Neuronal Representation of Social Information in the Medial Amygdala of Awake Behaving Mice.

The medial amygdala (MeA) plays a critical role in processing species- and sex-specific signals that trigger social and defensive behaviors. However, the principles by which this deep brain structure encodes social information is poorly understood. We used a miniature microscope to image the Ca2+ dynamics of large neural ensembles in awake behaving mice and tracked the responses of MeA neurons over several months. These recordings revealed spatially intermingled subsets of MeA neurons with distinct temporal dynamics. The encoding of social information in the MeA differed between males and females and relied on information from both individual cells and neuronal populations. By performing long-term Ca2+ imaging across different social contexts, we found that sexual experience triggers lasting and sex-specific changes in MeA activity, which, in males, involve signaling by oxytocin. These findings reveal basic principles underlying the brain's representation of social information and its modulation by intrinsic and extrinsic factors.

The vomeronasal system of the wolf (Canis lupus signatus): The singularities of a wild canid.

Wolves, akin to their fellow canids, extensively employ chemical signals for various aspects of communication, including territory maintenance, reproductive synchronisation and social hierarchy signalling. Pheromone-mediated chemical communication operates unconsciously among individuals, serving as an innate sensory modality that regulates both their physiology and behaviour. Despite its crucial role in the life of the wolf, there is a lacuna in comprehensive research on the neuroanatomical and physiological underpinnings of chemical communication within this species. This study investigates the vomeronasal system (VNS) of the Iberian wolf, simultaneously probing potential alterations brought about by dog domestication. Our findings demonstrate the presence of a fully functional VNS, vital for pheromone-mediated communication, in the Iberian wolf. While macroscopic similarities between the VNS of the wolf and the domestic dog are discernible, notable microscopic differences emerge. These distinctions include the presence of neuronal clusters associated with the sensory epithelium of the vomeronasal organ (VNO) and a heightened degree of differentiation of the accessory olfactory bulb (AOB). Immunohistochemical analyses reveal the expression of the two primary families of vomeronasal receptors (V1R and V2R) within the VNO. However, only the V1R family is expressed in the AOB. These findings not only yield profound insights into the VNS of the wolf but also hint at how domestication might have altered neural configurations that underpin species-specific behaviours. This understanding holds implications for the development of innovative strategies, such as the application of semiochemicals for wolf population management, aligning with contemporary conservation goals.

Histological features and Gαolf expression patterns in the nasal cavity of sea turtles.

Sea turtles use olfaction to detect volatile and water-soluble substances. The nasal cavity of green turtles (Chelonia mydas) comprises morphologically defined the anterodorsal, anteroventral, and posterodorsal diverticula, as well as a single posteroventral fossa. Here, we detailed the histological features of the nasal cavity of a mature female green turtle. The posterodorsal diverticulum contained spongy-like venous sinuses and a wave-shaped sensory epithelium that favored ventilation. Secretory structures that were significant in sensory and non-sensory epithelia were probably involved in protection against seawater. These findings suggested that green turtles efficiently intake airborne substances and dissolve water-soluble substances in mucous, while suppressing the effects of salts. In addition, positive staining of Gαs/olf that couples with olfactory, but not vomeronasal, receptors was predominant in all three types of sensory epithelium in the nasal cavity. Both of airborne and water-soluble odorants seemed to be detected in cells expressing Gαolf and olfactory receptors.

The vomeronasal system in semiaquatic beavers.

