The influences of age on olfaction: a review

Accelerated age-related olfactory decline among type 1 Usher patients

Usher Syndrome (USH) is a rare disease with hearing loss, retinitis pigmentosa and, sometimes, vestibular dysfunction. A phenotype heterogeneity is reported. Recent evidence indicates that USH is likely to belong to an emerging class of sensory ciliopathies. Olfaction has recently been implicated in ciliopathies, but the scarce literature about olfaction in USH show conflicting results. We aim to evaluate olfactory impairment as a possible clinical manifestation of USH. Prospective clinical study that included 65 patients with USH and 65 normal age-gender-smoking-habits pair matched subjects. A cross culturally validated version of the Sniffin’ Sticks olfaction test was used. Young patients with USH have significantly better olfactory scores than healthy controls. We observe that USH type 1 have a faster ageing olfactory decrease than what happens in healthy subjects, leading to significantly lower olfactory scores in older USH1 patients. Moreover, USH type 1 patients showed significantly higher olfactory scores than USH type 2, what can help distinguishing them. Olfaction represents an attractive tool for USH type classification and pre diagnostic screening due to the low cost and non-invasive nature of the testing. Olfactory dysfunction should be considered among the spectrum of clinical manifestations of Usher syndrome.

Deconstructing the molecular architecture of olfactory areas using proteomics

The anatomy of the olfactory system is highly complex, comprising a system of olfactory receptors, pathways for the transmission of olfactory information, and structures for the recognition, discrimination, and memorization of odors. During the last years, proteomics has emerged as a large-scale comprehensive approach to characterize and quantify specific olfactory-related proteomes in different biological conditions such as olfactory learning, neurodegeneration, and ageing between others. The current work reviews recent applications of proteomics to olfaction with particular focus on quantitative proteome profiling studies performed on olfactory areas from laboratory animal models as well as proteomic characterizations performed on specific brain structures and fluids involved in human smell. Finally, we will also discuss the potential application of proteomics to study global proteome dynamics and posttranslationally modified proteomes in order to unravel cell-signaling networks that occur from peripheral structures to olfactory cortical areas during odor processing.

New chemosensory component in the U.S. National Health and Nutrition Examination Survey (NHANES): first-year results for measured olfactory dysfunction

The U.S. NHANES included chemosensory assessments in the 2011-2014 protocol. We provide an overview of this protocol and 2012 olfactory exam findings. Of the 1818 NHANES participants aged ≥40 years, 1281 (70.5 %) completed the exam; non-participation mostly was due to time constraints. Health technicians administered an 8-item, forced-choice, odor identification task scored as normosmic (6-8 odors identified correctly) versus olfactory dysfunction, including hyposmic (4-5 correct) and anosmic/severe hyposmic (0-3 correct). Interviewers recorded self-reported smell alterations (during past year, since age 25, phantosmia), histories of sinonasal problems, xerostomia, dental extractions, head or facial trauma, and chemosensory-related treatment and changes in quality of life. Olfactory dysfunction was found in 12.4 % (13.3 million adults; 55 % males/45 % females) including 3.2 % anosmic/severe hyposmic (3.4 million; 74 % males/26 % females). Selected age-specific prevalences were 4.2 % (40-49 years), 12.7 % (60-69 years), and 39.4 % (80+ years). Among adults ≥70 years, misidentification rates for warning odors were 20.3 % for smoke and 31.3 % for natural gas. The highest sensitivity (correctly identifying dysfunction) and specificity (correctly identifying normosmia) of self-reported olfactory alteration was among anosmics/severe hyposmics (54.4 % and 78.1 %, respectively). In age- and sex-adjusted logistic regression analysis, risk factors of olfactory dysfunction were racial/ethnic minority, income-to-poverty ratio ≤ 1.1, education <high school, and heavy drinking. Moderate-to-vigorous physical activity reduced risk of impairment. Olfactory dysfunction is prevalent, particularly among older adults. Inexpensive, brief odor identification tests coupled with questions (smell problems past year, since age 25, phantosmia) could screen for marked dysfunction. Healthcare providers should be prepared to offer education on non-olfactory avoidance of hazardous events.

Analysis of Cell Turnover in the Bronchiolar Epithelium Through the Normal Aging Process

PURPOSE

Aging is associated with changes in the lung that leads to a decrease in its function. Alterations in structure and function in the small airways are well recognized in chronic lung diseases. The aim of this study was the assessment of cell turnover in the bronchiolar epithelium of mouse through the normal aging process.

METHODS

Lungs from CD1 mice at the age of 2, 6, 12, 18, or 24 months were fixed in neutral-buffered formalin and paraffin-embedded. Proliferating cell nuclear antigen was examined by immunohistochemistry. Apoptosis was analyzed by in situ end-labeling of fragmented DNA. Epithelial dimensions were analyzed by morphometry.

RESULTS

The 2-month-old mice showed significantly higher number of proliferating cells when compared with mice at all other age groups. The number of apoptotic cells in mice at 24 months of age was significantly greater than in mice at all other age groups. Thus, the number of epithelial cells decreased as the age of the subject increased. We also found reductions in both area and height of the bronchiolar epithelium in mice at 18 and 24 months of age.

CONCLUSIONS

We found a decrease in the total number of epithelial cells in the aged mice, which was accompanied by a thinning of the epithelium. These changes reflect a dysregulated tissue regeneration process in the bronchiolar epithelium that might predispose to respiratory diseases in elderly subjects.

