Olfactory Dysfunction in Neurodevelopmental Disorders: A Meta-analytic Review of Autism Spectrum Disorders, Attention Deficit/Hyperactivity Disorder and Obsessive-Compulsive Disorder

Joint exome and metabolome analysis in individuals with dyslexia: Evidence for associated dysregulations of olfactory perception and autoimmune functions

Dyslexia is a learning disability that negatively affects reading, writing, and spelling development at the word level in 5%-9% of children. The phenotype is variable and complex, involving several potential cognitive and physical concomitants such as sensory dysregulation and immunodeficiencies. The biological pathogenesis is not well-understood. Toward a better understanding of the biological drivers of dyslexia, we conducted the first joint exome and metabolome investigation in a pilot sample of 30 participants with dyslexia and 13 controls. In this analysis, eight metabolites of interest emerged (pyridoxine, kynurenic acid, citraconic acid, phosphocreatine, hippuric acid, xylitol, 2-deoxyuridine, and acetylcysteine). A metabolite-metabolite interaction analysis identified Krebs cycle intermediates that may be implicated in the development of dyslexia. Gene ontology analysis based on exome variants resulted in several pathways of interest, including the sensory perception of smell (olfactory) and immune system-related responses. In the joint exome and metabolite analysis, the olfactory transduction pathway emerged as the primary pathway of interest. Although the olfactory transduction and Krebs cycle pathways have not previously been described in dyslexia literature, these pathways have been implicated in other neurodevelopmental disorders including autism spectrum disorder and obsessive-compulsive disorder, suggesting the possibility of these pathways playing a role in dyslexia as well. Immune system response pathways, on the other hand, have been implicated in both dyslexia and other neurodevelopmental disorders.

Parenting behaviors in mice: Olfactory mechanisms and features in models of autism spectrum disorders

Rodents, along with numerous other mammals, heavily depend on olfactory cues to navigate their social interactions. Processing of olfactory sensory inputs is mediated by conserved brain circuits that ultimately trigger social behaviors, such as social interactions and parental care. Although innate, parenting is influenced by internal states, social experience, genetics, and the environment, and any significant disruption of these factors can impact the social circuits. Here, we review the molecular mechanisms and social circuits from the olfactory epithelium to central processing that initiate parental behaviors and their dysregulations that may contribute to the social impairments in mouse models of autism spectrum disorders (ASD). We discuss recent advances of the crucial role of olfaction in parental care, its consequences for social interactions, and the reciprocal influence on social interaction impairments in mouse models of ASD.

Olfactory Dysfunction and Glaucoma

BACKGROUND

Olfactory dysfunction is a well-known phenomenon in neurological diseases with anosmia and hyposmia serving as clinical or preclinical indicators of Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. Since glaucoma is a neurodegenerative disease of the visual system, it may also entail alterations in olfactory function, warranting investigation into potential sensory interconnections.

METHODS

A review of the current literature of the last 15 years (from 1 April 2008 to 1 April 2023) was conducted by two different authors searching for topics related to olfaction and glaucoma.

RESULTS

three papers met the selection criteria. According to these findings, patients with POAG appear to have worse olfaction than healthy subjects. Furthermore, certain predisposing conditions to glaucoma, such as pseudoexfoliation syndrome and primary vascular dysregulation, could possibly induce olfactory changes that can be measured with the Sniffin Stick test.

CONCLUSIONS

the scientific literature on this topic is very limited, and the pathogenesis of olfactory changes in glaucoma is not clear. However, if the results of these studies are confirmed by further research, olfactory testing may be a non-invasive tool to assist clinicians in the early diagnosis of glaucoma.