In contrast to the main olfactory system that detects volatile chemicals in the nasal air, the vomeronasal system can detect nonvolatile chemicals as well as volatiles. In the vomeronasal system, chemicals are perceived by the vomeronasal organ (VNO) projecting axons to the accessory olfactory bulb (AOB). Beavers (Castor spp.) are semiaquatic mammals that have developed chemical communication. It is possible that the beaver's anal gland secretions, nonvolatile and insoluble substances, may work as a messenger in the water and that beavers may detect the nonvolatile chemicals floating on the water surface via the VNO. The present study aimed to clarify the specificities of the beaver vomeronasal system by histologically and immunohistochemically analyzing the VNO and AOB of 12 Eurasian beavers (C. fiber). The VNO directly opened to the nasal cavity and was independent of a narrow nasopalatine duct connecting the oral and nasal cavities. The VNO comprised soft tissues including sensory and nonsensory epithelium, glands, a venous sinus, an artery, as well as cartilage inner, and bone outer enclosures. The AOB had distinct six layers, and anti-G protein α-i2 and α-o subunits were, respectively, immunoreactive in rostral and caudal glomeruli layers indicating expressions of V1Rs and V2Rs. According to gene repertories analysis, the beavers had 23 and six intact V1R and V2R genes respectively. These findings suggested that beavers recognize volatile odorants and nonvolatile substances using the vomeronasal system. The beaver VNO was developed as well as in other rodents, and it had two specific morphological features, namely, disadvantaged contact with the oral cavity because of a tiny nasopalatine duct, and a double bone and cartilage envelope. Our results highlight the importance of the vomeronasal system in beaver chemical communication and support the possibility that beavers can detect chemicals floating on the water surface via the VNO.

Do all mice smell the same? Chemosensory cues from inbred and wild mouse strains elicit stereotypic sensory representations in the accessory olfactory bulb.

BACKGROUND: For many animals, chemosensory cues are vital for social and defensive interactions and are primarily detected and processed by the vomeronasal system (VNS). These cues are often inherently associated with ethological meaning, leading to stereotyped behaviors. Thus, one would expect consistent representation of these stimuli across different individuals. However, individuals may express different arrays of vomeronasal sensory receptors and may vary in the pattern of connections between those receptors and projection neurons in the accessory olfactory bulb (AOB). In the first part of this study, we address the ability of individuals to form consistent representations despite these potential sources of variability. The second part of our study is motivated by the fact that the majority of research on VNS physiology involves the use of stimuli derived from inbred animals. Yet, it is unclear whether neuronal representations of inbred-derived stimuli are similar to those of more ethologically relevant wild-derived stimuli. RESULTS: First, we compared sensory representations to inbred, wild-derived, and wild urine stimuli in the AOBs of males from two distinct inbred strains, using them as proxies for individuals. We found a remarkable similarity in stimulus representations across the two strains. Next, we compared AOB neuronal responses to inbred, wild-derived, and wild stimuli, again using male inbred mice as subjects. Employing various measures of neuronal activity, we show that wild-derived and wild stimuli elicit responses that are broadly similar to those from inbred stimuli: they are not considerably stronger or weaker, they show similar levels of sexual dimorphism, and when examining population-level activity, cluster with inbred mouse stimuli. CONCLUSIONS: Despite strain-specific differences and apparently random connectivity, the AOB can maintain stereotypic sensory representations for broad stimulus categories, providing a substrate for common stereotypical behaviors. In addition, despite many generations of inbreeding, AOB representations capture the key ethological features (i.e., species and sex) of wild-derived and wild counterparts. Beyond these broad similarities, representations of stimuli from wild mice are nevertheless distinct from those elicited by inbred mouse stimuli, suggesting that laboratory inbreeding has indeed resulted in marked modifications of urinary secretions.

Synchronous Infra-Slow Oscillations Organize Ensembles of Accessory Olfactory Bulb Projection Neurons into Distinct Microcircuits.

The accessory olfactory system controls social and sexual behavior. In the mouse accessory olfactory bulb, the first central stage of information processing along the accessory olfactory pathway, projection neurons (mitral cells) display infra-slow oscillatory discharge with remarkable periodicity. The physiological mechanisms that underlie this default output state, however, remain controversial. Moreover, whether such rhythmic infra-slow activity patterns exist in awake behaving mice and whether such activity reflects the functional organization of the accessory olfactory bulb circuitry remain unclear. Here, we hypothesize that mitral cell ensembles form synchronized microcircuits that subdivide the accessory olfactory bulb into segregated functional clusters. We use a miniature microscope to image the Ca2+ dynamics within the apical dendritic compartments of large mitral cell ensembles in vivo We show that infra-slow periodic patterns of concerted neural activity, indeed, reflect the idle state of accessory olfactory bulb output in awake male and female mice. Ca2+ activity profiles are distinct and glomerulus-specific. Confocal time-lapse imaging in acute slices reveals that groups of mitral cells assemble into microcircuits that exhibit correlated Ca2+ signals. Moreover, electrophysiological profiling of synaptic connectivity indicates functional coupling between mitral cells. Our results suggest that both intrinsically rhythmogenic neurons and neurons entrained by fast synaptic drive are key elements in organizing the accessory olfactory bulb into functional microcircuits, each characterized by a distinct default pattern of infra-slow rhythmicity.SIGNIFICANCE STATEMENT Information processing in the accessory olfactory bulb (AOB) plays a central role in conspecific chemosensory communication. Surprisingly, many basic physiological principles that underlie neuronal signaling in the AOB remain elusive. Here, we show that AOB projection neurons (mitral cells) form parallel synchronized ensembles both in vitro and in vivo Infra-slow synchronous oscillatory activity within AOB microcircuits thus adds a new dimension to chemosensory coding along the accessory olfactory pathway.

