Neuronal morphologies built for reliable physiology in a rhythmic motor circuit

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in eLife 8 (2019): e41728. doi: 10.7554/eLife.41728.It is often assumed that highly-branched neuronal structures perform compartmentalized computations. However, previously we showed that the Gastric Mill (GM) neuron in the crustacean stomatogastric ganglion (STG) operates like a single electrotonic compartment, despite having thousands of branch points and total cable length >10 mm (Otopalik et al., 2017a; 2017b). Here we show that compact electrotonic architecture is generalizable to other STG neuron types, and that these neurons present direction-insensitive, linear voltage integration, suggesting they pool synaptic inputs across their neuronal structures. We also show, using simulations of 720 cable models spanning a broad range of geometries and passive properties, that compact electrotonus, linear integration, and directional insensitivity in STG neurons arise from their neurite geometries (diameters tapering from 10-20 µm to < 2 µm at their terminal tips). A broad parameter search reveals multiple morphological and biophysical solutions for achieving different degrees of passive electrotonic decrement and computational strategies in the absence of active properties.We thank Jennifer Bestman for assistance in spinning disk and confocal microscopy; the Marine Resources Center at the Marine Biological Laboratories for acquiring and maintaining animals; Louie Kerr at the Central Microscopy Facility; Dana Mock-Munoz de Luna for administrative support; Kam-ran Kodhakhah, Heather Rhodes, and the 2017 Grass Fellows for their support and feedback; and lastly, Edward Dougherty at the Brandeis University Confocal Imaging Lab for support and microscope maintenance. This study was funded by the Grass Foundation and NINDS awards to F31NS092126 to AO and R35NS097343 to EM

Born from pre-eclamptic pregnancies predisposes infants to altered cortisol metabolism in the first postnatal year

Pre-eclampsia leads to disturbed fetal organ development, including metabolic syndrome, attributed to altered pituitary-adrenal feedback loop. We measured cortisol metabolites in infants born from pre-eclamptic and normotensive women and hypothesised that glucocorticoid exposure would be exaggerated in the former. Twenty-four hour urine was collected from infants at months 3 and 12. Cortisol metabolites and apparent enzyme activities were analysed by gas chromatography-mass spectrometry. From 3 to 12 months, excretion of THS, THF and pregnandiol had risen in both groups; THF also rose in the pre-eclamptic group. No difference was observed with respect to timing of the visit or to hypertensive status for THE or total F metabolites (P>0.05). All apparent enzymes activities, except 17α-hydroxylase, were lower in infants at 12 compared to 3 months in the normotensive group. In the pre-eclamptic group, only 11β-HSD activities were lower at 12 months.17α-hydroxylase and 11β-HSD activities of tetrahydro metabolites were higher in the pre-eclamptic group at 3 months (P<0.05). 11β-hydroxylase activity increased in the pre-eclamptic group at 12 months. Cortisol excretion, determined by increased 11β-hydroxylase, compensates for high 11β-HSD-dependent cortisol degradation at 3 months and at 12 months counterbalances the reduced cortisol substrate availability in infants born from pre-eclamptic mothers

Verifying, Challenging, and Discovering New Synapses Among Fully EM-Reconstructed Neurons in the Leech Ganglion

Neural circuits underpin the production of animal behavior, largely based upon the precise pattern of synaptic connectivity among the neurons involved. For large numbers of neurons, determining such “connectomes” by direct physiological means is difficult, as physiological accessibility is ultimately required to verify and characterize the function of synapses. We collected a volume of images spanning an entire ganglion of the juvenile leech nervous system via serial blockface electron microscopy (SBEM). We validated this approach by reconstructing a well-characterized circuit of motor neurons involved in the swimming behavior of the leech by locating the synapses among them. We confirm that there are multiple synaptic contacts between connected pairs of neurons in the leech, and that these synapses are widely distributed across the region of neuropil in which the neurons’ arbors overlap. We verified the anatomical existence of connections that had been described physiologically among longitudinal muscle motor neurons. We also found that some physiological connections were not present anatomically. We then drew upon the SBEM dataset to design additional physiological experiments. We reconstructed an uncharacterized neuron and one of its presynaptic partners identified from the SBEM dataset. We subsequently interrogated this cell pair via intracellular electrophysiology in an adult ganglion and found that the anatomically-discovered synapse was also functional physiologically. Our findings demonstrate the value of combining a connectomics approach with electrophysiology in the leech nervous system

Induction and function of virus-specific CD4+ T cell responses

CD4+ T cells -- often referred to as T-helper cells -- play a central role in immune defense and pathogenesis. Virus infections and vaccines stimulate and expand populations of antigen-specific CD4+ T cells in mice and in man. These virus-specific CD4+ T cells are extremely important in antiviral protection: deficiencies in CD4+ T cells are associated with virus reactivation, generalized susceptibility to opportunistic infections, and poor vaccine efficacy. As described below, CD4+ T cells influence effector and memory CD8+ T cell responses, humoral immunity, and the antimicrobial activity of macrophages and are involved in recruiting cells to sites of infection. This review summarizes a few key points about the dynamics of the CD4+ T cell response to virus infection, the positive role of pro-inflammatory cytokines in the differentiation of virus-specific CD4+ T cells, and new areas of investigation to improve vaccines against virus infection

