First neuronal projection from Haller's organ to the synganglion and three-dimensional reconstruction of Amblyomma sculptum olfactory lobe.

Because information regarding neural and sensory functions of ticks is scarce, the aim of the present study was to ascertain the neuronal projection patterns of olfactory sensilla from Haller's organ to the olfactory lobes of the synganglion in Amblyomma sculptum adults. Additionally, the aim was to perform three-dimensional (3D) reconstruction of the glomeruli in the olfactory lobes. Unfed female and male adults of this tick species were immobilized, Haller's organ was sectioned, and the olfactory nerves were labelled with a neuronal tracer (1% dextran tetramethylrhodamine). The labelled olfactory lobes were observed under a confocal laser scanning microscope and the images were analyzed using the Reconstruct software. The neuronal projection originating from the olfactory sensilla of Haller's organ was found to be strictly confined to the olfactory lobes of the synganglion, which were organized into glomeruli. Males and females presented corresponding round-shaped glomeruli in the olfactory lobes. The number of glomeruli ranged from 26 to 30 in the males and 24-29 in the females. Positive correlations regarding the glomeruli volumes (µm3) intrasexually (females: r = 0.85, P < 0.05) and intersexually (r = 0.81, P < 0.05) were observed. This is the first report on 3D reconstruction of the olfactory lobes of a tick species.

Neuroanatomical MRI study: reference values for the measurements of brainstem, cerebellar vermis, and peduncles.

OBJECTIVES: To set age-specific normal reference values for brainstem, cerebellar vermis, and peduncles measurements and characterize values' variations according to gender, age, and age by gender interaction. METHODS: 565 normal brain magnetic resonance examinations with normal anatomy and signal intensity of the supra- and infratentorial structures were categorized into six age groups (infant, child, adolescent, young adult, middle-age adult, and old aged adults). Patients with congenital malformations, gross pathology of the supra- or infratentorial brain, brain volume loss, developmental delay, metabolic disorders, and neuropsychological disorders (n = 2.839) were excluded. On midsagittal T1 weighted and axial T2 weighted images specific linear diameters and ratios of the brainstem, cerebellar vermis, and peduncles were attained. Two observers assessed a random sample of 100 subjects to evaluate the inter- and intraobserver reproducibility. Intraclass correlation coefficients, means ± standard deviation, one and two-way analysis of variance tests were used in the statistical analysis. RESULTS: Good to excellent inter- and intraobserver measurements' reproducibility were observed, except for the transverse diameter of the midbrain, the anteroposterior diameter of the medulla oblongata at the pontomedullary and cervicomedullary junctions, cerebellar vermis anteroposterior diameter, and thickness of the superior cerebellar peduncle. Age-specific mean values of the investigated measurements were established. A significant gender-related variation was recorded in the anteroposterior diameter of the basis pontis (p = 0.044), the anteroposterior diameter of the medulla oblongata at the cervicomedullary junction (p = 0.044), and cerebellar vermis height (p = 0.018). A significant age-related change was detected in all measurements except the tectal ratio. Age by gender interaction had a statistically significant effect on the tectal ratio, inferior, and middle cerebellar peduncles' thickness (p = 0.001, 0.022, and 0.028, respectively). CONCLUSION: This study provides age-specific normal mean values for various linear dimensions and ratios of the posterior fossa structures with documentation of measurements' variability according to gender, age, and their interaction. ADVANCES IN KNOWLEDGE: It provides a valuable reference in the clinical practice for easier differentiation between physiological and pathological conditions of the posterior fossa structures especially various neurodegenerative diseases and congenital anomalies.

Greater hippocampal gray matter volume in subjective hyperosmia: a voxel-based morphometry study.

