Caudal Area Research Articles

Higher polygenic risk scores for anxiety disorders are associated with reduced area in the anterior cingulate gyrus

Anxiety disorders are heterogeneous, show a moderate genetic contribution and are associated with inconsistent cortical structure alterations. Here, we investigated whether genetic factors for anxiety disorders contribute to cortical alterations by conducting polygenic risk score (PRS) analyses. We calculated PRSs for anxiety disorders at several P value thresholds (from PT ≤ 5.0 × 10−8 to PT ≤ 1.0) based on the latest large-scale genome-wide association study of anxiety disorders from the UK biobank (25,453 cases; 58,113 controls) in an independent sample of psychiatrically and physically healthy subjects (n = 174). Using regression after adjusting for confounding factors, we tested whether these PRSs were associated with the surface area and cortical thickness in 34 bilateral brain regions extracted using FreeSurfer. A higher PRS for anxiety disorders at PT ≤ 1.0 was significantly associated with a reduced right caudal anterior cingulate area (beta = −0.25, puncorrected = 9.51 × 10−4, pcorrected = 0.032). PRSs based on more common SNPs, especially from PT ≤ 0.01 to PT ≤ 1.0, were associated with the right caudal anterior cingulate area (a maximum at PT ≤ 0.5: R2 = 0.066, beta = −0.27, puncorr = 3.81 × 10−4, pcorr = 0.013). Furthermore, individuals in the highest quartile for anxiety disorder PRS had lower surface area and volume in the right anterior cingulate gyrus than those in the lowest quartile. We suggest a shared genetic etiology between anxiety disorders and structural features of the anterior cingulate gyrus, possibly contributing to the pathogenesis of anxiety disorders via emotional dysregulations. Our findings suggest the potential usefulness of PRS to reduce pathological heterogeneity among anxiety disorders.

Axonal Barcode Analysis of Pyramidal Tract Projections from Mouse Forelimb M1 and M2.

Forelimb-related areas of the motor cortex communicate directly to downstream areas in the brainstem and spinal cord via axons that project to and through the pyramidal tract (PT). To better understand the diversity of the brainstem branching patterns of these pyramidal tract projections, we used MAPseq, a molecular barcode technique for population-scale sampling with single-axon resolution. In experiments using mice of both sexes, we first confirmed prior results demonstrating the basic efficacy of axonal barcode identification of primary motor cortex (M1) PT-type axons, including corticobulbar (CBULB) and corticospinal (CSPI) subclasses. We then used multiplexed MAPseq to analyze projections from M1 and M2 (caudal and rostral forelimb areas). The four basic axon subclasses comprising these projections (M1-CSPI, M1-CBULB, M2-CSPI, M2-CBULB) showed a complex mix of differences and similarities in their brainstem projection profiles. This included relatively abundant branching by all classes in the dorsal midbrain, by M2 subclasses in the pons, and by CSPI subclasses in the dorsal medulla. Cluster analysis showed graded distributions of the basic subclasses within the PT class. Clusters were of diversely mixed subclass composition and showed distinct rostrocaudal and/or dorsomedial projection biases. Exemplifying these patterns was a subcluster likely enriched in corticocuneate branches. Overall, the results indicate high yet systematic PT axon diversity at the level of brainstem branching patterns; projections of M1 and M2 appear qualitatively similar, yet with quantitative differences in subclasses and clusters.SIGNIFICANCE STATEMENT Axons of the PT class of cortical projection neurons, which includes corticospinal and corticobulbar neurons, anatomically link motor cortex to brainstem and spinal cord circuits. Both of these subclasses can form branches to brainstem destinations along the way, but the extent and diversity of these branching patterns is incompletely understood. Here, we used MAPseq to tag PT axons with individual molecular barcodes for high-throughput quantification of branching patterns across the brainstem. The results reveal diverse, complex, yet systematic branching patterns of corticospinal and corticobulbar neurons arising from two motor cortex areas, M1 and M2.

