High-density cortical µECoG arrays concurrently track spreading depolarizations and long-term evolution of stroke in awake rats.

Spreading depolarizations (SDs) are widely recognized as a major contributor to the progression of tissue damage from ischemic stroke even if blood flow can be restored. They are characterized by negative intracortical waveforms of up to -20 mV, propagation velocities of 3 - 6 mm/min, and massive disturbance of membrane ion homeostasis. High-density, micro-electrocorticographic (µECoG) epidural electrodes and custom, DC-coupled, multiplexed amplifiers, were used to continuously characterize and monitor SD and µECoG cortical signal evolution in awake, moving rats over days. This highly innovative approach can define these events over a large brain surface area (~ 3.4 × 3.4 mm), extending across the boundaries of the stroke, and offers sufficient electrode density (60 contacts total per array for a density of 5.7 electrodes / mm2) to measure and determine the origin of SDs in relation to the infarct boundaries. In addition, spontaneous ECoG activity can simultaneously be detected to further define cortical infarct regions. This technology allows us to understand dynamic stroke evolution and provides immediate cortical functional activity over days. Further translational development of this approach may facilitate improved treatment options for acute stroke patients.

Range-Wide Population Structure of 3 Deepwater Eteline Snappers Across the Indo-Pacific Basin.

Deep-sea habitats may drive unique dispersal and demographic patterns for fishes, but population genetic analyses to address these questions have rarely been conducted for fishes in these environments. This study investigates the population structure of 3 tropical deepwater snappers of the genus Etelis that reside at 100-400 m depth, with broad and overlapping distributions in the Indo-Pacific. Previous studies showed little population structure within the Hawaiian Archipelago for 2 of these species: Etelis coruscans and E. carbunculus. Here we extend sampling to the entire geographic range of each species to resolve the population genetic architecture for these 2 species, as well as a recently exposed cryptic species (Etelis sp.). One goal was to determine whether deepwater snappers are more dispersive than shallow-water fishes. A second goal was to determine whether submesophotic fishes have older, more stable populations than shallow reef denizens that are subject to glacial sea-level fluctuations. Both goals are pertinent to the management of these valuable food fishes. A total of 1153 specimens of E. coruscans from 15 geographic regions were analyzed, along with 1064 specimens of E. carbunculus from 11 regions, and 590 specimens of E. sp. from 16 regions. The first 2 species were analyzed with mtDNA and 9-11 microsatellite loci, while E. sp. was analyzed with mtDNA only. Etelis coruscans had a non-significant microsatellite global FST, but significant global mtDNA Ф ST = 0.010 (P = 0.0007), with the isolation of Seychelles in the western Indian Ocean, and intermittent signals of isolation for the Hawaiian Archipelago. Etelis carbunculus had a non-significant microsatellite global FST, and significant global mtDNA Ф ST = 0.021 (P = 0.0001), with low but significant levels of isolation for Hawai'i, and divergence between Tonga and Fiji. Etelis sp. had mtDNA Ф ST = 0.018 (P = 0.0005), with a strong pattern of isolation for both Seychelles and Tonga. Overall, we observed low population structure, shallow mtDNA coalescence (similar to near-shore species), and isolation at the fringes of the Indo-Pacific basin in Hawai'i and the western Indian Ocean. While most shallow-water species have population structure on the scale of biogeographic provinces, deepwater snapper populations are structured on the wider scale of ocean basins, more similar to pelagic fishes than to shallow-water species. This population structure indicates the capacity for widespread dispersal throughout the Indo-Pacific region.

A modular high-density µECoG system on macaque vlPFC for auditory cognitive decoding.