Subjective hyperosmia refers to a self-reported olfactory ability that is superior to a normal, intact sense of smell (normosmia), and is associated with olfactory emotional experience. The current study used voxel-based morphometry to investigate the gray matter volume (GMV) in people with self-rated hyperosmia (subjective hyperosmia, SH, N = 18) in comparison to people with self-rated normal olfaction (subjective normosmia, SN, N = 14). Participants' olfactory function were assessed by the extensive olfactory test battery, the "Sniffin' Sticks" test. Within the predicted brain regions (regions-of-interest analyses), the SH participants showed larger GMV of the left hippocampus as compared to SN participants (FWE corrected p < 0.05). Further, the whole-brain search indicated that SH had larger GMV of the bilateral hippocampus, the right hypothalamus, the left precuneus, and the left superior frontal gyrus as compared to the SN group. ROI analyses showed positive correlations between the left hippocampal GMV and odor threshold or discrimination scores across all participants. In addition, the whole-brain analysis suggested that the self-rated olfactory ability was positively associated with GMV in the cerebellum, superior frontal gyrus and the precentral gyrus among SH participants. In conclusion, the current results suggest that SH was associated with increased GMV in several brain regions that were previously shown to be involved in the processing of cognitive aspects of odors.

The brain of the African wild dog. II. The olfactory system.

Employing a range of neuroanatomical stains, we detail the organization of the main and accessory olfactory systems of the African wild dog. The organization of both these systems follows that typically observed in mammals, but variations of interest were noted. Within the main olfactory bulb, the size of the glomeruli, at approximately 350 µm in diameter, are on the larger end of the range observed across mammals. In addition, we estimate that approximately 3,500 glomeruli are present in each main olfactory bulb. This larger main olfactory bulb glomerular size and number of glomeruli indicates that enhanced peripheral processing of a broad range of odorants is occurring in the main olfactory bulb of the African wild dog. Within the accessory olfactory bulb, the glomeruli did not appear distinct, rather forming a homogenous syncytia-like arrangement as seen in the domestic dog. In addition, the laminar organization of the deeper layers of the accessory olfactory bulb was indistinct, perhaps as a consequence of the altered architecture of the glomeruli. This arrangement of glomeruli indicates that rather than parcellating the processing of semiochemicals peripherally, these odorants may be processed in a more nuanced and combinatorial manner in the periphery, allowing for more rapid and precise behavioral responses as required in the highly social group structure observed in the African wild dog. While having a similar organization to that of other mammals, the olfactory system of the African wild dog has certain features that appear to correlate to their environmental niche.

Structure and flexibility in cortical representations of odour space.

The cortex organizes sensory information to enable discrimination and generalization1-4. As systematic representations of chemical odour space have not yet been described in the olfactory cortex, it remains unclear how odour relationships are encoded to place chemically distinct but similar odours, such as lemon and orange, into perceptual categories, such as citrus5-7. Here, by combining chemoinformatics and multiphoton imaging in the mouse, we show that both the piriform cortex and its sensory inputs from the olfactory bulb represent chemical odour relationships through correlated patterns of activity. However, cortical odour codes differ from those in the bulb: cortex more strongly clusters together representations for related odours, selectively rewrites pairwise odour relationships, and better matches odour perception. The bulb-to-cortex transformation depends on the associative network originating within the piriform cortex, and can be reshaped by passive odour experience. Thus, cortex actively builds a structured representation of chemical odour space that highlights odour relationships; this representation is similar across individuals but remains plastic, suggesting a means through which the olfactory system can assign related odour cues to common and yet personalized percepts.

Functional morphology of the primary olfactory centers in the brain of the hermit crab Coenobita clypeatus (Anomala, Coenobitidae).

Terrestrial hermit crabs of the genus Coenobita display strong behavioral responses to volatile odors and are attracted by chemical cues of various potential food sources. Several aspects of their sense of aerial olfaction have been explored in recent years including behavioral aspects and structure of their peripheral and central olfactory pathway. Here, we use classical histological methods and immunohistochemistry against the neuropeptides orcokinin and allatostatin as well as synaptic proteins and serotonin to provide insights into the functional organization of their primary olfactory centers in the brain, the paired olfactory lobes. Our results show that orcokinin is present in the axons of olfactory sensory neurons, which target the olfactory lobe. Orcokinin is also present in a population of local olfactory interneurons, which may relay lateral inhibition across the array of olfactory glomeruli within the lobes. Extensive lateral connections of the glomeruli were also visualized using the histological silver impregnation method according to Holmes-Blest. This technique also revealed the structural organization of the output pathway of the olfactory system, the olfactory projection neurons, the axons of which target the lateral protocerebrum. Within the lobes, the course of their axons seems to be reorganized in an axon-sorting zone before they exit the system. Together with previous results, we combine our findings into a model on the functional organization of the olfactory system in these animals.