Olfactory bulb anomalies in KBG syndrome mouse model and patients

ANKRD11 (ankyrin repeat domain 11) is a chromatin regulator and the only gene associated with KBG syndrome, a rare neurodevelopmental disorder. We have previously shown that Ankrd11 regulates murine embryonic cortical neurogenesis. Here, we show a novel olfactory bulb phenotype in a KBG syndrome mouse model and two diagnosed patients. Conditional knockout of Ankrd11 in murine embryonic neural stem cells leads to aberrant postnatal olfactory bulb development and reduced size due to reduction of the olfactory bulb granule cell layer. We further show that the rostral migratory stream has incomplete migration of neuroblasts, reduced cell proliferation as well as aberrant differentiation of neurons. This leads to reduced neuroblasts and neurons in the olfactory bulb granule cell layer. In vitro, Ankrd11-deficient neural stem cells from the postnatal subventricular zone display reduced migration, proliferation, and neurogenesis. Finally, we describe two clinically and molecularly confirmed KBG syndrome patients with anosmia and olfactory bulb and groove hypo-dysgenesis/agenesis. Our report provides evidence that Ankrd11 is a novel regulator of olfactory bulb development and neuroblast migration. Moreover, our study highlights a novel clinical sign of KBG syndrome linked to ANKRD11 perturbations in mice and humans.

Shedding a Light on Dark Genes: A Comparative Expression Study of PRR12 Orthologues during Zebrafish Development

Haploinsufficiency of the PRR12 gene is implicated in a human neuro-ocular syndrome. Although identified as a nuclear protein highly expressed in the embryonic mouse brain, PRR12 molecular function remains elusive. This study explores the spatio-temporal expression of zebrafish PRR12 co-orthologs, prr12a and prr12b, as a first step to elucidate their function. In silico analysis reveals high evolutionary conservation in the DNA-interacting domains for both orthologs, with significant syntenic conservation observed for the prr12b locus. In situ hybridization and RT-qPCR analyses on zebrafish embryos and larvae reveal distinct expression patterns: prr12a is expressed early in zygotic development, mainly in the central nervous system, while prr12b expression initiates during gastrulation, localizing later to dopaminergic telencephalic and diencephalic cell clusters. Both transcripts are enriched in the ganglion cell and inner neural layers of the 72 hpf retina, with prr12b widely distributed in the ciliary marginal zone. In the adult brain, prr12a and prr12b are found in the cerebellum, amygdala and ventral telencephalon, which represent the main areas affected in autistic patients. Overall, this study suggests PRR12's potential involvement in eye and brain development, laying the groundwork for further investigations into PRR12-related neurobehavioral disorders.

Deficits in olfactory system neurogenesis in neurodevelopmental disorders

The role of neurogenesis in neurodevelopmental disorders (NDDs) merits much attention. The complex process by which stem cells produce daughter cells that in turn differentiate into neurons, migrate various distances, and form synaptic connections that are then refined by neuronal activity or experience is integral to the development of the nervous system. Given the continued postnatal neurogenesis that occurs in the mammalian olfactory system, it provides an ideal model for understanding how disruptions in distinct stages of neurogenesis contribute to the pathophysiology of various NDDs. This review summarizes and discusses what is currently known about the disruption of neurogenesis within the olfactory system as it pertains to attention-deficit/hyperactivity disorder, autism spectrum disorder, Down syndrome, Fragile X syndrome, and Rett syndrome. Studies included in this review used either human subjects, mouse models, or Drosophila models, and lay a compelling foundation for continued investigation of NDDs by utilizing the olfactory system.

Validation of the German Glasgow Sensory Questionnaire and replication of sensory processing differences in students with higher and lower Autism-Spectrum Quotient

BACKGROUND

The Glasgow Sensory Questionnaire (GSQ) gives insight into sensory processing differences (hypo- and hyper-sensitivity across modalities), which is a clinically defining characteristic of autism spectrum disorder (ASD). Because there is no validated German version of this instrument, this study aimed at validating the German GSQ. Further, a replication of the GSQ's sensory processing differences was intended.

METHODS

University students of Technische Universität or Universitätsklinikum in Dresden, Germany, were recruited via email distribution or the university homepage and 297 German-speaking students completed the online survey, comprising the German GSQ, Autism-Spectrum Quotient (AQ) and Symptom-Checklist (SCL-90). For validation of the German GSQ, confirmatory factor analyses followed by exploratory factor analyses were applied.