Autism Is Associated With Interindividual Variations of Gray and White Matter Morphology

BackgroundAlthough many studies have explored atypicalities in gray matter (GM) and white matter (WM) morphology of autism, most of them relied on unimodal analyses that did not benefit from the likelihood that different imaging modalities may reflect common neurobiology. We aimed to establish brain patterns of modalities that differentiate between individuals with and without autism and explore associations between these brain patterns and clinical measures in the autism group. MethodsWe studied 183 individuals with autism and 157 nonautistic individuals (age range, 6–30 years) in a large, deeply phenotyped autism dataset (EU-AIMS LEAP [European Autism Interventions—A Multicentre Study for Developing New Medications Longitudinal European Autism Project]). Linked independent component analysis was used to link all participants’ GM volume and WM diffusion tensor images, and group comparisons of modality shared variances were examined. Subsequently, we performed univariate and multivariate brain-behavior correlation analyses to separately explore the relationships between brain patterns and clinical profiles. ResultsOne multimodal pattern was significantly related to autism. This pattern was primarily associated with GM volume in bilateral insula and frontal, precentral and postcentral, cingulate, and caudate areas and co-occurred with altered WM features in the superior longitudinal fasciculus. The brain-behavior correlation analyses showed a significant multivariate association primarily between brain patterns that involved variation of WM and symptoms of restricted and repetitive behavior in the autism group. ConclusionsOur findings demonstrate the assets of integrated analyses of GM and WM alterations to study the brain mechanisms that underpin autism and show that the complex clinical autism phenotype can be interpreted by brain covariation patterns that are spread across the brain involving both cortical and subcortical areas.

Tissue regeneration effect of betulin via inhibition of ROS/MAPKs/NF-ĸB axis using zebrafish model

Betulin is the primary anti-inflammatory component of Betula platyphylla suk. cortex (birch bark), a time-honored Traditional Chinese Medicine (TCM) for healing trauma and tissue regeneration. However, the tissue regeneration effects and underlying molecular mechanism of betulin remain unknown. Therefore, it is necessary to investigate the wound repair effects and validate the mechanism of betulin in an appropriate model. In the present study, we evaluated the effects of tissue regeneration, melanin scavenging, and reactive oxygen species (ROS) inhibition of betulin using a zebrafish model. The mechanism of target genes and pathways were confirmed using quantitative polymerase chain reaction and western blotting in vivo, while molecular docking, absorption, distribution, metabolism, excretion, and toxicity investigations in-silico were conducted. Betulin significantly promoted the regeneration of zebrafish caudal fin length and area and alleviated melanin aggregation, as well as ROS generation. The relative mRNA expression of IL-1β, TNF-α, p38α, ERK1/2, and Caspase3, and the relative protein expression of p38α, ERK1/2, Caspase3, phosphorylated proteins of p-p38α, p-ERK1/2, and p-p65 were down-regulated following betulin administration. Meanwhile, the protein ratios of p-p38α/p38α, p-ERK/ERK, and p-p65/p65 were significantly decreased. In an in-silico study, binding affinities between betulin and P38α, ERK1, ERK2, and Caspase3, and the pharmacokinetic profile of betulin were predicted. The findings suggest that the tissue regeneration mechanism of betulin is based on the inhibition of excessive inflammatory responses, melanin aggregation, and the pro-apoptotic factor, Caspase3, during the proliferation phase via the ROS/MAPKs/NF-ĸB signaling axis. Our results suggest betulin as a potential candidate for tissue regeneration.

The Impact of Theta-Burst Stimulation on Cortical GABA and Glutamate in Treatment-Resistant Depression: A Surface-Based MRSI Analysis Approach.