Temporolimbic cortical volume is associated with semantic odor memory performance in aging.

Olfactory function, and specifically semantic olfactory memory (i.e., odor identification), has frequently been shown to predict cognitive functioning across multiple domains in old age. This observation suggests that olfactory function can serve as a marker for the integrity of temporolimbic cortical networks, but a clear delineation of this association is still missing. To address this issue, the present study employed voxel-based morphometry in a region of interest-based design to determine the extent to which gray matter volumes of core olfactory and memory areas are associated with olfactory memory performance in an aging population free from neurodegenerative disease. We further aimed to determine potential overlap in structural anatomical correlates, and differences in association strength, for semantic and episodic olfactory memory. Structural magnetic resonance imaging (MRI), episodic and semantic odor memory and episodic and semantic verbal memory data were collected in 422 participants from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), all aged â€‹≥ â€‹60 years. Controlling for age and education, semantic, but not episodic, olfactory memory was positively related to gray matter volume in a cluster extending from the anterior hippocampus and amygdala into the posterior piriform cortex. The observed associations remained even when verbal memory performance was controlled for, supporting a link between the olfactory memory domain and cortical volume over and above more generalized memory abilities. As such, our data provide evidence for distinct functional-structural associations for semantic odor memory, supporting the idea of temporolimbic integrity as a neurobiological substrate linking olfactory function to cognitive health in old age.

A gross morphometric study of olfactory brain components in the rufous sengi ( Elephantulus rufescens ) / Estudio morfométrico de los componentes olfativo del cerebro en el rufo sengi ( Elephantulus rufescens )

The gross morphometric features of mammalian olfactory system components show variations that may be attributed to dietary and ecological factors. We analyzed volumes and linear dimensions of olfactory brain components (OBC) namely, olfactory bulb (OB), olfactory tract (OT) and olfactory stria (OS) in an Afrotherian insectivore, the rufous sengi. These findings were then compared with those obtained previously in dogs (carnivore), goats (herbivore) and humans (omnivore). Volumes, lengths and breadths of the OBC were compared with those of the cerebral hemisphere (CH) and the whole brain (WB) by working out their ratios (%). In the sengi, the volume of OBC: WB was 1.03 %, length of OBC: CH = 58.08 % and breadth of OB: CH = 28.97 %. In an earlier report by Kavoi & Jameela respective values for the above parameters were 0.03 %, 21.47 % & 8.94 % in humans, 0.77 %, 51.87 % & 29.73 % in goats and 1.95 %, 72.30 % & 42.91 % in dogs. These observations suggest that the anatomical design of OBC happens in a manner that mimics an animal's level of reliance on the sense of smell vis-à-vis feeding lifestyles, habitat and dynamics of evolution.

Las características morfométricas de los componentes del sistema olfativo de los mamíferos muestran variaciones que pueden atribuirse a factores dietéticos y ecológicos. Analizamos los volúmenes y las dimensiones lineales de los componentes cerebrales olfativos (CCO), es decir, la médula oblonga (MO), el tracto olfatorio (TO) y la estría olfatoria (SO) en un insectívoro de Afrotherian, el sengi rufo. Estos hallazgos fueron comparados con los obtenidos previamente en perros (carnívoros), cabras (herbívoros) y humanos (omnívoros). Los volúmenes, longitudes y anchuras de los CCO se compararon con los del hemisferio cerebral (HC) y el cerebro completo (CC) mediante el cálculo de sus proporciones (%). En el sengi, el volumen de los CCO: CC fue de 1,03 %, la longitud de CCO: HC = 58,08 % y la amplitud de MO: HC = 28,97 %. En un informe anterior de Kavoi & Jameela, los valores respectivos para los parámetros anteriores fueron 0,03 %, 21,47 % y 8,94 % en humanos, 0,77 %, 51,87 % y 29,73 % en cabras y 1,95 %, 72,30 % y 42,91 % en perros. Estas observaciones sugieren que el diseño anatómico de la CCO se realiza de una manera que imita el nivel de confianza de un animal en el sentido del olfato en relación con los estilos de vida, el hábitat y la dinámica de la evolución.

Comparative Brain Morphology of the Greenland and Pacific Sleeper Sharks and its Functional Implications.