RESULTS

The German GSQ has moderate to low validity, good to acceptable reliability, and a different internal structure from the original GSQ. Replicating the sensory processing differences in students with higher and lower AQ was not successful.

CONCLUSIONS

Results indicate that the GSQ, developed especially for individuals with ASD, is less informative for the general population if there are not enough individuals with higher AQ scores in the sample.

Sex and Age-Dependent Olfactory Memory Dysfunction in ADHD Model Mice

ADHD is a typical neurodevelopmental disorder with a high prevalence rate. NSCs in the subventricular zone (SVZ) are closely related to neurodevelopmental disorder and can affect olfactory function by neurogenesis and migratory route. Although olfactory dysfunction is one of the symptoms of ADHD, the relevance of cells in the olfactory bulb derived from NSCs has not been studied. Therefore, we investigated olfactory memory and NSCs in Git1-deficient mice, under the ADHD model. Interestingly, only adult male G protein-coupled receptor kinase-interacting protein-1 (GIT1)-deficient (+/−, HE) mice showed impaired olfactory memory, suggesting sex and age dependence. We performed adult NSCs culture from the SVZ and observed distinct cell population in both sex and genotype. Taken together, our study suggests that the altered differentiation of NSCs in GIT1+/− mice can contribute to olfactory dysfunction in ADHD.

Modulation of the thermosensory system by oxytocin

Oxytocin (OT) is a neurohormone involved early in neurodevelopment and is implicated in multiple functions, including sensory modulation. Evidence of such modulation has been observed for different sensory modalities in both healthy and pathological conditions. This review summarizes the pleiotropic modulation that OT can exercise on an often overlooked sensory system: thermosensation. This system allows us to sense temperature variations and compensate for the variation to maintain a stable core body temperature. Oxytocin modulates autonomic and behavioral mechanisms underlying thermoregulation at both central and peripheral levels. Hyposensitivity or hypersensitivity for different sensory modalities, including thermosensitivity, is a common feature in autism spectrum disorder (ASD), recapitulated in several ASD mouse models. These sensory dysregulations occur early in post-natal development and are correlated with dysregulation of the oxytocinergic system. In this study, we discussed the potential link between thermosensory atypia and the dysregulation of the oxytocinergic system in ASD.

Olfactory modulation of the medial prefrontal cortex circuitry: Implications for social cognition

Olfactory dysfunction is manifested in a wide range of neurological and psychiatric diseases, and often emerges prior to the onset of more classical symptoms and signs. From a behavioral perspective, olfactory deficits typically arise in conjunction with impairments of cognition, motivation, memory, and emotion. However, a conceptual framework for explaining the impact of olfactory processing on higher brain functions in health and disease remains lacking. Here we aim to provide circuit-level insights into this question by synthesizing recent advances in olfactory network connectivity with other cortical brain regions such as the prefrontal cortex. We will focus on social cognition as a representative model for exploring and critically evaluating the relationship between olfactory cortices and higher-order cortical regions in rodent models. Although rodents do not recapitulate all dimensions of human social cognition, they have experimentally accessible neural circuits and well-established behavioral tests for social motivation, memory/recognition, and hierarchy, which can be extrapolated to other species including humans. In particular, the medial prefrontal cortex (mPFC) has been recognized as a key brain region in mediating social cognition in both rodents and humans. This review will highlight the underappreciated connectivity, both anatomical and functional, between the olfactory system and mPFC circuitry, which together provide a neural substrate for olfactory modulation of social cognition and social behaviors. We will provide future perspectives on the functional investigation of the olfactory-mPFC circuit in rodent models and discuss how to translate such animal research to human studies.