Paradoxically Sparse Chemosensory Tuning in Broadly Integrating External Granule Cells in the Mouse Accessory Olfactory Bulb.

The accessory olfactory bulb (AOB), the first neural circuit in the mouse accessory olfactory system, is critical for interpreting social chemosignals. Despite its importance, AOB information processing is poorly understood compared with the main olfactory bulb (MOB). Here, we sought to fill gaps in the understanding of AOB interneuron function. We used 2-photon GCaMP6f Ca2+ imaging in an ex vivo preparation to study chemosensory tuning in AOB external granule cells (EGCs), interneurons hypothesized to broadly inhibit activity in excitatory mitral cells (MCs). In ex vivo preparations from mice of both sexes, we measured MC and EGC tuning to natural chemosignal blends and monomolecular ligands, finding that EGC tuning was sparser, not broader, than upstream MCs. Simultaneous electrophysiological recording and Ca2+ imaging showed no differences in GCaMP6f-to-spiking relationships in these cell types during simulated sensory stimulation, suggesting that measured EGC sparseness was not due to cell type-dependent variability in GCaMP6f performance. Ex vivo patch-clamp recordings revealed that EGC subthreshold responsivity was far broader than indicated by GCaMP6f Ca2+ imaging, and that monomolecular ligands rarely elicited EGC spiking. These results indicate that EGCs are selectively engaged by chemosensory blends, suggesting different roles for EGCs than analogous interneurons in the MOB.SIGNIFICANCE STATEMENT The mouse accessory olfactory system (AOS) interprets social chemosignals, but we poorly understand AOS information processing. Here, we investigate the functional properties of external granule cells (EGCs), a major class of interneurons in the accessory olfactory bulb (AOB). We hypothesized that EGCs, which are densely innervated by excitatory mitral cells (MCs), would show broad chemosensory tuning, suggesting a role in divisive normalization. Using ex vivo GCaMP6f imaging, we found that EGCs were instead more sparsely tuned than MCs. This was not due to weaker GCaMP6f signaling in EGCs than in MCs. Instead, we found that many MC-activating chemosignals caused only subthreshold EGC responses. This indicates a different role for AOB EGCs compared with analogous cells in the main olfactory bulb.

Neural pathways of olfactory kin imprinting and kin recognition in zebrafish.

Teleost fish exhibit extraordinary cognitive skills that are comparable to those of mammals and birds. Kin recognition based on olfactory and visual imprinting requires neuronal circuits that were assumed to be necessarily dependent on the interaction of mammalian amygdala, hippocampus, and isocortex, the latter being a structure that teleost fish are lacking. We show that teleosts-beyond having a hippocampus and pallial amygdala homolog-also have subpallial amygdalar structures. In particular, we identify the medial amygdala and neural olfactory central circuits related to kin imprinting and kin recognition corresponding to an accessory olfactory system despite the absence of a separate vomeronasal organ.

Can social behaviour drive accessory olfactory bulb asymmetries? Sister species of caviomorph rodents as a case in point.