OBJECTIVE: A fundamental goal of the auditory system is to parse the auditory environment into distinct perceptual representations. Auditory perception is mediated by the ventral auditory pathway, which includes the ventrolateral prefrontal cortex (vlPFC). Because large-scale recordings of auditory signals are quite rare, the spatiotemporal resolution of the neuronal code that underlies vlPFC's contribution to auditory perception has not been fully elucidated. Therefore, we developed a modular, chronic, high-resolution, multi-electrode array system with long-term viability in order to identify the information that could be decoded from µECoG vlPFC signals. APPROACH: We molded three separate µECoG arrays into one and implanted this system in a non-human primate. A custom 3D-printed titanium chamber was mounted on the left hemisphere. The molded 294-contact µECoG array was implanted subdurally over the vlPFC. µECoG activity was recorded while the monkey participated in a 'hearing-in-noise' task in which they reported hearing a 'target' vocalization from a background 'chorus' of vocalizations. We titrated task difficulty by varying the sound level of the target vocalization, relative to the chorus (target-to-chorus ratio, TCr). MAIN RESULTS: We decoded the TCr and the monkey's behavioral choices from the µECoG signal. We analyzed decoding accuracy as a function of number of electrodes, spatial resolution, and time from implantation. Over a one-year period, we found significant decoding with individual electrodes that increased significantly as we decoded simultaneously more electrodes. Further, we found that the decoding for behavioral choice was better than the decoding of TCr. Finally, because the decoding accuracy of individual electrodes varied on a day-by-day basis, electrode arrays with high channel counts ensure robust decoding in the long term. SIGNIFICANCE: Our results demonstrate the utility of high-resolution and high-channel-count, chronic µECoG recording. We developed a surface electrode array that can be scaled to cover larger cortical areas without increasing the chamber footprint.

3D Printed Cranial Window System for Chronic µECoG Recording.

Chronic studies of flexible µECoG electrodes and the electrode-brain interface have been limited by the inability to assess tissue response over time. The electrophysiological system presented here combines epidural microelectrocorticographic (µECoG) recording capabilities with the ability to visualize tissue response over time through light microscopy and optical coherence tomography (OCT). With the ability to interchange both the electrode and the electronics, and a flushing port for injection of flushing saline and/or drugs, this 3D printed system has future applications in chronic electrophysiology, optogenetics, and advanced imaging methods.

A Novel µECoG Electrode Interface for Comparison of Local and Common Averaged Referenced Signals.

Micro-electrocorticography (µECoG) is a minimally invasive neural interface that allows for recording from the surface of the brain with high spatial and temporal resolution [1], [2]. However, discerning multi-unit and local field potential (LFP) activity with potentially highly-correlated signals across a dense µECoG array can be challenging. Here we describe a novel µECoG design to compare the effect of referencing recordings to a local reference electrode and common average referencing (CAR). The filtering effect and the significant increase in signal to noise ratio of the evoked response (ESNR) can be seen after re-referencing for both types of referencing. In a preliminary analysis, re-referencing the µECoG signals can increase recording performance at high contact densities in the auditory cortex. This also provides promising evidence for a versatile in-house fabricated µECoG electrode.

Effect of shear stress on iPSC-derived human brain microvascular endothelial cells (dhBMECs).

BACKGROUND: The endothelial cells that form the lumen of capillaries and microvessels are an important component of the blood-brain barrier. Cell phenotype is regulated by transducing a range of biomechanical and biochemical signals in the local microenvironment. Here we report on the role of shear stress in modulating the morphology, motility, proliferation, apoptosis, and protein and gene expression, of confluent monolayers of human brain microvascular endothelial cells derived from induced pluripotent stem cells. METHODS: To assess the response of derived human brain microvascular endothelial cells (dhBMECs) to shear stress, confluent monolayers were formed in a microfluidic device. Monolayers were subjected to a shear stress of 4 or 12 dyne cm-2 for 40 h. Static conditions were used as the control. Live cell imaging was used to assess cell morphology, cell speed, persistence, and the rates of proliferation and apoptosis as a function of time. In addition, immunofluorescence imaging and protein and gene expression analysis of key markers of the blood-brain barrier were performed. RESULTS: Human brain microvascular endothelial cells exhibit a unique phenotype in response to shear stress compared to static conditions: (1) they do not elongate and align, (2) the rates of proliferation and apoptosis decrease significantly, (3) the mean displacement of individual cells within the monolayer over time is significantly decreased, (4) there is no cytoskeletal reorganization or formation of stress fibers within the cell, and (5) there is no change in expression levels of key blood-brain barrier markers. CONCLUSIONS: The characteristic response of dhBMECs to shear stress is significantly different from human and animal-derived endothelial cells from other tissues, suggesting that this unique phenotype that may be important in maintenance of the blood-brain barrier. The implications of this work are that: (1) in confluent monolayers of dhBMECs, tight junctions are formed under static conditions, (2) the formation of tight junctions decreases cell motility and prevents any morphological transitions, (3) flow serves to increase the contact area between cells, resulting in very low cell displacement in the monolayer, (4) since tight junctions are already formed under static conditions, increasing the contact area between cells does not cause upregulation in protein and gene expression of BBB markers, and (5) the increase in contact area induced by flow makes barrier function more robust.