Olfactory phenotypic expression unveils human aging

The mechanism of the natural aging of olfaction and its declinein the absence of any overt disease conditions remains unclear. Here, we investigated this mechanism through measurement of one of the parameters of olfactory function, the absolute threshold, in a healthy population from childhood to old age. The absolute olfactory threshold data were collected from an Italian observational study with 622 participants aged 5-105 years. A subjective testing procedure of constant stimuli was used, which was also compared to the 'staircase' method, with the calculation of the reliability. The n-butanol stimulus was used as an ascending series of nine molar concentrations that were monitored using an electronic nose. The data were analyzed using nonparametric statistics because of the multimodal distribution. We show that the age-related variations in the absolute olfactory threshold are not continuous; instead, there are multiple olfactory phenotypes. Three distinct age-related phenotypes were defined, termed as 'juvenile', 'mature' and 'elder'. The frequency of these three phenotypes depends on age. Our data suggest that the sense of smell does not decrease linearly with aging. Our findings provide the basis for further understanding of olfactory loss as an anticipatory sign of aging and neurodegenerative processes.

Chronic Rhinosinusitis-Related Smell Loss: Medical And Surgical Treatment Efficacy

Chronic rhinosinusitis (CRS) is an inflammatory disorder of the nasal cavities and paranasal sinuses. Olfactory dysfunction is a common manifestation of CRS and one of its cardinal diagnostic features. A decreased sense of smell can have a profound impact on a CRS patient's quality of life and overall wellbeing. The treatment of CRS-associated olfactory dysfunction includes a wide range of medical interventions, including anti-inflammatory and antibiotic medications, and surgical interventions, including endoscopic sinus and nasal surgery. The evidence and treatment efficacy for these interventions is quite varied. This review provides a summary of the efficacy of the medical and surgical therapeutic options for CRS-associated olfactory dysfunction.

Odor-Specific Loss of Smell Sensitivity with Age as Revealed by the Specific Sensitivity Test

The perception of odor mixtures plays an important role in human food intake, behavior, and emotions. Decline of smell acuity with normal aging could impact food perception and preferences at various ages. However, since the landmark Smell Survey by National Geographic, little has been elucidated on differences in the onset and extent of loss in olfactory sensitivity toward single odorants. Here, using the Specific Sensitivity test, we show the onset and extent of loss in both identification and detection thresholds of odorants with age are odorant-specific. Subjects of Chinese descent in Singapore (186 women, 95 men), aged 21-80 years, were assessed for olfactory sensitivity of 10 odorants from various odor groups. Notably, subjects in their 70s required 179 times concentration of rose-like odorant (2-phenylethanol) than subjects in the 20s, while thresholds for onion-like 2-methyloxolane-3-thiol only differed by 3 times between the age groups. In addition, identification rate for 2-phenylethanol was negatively correlated with age throughout adult life whereas mushroom-like oct-1-en-3-ol was equally identified by subjects across all ages. Our results demonstrated the girth of differentiated olfactory loss due to normal ageing, which potentially affect overall perception and preferences of odor mixtures with age.

Olfactory dysfunction in behavioral variant frontotemporal dementia

OBJECTIVE

Several neurodegenerative disorders show olfactory dysfunction. In patients with frontotemporal dementia (FTD), olfactory impairment is probably due to the involvement of the temporal and orbitofrontal lobes. We hypothesized that due to the disrupted areas in FTD, there would be an impairment in smell identification, differentiation and association. Moreover, we hypothesized that there would be a correlation between the severity of FTD and the severity of odor dysfunction.

METHODS

In the current study, we compared odor identification, discrimination and association of nine patients with behavioral variant FTD with eleven healthy controls using the Brief Smell Identification Test and the Odor Perception and Semantics Battery.

RESULTS

The results showed significant differences in the odor association test, but not in the identification or discrimination test. There was no correlation between disease severity and the performance in the odor tests.

CONCLUSION

We showed impairment of odor association that is most likely due to disruption of specific associative areas involved in olfactory processing. Specifically, we propose that the impairment may well be due to disrupted areas in the temporal lobe and amygdala.

Olfaction in People with Down Syndrome: A Comprehensive Assessment across Four Decades of Age

Background

Down syndrome (DS) shows neuropathology similar to Alzheimer disease, which presents olfactory impairment. Previous work showed olfactory impairment in DS, but a comprehensive evaluation of olfactory function in DS is lacking.

Methods

We investigated a large number (n = 56; M = 31, F = 25) DS participants (age range18-57y) using the “Sniffin’ Sticks” Extended test. This comprises three subtests (threshold, discrimination, and identification) yielding a global score (TDI) defining normosmia, hyposmia, and functional anosmia. To the best of our knowledge, this is the second largest group of DS people investigated for olfactory function ever. Age- and sex matched euploid individuals (n = 53) were the control.

Results

In DS, TDI was lower (16.7±5.13 vs. 35.4±3.74; P<0.001), with DS people performing worse in any subtests (P<0.001 for all); 27 DS participants showed functional anosmia (i.e., TDI<16). In DS, age was weakly and negatively correlated with TDI (r = -0.28, P = 0.036) and identification (r = -0.34, P = 0.012). When participants were stratified in young adults (18-29y) and older adults (30-61y), a significant effect of age was found for identification in both DS (young adults, 8.3±2.58; older adults, 6.9±2.99; P = 0.031) and control (young-adult, 14.3±1.18, older adult, 13.0±1.54; P = 0.016).