In mammals, the accessory olfactory or vomeronasal system exhibits a wide variety of anatomical arrangements. In caviomorph rodents, the accessory olfactory bulb (AOB) exhibits a dichotomic conformation, in which two subdomains, the anterior (aAOB) and the posterior (pAOB), can be readily distinguished. Interestingly, different species of this group exhibit bias of different sign between the AOB subdomains (aAOB larger than pAOB or vice versa). Such species-specific biases have been related with contrasting differences in the habitat of the different species (e.g. arid vs. humid environments). Aiming to deepen these observations, we performed a morphometric comparison of the AOB subdomains between two sister species of octodontid rodents, Octodon lunatus and Octodon degus. These species are interesting for comparative purposes, as they inhabit similar landscapes but exhibit contrasting social habits. Previous reports have shown that O. degus, a highly social species, exhibits a greatly asymmetric AOB, in which the aAOB has twice the size of the pAOB and features more and larger glomeruli in its glomerular layer (GL). We found that the same as in O. degus, the far less social O. lunatus also exhibits a bias, albeit less pronounced, to a larger aAOB. In both species, this bias was also evident for the mitral/tufted cells number. But unlike in O. degus, in O. lunatus this bias was not present at the GL. In comparison with O. degus, in O. lunatus the aAOB GL was significantly reduced in volume, while the pAOB GL displayed a similar volume. We conclude that these sister species exhibit a very sharp difference in the anatomical conformation of the AOB, namely, the relative size of the GL of the aAOB subdomain, which is larger in O. degus than in O. lunatus. We discuss these results in the context of the differences in the lifestyle of these species, highlighting the differences in social behaviour as a possible factor driving to distinct AOB morphometries.

Temporal Response Properties of Accessory Olfactory Bulb Neurons: Limitations and Opportunities for Decoding.

The vomeronasal system (VNS) is a major vertebrate chemosensory system that functions in parallel to the main olfactory system (MOS). Despite many similarities, the two systems dramatically differ in the temporal domain. While MOS responses are governed by breathing and follow a subsecond temporal scale, VNS responses are uncoupled from breathing and evolve over seconds. This suggests that the contribution of response dynamics to stimulus information will differ between these systems. While temporal dynamics in the MOS are widely investigated, similar analyses in the accessory olfactory bulb (AOB) are lacking. Here, we have addressed this issue using controlled stimulus delivery to the vomeronasal organ of male and female mice. We first analyzed the temporal properties of AOB projection neurons and demonstrated that neurons display prolonged, variable, and neuron-specific characteristics. We then analyzed various decoding schemes using AOB population responses. We showed that compared with the simplest scheme (i.e., integration of spike counts over the entire response period), the division of this period into smaller temporal bins actually yields poorer decoding accuracy. However, optimal classification accuracy can be achieved well before the end of the response period by integrating spike counts within temporally defined windows. Since VNS stimulus uptake is variable, we analyzed decoding using limited information about stimulus uptake time, and showed that with enough neurons, such time-invariant decoding is feasible. Finally, we conducted simulations that demonstrated that, unlike the main olfactory bulb, the temporal features of AOB neurons disfavor decoding with high temporal accuracy, and, rather, support decoding without precise knowledge of stimulus uptake time.SIGNIFICANCE STATEMENT A key goal in sensory system research is to identify which metrics of neuronal activity are relevant for decoding stimulus features. Here, we describe the first systematic analysis of temporal coding in the vomeronasal system (VNS), a chemosensory system devoted to socially relevant cues. Compared with the main olfactory system, timescales of VNS function are inherently slower and variable. Using various analyses of real and simulated data, we show that the consideration of response times relative to stimulus uptake can aid the decoding of stimulus information from neuronal activity. However, response properties of accessory olfactory bulb neurons favor decoding schemes that do not rely on the precise timing of stimulus uptake. Such schemes are consistent with the variable nature of VNS stimulus uptake.

Convergent vomeronasal system reduction in mammals coincides with convergent losses of calcium signalling and odorant-degrading genes.

