University of Pennsylvania Smell Identification Test (UPSIT). The olfactory impairment found in MND patients compared with age and sex matched controls is statistically significant at the 0.005 level. The relationship with Parkinson's disease, with Alzheimer's dementia and the possible aetiological implications of this new aspect of the MND are discussed.

The nature of unilateral neglect in the olfactory sensory system

This study investigated two major theories of unilateral neglect utilizing the ipsilaterally innervated olfactory sense. The sensory theory states that unilateral neglect is due to a diminished or attenuated sensory input. The representational theory states that unilateral neglect is due to a disordered internal representation, which is not dependent on sensory input. Results of the study revealed that right hemisphere lesion patients with left unilateral neglect failed to respond to their left contralateral nostril on olfactory double simultaneous stimulation, consistent with the representational theory because the left nostril has no direct sensory input to the right hemisphere.

[Electric stimulation of the human olfactory nerve--an approach to short-term memory?]

Electrical stimulation of the human olfactory mucosa was performed by means of an electrode, which was attached to a rhinoscope. Stimulations of the nasal mucosa did not evoke the sensation of smell, but suppressed smell sensations of presented odorants. When electrical stimulation followed the exposure to an odorant within a certain interval, the stimulus recalled the faded sensation of the preceding odorant. Electrical stimulation without prior natural stimulation produced unpleasant sensations in three patients with a history of temporal lobe seizures and olfactory auras, but not in patients with primary generalized or focal epilepsy.

Odor perception in children in relation to nasal obstruction

To determine whether nasal obstruction in children results in impaired nasal function, olfactory sensitivity was assessed in 65 children with various degrees of nasal obstruction and in 13 children without nasal obstruction. Overall, olfactory detection thresholds were directly related to clinical ratings of degree of nasal obstruction. Of the subjects with nasal obstruction attributable to adenoid hypertrophy, 28 received adenoidectomy; when retested 2 to 28 months later, 20 of the 28 subjects showed generally commensurate reductions in nasal obstruction ratings and olfactory detection thresholds. In a comparison subgroup of 16 subjects retested after intervals of 5 to 13 months without having received intervening adenoidectomy, both the nasal obstruction ratings and the olfactory detection thresholds remained relatively unchanged. These results suggest that, in children, nasal obstruction of varied degree is associated with commensurate impairment of the ability to smell, and that reduction in the degree of nasal obstruction results in commensurate recovery of the ability to smell. Olfactory function, although hitherto accorded little pediatric attention, deserves consideration both in weighing the importance of nasal obstruction in children and in deciding about therapeutic intervention.

[Preservation of the olfactory tract following surgery on anterior communicating artery aneurysm using bifrontal craniotomy, and its functional prognosis (author's transl)]

Based upon 110 cases of AComA aneurysm approached via bifrontal craniotomy, we discuss preservation of the olfactory tracts and the functional prognosis for olfaction. (1) It is possible to preserve the olfactory tracts bilaterally or unilaterally in over 80% of such cases. (2) With regard to the correlation between surgical findings and subjective sense of olfaction, it was found that 47% of the cases with bilateral preservation, 34% with unilateral preservation and 33% of the cases with bilateral olfactory tract damage reported normal olfaction. (3) Objective examination of olfaction by an otolaryngologist showed that 84% of the patients reporting normal olfaction indeed had normal olfaction, whereas 91% of those reporting no olfaction were anosmic.