Sensory Deprivation and Psychiatric Disorders: Association, Assessment and Management Strategies

BACKGROUND

Sensory deprivation (SD) is a widely prevalent condition that leads to various health-related consequences and is also an important cause of disability worldwide. Earlier, SD experiments were used as research modalities to alter human behavior. In recent years, the focus has shifted to understand how SD can affect the mental health of individuals (with congenital or acquired sensory impairments). This narrative review focuses on the current understanding about the association of SD and psychiatric disorders.

METHODS

A comprehensive literature search was done PubMed, Scopus, PsycINFO, and Google Scholar and in the cross-references of relevant articles. Keywords included "sensory deprivation," "blindness," "deafness," "mental illness," "psychiatric disorders," "prevalence," "assessment," and "management" in various combinations. Only original articles (abstract and full text) published in English till October 2020 were included.

RESULTS

The prevalence of anxiety, depression, dementia, suicidality, and psychosis in persons with SD is higher than the general population (highest being in persons with dementia with comorbid SD). Several mechanisms/hypotheses have been proposed to explain these associations. Assessment of SD includes a thorough history taking, with adequate awareness about the difficulties faced during a psychiatric interview in this population. Modifications in the psychometric assessment procedures are warranted. Management depends on a multi-disciplinary approach that includes proper referral to specialties, pharmacological management (depending on diagnosis as well as taking care of ototoxic/ocular side-effect profile of the drugs), and nonpharmacological supportive measures.

CONCLUSIONS

SD is a complex condition, and evidence suggests that persons with SD have higher psychiatric morbidity. A comprehensive assessment, along with holistic management approach is warranted.

Odor identification impairment in autism spectrum disorder might be associated with mitochondrial dysfunction

Deficits in olfactory function in autism spectrum disorder (ASD) have already been reported. However, the results of previous studies are not consistent, and the pathophysiological mechanisms of olfactory dysfunction in ASD are not clear. Fifty-three male ASD children or teenagers aged 9-16 years were recruited for the study. The identification and discrimination portion of the Sniffin' Sticks test (SST) was used to assess the olfactory function of the enrolled subjects. The severity of ASD core symptoms and the intelligence quotient (IQ) of participants were assessed. In addition, to explore the potential mechanism underlying olfactory dysfunction, a series of plasma biochemical indicators of oxidative stress, mitochondrial function and inflammation were measured. The mean raw scores on the SST identification and discrimination test of the study subjects were significantly lower than those of typically developing subjects reported in normative data studies. After adjusting for IQ, the odor identification score was not significantly associated with any ASD symptoms. Odor identification was found to be significantly associated with the ratio of L-lactate (L)/pyruvate (P) but not with other measured indicators. The current study validates the impairment of odor identification and discrimination in Chinese ASD children. Odor identification dysfunction may be an independent clinical symptom of ASD. The plasma L/P ratio was found to be significantly associated with odor identification performance, which suggests that mitochondrial dysfunction may be a potential mechanism underlying odor identification impairment in ASD.

Modelling the neurodevelopmental pathogenesis in neuropsychiatric disorders. Bioactive kynurenines and their analogues as neuroprotective agents-in celebration of 80th birthday of Professor Peter Riederer

Following introduction of the monoamine oxidase type B inhibitor selegiline for the treatment of Parkinson's disease (PD), discovery of the action mechanism of Alzheimer's disease-modifying agent memantine, the role of iron in PD, and the loss of electron transport chain complex I in PD, and development of the concept of clinical neuroprotection, Peter Riederer launched one of the most challenging research project neurodevelopmental aspects of neuropsychiatric disorders. The neurodevelopmental theory holds that a disruption of normal brain development in utero or during early life underlies the subsequent emergence of neuropsychiatric symptoms during later life. Indeed, the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition and the International Classification of Diseases, 11th Revision categorize autism spectrum disorder and attention deficit hyperactivity disorder in neurodevelopmental disorders (NDDs). More and more evidence, especially from preclinical studies, is revealing that neurodevelopmental pathology is not limited to the diagnostic class above, but also contributes to the development of other psychiatric disorders such as schizophrenia, bipolar disorder, and obsessive-compulsive disorder as well as neurodegenerative diseases such as PD and Huntington's disease. Preclinical animal research is taking a lead in understanding the pathomechanisms of NDDs, searching for novel targets, and developing new neuroprotective agents against NDDs. This narrative review discusses emerging evidence of the neurodevelopmental etiology of neuropsychiatric disorders, recent advances in modelling neurodevelopmental pathogenesis, potential strategies of clinical neuroprotection using novel kynurenine metabolites and analogues, and future research direction for NDDs.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Sensory over-responsivity and symptoms across the obsessive-compulsive spectrum: a web-based study (Preprint)