The vomeronasal system (VNS) serves crucial functions for detecting olfactory clues often related to social and sexual behaviour. Intriguingly, two of the main components of the VNS, the vomeronasal organ (VNO) and the accessory olfactory bulb, are regressed in aquatic mammals, several bats and primates, likely due to adaptations to different ecological niches. To detect genomic changes that are associated with the convergent reduction of the VNS, we performed the first systematic screen for convergently inactivated protein-coding genes associated with convergent VNS reduction, considering 106 mammalian genomes. Extending previous studies, our results support that Trpc2, a cation channel that is important for calcium signalling in the VNO, is a predictive molecular marker for the presence of a VNS. Our screen also detected the convergent inactivation of the calcium-binding protein S100z, the aldehyde oxidase Aox2 that is involved in odorant degradation, and the uncharacterized Mslnl gene that is expressed in the VNO and olfactory epithelium. Furthermore, we found that Trpc2 and S100z or Aox2 are also inactivated in otters and Phocid seals for which no morphological data about the VNS are available yet. This predicts a VNS reduction in these semi-aquatic mammals. By examining the genomes of 115 species in total, our study provides a detailed picture of how the convergent reduction of the VNS coincides with gene inactivation in placental mammals. These inactivated genes provide experimental targets for studying the evolution and biological significance of the olfactory system under different environmental conditions.

Genetic dissection of pheromone processing reveals main olfactory system-mediated social behaviors in mice.

Most mammals have two major olfactory subsystems: the main olfactory system (MOS) and vomeronasal system (VNS). It is now widely accepted that the range of pheromones that control social behaviors are processed by both the VNS and the MOS. However, the functional contributions of each subsystem in social behavior remain unclear. To genetically dissociate the MOS and VNS functions, we established two conditional knockout mouse lines that led to either loss-of-function in the entire MOS or in the dorsal MOS. Mice with whole-MOS loss-of-function displayed severe defects in active sniffing and poor survival through the neonatal period. In contrast, when loss-of-function was confined to the dorsal MOB, sniffing behavior, pheromone recognition, and VNS activity were maintained. However, defects in a wide spectrum of social behaviors were observed: attraction to female urine and the accompanying ultrasonic vocalizations, chemoinvestigatory preference, aggression, maternal behaviors, and risk-assessment behaviors in response to an alarm pheromone. Functional dissociation of pheromone detection and pheromonal induction of behaviors showed the anterior olfactory nucleus (AON)-regulated social behaviors downstream from the MOS. Lesion analysis and neural activation mapping showed pheromonal activation in multiple amygdaloid and hypothalamic nuclei, important regions for the expression of social behavior, was dependent on MOS and AON functions. Identification of the MOS-AON-mediated pheromone pathway may provide insights into pheromone signaling in animals that do not possess a functional VNS, including humans.

Interdependent Conductances Drive Infraslow Intrinsic Rhythmogenesis in a Subset of Accessory Olfactory Bulb Projection Neurons.

The accessory olfactory system controls social and sexual behavior. However, key aspects of sensory signaling along the accessory olfactory pathway remain largely unknown. Here, we investigate patterns of spontaneous neuronal activity in mouse accessory olfactory bulb mitral cells, the direct neural link between vomeronasal sensory input and limbic output. Both in vitro and in vivo, we identify a subpopulation of mitral cells that exhibit slow stereotypical rhythmic discharge. In intrinsically rhythmogenic neurons, these periodic activity patterns are maintained in absence of fast synaptic drive. The physiological mechanism underlying mitral cell autorhythmicity involves cyclic activation of three interdependent ionic conductances: subthreshold persistent Na(+) current, R-type Ca(2+) current, and Ca(2+)-activated big conductance K(+) current. Together, the interplay of these distinct conductances triggers infraslow intrinsic oscillations with remarkable periodicity, a default output state likely to affect sensory processing in limbic circuits. SIGNIFICANCE STATEMENT: We show for the first time that some rodent accessory olfactory bulb mitral cells-the direct link between vomeronasal sensory input and limbic output-are intrinsically rhythmogenic. Driven by ≥ 3 distinct interdependent ionic conductances, infraslow intrinsic oscillations show remarkable periodicity both in vitro and in vivo. As a novel default state, infraslow autorhythmicity is likely to affect limbic processing of pheromonal information.

Embryology of the VNO and associated structures in the grass snake Natrix natrix (Squamata: Naticinae): a 3D perspective.