Background: Theta burst stimulation (TBS) belongs to one of the biological antidepressant treatment options. When applied bilaterally, excitatory intermittent TBS (iTBS) is commonly targeted to the left and inhibitory continuous TBS (cTBS) to the right dorsolateral prefrontal cortex. TBS was shown to influence neurotransmitter systems, while iTBS is thought to interfere with glutamatergic circuits and cTBS to mediate GABAergic neurotransmission.Objectives: We aimed to expand insights into the therapeutic effects of TBS on the GABAergic and glutamatergic system utilizing 3D-multivoxel magnetic resonance spectroscopy imaging (MRSI) in combination with a novel surface-based MRSI analysis approach to investigate changes of cortical neurotransmitter levels in patients with treatment-resistant depression (TRD).Methods: Twelve TRD patients (five females, mean age ± SD = 35 ± 11 years) completed paired MRSI measurements, using a GABA-edited 3D-multivoxel MEGA-LASER sequence, before and after 3 weeks of bilateral TBS treatment. Changes in cortical distributions of GABA+/tNAA (GABA+macromolecules relative to total N-acetylaspartate) and Glx/tNAA (Glx = mixed signal of glutamate and glutamine), were investigated in a surface-based region-of-interest (ROI) analysis approach.Results: ANCOVAs revealed a significant increase in Glx/tNAA ratios in the left caudal middle frontal area (pcorr. = 0.046, F = 13.292), an area targeted by iTBS treatment. Whereas, contralateral treatment with cTBS evoked no alterations in glutamate or GABA concentrations.Conclusion: This study demonstrates surface-based adaptions in the stimulation area to the glutamate metabolism after excitatory iTBS but not after cTBS, using a novel surface-based analysis of 3D-MRSI data. The reported impact of facilitatory iTBS on glutamatergic neurotransmission provides further insight into the neurobiological effects of TBS in TRD.

Soft Attention Based DenseNet Model for Parkinson's Disease Classification Using SPECT Images.

ObjectiveDeep learning algorithms have long been involved in the diagnosis of severe neurological disorders that interfere with patients’ everyday tasks, such as Parkinson’s disease (PD). The most effective imaging modality for detecting the condition is DaTscan, a variety of single-photon emission computerized tomography (SPECT) imaging method. The goal is to create a convolutional neural network that can specifically identify the region of interest following feature extraction.MethodsThe study comprised a total of 1,390 DaTscan imaging groups with PD and normal classes. The architecture of DenseNet-121 is leveraged with a soft-attention block added before the final classification layer. For visually analyzing the region of interest (ROI) from the images after classification, Soft Attention Maps and feature map representation are used.OutcomesThe model obtains an overall accuracy of 99.2% and AUC-ROC score 99%. A sensitivity of 99.2%, specificity of 99.4% and f1-score of 99.1% is achieved that surpasses all prior research findings. Soft-attention map and feature map representation aid in highlighting the ROI, with a specific attention on the putamen and caudate regions.ConclusionWith the deep learning framework adopted, DaTscan images reveal the putamen and caudate areas of the brain, which aid in the distinguishing of normal and PD cohorts with high accuracy and sensitivity.

Assessment of Nasal Structure Using CT Imaging of Brachycephalic Dog Breeds.

Simple SummaryFrench bulldogs and pugs are classified as brachycephalic dogs and are characterized by short, stenotic noses. The outward characteristics of this breed can cause dyspnea, which may be surgically improved. However, brachycephalic dog breeds have different rates of disease progression and response to treatment. We hypothesized that this difference was due to the difference in the structure of the nasal cavity. To verify this, the ratio of the airway cross-sectional area to the total nasal cavity area was compared between the three brachycephalic dog breeds using head computed tomography (CT) images. The results revealed that the distribution of narrow and wide airway locations in the nasal cavity differed among the breeds. The method used in this study was suitable for observing and evaluating canine nasal structures. These results provide a new approach for the diagnosis of canine respiratory diseases and improve our understanding of the pathogenesis of brachycephalic dogs.The response to treatment of brachycephalic airway syndrome (BAS) varies among brachycephalic dog breeds. We hypothesized that variations in nasal structure are one of the factors responsible for this difference. To confirm this variation, we measured the ratio of the airway cross-sectional area to the total nasal cavity area (AA/NC) in three brachycephalic dog breeds. Head CT images of French bulldogs, shih tzus, and pugs were retrospectively collected. Four specific transverse planes were used to calculate AA/NC ratios. Fifty brachycephalic dogs were included in the study: French bulldogs (n = 20), shih tzus (n = 20), and pugs (n = 10). The AA/NC ratio of Shih Tzus was larger in the rostral nasal cavity and smaller toward the caudal area, whereas the other two breeds showed an inverse tendency. The results obtained from the current research indicate that the AA/NC ratio can be used to evaluate the structure of the nasal cavity. Moreover, analyzing the point with the smallest AA/NC ratio can be useful in quantifying nasal airway obstruction and the severity of BAS. These results will be useful in understanding the complexity of BAS pathophysiology and in the implementation of treatment.