BACKGROUND

Sensory overresponsivity (SOR) has emerged as a potential endophenotype in obsessive-compulsive disorder (OCD), but few studies have examined SOR in relation to the major symptom dimensions of OCD and to symptoms across the full obsessive-compulsive (OC) symptom spectrum.

OBJECTIVE

This study had 2 main objectives. First, we examined the psychometric properties of the SOR Scales in a community-based sample of Spanish adolescents and adults. Second, we identified how SOR difficulties are related to symptoms across the full OC spectrum (eg, OC, body dysmorphic, hoarding, skin-picking, and hair-pulling symptoms), including the heterogeneity of OC symptoms.

METHODS

We translated the SOR Scales into Spanish-a measure that assesses SOR across the 5 sensory modalities-and created a web-based version of the measure. A sample of 1454 adolescents and adults (mean age 23.84, SD 8.46 years) participated in the study, and 388 (26.69%) participants completed the survey twice (approximately 8 months apart). The survey also contained a web-based measure that assesses symptoms across the full OC spectrum: harm and checking, taboo obsessions, contamination or cleaning, symmetry and ordering, body dysmorphic, hoarding, hair-pulling, and skin-picking symptoms.

RESULTS

The psychometric properties of the SOR Scales were excellent, and the test-retest reliability was adequate. All types of SOR were related to all major symptom dimensions of OCD and to all OC spectrum symptoms.

CONCLUSIONS

SOR across the sensory modalities can be validly assessed using a web-based measure. SOR emerged as a pure transdiagnostic phenomenon in relation to symptoms across the OC spectrum, with no specific sensory modality being more strongly related to OC symptoms. SOR can shed much needed light on basic mechanisms that are important for the onset and maintenance of OC spectrum symptoms, and this study shows that large-scale web-based studies can aid in this endeavor. Future studies should examine whether SOR precedes or emerges alongside OC symptoms.

Olfactory identification impairment in early-and late-onset obsessive-compulsive disorder

BACKGROUND

Early-onset obsessive-compulsive disorder (EOCD) is a comparatively severe subtype of obsessive-compulsive disorder (OCD). Olfactory dysfunction is a common symptom of OCD, but all previous studies have focused on late-onset OCD (LOCD).

METHODS

The current study compared olfactory identification ability in EOCD patients and age-matched and sex-matched LOCD patients and healthy controls. Thirty patients with EOCD, 30 patients with LOCD and 30 healthy controls were included in the study. Olfactory function was measured using the University of Pennsylvania Smell Identification Test. The Logical Memory and Visual Reproduction components of the Revised Wechsler Memory Scale were used to evaluate verbal and visual memory.

RESULTS

There were significant differences in olfactory identification ability between the three groups. EOCD patients were comparable to LOCD patients, while both patients' group showing worse olfactory identification ability than controls. Olfactory identification ability was not significantly correlated with verbal and visual memory or clinical symptoms in the EOCD group or the LOCD group.

CONCLUSIONS

The results of the present study suggest that olfactory identification ability may be a relatively stable indicator of OCD, independent of age, duration of illness, verbal and visual memory, and severity of clinical symptoms.