Conclusion

Olfactory function is overall severely impaired in DS people and may be globally impaired at relatively young age, despite of reportedly normal smell. However, specificity of this olfactory profile to DS should be considered with some caution because cognition was not evaluated in all DS participants and comparison with a control group of non-DS individuals having cognitive disabilities was lacking. Further study is required to longitudinally assess olfactory dysfunction in DS and to correlate it with brain pathology.

Basics of neuroanatomy and neurophysiology

This chapter presents an overview of the anatomy and functioning of the central nervous system. We begin the discussion by first examining the cellular basis of neural transmission. Then we present a brief description of the brain's white and gray matter and associated diseases, including a discussion of white-matter lesions. Finally, we place this information into context by discussing how the central nervous system integrates complex information to guide key functional systems, including the visual, auditory, chemosensory, somatic, limbic, motor, and autonomic systems. Where appropriate, we have supplied information pertaining to pathologic and functional outcomes of damage to the central nervous system. Also included is a brief description of important tools and methods used in the study of neuroanatomy and neurophysiology. Overall, this chapter provides a basic review of the concepts required to understand and interpret the clinical disorders and related material presented in the subsequent chapters of this book.

Olfactory memory in the old and very old: relations to episodic and semantic memory and APOE genotype

The neuroanatomical organization that underlies olfactory memory is different from that of other memory types. The present work examines olfactory memory in an elderly population-based sample (Swedish National Study on Aging and Care in Kungsholmen) aged 60-100 years (n = 2280). We used structural equation modeling to investigate whether olfactory memory in old age is best conceptualized as a distinct category, differentiated from episodic and semantic memory. Further, potential olfactory dedifferentiation and genetic associations (APOE) to olfactory function in late senescence were investigated. Results are in support of a 3-factor solution where olfactory memory, as indexed by episodic odor recognition and odor identification, is modeled separately from episodic and semantic memory for visual and verbal information. Increasing age was associated with poorer olfactory memory performance, and observed age-related deficits were further exacerbated for carriers of the APOE ε4 allele; these effects tended to be larger for olfactory memory compared to episodic and semantic memory pertaining to other sensory systems (vision, auditory). Finally, stronger correlations between olfactory and episodic memory, indicating dedifferentiation, were observed in the older age groups.

SNP genotypes of olfactory receptor genes associated with olfactory ability in German Shepherd dogs

To find out the relationship between SNP genotypes of canine olfactory receptor genes and olfactory ability, 28 males and 20 females from German Shepherd dogs in police service were scored by odor detection tests and analyzed using the Beckman GenomeLab SNPstream. The representative 22 SNP loci from the exonic regions of 12 olfactory receptor genes were investigated, and three kinds of odor (human, ice drug and trinitrotoluene) were detected. The results showed that the SNP genotypes at the OR10H1-like:c.632C>T, OR10H1-like:c.770A>T, OR2K2-like:c.518G>A, OR4C11-like:c.511T>G and OR4C11-like:c.692G>A loci had a statistically significant effect on the scenting abilities (P < 0.001). The kind of odor influenced the performances of the dogs (P < 0.001). In addition, there were interactions between genotype and the kind of odor at the following loci: OR10H1-like:c.632C>T, OR10H1-like:c.770A>T, OR4C11-like:c.511T>G and OR4C11-like:c.692G>A (P < 0.001). The dogs with genotype CC at the OR10H1-like:c.632C>T, genotype AA at the OR10H1-like:c.770A>T, genotype TT at the OR4C11-like:c.511T>G and genotype GG at the OR4C11-like:c.692G>A loci did better at detecting the ice drug. We concluded that there was linkage between certain SNP genotypes and the olfactory ability of dogs and that SNP genotypes might be useful in determining dogs' scenting potential.

Genome-wide Meta-analysis on the Sense of Smell Among US Older Adults

Olfactory dysfunction is common among older adults and affects their safety, nutrition, quality of life, and mortality. More importantly, the decreased sense of smell is an early symptom of neurodegenerative diseases such as Parkinson disease (PD) and Alzheimer disease. However, the genetic determinants for the sense of smell have been poorly investigated. We here performed the first genome-wide meta-analysis on the sense of smell among 6252 US older adults of European descent from the Atherosclerosis Risk in Communities (ARIC) study, the Health, Aging, and Body Composition (Health ABC) study, and the Religious Orders Study and the Rush Memory and Aging Project (ROS/MAP). Genome-wide association study analysis was performed first by individual cohorts and then meta-analyzed using fixed-effect models with inverse variance weights. Although no SNPs reached genome-wide statistical significance, we identified 13 loci with suggestive evidence for an association with the sense of smell (Pmeta < 1 × 10). Of these, 2 SNPs at chromosome 17q21.31 (rs199443 in NSF, P = 3.02 × 10; and rs2732614 in KIAA1267-LRRC37A, P = 6.65 × 10) exhibited cis effects on the expression of microtubule-associated protein tau (MAPT, 17q21.31) in 447 frontal-cortex samples obtained postmortem and profiled by RNA-seq (P < 1 × 10). Gene-based and pathway-enrichment analyses further implicated MAPT in regulating the sense of smell in older adults. Similar results were obtained after excluding participants who reported a physician-diagnosed PD or use of PD medications. In conclusion, we provide preliminary evidence that the MAPT locus may play a role in regulating the sense of smell in older adults and therefore offer a potential genetic link between poor sense of smell and major neurodegenerative diseases.