BACKGROUND: Snakes are considered to be vomerolfaction specialists. They are members of one of the most diverse groups of vertebrates, Squamata. The vomeronasal organ and the associated structures (such as the lacrimal duct, choanal groove, lamina transversalis anterior and cupola Jacobsoni) of adult lizards and snakes have received much anatomical, histological, physiological and behavioural attention. However, only limited embryological investigation into these structures, constrained to some anatomical or cellular studies and brief surveys, has been carried out thus far. The purpose of this study was, first, to examine the embryonic development of the vomeronasal organ and the associated structures in the grass snake (Natrix natrix), using three-dimensional reconstructions based on histological studies, and, second, to compare the obtained results with those presented in known publications on other snakes and lizards. RESULTS: Five major developmental processes were taken into consideration in this study: separation of the vomeronasal organ from the nasal cavity and its specialization, development of the mushroom body, formation of the lacrimal duct, development of the cupola Jacobsoni and its relation to the vomeronasal nerve, and specialization of the sensory epithelium. Our visualizations showed the VNO in relation to the nasal cavity, choanal groove, lacrimal duct and cupola Jacobsoni at different embryonic stages. We confirmed that the choanal groove disappears gradually, which indicates that this structure is absent in adult grass snakes. On our histological sections, we observed a gradual growth in the height of the columns of the vomeronasal sensory epithelium and widening of the spaces between them. CONCLUSIONS: The main ophidian taxa (Scolecophidia, Henophidia and Caenophidia), just like other squamate clades, seem to be evolutionarily conservative at some levels with respect to the VNO and associated structures morphology. Thus, it was possible to homologize certain embryonic levels of the anatomical and histological complexity, observed in the grass snake, with adult conditions of certain groups of Squamata. This may reflect evolutionary shift in Squamata from visually oriented predators to vomerolfaction specialists. Our descriptions offer material useful for future comparative studies of Squamata, both at their anatomical and histological levels.

Histological Properties of Main and Accessory Olfactory Bulbs in the Common Hippopotamus.

The olfactory system of mammals comprises a main olfactory system that detects hundreds of odorants and a vomeronasal system that detects specific chemicals such as pheromones. The main (MOB) and accessory (AOB) olfactory bulbs are the respective primary centers of the main olfactory and vomeronasal systems. Most mammals including artiodactyls possess a large MOB and a comparatively small AOB, whereas most cetaceans lack olfactory bulbs. The common hippopotamus (Hippopotamus amphibius) is semiaquatic and belongs to the order Cetartiodactyla, family Hippopotamidae, which seems to be the closest extant family to cetaceans. The present study evaluates the significance of the olfactory system in the hippopotamus by histologically analyzing the MOB and AOB of a male common hippopotamus. The MOB comprised six layers (olfactory nerve, glomerular, external plexiform, mitral cell, internal plexiform, and granule cell), and the AOB comprised vomeronasal nerve, glomerular, plexiform, and granule cell layers. The MOB contained mitral cells and tufted cells, and the AOB possessed mitral/tufted cells. These histological features of the MOB and the AOB were similar to those in most artiodactyls. All glomeruli in the AOB were positive for anti-Gαi2, but weakly positive for anti-Gαo, suggesting that the hippopotamus vomeronasal system expresses vomeronasal type 1 receptors with a high affinity for volatile compounds. These findings suggest that the olfactory system of the hippopotamus is as well developed as that of other artiodactyl species and that the hippopotamus might depend on its olfactory system for terrestrial social communication.

Neural map formation and sensory coding in the vomeronasal system.

Sensory systems enable us to encode a clear representation of our environment in the nervous system by spatially organizing sensory stimuli being received. The organization of neural circuitry to form a map of sensory activation is critical for the interpretation of these sensory stimuli. In rodents, social communication relies strongly on the detection of chemosignals by the vomeronasal system, which regulates a wide array of behaviours, including mate recognition, reproduction, and aggression. The binding of these chemosignals to receptors on vomeronasal sensory neurons leads to activation of second-order neurons within glomeruli of the accessory olfactory bulb. Here, vomeronasal receptor activation by a stimulus is organized into maps of glomerular activation that represent phenotypic qualities of the stimuli detected. Genetic, electrophysiological and imaging studies have shed light on the principles underlying cell connectivity and sensory map formation in the vomeronasal system, and have revealed important differences in sensory coding between the vomeronasal and main olfactory system. In this review, we summarize the key factors and mechanisms that dictate circuit formation and sensory coding logic in the vomeronasal system, emphasizing differences with the main olfactory system. Furthermore, we discuss how detection of chemosignals by the vomeronasal system regulates social behaviour in mice, specifically aggression.