Odour detection in children and young people with profound intellectual and multiple disabilities

BACKGROUND

Olfaction provides information on very important dimensions of the environment; however the olfactory abilities of children and young people with profound intellectual and multiple disabilities (PIMD) remain largely unknown. This within-subjects study explores olfactory detection abilities in children with PIMD.

METHOD

Twenty-two children and young people with PIMD (7-18 years) were presented with 18 medium intensity odours and an odourless control stimulus. Odorants were presented one by one in a randomised order. The neutral stimulus was presented prior to each odorant. Participants' responses were measured using 21 behavioural indicators.

RESULTS

Results show that participants make a clear distinction between odorous and neutral conditions, between food and non-food, and between pleasant and unpleasant odours. The detection abilities are manifested by several behaviours, in particular by the duration of the head alignment on the odorant.

CONCLUSIONS

This study shows that participants detect the stimuli and act differently depending on the category.

Criss-crossing autism spectrum disorder and adult neurogenesis

Autism spectrum disorder (ASD) comprises a group of multifactorial neurodevelopmental disorders primarily characterized by deficits in social interaction and repetitive behavior. Although the onset is typically in early childhood, ASD poses a lifelong challenge for both patients and caretakers. Adult neurogenesis (AN) is the process by which new functional neurons are created from neural stem cells existing in the post-natal brain. The entire event is based on a sequence of cellular processes, such as proliferation, specification of cell fate, maturation, and ultimately, synaptic integration into the existing neural circuits. Hence, AN is implicated in structural and functional brain plasticity throughout life. Accumulating evidence shows that impaired AN may underlie some of the abnormal behavioral phenotypes seen in ASD. In this review, we approach the interconnections between the molecular pathways related to AN and ASD. We also discuss existing therapeutic approaches targeting such pathways both in preclinical and clinical studies. A deeper understanding of how ASD and AN reciprocally affect one another could reveal important converging pathways leading to the emergence of psychiatric disorders.

Perception and Motion in Real and Virtual Environments: A Narrative Review of Autism Spectrum Disorders

Atypical sensorimotor developmental trajectories greatly contribute to the profound heterogeneity that characterizes Autism Spectrum Disorders (ASD). Individuals with ASD manifest deviations in sensorimotor processing with early markers in the use of sensory information coming from both the external world and the body, as well as motor difficulties. The cascading effect of these impairments on the later development of higher-order abilities (e.g., executive functions and social communication) underlines the need for interventions that focus on the remediation of sensorimotor integration skills. One of the promising technologies for such stimulation is Immersive Virtual Reality (IVR). In particular, head-mounted displays (HMDs) have unique features that fully immerse the user in virtual realities which disintegrate and otherwise manipulate multimodal information. The contribution of each individual sensory input and of multisensory integration to perception and motion can be evaluated and addressed according to a user’s clinical needs. HMDs can therefore be used to create virtual environments aimed at improving people’s sensorimotor functioning, with strong potential for individualization for users. Here we provide a narrative review of the sensorimotor atypicalities evidenced by children and adults with ASD, alongside some specific relevant features of IVR technology. We discuss how individuals with ASD may interact differently with IVR versus real environments on the basis of their specific atypical sensorimotor profiles and describe the unique potential of HMD-delivered immersive virtual environments to this end.

Food preferences, food neophobia and chemosensation among adolescents with ADHD

AIM

It has been suggested that adolescents diagnosed with ADHD have an unhealthier diet compared to their peers without ADHD. The association between chemosensation (smell and taste) and dietary patterns remains unknown. The aim is to investigate unhealthy food preferences and food neophobic behaviour among adolescents diagnosed with ADHD. Additionally, it is to investigate the relationship between dietary patterns and chemosensory function.

METHODS

We enrolled 36 adolescents with and without ADHD to complete a food item and a food neophobia questionnaire and to undergo chemosensory testing.

RESULTS

Adolescents with ADHD performed significantly worse on both chemosensory tests compared to the non-ADHD group. No difference in food preferences nor food neophobia was found between the two groups.