Olfactory dysfunction and its measurement in the clinic

The sense of smell is largely taken for granted by laypersons and medical professionals alike. Indeed, its role in determining the flavor of foods and beverages, as well as in warning of, or protecting against, environmental hazards, often goes unrecognized. This is exemplified, in part, by the fact that most patients presenting to medical clinics with "taste" problems are typically subjected to complex brain imaging and gastroenterological tests without the sense of smell even being tested or considered as a basis of the problem. Aside from frank deficiencies in sweet, sour, bitter, salty and savory (umami) sensations, "taste" disorders most commonly reflect inadequate stimulation of the olfactory receptors via the retronasal route; i.e., from volatiles passing to the receptors from the oral cavity through the nasal pharynx. This article describes the two most common procedures for measuring the sense of smell in the clinic and provides examples of the application of these tests to diseases and other disorders frequently associated with smell loss. Basic issues related to olfactory testing and evaluation are addressed. It is pointed out that smell loss, particularly in later life, can be a harbinger for not only a range of neurodegenerative diseases, but can be a prognostic indicator of early mortality.

Olfactory dysfunction in chronic stroke patients

Background

The aim of the study was to investigate odor identification performance in patients one year after hospital admittance due to stroke. Predictors for olfactory dysfunction were investigated as well as self-reported olfactory function and pleasantness of olfactory items.

Methods

A 1-year prospective study was performed. Stroke location, classification and comorbidities were registered at hospital admission. One year after admission, olfactory function was assessed using standardized olfactory methods (screening for loss of detection sensitivity and an odor identification test). A group of matched controls was derived from a population-based study to compare odor identification performance between groups. Patients were asked for their personal judgment regarding their olfactory function and pleasantness of odorous items. In addition, global cognitive function and symptoms of depression were assessed.

Results

A total of 78 patients were enrolled (46 males, 32 females; mean age 68 years) of which 28.2 % exhibited reduced olfactory function (hyposmia) and 15.4 % exhibited loss of olfactory function (10.3 % functional anosmia, 5.1 % complete anosmia). Patients showed significantly lower olfactory performance compared to age- and sex-mated matched controls. Predictors of impaired olfactory function were age and NIHSS score. Self-reports indicated no significant differences between patients with normal olfactory function and those with reduced function. Yet, patients having an olfactory dysfunction rated odorous items as significantly less pleasant compared to patients without dysfunction.

Conclusions

Olfactory dysfunction seems to occur frequently after stoke even one year after initial admission. The deficits seem to relate to hyposmia and functional anosmia, and less to a complete loss of smell sensitivity.

An algorithmic approach to the evaluation and treatment of olfactory disorders

PURPOSE OF REVIEW

To review the current evidence in diagnosing olfactory disorders and suggest an algorithmic approach to patients with relevant complaints.

RECENT FINDINGS

New literature suggests that the incidence of olfactory loss increases with age. Age-associated olfactory loss is often multifactorial and requires careful history and physical exam. Psychophysical tests have a role in screening patients at risk for Parkinson's and Alzheimer's disease, but there is lack of evidence regarding timing and patient selection. Prediction of olfactory improvement in patients with chronic rhinosinusitis (CRS) is difficult with variable results from different studies. Olfactory training is suggested to be an emerging modality in patients with postinfectious olfactory loss.

SUMMARY

There is no standard treatment for olfactory loss. Each patient must be approached individually based on the suspected cause. Patients with CRS may require medical management and surgical treatment for alleviation of their olfactory dysfunction.

Circuit mechanisms encoding odors and driving aging-associated behavioral declines in Caenorhabditis elegans

Chemosensory neurons extract information about chemical cues from the environment. How is the activity in these sensory neurons transformed into behavior? Using Caenorhabditis elegans, we map a novel sensory neuron circuit motif that encodes odor concentration. Primary neurons, AWC^ON and AWA, directly detect the food odor benzaldehyde (BZ) and release insulin-like peptides and acetylcholine, respectively, which are required for odor-evoked responses in secondary neurons, ASEL and AWB. Consistently, both primary and secondary neurons are required for BZ attraction. Unexpectedly, this combinatorial code is altered in aged animals: odor-evoked activity in secondary, but not primary, olfactory neurons is reduced. Moreover, experimental manipulations increasing neurotransmission from primary neurons rescues aging-associated neuronal deficits. Finally, we correlate the odor responsiveness of aged animals with their lifespan. Together, these results show how odors are encoded by primary and secondary neurons and suggest reduced neurotransmission as a novel mechanism driving aging-associated sensory neural activity and behavioral declines.

DOI:http://dx.doi.org/10.7554/eLife.10181.001

A sense of smell can help animals to find food and detect danger. Odor molecules activate so-called olfactory neurons that relay signals to the brain in the form of nerve impulses. This information is then processed, and the appropriate response is triggered; for example, an animal might move towards the smell of food, or away from the scent of a predator. But how can the activity of olfactory neurons trigger the right behavioral response?