Observations on the effects of odours on the homeopathic response.

Samuel Hahnemann described incidences where the homeopathic response was disrupted by noxious smells in the environment. An earlier paper proposed that homeopathic medicines may be sensed by vomeronasal cells (VNCs) i.e. microvillus or brush cells in the vomeronasal organ (VNO), the taste buds and associated with the trigeminal nerve and nervus terminalis. This paper proposes an extension to the theory and suggests that a subset of solitary chemosensory cells (SCCs) in the diffuse chemosensory system (DCS) that is morphologically similar to VNCs might also be receptive to homeopathic medicines. The types of odours that may interfere with this process are described. Two clinical cases of disruption of the homeopathic response are given as examples, showing that successful re-establishment of remedy action can be produced by timely repetition of the medicine. The ramifications on clinical homeopathic practice are discussed.

Neural basis for pheromone signal transduction in mice.

Pheromones are specialized chemical messengers used for inter-individual communication within the same species, playing crucial roles in modulating behaviors and physiological states. The detection mechanisms of these signals at the peripheral organ and their transduction to the brain have been unclear. However, recent identification of pheromone molecules, their corresponding receptors, and advancements in neuroscientific technology have started to elucidate these processes. In mammals, the detection and interpretation of pheromone signals are primarily attributed to the vomeronasal system, which is a specialized olfactory apparatus predominantly dedicated to decoding socio-chemical cues. In this mini-review, we aim to delineate the vomeronasal signal transduction pathway initiated by specific vomeronasal receptor-ligand interactions in mice. First, we catalog the previously identified pheromone ligands and their corresponding receptor pairs, providing a foundational understanding of the specificity inherent in pheromonal communication. Subsequently, we examine the neural circuits involved in processing each pheromone signal. We focus on the anatomical pathways, the sexually dimorphic and physiological state-dependent aspects of signal transduction, and the neural coding strategies underlying behavioral responses to pheromonal cues. These insights provide further critical questions regarding the development of innate circuit formation and plasticity within these circuits.

Assessment of social behavior and chemosensory cue detection in an animal model of neurodegeneration.

Numerous studies have shown that aging in humans leads to a decline in olfactory function, resulting in deficits in acuity, detection threshold, discrimination, and olfactory-associated memories. Furthermore, impaired olfaction has been identified as a potential indicator for the onset of age-related neurodegenerative diseases, including Alzheimer's disease (AD). Studies conducted on mouse models of AD have largely mirrored the findings in humans, thus providing a valuable system to investigate the cellular and circuit adaptations of the olfactory system during natural and pathological aging. However, the majority of previous research has focused on assessing the detection of neutral or synthetic odors, with little attention given to the impact of aging and neurodegeneration on the recognition of social cues-a critical feature for the survival of mammalian species. Therefore, in this study, we present a battery of olfactory tests that use conspecific urine samples to examine the changes in social odor recognition in a mouse model of neurodegeneration.

Socially-mediated activation in the snake social-decision-making network.

Brain areas important for social perception, social reward, and social behavior - collectively referred to as the social-decision-making network (SDN) - appear to be highly conserved across taxa. These brain areas facilitate a variety of social behaviors such as conspecific approach/avoidance, aggression, mating, parental care, and recognition. Although the SDN has been investigated across taxa, little is known about its functioning in reptiles. Research on the snake SDN may provide important new insights, as snakes have a keen social perceptual system and express a relatively reduced repertoire of social behaviors. Here, we present the results of an experiment in which ball pythons (Python regius) interacted with a same-sex conspecific for one hour and neural activation was investigated through Fos immunoreactivity. Compared to controls, snakes that interacted socially had higher Fos counts in brain areas implicated in social behavior across taxa, such as the medial amygdala, preoptic area, nucleus accumbens, and basolateral amygdala. Additionally, we found differential Fos immunoreactivity in the ventral amygdala, which facilitates communication between social brain areas. In many of these areas, Fos counts differed by sex, which may be due to increased competition between males. Fos counts did not differ in early sensory (i.e., vomeronasal) processing structures. As ball python social systems lack parental care, cooperation, or long-term group living, these results provide valuable insight into the basal functions of the vertebrate social decision-making network.