CONCLUSION

Adolescents with ADHD have a lower score on chemosensory tests compared to their peers, suggesting impaired chemosensory function. No differences in dietary preferences nor food neophobia were seen between the two groups.

A systematic-review of olfactory deficits in neurodevelopmental disorders: From mouse to human

Olfactory impairment is a common clinical motif across neurodevelopmental disorders, suggesting olfactory circuits are particularly vulnerable to disease processes and can provide insight into underlying disease mechanisms. The mouse olfactory bulb is an ideal model system to study mechanisms of neurodevelopmental disease due to its anatomical accessibility, behavioral relevance, ease of measuring circuit input and output, and the feature of adult neurogenesis. Despite the clinical relevance and experimental benefits, olfactory testing across animal models of neurodevelopmental disease has been inconsistent and non-standardized. Here we performed a systematic literature review of olfactory function testing in mouse models of neurodevelopmental disorders, and identified intriguing inconsistencies that include evidence for both increased and decreased acuity in odor detection in various mouse models of Autism Spectrum Disorder (ASD). Based on our identified gaps in the literature, we recommend direct comparison of different mouse models of ASD using standardized tests for odor detection and discrimination. This review provides a framework to guide future olfactory function testing in mouse models of neurodevelopmental diseases.

Oxytocin modulates neural processing of mitral/tufted cells in the olfactory bulb

AIM

Oxytocin plays an important role in social recognition in rodents, which is mediated predominantly by the olfactory system. Although oxytocin modulates neural activity in the olfactory bulb, the underlying mechanism is largely unknown. Here, we studied how direct infusion of oxytocin into the olfactory bulb affect social interactions in mice and modulate the neural activity of mitral/tufted cells in the olfactory bulb.

METHODS

A three-chamber social interaction test was used in the behavioural test. For in vivo studies, single unit recordings, local field potential recordings and fibre photometry recordings were used to record the neural activity of olfactory bulb. For in vitro studies, we performed patch clamp recordings in the slice of the olfactory bulb.

RESULTS

Behaviourally, direct oxytocin infusion in olfactory bulb increased performance in a social interaction task. Moreover, odour-evoked responses of mitral/tufted cells and neural discrimination of odours were both enhanced by oxytocin, whereas the spontaneous firing rate of mitral/tufted cells was reduced. At the neural network level, oxytocin decreased the amplitude of odour-evoked high gamma responses. At the cell population level, oxytocin decreased odour-evoked calcium responses (reflecting neural activity) specifically in granule cells. Moreover, in vitro slice recordings revealed that the inhibitory effect of oxytocin on mitral cell activity is mediated mainly by modulation of ATP-sensitive potassium channels and involves the oxytocin receptor-Gq-PLC-IP₃ signalling pathway.

CONCLUSION

Oxytocin modulates social interaction, likely by increasing the signal-to-noise ratio of odour responses in mitral cells which is partly through ATP-sensitive potassium channel.

Touch and olfaction/taste differentiate children carrying a 16p11.2 deletion from children with ASD

Background

Sensory processing atypicalities are frequent in Autism Spectrum Disorder (ASD) and neurodevelopmental disorders (NDD). Different domains of sensory processing appear to be differentially altered in these disorders. In this study, we explored the sensory profile of two clinical cohorts, in comparison with a sample of typically developing children.

Methods

Behavioral responses to sensory stimuli were assessed using the Sensory Processing Measure (parent-report questionnaire). We included 121 ASD children, 17 carriers of the 16p11.2 deletion (Del 16p11.2) and 45 typically developing (TD) children. All participants were aged between 2 and 12 years. Additional measures included the Tactile Defensiveness and Discrimination Test-Revised, Wechsler Intelligence Scales and Autism Diagnostic Observation Schedule (ADOS-2). Statistical analyses included MANCOVA and regression analyses.