Leinwand et al. have now explored the activity of olfactory neurons in a roundworm called C. elegans. The experiments revealed that a food odor activated two olfactory neurons directly, and that each of these ‘primary’ neurons then in turn activated another ‘secondary’ olfactory neuron. This communication between primary and secondary olfactory neurons was essential for worms to respond to the food odor. Further experiments revealed that the primary olfactory neurons send chemical signals, called neurotransmitters and neuropeptides, to communicate with the secondary neurons. Importantly, mutations that blocked this chemical signaling prevented the worms from responding appropriately to the smell of food.

Aging animals, including people, often have impaired senses and can therefore find it difficult to identify and respond to odors. Leinwand et al. found that aged worms were no different. Further experiments suggested that aging worms' responses to odor decline because the communication between the primary and secondary olfactory neurons may be impaired with age. When Leinwand et al. strengthened this communication it reversed the effects of aging on the worms' sense of smell. Moreover, the experiments also showed that an animal's performance on the odor task was correlated with its longevity, such that the better performers also lived longer. A challenge for the future is to understand the precise changes that occur at early stages of aging to impair the sense of smell. Future studies could also test if similar combinations of olfactory neurons are needed to trigger certain behavioral responses to odors in young and old mammals.

DOI:http://dx.doi.org/10.7554/eLife.10181.002

Effects of age and cognition on a cross-cultural paediatric adaptation of the Sniffin' Sticks Identification Test

Objectives

To study the effects of age and cognition on the performance of children aged 3 to 18 years on a culturally adapted version of the 16 item smell identification test from Sniffin' Sticks (SS16).

Methods

A series of pilots were conducted on 29 children aged 3 to 18 years old and 23 adults to produce an adapted version of the SS16 suitable for Brazilian children (SS16-Child). A final version was applied to 51 children alongside a picture identification test (PIT-SS16-Child) to access cognitive abilities involved in the smell identification task. In addition 20 adults performed the same tasks as a comparison group.

Results

The final adapted SS16-Child was applied to 51 children with a mean age of 9.9 years (range 3-18 years, SD=4.25 years), of which 68.3% were girls. There was an independent effect of age (p<0.05) and PIT-SS16-Child (p<0.001) on the performance on the SS16-Child, and older children reached the ceiling for scoring in the cognitive and olfactory test. Pre-school children had difficulties identifying items of the test.

Discussion/Conclusions

A cross-culturally adapted version of the SS16 can be used to test olfaction in children but interpretation of the results must take age and cognitive abilities into consideration.

Olfactory identification deficits and increased mortality in the community

OBJECTIVE

To examine the association between odor identification deficits and future mortality in a multiethnic community cohort of older adults.

METHODS

Participants were evaluated with the 40-item University of Pennsylvania Smell Identification Test (UPSIT). Follow-up occurred at 2-year intervals with information on death obtained from informant interviews and the National Death Index.

RESULTS

During follow-up (mean = 4.1 years, standard deviation = 2.6), 349 of 1,169 (29.9%) participants died. Participants who died were more likely to be older (p < 0.001), be male (p < 0.001), have lower UPSIT scores (p < 0.001), and have a diagnosis of dementia (p < 0.001). In a Cox model, the association between lower UPSIT score and mortality (hazard ratio [HR] = 1.07 per point interval, 95% confidence interval [CI] = 1.05-1.08, p < 0.001) persisted after controlling for age, gender, education, ethnicity, language, modified Charlson medical comorbidity index, dementia, depression, alcohol abuse, head injury, smoking, body mass index, and vision and hearing impairment (HR = 1.05, 95% CI = 1.03-1.07, p < 0.001). Compared to the fourth quartile with the highest UPSIT scores, HRs for mortality for the first, second, and third quartiles of UPSIT scores were 3.81 (95% CI = 2.71-5.34), 1.75 (95% CI = 1.23-2.50), and 1.58 (95% CI = 1.09-2.30), respectively. Participant mortality rate was 45% in the lowest quartile of UPSIT scores (anosmia) and 18% in the highest quartile of UPSIT scores.

INTERPRETATION

Impaired odor identification, particularly in the anosmic range, is associated with increased mortality in older adults even after controlling for dementia and medical comorbidity.

Simple and Computer-assisted Olfactory Testing for Mice

Olfaction is highly conserved among species and is required for reproduction and survival. In humans, olfaction is also one of the senses that is affected with aging and is a strong predictor of neurodegenerative diseases. Thus, olfaction testing is used as a non-invasive diagnostic method to detect neurological deficits early on. In order to understand the mechanisms underlying olfactory network susceptibility, olfactory research in rodents has gained momentum in the past decade. Here, we present a very simple, time efficient and reproducible olfactory testing method of innate odor perception and sensitivity in mice without the need of any prior food or water restriction. The tests are performed in a familiar environment to the mice, require only the scents and a 2 min session of odorant exposure. The analysis is performed, post-hoc, using computer-assisted commands on ImageJ and can be, therefore, carried out from start to end by one researcher. This protocol does not require any special hardware or setup and is indicated for any laboratory interested in testing olfactory perception and sensitivity.

Anorexia of Aging

The anorexia of aging is common, leading to adverse health consequences. As populations age, the impacts from anorexia in the older population are set to increase. Only greater awareness will allow for prevention or early intervention. This article discusses the physiologic anorexia of aging, highlights contributing factors, and proposes management strategies, including screening, especially in primary care. Many neuroendocrine factors have been implicated in the pathophysiology; it is clear that further human research is necessary if there is to be a pharmacologic breakthrough. There are currently no approved pharmacologic treatment strategies to prevent or treat the anorexia of aging.