In cartilaginous fishes, variability in the size of the brain and its major regions is often associated with primary habitat and/or specific behavior patterns, which may allow for predictions on the relative importance of different sensory modalities. The Greenland (Somniosus microcephalus) and Pacific sleeper (S. pacificus) sharks are the only non-lamnid shark species found in the Arctic and are among the longest living vertebrates ever described. Despite a presumed visual impairment caused by the regular presence of parasitic ocular lesions, coupled with the fact that locomotory muscle power is often depressed at cold temperatures, these sharks remain capable of capturing active prey, including pinnipeds. Using magnetic resonance imaging (MRI), brain organization of S. microcephalus and S. pacificus was assessed in the context of up to 117 other cartilaginous fish species, using phylogenetic comparative techniques. Notably, the region of the brain responsible for motor control (cerebellum) is small and lacking foliation, a characteristic not yet described for any other large-bodied (>3 m) shark. Further, the development of the optic tectum is relatively reduced, while olfactory brain regions are among the largest of any shark species described to date, suggestive of an olfactory-mediated rather than a visually-mediated lifestyle.

Functional and anatomical specificity in a higher olfactory centre.

Most sensory systems are organized into parallel neuronal pathways that process distinct aspects of incoming stimuli. In the insect olfactory system, second order projection neurons target both the mushroom body, required for learning, and the lateral horn (LH), proposed to mediate innate olfactory behavior. Mushroom body neurons form a sparse olfactory population code, which is not stereotyped across animals. In contrast, odor coding in the LH remains poorly understood. We combine genetic driver lines, anatomical and functional criteria to show that the Drosophila LH has ~1400 neurons and >165 cell types. Genetically labeled LHNs have stereotyped odor responses across animals and on average respond to three times more odors than single projection neurons. LHNs are better odor categorizers than projection neurons, likely due to stereotyped pooling of related inputs. Our results reveal some of the principles by which a higher processing area can extract innate behavioral significance from sensory stimuli.

Neurogenetic dissection of the Drosophila lateral horn reveals major outputs, diverse behavioural functions, and interactions with the mushroom body.

Animals exhibit innate behaviours to a variety of sensory stimuli including olfactory cues. In Drosophila, one higher olfactory centre, the lateral horn (LH), is implicated in innate behaviour. However, our structural and functional understanding of the LH is scant, in large part due to a lack of sparse neurogenetic tools for this region. We generate a collection of split-GAL4 driver lines providing genetic access to 82 LH cell types. We use these to create an anatomical and neurotransmitter map of the LH and link this to EM connectomics data. We find ~30% of LH projections converge with outputs from the mushroom body, site of olfactory learning and memory. Using optogenetic activation, we identify LH cell types that drive changes in valence behavior or specific locomotor programs. In summary, we have generated a resource for manipulating and mapping LH neurons, providing new insights into the circuit basis of innate and learned olfactory behavior.

Marked interspecific differences in the neuroanatomy of the male olfactory system of honey bees (genus Apis).

All honey bee species (genus Apis) display a striking mating behavior with the formation of male (drone) congregations, in which virgin queens mate with many drones. Bees' mating behavior relies on olfactory communication involving queen-but also drone pheromones. To explore the evolution of olfactory communication in Apis, we analyzed the neuroanatomical organization of the antennal lobe (primary olfactory center) in the drones of five species from the three main lineages (open-air nesting species: dwarf honey bees Apis florea and giant honey bees Apis dorsata; cavity-nesting species: Apis mellifera, Apis kochevnikovi, and Apis cerana) and from three populations of A. cerana (Borneo, Thailand, and Japan). In addition to differences in the overall number of morphological units, the glomeruli, our data reveal marked differences in the number and position of macroglomeruli, enlarged units putatively dedicated to sex pheromone processing. Dwarf and giant honey bee species possess two macroglomeruli while cavity-nesting bees present three or four macroglomeruli, suggesting an increase in the complexity of sex communication during evolution in the genus Apis. The three A. cerana populations showed differing absolute numbers of glomeruli but the same three macroglomeruli. Overall, we identified six different macroglomeruli in the genus Apis. One of these (called MGb), which is dedicated to the detection of the major queen compound 9-ODA in A. mellifera, was conserved in all species. We discuss the implications of these results for our understanding of sex communication in honey bees and propose a putative scenario of antennal lobe evolution in the Apis genus.