Untangling the ganglion: connectomics in the medicinal leech

The behaviors generated by neural circuits are constrained by the connectivity pattern among the neurons involved. Determining this connectivity pattern for circuits involving more than a handful of neurons becomes infeasible for physiological approaches that measure how the membrane potential of one neuron is affected by currents elicited in another. On the other hand, determining connectivity by anatomically discovering synapses is difficult due to the complicated and intertwining arbors that neurons possess. One approach to unravel this knotty problem is to image serial thin sections of neural tissue with an electron microscope. In this thesis, I describe the first application of large scale serial electron microscopy to the ganglion of the medicinal leech, Hirudo verbana. The leech ganglion is an ideal preparation for this experiment as it is compact enough in size that it is feasible to collect images spanning an entire ganglion. Here, I discuss results we collected from two image volumes of leech tissue. One spans a small region of adult ganglion neuropil, while the other includes an entire ganglion belonging to a juvenile leech. In these volumes, I reconstruct three-dimensional representations of neuronal arbors and locate the synapses between them. In Chapter 2, I show that we can differentiate neurons on the basis of where synaptic input and output sites are distributed throughout their arbors. In Chapter 3, I show that we can locate the synapses between pairs of neurons previously known to be connected, and that we can discover new synapses anatomically that are then recovered physiologically. Together, these results demonstrate the potential that this “connectomics” approach has when applied to the already physiologically accessible leech ganglion

Spinning Disk Images

Spinning disk image stacks for neurons displayed in Figure 2C. These files can be opened in ImageJ/FIJI

Electrophysiology and Photo-uncaging Experiments

This compressed folder contains raw time-series recordings for all electrophysiology and photo-uncaging experiments included in the paper. Recordings are the .abf format (acquired with Clampex software (Axon Instruments) and can be opened and viewed with either Clampfit Software (Axon Instruments) or another computing platform (e.g. MATLAB (Mathworks) using the AbfLoad function, see the Marder Lab GitHub)

Data from: Neuronal morphologies built for reliable physiology in a rhythmic motor circuit

It is often assumed that highly-branched neuronal structures perform compartmentalized computations. However, previously we showed that the Gastric Mill (GM) neuron in the crustacean stomatogastric ganglion (STG) operates like a single electrotonic compartment, despite having thousands of branch points and total cable length >10 mm (Otopalik et al., 2017a; 2017b). Here we show that compact electrotonic architecture is generalizable to other STG neuron types, and that these neurons present direction-insensitive, linear voltage integration, suggesting they pool synaptic inputs across their neuronal structures. We also show, using simulations of 720 cable models spanning a broad range of geometries and passive properties, that compact electrotonus, linear integration, and directional insensitivity in STG neurons arise from their neurite geometries (diameters tapering from 10-20 µm to < 2 µm at their terminal tips). A broad parameter search reveals multiple morphological and biophysical solutions for achieving different degrees of passive electrotonic decrement and computational strategies in the absence of active properties

Effect of Social Determinants of Health on Uncontrolled Human Immunodeficiency Virus (HIV) Infection Among Persons With HIV in San Francisco, California.

BackgroundIn 2010-2014, the San Francisco Department of Public Health (SFDPH) established programs to rapidly link people with human immunodeficiency virus (PWH) to care and offer antiretroviral therapy (ART) at human immunodeficiency virus (HIV) diagnosis. Such programs reduced the number of PWH out of care or with detectable HIV viral load (ie, uncontrolled HIV infection). We investigated the role of social determinants of health (SDH) on uncontrolled HIV.MethodsCross-sectional data from adult PWH diagnosed and reported to the SFDPH as of December 31, 2019, prescribed ART, and with confirmed San Francisco residency during 2017-2019 were analyzed in conjunction with SDH metrics derived from the American Community Survey 2015-2019. We focused on 5 census tract-level SDH metrics: percentage of residents below the federal poverty level, with less than a high school diploma, or uninsured; median household income; and Gini index. We compared uncontrolled HIV prevalence odds ratios (PORs) across quartiles of each metric independently using logistic regression models.ResultsThe analysis included 7486 PWH (6889 controlled HIV; 597 uncontrolled HIV). Unadjusted PORs of uncontrolled HIV rose with increasingly marginalized quartiles, compared to the least marginalized quartile for each metric. Adjusting for demographics and transmission category, the POR for uncontrolled HIV for PWH in the most marginalized quartile remained significant across metrics for poverty (POR = 2.0; confidence interval [CI] = 1.5-2.6), education (POR = 2.4; CI = 1.8-3.2), insurance (POR = 1.8; CI = 1.3-2.5), income (POR = 1.8; CI = 1.4-2.3), and income inequality (POR = 1.5; CI = 1.1-2.0).ConclusionsBeyond demographics, SDH differentially affected the ability of PWH to control HIV. Despite established care programs, PWH experiencing socioeconomic marginalization require additional support to achieve health outcome goals