Olfactory dysfunction in Parkinson's disease: Positive effect of cigarette smoking

BACKGROUND

There is compelling evidence from over 60 epidemiological studies that smoking significantly reduces the risk of Parkinson's disease (PD). In general, those who currently smoke cigarettes, as well as those with a past history of such smoking, have a reduced risk of PD compared to those who have never smoked. Recently it has been suggested that a cardinal nonmotor sensory symptom of PD, olfactory dysfunction, may be less severe in PD patients who smoke than in PD patients who do not, in contrast to the negative effect of smoking on olfaction described in the general population.

METHODS

We evaluated University of Pennsylvania Smell Identification Test (UPSIT) scores from 323 PD patients and 323 controls closely matched individually on age, sex, and smoking history (never, past, or current).

RESULTS

Patients exhibited much lower UPSIT scores than did the controls (P < 0.0001). The relative decline in dysfunction of the current PD smokers was less than that of the never- and past-PD smokers (respective Ps = 0.0005 and 0.0019). Female PD patients outperformed their male counterparts by a larger margin than did the female controls (3.66 vs. 1.07 UPSIT points; respective Ps < 0.0001 and 0.06). Age-related declines in UPSIT scores were generally present (P < 0.0001). No association between the olfactory measure and smoking dose, as indexed by pack-years, was evident.

CONCLUSIONS

PD patients who currently smoke do not exhibit the smoking-related decline in olfaction observed in non-PD control subjects who currently smoke. The physiological basis of this phenomenon is yet to be defined.

Olfactory thresholds of the U.S. Population of home-dwelling older adults: development and validation of a short, reliable measure

Current methods of olfactory sensitivity testing are logistically challenging and therefore infeasible for use in in-home surveys and other field settings. We developed a fast, easy and reliable method of assessing olfactory thresholds, and used it in the first study of olfactory sensitivity in a nationally representative sample of U.S. home-dwelling older adults. We validated our method via computer simulation together with a model estimated from 590 normosmics. Simulated subjects were assigned n-butanol thresholds drawn from the estimated normosmic distribution and based on these and the model, we simulated administration of both the staircase and constant stimuli methods. Our results replicate both the correlation between the two methods and their reliability as previously reported by studies using human subjects. Further simulations evaluated the reliability of different constant stimuli protocols, varying both the range of dilutions and number of stimuli (6–16). Six appropriately chosen dilutions were sufficient for good reliability (0.67) in normosmic subjects. Finally, we applied our method to design a 5-minute, in-home assessment of older adults (National Social Life, Health and Aging Project, or NSHAP), which had comparable reliability (0.56), despite many subjects having estimated thresholds above the strongest dilution. Thus, testing with a fast, 6-item constant stimuli protocol is informative, and permits olfactory testing in previously inaccessible research settings.

Influences of hormone replacement therapy on olfactory and cognitive function in postmenopausal women

Olfactory dysfunction can be an early sign of Alzheimer's disease. Since hormone replacement therapy (HRT) may protect against Alzheimer's disease in postmenopausal women, the question arises as to whether it also protects against olfactory dysfunction in such women. A total of three olfactory and 12 neurocognitive tests were administered to 432 healthy postmenopausal women with varied HRT histories. Serum levels of reproductive hormones were obtained for all subjects; APOE-ε4 haplotype was determined for 77 women. National Adult Reading Test and Odor Memory/Discrimination Test scores were positively influenced by HRT. Odor Identification and Odor Memory/Discrimination Test scores were lower for women who scored poorly on a delayed recall test, a surrogate for mild cognitive impairment. The Wechsler Adult Intelligence Scale, Revised, as a Neuropsychological Instrument Spatial Span Backwards Test scores were higher in women receiving estrogen and progestin HRT and directly correlated with serum testosterone levels, the latter implying a positive effect of testosterone on spatial memory. APOE-ε4 was associated with poorer odor threshold test scores. These data suggest that HRT positively influences a limited number of olfactory and cognitive measures during menopause.

A Pilot Study of the Self-Administered Computerized Olfactory Testing System

Background

The Self-Administered Computerized Olfactory Testing System (SCOTS) was developed recently to perform the olfactory threshold test under computer control. The aim of this study was to evaluate the validity and test-retest reliability of the SCOTS.

Methodology

A total of 180 subjects were tested for olfactory thresholds using an odor detection threshold test and the SCOTS. There were 60 normosmic volunteers, 60 hyposmic patients, and 60 anosmic patients. Among them, 30 normosmic subjects were retested with the SCOTS at least 1 day after the first test occasion. The olfactory threshold test and retest results from the SCOTS were compared.

Results

The mean olfactory threshold attained from the SCOTS was -5.48 for normosmic subjects, -3.18 for hyposmic patients, and -2 for anosmic patients. The olfactory thresholds among the normosmic, hyposmic, and anosmic patients were significantly different (p < .001). The correlation coefficient between the olfactory thresholds of an odor detection threshold test and the SCOTS was 0.809 (p < .001). The test-retest correlation for the SCOTS-based olfactory thresholds was strong (r = 0.671; p < .001).

Conclusion

Our results show that on the basis of its validity and test-retest reliability, the SCOTS was appropriate for self-administered tests of the olfactory threshold.