Diagnostic imaging of the equine cervical spine – Are radiographs enough?

Diagnostic imaging of the equine cervical spine – Are radiographs enough?

1314-P: Activating GABAergic Neurons in the Caudal Preoptic Area Promote Energy Expenditure in Diet-Induced Obesity

Obesity results from the imbalance between energy intake and energy expenditure, which are tightly regulated by dynamic hypothalamic circuits. Our goal is to identify and leverage hypothalamic components that promote energy expenditure for successful weight loss. Vesicular communication by ventromedial hypothalamic nucleus (VMN) steroidogenic factor 1 (Sf1) neurons is required for maintaining body weight, due at least in part to stimulating metabolic activity in adipose tissue, but the mechanistic details are unclear. VMNSf1 neurons efferently communicate with relatively few places in the brain but the most prominent projections are in the most caudal regions of the preoptic area (cPOA) (+0.1 to -0.3mm bregma, lateral to the suprachiasmatic nucleus) . We tested the hypothesis that GABAergic cPOA neurons promote energy expenditure and weight loss by activating either GABAergic or glutamatergic neurons via hM3dq, using vGATCre (vesicular GABAergic transporter) or vGLUT2Cre (vesicular glutamatergic transporter 2) in diet-induced obese male mice. Activating vGATcPOA neurons reduced body weight and adiposity without altering food intake. Activating vGLUT2cPOA neurons reduced body weight and food intake but did not reduce adiposity. Activating vGLUT2cPOA neurons reduced core body temperature, but not vGATcPOA neurons. We are currently investigating the mechanisms for how vGATcPOA neurons reduce adiposity. Weight loss is not likely mediated by direct inhibition of vGLUT2cPOA neurons because diet induced obese male mice with CNO-initiated signaling of hM4di in vglut2cPOA neurons does not reduce adiposity or body weight. Alternatively, vGATcPOA neurons may communicate with a distinct efferent system. Indeed, vGATcPOA, but not vGLUT2cPOA, neurons project to the lateral hypothalamus and medial raphe. Future studies will reveal the functional connection between VMNSf1 neurons and vGATcPOA neurons, and the descending circuitry that promotes energy expenditure. Disclosure R.Basu: None. A.J.Elmendorf: Research Support; Eli Lilly and Company. C.A.Mahler: Stock/Shareholder; AstraZeneca, Pfizer Inc. J.Flak: Research Support; Eli Lilly and Company. Funding American Diabetes Association (17-INI-15) ; IU CDMD NIH/NIDDK (P30 DK097512)

Clinical, imaging, and pathologic features in cases of neurologic disease in 3 psittacine birds.

We used magnetic resonance imaging (MRI) to evaluate the CNS, and confirmed CNS lesions histologically, in 3 psittacine birds with neurologic signs. One bird was recumbent as a result of non-ambulatory paraparesis, and 2 birds were ataxic with impaired proprioception. In all 3 cases, imaging was performed, and infectious diseases were excluded in cases 1 and 2. In case 1, a large mass arose from the left lung; in case 2, a multinodular coelomic mass encompassed the left caudal pulmonary area to the left cranial renal pole; and in case 3, a diffuse hyperintensity affected the lumbar spinal cord. In the first 2 cases, masses invaded the vertebral canal, causing spinal cord compression. All 3 birds were euthanized given the poor prognosis, and postmortem examinations were performed. The final diagnoses were pulmonary adenocarcinoma in cases 1 and 2, and granulomatous and lymphocytic leptomeningitis caused by Mycobacterium genavense in case 3. MRI enabled visualization of the lesions in the affected area of the CNS, and MRI findings were confirmed by histopathology.