Results

ASD children score significantly higher on all SPM subscales compared to TD. Del16p11.2 also scored higher than TD on all subscales except for tactile and olfactory/taste processing, in which they score similarly to TD. When assessing sensory modulation patterns (hyper-, hypo-responsiveness and seeking), ASD did not significantly differ from del16p11.2. Both groups had significantly higher scores across all patterns than the TD group. There was no significant association between the SPM Touch subscale and the TDDT-R.

Limitations

Sensory processing was assessed using a parent-report questionnaire. Even though it captures observable behavior, a questionnaire does not assess sensory processing in all its complexity. The sample size of the genetic cohort and the small subset of ASD children with TDDT-R data render some of our results exploratory. Divergence between SPM Touch and TDDT-R raises important questions about the nature of the process that is assessed.

Conclusions

Touch and olfaction/taste seem to be particularly affected in ASD children compared to del16p11.2. These results indicate that parent report measures can provide a useful perspective on behavioral expression. Sensory phenotyping, when combined with neurobiological and psychophysical methods, might have the potential to provide a better understanding of the sensory processing in ASD and in other NDD.

The Role of Copy Number Variations and FHIT Gene on Phenotypic Characteristics of Cases Diagnosed with Autism Spectrum Disorder

Copy number variations (CNVs) have been implied in the etiology of autism spectrum disorder (ASD), and microarray-based techniques are performed as a first-step genetic test. Our aim was to present clinical features and CNV profiles of patients with ASD and their parents. Array-CGH was applied to detect CNVs. Previously as likely pathogenic reported duplications were detected at 16p13.11 and 11p15.2p15.1. Other variants were found in 16p11.2p11.1, 3p14.2, 15q11.2, 10q11.22, 3p26.3, 4q13.3, 22q13.32q13.33, and 1q44 and were classified as variants of unknown significance. Deletion of the FHIT gene was associated with the regression of language and social skills without mental impairment. Paternal inheritance of difficulty in social skills and the FHIT gene was documented. In addition, varying olfactory receptor family genes were implicated in de novo and hereditary CNVs. In this study, we aimed to present the clinical characteristics of the cases and parents in more detail, especially in pathogenic CNV cases, which enables us to increase our knowledge on inherited CNVs and genotype-phenotype correlation. We suggest that both genetic and psychiatric evaluation of the parents of the cases is important for better understanding the clinical relevance of the CNV results.

Lisdexamfetamine Alters BOLD-fMRI Activations Induced by Odor Cues in Impulsive Children

INTRODUCTION

Lisdexamfetamine (LDX) is a drug used to treat ADHD/impulsive patients. Impulsivity is known to affect inhibitory, emotional and cognitive function. On the other hand, smell and odor processing are known to be affected by neurological disorders, as they are modulators of addictive and impulsive behaviors specifically. We hypothesize that, after LDX ingestion, inhibitory pathways of the brain would change, and complementary behavioral regulation mechanisms would appear to regulate decision-making and impulsivity.

METHODS

20 children were studied in an aleatory crossover study. Imaging of BOLD-fMRI activity, elicited by olfactory stimulation in impulsive children, was performed after either LDX or placebo ingestion.

RESULTS

Findings showed that all subjects who underwent odor stimulation presented activations of similar intensities in the olfactory centers of the brain. This contrasted with inhibitory regions of the brain such as the cingulate cortex and frontal lobe regions, which demonstrated changed activity patterns and intensities. While some differences between the placebo and medicated states were found in motor areas, precuneus, cuneus, calcarine, supramarginal, cerebellum and posterior cingulate cortex, the main changes were found in frontal, temporal and parietal cortices. When comparing olfactory cues separately, pleasant food smells like chocolate seemed not to present large differences between the medicated and placebo scenarios, when compared to non-food-related smells.

CONCLUSION

It was demonstrated that LDX, first, altered the inhibitory pathways of the brain, secondly it increased activity in several brain regions which were not activated by smell in drug-naïve patients, and thirdly, it facilitated a complementary behavioral regulation mechanism, run by the cerebellum, which regulated decision-making and impulsivity in motor and frontal structures.