The response of rodents to scent marks: four broad hypotheses

This article is part of a Special Issue "Chemosignals and Reproduction". Many terrestrial mammals must be able to distinguish between the myriad of scent marks they encounter in order for them to facilitate or deter direct interactions with their scent donors. I review studies that examine how rodents, mainly meadow voles (Microtus pennsylvanicus), respond when they encounter the scent marks of conspecifics and heterospecifics, and how context, as well as the age and condition of senders and receivers, affect their responses. The review uses four broad hypotheses to discuss the response of rodents to scent marks. The four hypotheses are as follows: 1) Scent marks convey accurate information to the receiver about the sender's state and phenotype and genotype. 2) Scent marks are individually distinct. 3) The response of receivers to scent marks is flexible and would be modulated by the cognitive abilities of receivers. 4) Receivers respond to the information contained or conveyed by the scent mark in a manner that will increase their survival and fitness. The studies cited in this review show that scent marks signal accurate information about the sender's phenotype, genotype, and condition, which receivers use to distinguish among the scent marks of different conspecifics and heterospecifics, and by doing so, receivers tailor their response accordingly to increase their survival and fitness. Thus, the four broad hypotheses may serve as guide to increase our understanding of the response of receivers to scent marks and provide a conceptual framework for future research and the development of additional hypotheses.

Olfactory function in Wave 2 of the National Social Life, Health, and Aging Project

OBJECTIVE

To investigate the sense of smell, including sensitivity and odor identification, and characterize the U.S. national prevalence of olfactory dysfunction in older adults, thereby facilitating further investigation of the substantial risks for older adults associated with this basic sensory ability.

METHOD

The sense of smell was evaluated using the Olfactory Function Field Exam (OFFE), a measure designed specifically for field research, which assesses 3 components of olfaction: sensitivity to n-butanol (a standard testing odorant) and androstadienone (AND, a key social odor produced by humans), as well as the ability to identify odors. Respondents were randomly selected from the National Social Life, Health, and Aging Project Wave 2 sample to receive the OFFE (n = 2,304), and 2,212 consented to participate.

RESULTS

In the U.S. population aged 62-90, n-butanol detection ability was significantly worse at older ages (ordinal logistic regression, p < .001); however, there was no difference in detection ability between genders (p = .60). AND detection ability was also significantly worse at older ages (p = .003), but in contrast to n-butanol, women outperformed men (p = .001). As expected, odor identification ability was worse in older people than in younger (p < .001), and women were more accurate than men (p = .001).

DISCUSSION

We report for the first time 3 facets of olfactory function and its association with age and gender in a representative sample of U.S. older adults. Future analyses of these data are needed to elucidate the sense of smell's role in physical, social, and mental health with aging.

Olfactory deficits predict cognitive decline and Alzheimer dementia in an urban community

OBJECTIVE

To determine the predictive utility of baseline odor identification deficits for future cognitive decline and the diagnosis of Alzheimer disease (AD) dementia.

METHODS

In a multiethnic community cohort in North Manhattan, NY, 1,037 participants without dementia were evaluated with the 40-item University of Pennsylvania Smell Identification Test (UPSIT). In 757 participants, follow-up occurred at 2 years and 4 years.

RESULTS

In logistic regression analyses, lower baseline UPSIT scores were associated with cognitive decline (relative risk 1.067 per point interval; 95% confidence interval [CI] 1.040, 1.095; p < 0.0001), and remained significant (relative risk 1.065 per point interval; 95% CI 1.034, 1.095; p < 0.0001) after including covariates. UPSIT, but not Selective Reminding Test-total immediate recall, predicted cognitive decline in participants without baseline cognitive impairment. During follow-up, 101 participants transitioned to AD dementia. In discrete time survival analyses, lower baseline UPSIT scores were associated with transition to AD dementia (hazard ratio 1.099 per point interval; 95% CI 1.067, 1.131; p < 0.0001), and remained highly significant (hazard ratio 1.072 per point interval; 95% CI 1.036, 1.109; p < 0.0001) after including demographic, cognitive, and functional covariates.

CONCLUSIONS

Impairment in odor identification was superior to deficits in verbal episodic memory in predicting cognitive decline in cognitively intact participants. The findings support the cross-cultural use of a relatively inexpensive odor identification test as an early biomarker of cognitive decline and AD dementia. Such testing may have the potential to select/stratify patients in treatment trials of cognitively impaired patients or prevention trials in cognitively intact individuals.

Olfactory dysfunction in dementia

The natural aging process brings about some inevitable consequences, such as olfactory dysfunction, which is also frequently linked to numerous neurodegenerative disorders. Many age-related dementia, such as Alzheimer’s disease, Vascular dementia, Parkinson’s disease, and Frontotemporal Dementia often display olfactory dysfunction. Despite the overwhelming evidence of above mentioned facts, the symptomatic relevance and potential clinical and pre-clinical value of olfactory dysfunction remains overlooked by many clinicians and public alike. Olfactory dysfunction has strong practical implications on daily activities and, although not as prominent as in other mammals, olfaction is still an evolutionarily relevant sense involved in human survival (e.g., smelling gas; bad food). In this work, we provide a brief review of current research related to the olfactory dysfunction profiles in different types of dementia. Additionally, we present a compilation of accessible, easy to use olfaction assessment tools; and highlight future directions in terms of improving clinical diagnosis in patient care and research.

