77 research outputs found

    Cell-type specific cholinergic modulation in anterior cingulate and lateral prefrontal cortices of the rhesus macaque

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    The lateral prefrontal cortex (LPFC) and the anterior cingulate cortex (ACC) are two key regions of the frontal executive control network. Ascending cholinergic pathways differentially innervate these two functionally distinct cortices to modulate arousal and motivational signaling for higher-order functions. The action of acetylcholine (ACh) in sensory cortices is constrained by layer, anatomical cell type, and subcellular localization of distinct receptors, but little is known about the nature and organization of frontal-cholinergic circuitry in primates. In this dissertation, we characterized the anatomical localization of muscarinic acetylcholine receptors (mAChRs), m1 and m2–the predominant subtypes in the cortex–and their expression profiles on distinct cell types and pathways in ACC and LPFC of the rhesus monkey, using immunohistochemistry, anatomical tract-tracing, whole cell patch-clamp recordings, and single nucleus RNA sequencing. In the first series of studies (Chapter 2), we used immunohistochemistry and high-resolution confocal microscopy to reveal regional differences in m1 and m2 receptor localization on excitatory pyramidal and inhibitory neuron subpopulations and subcellular compartments in ACC (A24) versus LPFC (A46) of adult rhesus monkeys (Macaca mulatta; aged 7-11 yrs; 4 males and 2 females). The ACC exhibited a greater proportion of m2+ inhibitory neurons and a greater density of presynaptic m2+ receptors localized on inhibitory (VGAT+) terminations on pyramidal neurons compared to the LPFC. This result suggests a greater cholinergic suppression of GABAergic neurotransmission in ACC. In a second set of experiments (Chapter 3), we examined the heterogeneity of m1 and m2 laminar expression in functionally distinct ACC areas A24, A25, and A32. These differ in their connections with higher order cortical areas and limbic structures, such as the amygdala (AMY). The density of m1+ and/or m2 expressing (m1+/m2+) pyramidal neurons was significantly greater in A24 compared to A25 and to A32, while A25 exhibited a significantly greater density of m2+VGAT+ terminals. In addition, we examined the substrates for cholinergic modulation of long-range cortico-limbic processing using bidirectional neural tracers to label one specific subtype, the AMY-targeting projection neurons in these ACC areas. Compared to A24 and A32, the limbic ventral A25 had a greater density of m1+/m2+ AMY-targeting pyramidal neurons across upper layers 2-3 and deep layers 5-6, suggesting stronger cholinergic modulation of amygdalar outputs. Lastly (Chapter 4), we assessed the functional effects of cholinergic modulation on excitatory and inhibitory synaptic activity as well as the molecular signatures related to m1 and m2 receptor expression. In experiments using in vitro whole-cell patch-clamp recordings of layer 3 pyramidal neurons in ACC and LPFC, we found that application of the cholinergic agonist carbachol (CCh) significantly decreased the frequency of excitatory postsynaptic currents (EPSCs) to a greater extent in ACC A24 than in LPFC A46. Using single nucleus RNA sequencing, we found that enriched m1 and m2 transcriptional profiles in distinct cell-types and frontal areas (ACC A24 and LPFC A46) had differentially expressed genes associated with down-stream signaling cascades related to synaptic signaling and plasticity. Together, these data reveal the anatomical, functional, and transcriptomic neural substrates of diverse cholinergic modulation of local excitatory and inhibitory circuits and long-range cortico-limbic pathways in functionally-distinct ACC and LPFC frontal areas that are important for cognitive-emotional integration