Structural organization of the olfactory organ in an amphihaline migratory fish Hilsa, Tenualosa ilisha.

The histological as well as ultramicroscopic structures of olfactory system of an amphihaline migratory fish hilsa Tenualosa ilisha, were studied. The sexually matured riverine fish were collected from a common breeding habitat-the Hooghly, a tributary of river Ganga, West Bengal, India. This study revealed that the riverine hilsa has larger olfactory bulb compared to marine hilsa with the olfactory lobes well exposed through nostrils. The olfactory lamellae (OL) are 40-45 in number and posses three distinct layers of sensory cells across each lamellae, namely, outer receptor cells (RC), middle sensory cells, and inner basal cells (BC). Besides the above arrangement, the sensory part of olfactory epithelium (OE) also bears rich microvillous cells exposed to the surface of the OE. The sensory and non-sensory surfaces on OL are distinguishable, with clear dendritic cells on sensory epithelium and solitary chemosensory cells on non sensory OE. Abundance of both types of cells in the OE is an indication of its chemoattraction ability towards molecules of amino acid origin. The feature of having abundant, dense, and large dendritic knobs on the surface of OE describes resemblance to the typical morphology of the chemosensory septal organs neuron. The expression of four G protein subunits, like Gαs/olf, Gαq, Gαo, and Gαi-3 in OE indicate that its olfaction is a functional attributes of two olfactory systems, namely main olfactory system and Vomaronasal Olfactory System. Expression of ACIII and PLCß2 in OE further confirms two signaling pathways involved in odorant reception in hilsa. RESEARCH HIGHLIGHTS: The olfactory bulb in the amphihaline migratory fish hilsa is big in size, with 40-45 lamellae. Its sensory areas showed multilayered cellular features with prominent sensory as well as microvillous cells, whereas non-sensory area possesses solitary chemosensory cells. The expression of four G protein subunits, Gαs/olf, Gαq, Gαo, and Gαi-3 in olfactory epithelium indicates that its olfaction is a functional attributes of two olfactory systems, namely main olfactory system and vomaronasal olfactory system.

Hippocampal projections to the anterior olfactory nucleus differentially convey spatiotemporal information during episodic odour memory.

The hippocampus is essential for representing spatiotemporal context and establishing its association with the sensory details of daily life to form episodic memories. The olfactory cortex in particular shares exclusive anatomical connections with the hippocampus as a result of their common evolutionary history. Here we selectively inhibit hippocampal projections to the anterior olfactory nucleus (AON) during behavioural tests of contextually cued odour recall. We find that spatial odour memory and temporal odour memory are independently impaired following inhibition of distinct, topographically organized hippocampal-AON pathways. Our results not only reveal a longstanding unknown function for the AON but offer new mechanistic insights regarding the representation of odours in episodic memory.

Cholinesterases in normal and Alzheimer's disease primary olfactory gyrus.

AIMS: Alzheimer's disease (AD) is characterized by cholinergic dysfunction and deposition of ß-amyloid (Aß) plaques and tau neurofibrillary tangles (NFTs) in the brain. Olfactory abnormalities often precede cognitive symptoms in AD, indicating early involvement of pathology in olfactory structures. The cholinergic system is important not only in cognition but also in modulation of the olfactory system. The primary olfactory gyrus (POG) is comprised of the olfactory tract, anterior olfactory nucleus (AON) and olfactory area (OA). Because of the importance of the olfactory and cholinergic systems, we examined the anatomical and cholinergic organization of the POG in normal human brain and neuropathology in AD. METHODS: Cytoarchitecture of the POG was studied using Nissl staining in normal (n = 8) and AD (n = 6) brains. Distributions of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) were determined using histochemical methods. Aß plaques and tau NFTs were detected using immunohistochemistry. Abundance of AD pathology was assessed using a semi-quantitative approach. RESULT: Nissl staining showed pyramidal cells in the AON and paleocortical organization of the OA. AChE stained neurons and neuropil in the AON and OA, while BChE activity was noted in the olfactory tract and in AON and OA neurons. Pathology was frequent in the AD POG and the abundance of BChE-associated AD pathology was greater than that associated with AChE. CONCLUSIONS: AChE and BChE activities in normal POG recapitulated their distributions in other cortical regions. Greater abundance of BChE-associated, in comparison to AChE-associated, AD pathology in the POG suggests preferential involvement of BChE in olfactory dysfunction in AD.