Sexual dimorphism in the human olfactory bulb: females have more neurons and glial cells than males

Sex differences in the human olfactory function reportedly exist for olfactory sensitivity, odorant identification and memory, and tasks in which odors are rated based on psychological features such as familiarity, intensity, pleasantness, and others. Which might be the neural bases for these behavioral differences? The number of cells in olfactory regions, and especially the number of neurons, may represent a more accurate indicator of the neural machinery than volume or weight, but besides gross volume measures of the human olfactory bulb, no systematic study of sex differences in the absolute number of cells has yet been undertaken. In this work, we investigate a possible sexual dimorphism in the olfactory bulb, by quantifying postmortem material from 7 men and 11 women (ages 55–94 years) with the isotropic fractionator, an unbiased and accurate method to estimate absolute cell numbers in brain regions. Female bulbs weighed 0.132 g in average, while male bulbs weighed 0.137 g, a non-significant difference; however, the total number of cells was 16.2 million in females, and 9.2 million in males, a significant difference of 43.2%. The number of neurons in females reached 6.9 million, being no more than 3.5 million in males, a difference of 49.3%. The number of non-neuronal cells also proved higher in women than in men: 9.3 million and 5.7 million, respectively, a significant difference of 38.7%. The same differences remained when corrected for mass. Results demonstrate a sex-related difference in the absolute number of total, neuronal and non-neuronal cells, favoring women by 40–50%. It is conceivable that these differences in quantitative cellularity may have functional impact, albeit difficult to infer how exactly this would be, without knowing the specific circuits cells make. However, the reported advantage of women as compared to men may stimulate future work on sex dimorphism of synaptic microcircuitry in the olfactory bulb.

Changes of olfactory abilities in relation to age: odor identification in more than 1400 people aged 4 to 80 years

The currently presented large dataset (n = 1,422) consists of results that have been assembled over the last 8 years at science fairs using the 16-item odor identification part of the “Sniffin’ Sticks”. In this context, the focus was on olfactory function in children; in addition before testing, we asked participants to rate their olfactory abilities and the patency of the nasal airways. We reinvestigated some simple questions, e.g., differences in olfactory odor identification abilities in relation to age, sex, self-ratings of olfactory function and nasal patency. Three major results evolved: first, consistent with previously published reports, we found that identification scores of the youngest and the oldest participants were lower than the scores obtained by people aged 20–60. Second, we observed an age-related increase in the olfactory abilities of children. Moreover, the self-assessed olfactory abilities were related to actual performance in the smell test, but only in adults, and self-assessed nasal patency was not related to the “Sniffin’ Sticks” identification score.

[Olfactory function in old age]

Olfactory function decreases with age. This is frequent: one in four individuals above 52 years of age exhibits olfactory loss. This decrease in olfactory function can be seen at all levels of olfactory information processing, both on a functional and a morphological level. Recent studies, however, indicate that olfactory loss with age may not be an inevitable fate.

A lifetime of neurogenesis in the olfactory system

Neurogenesis continues well beyond embryonic and early postnatal ages in three areas of the nervous system. The subgranular zone supplies new neurons to the dentate gyrus of the hippocampus. The subventricular zone supplies new interneurons to the olfactory bulb, and the olfactory neuroepithelia generate new excitatory sensory neurons that send their axons to the olfactory bulb. The latter two areas are of particular interest as they contribute new neurons to both ends of a first-level circuit governing olfactory perception. The vomeronasal organ and the main olfactory epithelium comprise the primary peripheral olfactory epithelia. These anatomically distinct areas share common features, as each exhibits extensive neurogenesis well beyond the juvenile phase of development. Here we will discuss the effect of age on the structural and functional significance of neurogenesis in the vomeronasal and olfactory epithelia, from juvenile to advanced adult ages, in several common model systems. We will next discuss how age affects the regenerative capacity of these neural stem cells in response to injury. Finally, we will consider the integration of newborn neurons into an existing circuit as it is modified by the age of the animal.

The lateralized smell test for detecting Alzheimer's disease: failure to replicate

OBJECTIVES

A widely publicized study by Stamps, Bartoshuk and Heilman (2013) reported that a simple measure of left:right naris differences in the ability to detect the odor of peanut butter is a sensitive marker of Alzheimer's disease (AD). AD patients were said to have abnormal smell function on the left side of the nose and normal function on right side of the nose. In light of its implications for medical practice and the world-wide publicity that it engendered, we sought to replicate and expand this work.

METHODS

Two studies were performed. In the first, 15 AD patients were tested according to the procedures described by Stamps et al. in which the nostril contralateral to the tested side was occluded by the patient using lateral pressure from the index finger. Since this can potentially distort the contralateral naris, we repeated the testing using tape for naris occlusion. In the second, 20 AD patients were administered 20 odors of the University of Pennsylvania Smell Identification Test (UPSIT) to each side of the nose, with the contralateral naris being closed with tape. In both studies, the order of the side of testing was systematically counterbalanced.

RESULTS

No evidence of a left:right asymmetry on any test measure was observed.

CONCLUSION

Although hyposmia is well-established in AD, no meaningful asymmetry in smell perception is apparent. If olfactory function on the right side of the nose was normal as claimed, then AD patients should exhibit normal function when tested bilaterally, a phenomenon not seen in dozens of AD-related olfactory studies.