    SPINAL CORD BIOLOGY AT A SINGLE CELL RESOLUTION: INTRINSIC POTENTIAL FOR NEURONAL DEGENERATION AND REGENERATION

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    The spinal cord enables movement and sensation. The cells within the spinal cord form a complex community which gives rise to its wide repertoire of functions. Recent advances in singe cell sequencing have given unparalleled access to analyzing diverse cell types within a single experiment. This enables the examination of gene expression at a single cell level, as well as an ability to understand the core organizing principles of cells. The following work examines the biology of the spinal cord at a single cell resolution, highlighting intrinsic potential for degeneration and regeneration of spinal cord neurons. We first present an optimized protocol for isolating nuclei from the spinal cord, enabling downstream single nucleus RNA sequencing (snRNA-Seq). With this technique, we examined the cellular diversity in the spinal cord of mice. Next, we sought to characterize the human spinal cord, including fundamental molecular features and those specific to human pathology. We present an atlas of the adult human spinal cord, with snRNA-Seq, spatial transcriptomics and antibody validation. We demonstrated the utility of this atlas by focusing on the transcriptome of spinal motoneurons that are selectively vulnerable to neurodegeneration in amyotrophic lateral sclerosis (ALS). We found that human motoneurons were enriched in genes related to cell size, cytoskeletal structure and ALS. These features that are related to maintaining large size of human motoneurons but their expression may also underly the selective vulnerability of motoneurons in neurodegeneration. Lastly, we used a mouse model to examine how the spinal cord responds in the context of injury. We used snRNA-Seq to profile cell types in the spared lumbar tissue below a thoracic injury at multiple timepoints after spinal cord injury (SCI) using a clinically-relevant contusion injury model in mice. This included an acute timepoint (1 day post-SCI), an intermediate timepoint (1 week post-SCI) and chronic timepoints (3 and 6 weeks post-SCI), as well as a baseline healthy controls. We found a rare spinal neuron that expressed a pro- regenerative signature and identified a major subset as spinocerebellar neurons, which displayed axon outgrowth after injury. This work highlights a rare molecular response to injury in the central nervous system that indicates plasticity within spinal cord neurons after injury and a potential for structural remodeling which could lead to recovery. Taken together, this work indicates cell-intrinsic potential for neuronal degeneration and regeneration in the spinal cord, which may serve as a basis for new therapeutic targets

    The 26th Annual Boston University Undergraduate Research (UROP) Abstracts

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    The file is available to be viewed by anyone in the BU community. To view the file, click on "Login" or the Person icon top-right with your BU Kerberos password. You will then be able to see an option to View.Abstracts for the 2023 UROP Symposium, held at Boston University on October 20, 2023 at GSU Metcalf Ballroom. Cover and logo design by Morgan Danna. Booklet compiled by Molly Power

    The effect of alterations of schizophrenia-associated genes on gamma band oscillations

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    © The Author(s) 2022. This article is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.Abnormalities in the synchronized oscillatory activity of neurons in general and, specifically in the gamma band, might play a crucial role in the pathophysiology of schizophrenia. While these changes in oscillatory activity have traditionally been linked to alterations at the synaptic level, we demonstrate here, using computational modeling, that common genetic variants of ion channels can contribute strongly to this effect. Our model of primary auditory cortex highlights multiple schizophrenia-associated genetic variants that reduce gamma power in an auditory steady-state response task. Furthermore, we show that combinations of several of these schizophrenia-associated variants can produce similar effects as the more traditionally considered synaptic changes. Overall, our study provides a mechanistic link between schizophrenia-associated common genetic variants, as identified by genome-wide association studies, and one of the most robust neurophysiological endophenotypes of schizophrenia.Peer reviewedFinal Published versio

    The Retina in Health and Disease

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    Vision is the most important sense in higher mammals. The retina is the first step in visual processing and the window to the brain. It is not surprising that problems arising in the retina lead to moderate to severe visual impairments. We offer here a collection of reviews as well as original papers dealing with various aspects of retinal function as well as dysfunction. New approaches in retinal research are described, such as the expression and localization of the endocannabinoid system in the normal retina and the role of cannabinoid receptors that could offer new avenues of research in the development of potential treatments for retinal diseases. Moreover, new insights are offered in advancing knowledge towards the prevention and cure of visual pathologies, mainly AMD, RP, and diabetic retinopathy