Cingulate and hippocampal subregion abnormalities in combat-exposed veterans with PTSD

BackgroundThe hippocampus and cingulate gyrus are strongly interconnected brain regions that have been implicated in the neurobiology of post-traumatic stress disorder (PTSD). These brain structures are comprised of functionally distinct subregions that may contribute to the expression of PTSD symptoms or associated cardio-metabolic markers, but have not been well investigated in prior studies. MethodsTwo divisions of the cingulate cortex (i.e., rostral and caudal) and 11 hippocampal subregions were investigated in 22 male combat-exposed veterans with PTSD and 22 male trauma-exposed veteran controls (TC). Cardio-metabolic measures included cholesterol, body mass index, and mean arterial pressure. ResultsIndividuals with PTSD had less caudal cingulate area compared to TC even after controlling for caudal cingulate thickness. Total hippocampus volume was lower in PTSD compared to TC, accounted for by differences in CA1-CA4, granule cell layer of the dentate gyrus, molecular layer, and subiculum. Individuals with PTSD had higher mean arterial pressure compared to TC, which correlated with hippocampus volume only in the PTSD group. LimitationsSample size, cross-sectional analysis, no control for medications and findings limited to males. ConclusionsThese data demonstrate preferential involvement of caudal cingulate area (vs. thickness) and hippocampus subregions in PTSD. The inverse association between hippocampus volume and mean arterial pressure may contribute to accelerated aging known to be associated with PTSD.

Hammer it out: shifts in habitat are associated with changes in fin and body shape in the scalloped hammerhead (Sphyrna lewini)

Abstract Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.

Anatomical and functional connectivity support the existence of a salience network node within the caudal ventrolateral prefrontal cortex.

Three large-scale networks are considered essential to cognitive flexibility: the ventral and dorsal attention (VANet and DANet) and salience (SNet) networks. The ventrolateral prefrontal cortex (vlPFC) is a known component of the VANet and DANet, but there is a gap in the current knowledge regarding its involvement in the SNet. Herein, we used a translational and multimodal approach to demonstrate the existence of a SNet node within the vlPFC. First, we used tract-tracing methods in non-human primates (NHP) to quantify the anatomical connectivity strength between different vlPFC areas and the frontal and insular cortices. The strongest connections were with the dorsal anterior cingulate cortex (dACC) and anterior insula (AI) - the main cortical SNet nodes. These inputs converged in the caudal area 47/12, an area that has strong projections to subcortical structures associated with the SNet. Second, we used resting-state functional MRI (rsfMRI) in NHP data to validate this SNet node. Third, we used rsfMRI in the human to identify a homologous caudal 47/12 region that also showed strong connections with the SNet cortical nodes. Taken together, these data confirm a SNet node in the vlPFC, demonstrating that the vlPFC contains nodes for all three cognitive networks: VANet, DANet, and SNet. Thus, the vlPFC is in a position to switch between these three networks, pointing to its key role as an attentional hub. Its additional connections to the orbitofrontal, dorsolateral, and premotor cortices, place the vlPFC at the center for switching behaviors based on environmental stimuli, computing value, and cognitive control.

Complex forelimb movements and cortical topography evoked by intracortical microstimulation in male and female mice.

The motor cortex is crucial for the voluntary control of skilled movement in mammals and is topographically organized into representations of the body (motor maps). Intracortical microstimulation of the motor cortex with long-duration pulse trains (LD-ICMS; ~500ms) evokes complex movements, occurring in multiple joints or axial muscles, with characteristic movement postures and cortical topography across a variety of mammalian species. Although the laboratory mouse is extensively used in basic and pre-clinical research, high-resolution motor maps elicited with electrical LD-ICMS in both sexes of the adult mouse has yet to be reported. To address this knowledge gap, we performed LD-ICMS of the forelimb motor cortex in both male (n = 10) and naturally cycling female (n = 8) C57/BL6J mice under light ketamine-xylazine anesthesia. Complex and simple movements were evoked from historically defined caudal (CFA) and rostral (RFA) forelimb areas. Four complex forelimb movements were identified consisting of Elevate, Advance, Dig, and Retract postures with characteristic movement sequences and endpoints. Furthermore, evoked complex forelimb movements and cortical topography in mice were organized within the CFA in a unique manner relative to a qualitative comparison with the rat.

Movement-specific signaling is differentially distributed across motor cortex layer 5 projection neuron classes.