Phylogeny of deepwater snappers (Genus Etelis) reveals a cryptic species pair in the Indo-Pacific and Pleistocene invasion of the Atlantic.

Evolutionary genetic patterns in shallow coastal fishes are documented with dozens of studies, but corresponding surveys of deepwater fishes (>200m) are scarce. Here we investigate the evolutionary history of deepwater snappers (genus Etelis), comprised of three recognized Indo-Pacific species and one Atlantic congener, by constructing a phylogeny of the genus with two mtDNA loci and two nuclear introns. Further, we apply range-wide Indo-Pacific sampling to test for the presence and distribution of a putative cryptic species pair within E. carbunculus using morphological analyses and mtDNA cytochrome b sequences from 14 locations across the species range (N=1696). These analyses indicate that E. carbunculus is comprised of two distinct, non-interbreeding lineages separated by deep divergence (d=0.081 in cytochrome b). Although these species are morphologically similar, we identified qualitative differences in coloration of the upper-caudal fin tip and the shape of the opercular spine, as well as significant differences in adult body length, body depth, and head length. These two species have overlapping Indo-Pacific distributions, but one species is more widespread across the Indo-Pacific, whereas the other species is documented in the Indian Ocean and Western Central Pacific. The dated Etelis phylogeny places the cryptic species divergence in the Pliocene, indicating that the biogeographic barrier between the Indian and Pacific Oceans played a role in speciation. Based on historic taxonomy and nomenclature, the species more widespread in the Pacific Ocean is E. carbunculus, and the other species is previously undescribed (referred to here as E. sp.). The Atlantic congener E. oculatus has only recently (∼0.5Ma) diverged from E. coruscans in the Indo-Pacific, indicating colonization via southern Africa. The pattern of divergence at the Indo-Pacific barrier, and Pleistocene colonization from the Indian Ocean into the Atlantic, is concordant with patterns observed in shallow coastal fishes, indicating similar drivers of evolutionary processes.

Species distribution models of tropical deep-sea snappers.

Deep-sea fisheries provide an important source of protein to Pacific Island countries and territories that are highly dependent on fish for food security. However, spatial management of these deep-sea habitats is hindered by insufficient data. We developed species distribution models using spatially limited presence data for the main harvested species in the Western Central Pacific Ocean. We used bathymetric and water temperature data to develop presence-only species distribution models for the commercially exploited deep-sea snappers Etelis Cuvier 1828, Pristipomoides Valenciennes 1830, and Aphareus Cuvier 1830. We evaluated the performance of four different algorithms (CTA, GLM, MARS, and MAXENT) within the BIOMOD framework to obtain an ensemble of predicted distributions. We projected these predictions across the Western Central Pacific Ocean to produce maps of potential deep-sea snapper distributions in 32 countries and territories. Depth was consistently the best predictor of presence for all species groups across all models. Bathymetric slope was consistently the poorest predictor. Temperature at depth was a good predictor of presence for GLM only. Model precision was highest for MAXENT and CTA. There were strong regional patterns in predicted distribution of suitable habitat, with the largest areas of suitable habitat (> 35% of the Exclusive Economic Zone) predicted in seven South Pacific countries and territories (Fiji, Matthew & Hunter, Nauru, New Caledonia, Tonga, Vanuatu and Wallis & Futuna). Predicted habitat also varied among species, with the proportion of predicted habitat highest for Aphareus and lowest for Etelis. Despite data paucity, the relationship between deep-sea snapper presence and their environments was sufficiently strong to predict their distribution across a large area of the Pacific Ocean. Our results therefore provide a strong baseline for designing monitoring programs that balance resource exploitation and conservation planning, and for predicting future distributions of deep-sea snappers.