Development and Organization of the Evolutionarily Conserved Three-Layered Olfactory Cortex.

The olfactory cortex is part of the mammalian cerebral cortex together with the neocortex and the hippocampus. It receives direct input from the olfactory bulbs and participates in odor discrimination, association, and learning (Bekkers and Suzuki, 2013). It is thought to be an evolutionarily conserved paleocortex, which shares common characteristics with the three-layered general cortex of reptiles (Aboitiz et al., 2002). The olfactory cortex has been studied as a "simple model" to address sensory processing, though little is known about its precise cell origin, diversity, and identity. While the development and the cellular diversity of the six-layered neocortex are increasingly understood, the olfactory cortex remains poorly documented in these aspects. Here is a review of current knowledge of the development and organization of the olfactory cortex, keeping the analogy with those of the neocortex. The comparison of olfactory cortex and neocortex will allow the opening of evolutionary perspectives on cortical development.

Differential investment in visual and olfactory brain areas reflects behavioural choices in hawk moths.

Nervous tissue is one of the most metabolically expensive animal tissues, thus evolutionary investments that result in enlarged brain regions should also result in improved behavioural performance. Indeed, large-scale comparative studies in vertebrates and invertebrates have successfully linked differences in brain anatomy to differences in ecology and behaviour, but their precision can be limited by the detail of the anatomical measurements, or by only measuring behaviour indirectly. Therefore, detailed case studies are valuable complements to these investigations, and have provided important evidence linking brain structure to function in a range of higher-order behavioural traits, such as foraging experience or aggressive behaviour. Here, we show that differences in the size of both lower and higher-order sensory brain areas reflect differences in the relative importance of these senses in the foraging choices of hawk moths, as suggested by previous anatomical work in Lepidopterans. To this end we combined anatomical and behavioural quantifications of the relative importance of vision and olfaction in two closely related hawk moth species. We conclude that differences in sensory brain volume in these hawk moths can indeed be interpreted as differences in the importance of these senses for the animal's behaviour.

The Hitchhiker's guide to the rhinencephalon.

Pathology of the rhinencephalon has been a subject of interest in the fields of neurodegenerative diseases, trauma, epilepsy and other neurological conditions. Most of what is known about the human rhinencephalon comes from comparative anatomy studies in other mammals and histological studies in primates. Functional imaging studies can provide new and important insight into the function of the rhinencephalon in humans but have limited spatial resolution, limiting its contribution to the study of the anatomy of the human rhinencephalon. In this study we aim to provide a brief and objective review of the anatomy of this important and often overlooked area of the nervous system.

The Hitchhiker’s guide to the rhinencephalon / Um guia prático sobre a anatomia do rinencéfalo

ABSTRACT Pathology of the rhinencephalon has been a subject of interest in the fields of neurodegenerative diseases, trauma, epilepsy and other neurological conditions. Most of what is known about the human rhinencephalon comes from comparative anatomy studies in other mammals and histological studies in primates. Functional imaging studies can provide new and important insight into the function of the rhinencephalon in humans but have limited spatial resolution, limiting its contribution to the study of the anatomy of the human rhinencephalon. In this study we aim to provide a brief and objective review of the anatomy of this important and often overlooked area of the nervous system.

RESUMO As patologias do rinencéfalo tem sido assunto de interesse para os estudiosos das doenças neurodegenerativas, do traumatismo cranio-encefálico, epilepsia e outras doenças neurológicas. A maior parte do conhecimento sobre a anatomia do rinencéfalo vem de estudos de anatomia comparativa com outros mamíferos e estudos histológicos em primatas. Estudos de imagem funcional, apesar de proporcionarem informações úteis e interessantes a respeito do funcionamento do rinencéfalo em humanos, sofrem de resolução espacial limitada, e portanto contribuem de maneira restrita ao estudo dos limites das áreas anatômicas. Neste artigo buscamos proporcionar ao neurologista e neurocientista interessado uma revisão prática e objetiva da anatomia desta área importante e muitas vezes esquecida do sistema nervoso.