Motor cortex generates descending output necessary for executing a wide range of limb movements. Although movement-related activity has been described throughout motor cortex, the spatiotemporal organization of movement-specific signaling in deep layers remains largely unknown. Here we record layer 5B population dynamics in the caudal forelimb area of motor cortex while mice perform a forelimb push/pull task and find that most neurons show movement-invariant responses, with a minority displaying movement specificity. Using cell-type-specific imaging, we identify that invariant responses dominate pyramidal tract (PT) neuron activity, with a small subpopulation representing movement type, whereas a larger proportion of intratelencephalic (IT) neurons display movement-type-specific signaling. The proportion of IT neurons decoding movement-type peaks prior to movement initiation, whereas for PT neurons, this occurs during movement execution. Our data suggest that layer 5B population dynamics largely reflect movement-invariant signaling, with information related to movement-type being routed through relatively small, distributed subpopulations of projection neurons.

A new “flagship” ciliate, Pseudostylonychia obliquocaudata n. gen., n. sp. (Ciliophora, Hypotricha), from South Korea

The morphology, ontogenesis, and molecular phylogeny of a new ciliate, Pseudostylonychia obliquocaudata n. gen., n. sp., discovered in a semiterrestrial habitat in South Korea, were investigated. The new species is characterized by an obovate or triangular body with pointed posterior end. The caudal area is distinctly obliquely truncated rightwards. Pseudostylonychia n. gen. is established and characterized by the obovate or triangular body, Stylonychia-like infraciliature and macronuclear pattern, and undulating membranes in Laurentiella pattern. It is also characterized by the involvement of cirri III/2 and IV/3 in primordia formation. SEM investigations show that the resting cyst has high, spirally arranged ridges. Phylogenetic analyses based on SSU rRNA gene sequences show that the new species is placed as a sister to the clade containing sequences of Stylonychia mytilus complex, Stylonychia (Metastylonychia), and Coniculostomum. Furthermore, Stylonychia koreana Kumar et al., 2016 nov. stat. is raised to species level based on the differences in the cyst morphology between the two subspecies of S. ammermanni. Also, Metastylonychia Kumar and Foissner, 2017 nov. stat. is raised to genus rank based on the new molecular data and the morphological and ontogenetic differences to Coniculostomum and Stylonychia.

Decoding sensorimotor information from superior parietal lobule of macaque via Convolutional Neural Networks

Despite the well-recognized role of the posterior parietal cortex (PPC) in processing sensory information to guide action, the differential encoding properties of this dynamic processing, as operated by different PPC brain areas, are scarcely known. Within the monkey’s PPC, the superior parietal lobule hosts areas V6A, PEc, and PE included in the dorso-medial visual stream that is specialized in planning and guiding reaching movements. Here, a Convolutional Neural Network (CNN) approach is used to investigate how the information is processed in these areas. We trained two macaque monkeys to perform a delayed reaching task towards 9 positions (distributed on 3 different depth and direction levels) in the 3D peripersonal space. The activity of single cells was recorded from V6A, PEc, PE and fed to convolutional neural networks that were designed and trained to exploit the temporal structure of neuronal activation patterns, to decode the target positions reached by the monkey. Bayesian Optimization was used to define the main CNN hyper-parameters. In addition to discrete positions in space, we used the same network architecture to decode plausible reaching trajectories. We found that data from the most caudal V6A and PEc areas outperformed PE area in the spatial position decoding. In all areas, decoding accuracies started to increase at the time the target to reach was instructed to the monkey, and reached a plateau at movement onset. The results support a dynamic encoding of the different phases and properties of the reaching movement differentially distributed over a network of interconnected areas. This study highlights the usefulness of neurons’ firing rate decoding via CNNs to improve our understanding of how sensorimotor information is encoded in PPC to perform reaching movements. The obtained results may have implications in the perspective of novel neuroprosthetic devices based on the decoding of these rich signals for faithfully carrying out patient’s intentions.