    Whole Brain Network Dynamics of Epileptic Seizures at Single Cell Resolution

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    Epileptic seizures are characterised by abnormal brain dynamics at multiple scales, engaging single neurons, neuronal ensembles and coarse brain regions. Key to understanding the cause of such emergent population dynamics, is capturing the collective behaviour of neuronal activity at multiple brain scales. In this thesis I make use of the larval zebrafish to capture single cell neuronal activity across the whole brain during epileptic seizures. Firstly, I make use of statistical physics methods to quantify the collective behaviour of single neuron dynamics during epileptic seizures. Here, I demonstrate a population mechanism through which single neuron dynamics organise into seizures: brain dynamics deviate from a phase transition. Secondly, I make use of single neuron network models to identify the synaptic mechanisms that actually cause this shift to occur. Here, I show that the density of neuronal connections in the network is key for driving generalised seizure dynamics. Interestingly, such changes also disrupt network response properties and flexible dynamics in brain networks, thus linking microscale neuronal changes with emergent brain dysfunction during seizures. Thirdly, I make use of non-linear causal inference methods to study the nature of the underlying neuronal interactions that enable seizures to occur. Here I show that seizures are driven by high synchrony but also by highly non-linear interactions between neurons. Interestingly, these non-linear signatures are filtered out at the macroscale, and therefore may represent a neuronal signature that could be used for microscale interventional strategies. This thesis demonstrates the utility of studying multi-scale dynamics in the larval zebrafish, to link neuronal activity at the microscale with emergent properties during seizures

    An investigation into the role of MeCP2 in sleep-related brain rhythms and memory consolidation

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    Methyl-CpG binding protein 2 (MeCP2) is a chromatin-associated protein which functions in epigenetic gene regulation. Mutations in MeCP2 lead to a variety of neurological disorders, including Rett Syndrome (RTT). Learning and memory deficits are prevalent in RTT, as are sleep disturbances: throughout the night, RTT patients spend less time in Stage 3 non-rapid eye movement (NREM) sleep. Delta oscillations (0.5 – 4 Hz) are the main constituent of Stage 3 NREM sleep, and are thought to be vital for sleep-related memory consolidation. In this thesis, the mechanisms and networks involved in delta oscillation generation were studied in a mouse model of RTT. In isolated sections of somatosensory cortex, loss of MeCP2 function resulted in the disruption of pharmacologically-induced cortical delta oscillations. In contrast, delta oscillations that arise via the thalamic generator remained intact. Pre-symptomatic Mecp2-null animals showed partial preservation of cortical delta oscillations, suggesting that neurological deficits precede phenotype onset. Intracellular current clamp recordings revealed that loss of MeCP2 function impairs the firing pattern of layer V intrinsically bursting pyramidal neurons, the cells responsible for generating the cortical delta rhythm. The bursting mechanism of these cells was restored by reducing the intracellular calcium ion concentration in these cells, which was also sufficient to reinstate the cortical delta rhythm. Finally, delta oscillations, sleep spindles and hippocampal sharp-wave ripples were studied in vivo during NREM sleep, since the coupling of these rhythms is thought to facilitate sleep-related memory consolidation. Rhythm coupling was unaffected by the loss of MeCP2 function, however the incidence of all three rhythms was significantly reduced, resulting in impaired performance on a hippocampus-dependent spatial memory task. The implication of these results on our understanding of the precise role of MeCP2 in coordinating NREM-associated brain rhythms and on the development of learning and memory deficits in RTT are discussed

    Advances in Neural Signal Processing

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    Neural signal processing is a specialized area of signal processing aimed at extracting information or decoding intent from neural signals recorded from the central or peripheral nervous system. This has significant applications in the areas of neuroscience and neural engineering. These applications are famously known in the area of brain–machine interfaces. This book presents recent advances in this flourishing field of neural signal processing with demonstrative applications
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