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The claustrum (CLA) is a conspicuous subcortical structure interconnected with cortical and subcortical regions. However, its regional anatomy and cell-type-specific connections in the mouse remain largely undetermined. Here, we accurately delineated the boundary of the mouse CLA and quantitatively investigated its inputs and outputs brain-wide using anterograde and retrograde viral tracing and fully reconstructed single claustral principal neurons. At a population level, the CLA reciprocally connects with all isocortical modules. It also receives inputs from at least 35 subcortical structures but sends projections back to only a few of them. We found that cell types projecting to the CLA are differentiated by cortical areas and layers. We classified single CLA principal neurons into at least 9 cell types that innervate the diverse sets of functionally linked cortical targets. Axons of interneurons within the CLA arborize along almost its entire anteroposterior extent. Together, this detailed wiring diagram of the cell-type-specific connections of the mouse CLA lays a foundation for studying its functions.

In the neocortex, subcerebral axonal projections originate largely from layer 5 (L5) extratelencephalic-projecting (ET) neurons. The highly distinctive morpho-electric properties of these neurons have mainly been described in rodents, where ET neurons can be labeled by retrograde tracers or transgenic lines. Similar labeling strategies are not possible in the human neocortex, rendering the translational relevance of findings in rodents unclear. We leveraged the recent discovery of a transcriptomically-defined L5 ET neuron type to study the properties of human L5 ET neurons in neocortical brain slices derived from neurosurgeries. Patch-seq recordings, where transcriptome, physiology and morphology are assayed from the same cell, revealed many conserved morpho-electric properties of human and rodent L5 ET neurons. Divergent properties were also apparent but were often smaller than differences between cell types within these two species. These data suggest a conserved function of L5 ET neurons in the neocortical hierarchy, but also highlight marked phenotypic divergence possibly related to functional specialization of human neocortex.

Neuronal anatomy is central to the organization and function of brain cell types. However, anatomical variability within apparently homogeneous populations of cells can obscure such insights. Here, we report large-scale automation of arbor reconstruction on a dataset of 802 inhibitory neurons characterized using the Patch-seq method, which enables measurement of multiple properties from individual neurons, including local morphology and transcriptional signature. We demonstrate that these automated reconstructions can be used in the same manner as manual reconstructions to understand the relationship between many cellular properties used to define cell types. We uncover molecular correlates of laminar innervation on multiple molecularly defined neuronal subclasses and types. In particular, our results reveal molecular correlates of the variability in Layer 1 (L1) innervation even in a transcriptomically defined subpopulation of Martinotti cells in the adult mouse neocortex.

Total Organic Carbon (TOC) is a characteristic of the amount of organic carbon present in a chemical compound or mixture, such as a hydrocarbon-bearing formation, water, or even a fracturing fluid. Organic carbon is a potential measure of food available for bacteria, and, as such, an indirect measure for the potential for wellbore fouling, formation damage, and regained permeability. For this reason, TOC is often used as an indicator of overall water quality across multiple industries, and is becoming more prevalent as a general indicator of water quality for frac reuse. TOC has been demonstrated to be directly correlative to the much-more difficult and time-dependent determination of Biochemical Oxygen Demand (BOD), and a recently developed method by which TOC can be analyzed in the field has made TOC determinations even more accessible. The paper provides a theoretical determination of the TOC of over 100 fracturing fluid additives and compares the results with a field method for making TOC determinations. Also provided are examples on how to use TOC values for individual stimulation fluid additives to estimate the TOC of the entire frac fluid as pumped. The result of the exercise in assessing the TOC content of various slickwater and crosslinked polymer fluids provides a comparative guide for potential downhole bacterial and formation damage issues. It is therefore possible to estimate the potential for proppant pack and/or formation damage with knowledge of the TOC of a fracturing fluid prior to its selection without having to resort to an analysis of the fluid. Also provided are insight into the range of TOC's that might be observed in various spent frac flowback waters as they are associated with general frac fluid types, such as Slickwater or Crosslinked frac fluids. Armed with knowledge of the TOC of actual flowback it may be possible to determine whether or not additional well cleanout operations might improve well productivity.