The impact of evolutionary trade-offs among bioluminescent organs and body shape in the deep sea: A case study on lanternfishes

Functional innovations play major roles in constraining or contributing to the evolutionary diversification of organismal morphology. Among fish key innovations, bioluminescence is critical to the success of many deep-sea fishes. Understanding evolutionary dynamics of deep-sea fish lineages and the role bioluminescent light organs have on their evolution is a continuing effort of many deep-sea biologists. This study focused on assessing how bioluminescent structures involved with sexual communication may be impacting the evolution of body shape in the lanternfishes (Myctophiformes), a lineage of fishes possessing some of the most extensive sexual dimorphism in bioluminescent structures seen in deep-sea organisms. Results from this study using geometric morphometrics integrated with a phylogenetic hypothesis of lanternfish relationships suggest there is significant evolutionary modularity between the caudal peduncle and the rest of the body within lanternfishes. Our results also show that most lanternfish species lacking caudal light organs cluster together in morphospace (Diaphus, Hintonia, Neoscopelidae), possess enlarged headlight organs (Diaphus), and exhibit lower phylogenetic signal than species possessing caudal light organs. These results support the hypothesis that lanternfish body-shape evolution is influenced by selective pressures on their light-producing tail organs and that the importance of caudal light organs in lanternfish communication may result in differential selection on the caudal area in species that possess them. One possible interpretation for why lanternfishes without caudal light organs coalesce in morphospace may be that by removing the caudal light organ, natural selection would select for a lanternfish caudal morphology optimized for the physical landscape of the midwater that they live in, favoring more energy efficient and slow sustained swimming styles.

An evolutionary gap in primate default mode network organization

SUMMARYThe human default mode network (DMN) is engaged at rest and in cognitive states such as self-directed thoughts. Interconnected homologous cortical areas in primates constitute a network considered as the equivalent. Here, based on a cross-species comparison of the DMN between humans and non-hominoid primates (macaques, marmosets, and mouse lemurs), we report major dissimilarities in connectivity profiles. Most importantly, the medial prefrontal cortex (mPFC) of non-hominoid primates is poorly engaged with the posterior cingulate cortex (PCC), though strong correlated activity between the human PCC and the mPFC is a key feature of the human DMN. Instead, a fronto-temporal resting-state network involving the mPFC was detected consistently across non-hominoid primate species. These common functional features shared between non-hominoid primates but not with humans suggest a substantial gap in the organization of the primate’s DMN and its associated cognitive functions.

The impact of closed-loop intracortical stimulation on neural activity in brain-injured, anesthetized animals

BackgroundAcquired brain injuries, such as stroke, are a major cause of long-term disability worldwide. Intracortical microstimulation (ICMS) can be used successfully to assist in guiding appropriate connections to restore lost sensorimotor integration. Activity-Dependent Stimulation (ADS) is a specific type of closed-loop ICMS that aims at coupling the activity of two different brain regions by stimulating one in response to activity in the other. Recently, ADS was used to effectively promote behavioral recovery in rodent models following a unilateral traumatic brain injury in the primary motor cortex. While behavioral benefits have been described, the neurophysiological changes in spared areas in response to this type of stimulation have not been fully characterized. Here we explored how single-unit spiking activity is impacted by a focal ischemic lesion and, subsequently, by an ADS treatment.MethodsIntracortical microelectrode arrays were implanted in the ipsilesional rostral forelimb area (RFA) to record spike activity and to trigger intracortical microstimulation in the primary somatosensory area (S1) of anaesthetized Long Evans rats. An ischemic injury was induced in the caudal forelimb area through microinjections of Endothelin-1. Activity from both RFA and S1 was recorded and analyzed off-line by evaluating possible changes, either induced by the lesion in the Control group or by stimulation in the ADS group.ResultsWe found that the ischemic lesion in the motor area led to an overall increase in spike activity within RFA and a decrease in S1 with respect to the baseline condition. Subsequent treatment with ADS increased the firing rate in both RFA and S1. Post-stimulation spiking activity was significantly higher compared to pre-stimulation activity in the ADS animals versus non-stimulated controls. Moreover, stimulation promoted the generation of highly synchronized bursting patterns in both RFA and S1 only in the ADS group.ConclusionsThis study describes the impact on single-unit activity in ipsilesional areas immediately following a cortical infarct and demonstrates that application of ADS is effective in altering this activity.