Maturity ogives for South Pacific albacore tuna (Thunnus alalunga) that account for spatial and seasonal variation in the distributions of mature and immature fish.

Length and age at maturity are important life history parameters for estimating spawning stock biomass and reproductive potential of fish stocks. Bias in estimates of size and age at maturity can arise when disparate distributions of mature and immature fish within a population are not accounted for in the analysis. Here we investigate the spatial and temporal variability in observed size and age at maturity of female albacore tuna, Thunnus alalunga, using samples collected across the South Pacific. Maturity status was identified using consistent histological criteria that were precise enough to allow for mature but regenerating females to be distinguished from immature females during the non-spawning season, permitting year-round sampling for maturity estimation in albacore. Using generalised linear mixed models, we found that the proportion of mature females at length varied significantly with latitude and time of year. Specifically, females at northern latitudes (∼10-20°S, where spawning occurs) were mature at significantly smaller lengths and ages than females at southern latitudes (∼20-40°S), particularly during the spawning season (October-March). This variation was due to different geographic distributions of mature and immature fish during the year. We present a method for estimating an unbiased maturity ogive that takes into account the latitudinal variation in proportion mature at length during a given season (spawning or non-spawning). Applying this method to albacore samples from the western region of the South Pacific gave a predicted length at 50% mature of ∼87 cm fork length (4.5 years).

Reproductive dynamics and potential annual fecundity of South Pacific albacore tuna (Thunnus alalunga).

The reproductive biology of albacore tuna, Thunnus alalunga, in the South Pacific Ocean was investigated with samples collected during broad-scale sampling between 2006 and 2011. Histology was done in a single laboratory according to standard protocols and the data analysed using generalized linear mixed-effects models. The sex ratio of albacore was female biased for fish smaller than approximately 60 cm FL and between 85 and 95 cm, and progressively more male biased above 95 cm FL. Spawning activity was synchronised across the region between 10°S and 25°S during the austral spring and summer where sea surface temperatures were ≥24 °C. The average gonad index varied among regions, with fish in easterly longitudes having heavier gonads for their size than fish in westerly longitudes. Albacore, while capable of spawning daily, on average spawn every 1.3 days during the peak spawning months of October to December. Spawning occurs around midnight and the early hours of the morning. Regional variation in spawning frequency and batch fecundity were not significant. The proportion of active females and the spawning fraction increased with length and age, and mature small and young fish were less active at either end of the spawning season than larger, older fish. Batch fecundity estimates ranged from 0.26 to 2.83 million oocytes with a mean relative batch fecundity of 64.4 oocytes per gram of body weight. Predicted batch fecundity and potential annual fecundity increased with both length and age. This extensive set of reproductive parameter estimates provides many of the first quantitative estimates for this population and will substantially improve the quality of biological inputs to the stock assessment for South Pacific albacore.

Spatial and sex-specific variation in growth of albacore tuna (Thunnus alalunga) across the South Pacific Ocean.

Spatial variation in growth is a common feature of demersal fish populations which often exist as discrete adult sub-populations linked by a pelagic larval stage. However, it remains unclear whether variation in growth occurs at similar spatial scales for populations of highly migratory pelagic species, such as tuna. We examined spatial variation in growth of albacore Thunnus alalunga across 90° of longitude in the South Pacific Ocean from the east coast of Australia to the Pitcairn Islands. Using length-at-age data from a validated ageing method we found evidence for significant variation in length-at-age and growth parameters (L(∞) and k) between sexes and across longitudes. Growth trajectories were similar between sexes up until four years of age, after which the length-at-age for males was, on average, greater than that for females. Males reached an average maximum size more than 8 cm larger than females. Length-at-age and growth parameters were consistently greater at more easterly longitudes than at westerly longitudes for both females and males. Our results provide strong evidence that finer spatial structure exists within the South Pacific albacore stock and raises the question of whether the scale of their "highly migratory" nature should be re-assessed. Future stock assessment models for South Pacific albacore should consider sex-specific growth curves and spatial variation in growth within the stock.