Biology subjects

Olah, V. J.

Publications and source records attributed to Olah, V. J..

10 recordsLinked to original sources

bioRxiv2025

Selective targeting of hippocampal fast-spiking basket cell interneurons via noninvasive enhancer-AAV delivery

Accurate targeting of specific brain regions through non-invasive methods has long been a major goal of basic and translational neuroscience. Systemic delivery of AAVs expressing highly region- and cell-type-specific regulatory elements (enhancer-AAVs) continues to emerge as a tractable solution. Here we performed an independent characterization of a novel enhancer element with apparent robust transgene expression in fast-spiking basket cell interneurons in mouse hippocampus. Surprisingly, this vector did not induce expression in other brain regions harboring the same neuron class. Following intravenous administration in mice, robust labeling of FS-BCs across all hippocampal subfields was observed. We validated the FS-BC specificity in hippocampus using immunofluorescence and electrophysiological recordings. Viral labeling was confined to parvalbumin-positive cells exhibiting basket cell morphology and fast-spiking responses. This approach represents a promising avenue for both mechanistic investigation of hippocampal circuit function and potential therapeutic interventions targeting hippocampal pathophysiologies such as epilepsy, schizophrenia, and other neurological disorders in mice and potentially other species.

neuroscience↗

bioRxiv2024

An enhancer-AAV toolbox to target and manipulate distinct interneuron subtypes

In recent years, we and others have identified a number of enhancers that, when incorporated into rAAV vectors, can restrict the transgene expression to particular neuronal populations. Yet, viral tools to access and manipulate specific neuronal subtypes are still limited. Here, we performed systematic analysis of single cell genomic data to identify enhancer candidates for each of the telencephalic interneuron subtypes. We established a set of enhancer-AAV tools that are highly specific for distinct cortical interneuron populations and striatal cholinergic interneurons. These enhancers, when used in the context of different effectors, can target (fluorescent proteins), observe activity (GCaMP) and manipulate (opto-genetics) specific neuronal subtypes. We also validated our enhancer-AAV tools across species. Thus, we provide the field with a powerful set of tools to study neural circuits and functions and to develop precise and targeted therapy.

neuroscience↗

bioRxiv2023

Entorhinal cortex vulnerability to human APP expression promotes hyperexcitability and tau pathology

Preventative treatment for Alzheimers Disease is of dire importance, and yet, cellular mechanisms underlying early regional vulnerability in Alzheimers Disease remain unknown. In human patients with Alzheimers Disease, one of the earliest observed pathophysiological correlates to cognitive decline is hyperexcitability. In mouse models, early hyperexcitability has been shown in the entorhinal cortex, the first cortical region impacted by Alzheimers Disease. The origin of hyperexcitability in early-stage disease and why it preferentially emerges in specific regions is unclear. Using cortical-region and cell-type-specific proteomics coupled with ex vivo and in vivo electrophysiology, we uncovered differential susceptibility to human-specific amyloid precursor protein (hAPP) in a model of sporadic Alzheimers. Unexpectedly, our findings reveal that early entorhinal hyperexcitability may result from intrinsic vulnerability of parvalbumin (PV) interneurons, rather than the suspected layer II excitatory neurons. This vulnerability of entorhinal PV interneurons is specific to hAPP, as it could not be recapitulated with increased murine APP expression. However, partial replication of the findings could be seen after introduction of a murine APP chimera containing a humanized amyloid-beta sequence. Surprisingly, neurons in the Somatosensory Cortex showed no such vulnerability to adult-onset hAPP expression. hAPP-induced hyperexcitability in entorhinal cortex could be ameliorated by enhancing PV interneuron excitability in vivo. Co-expression of human Tau with hAPP decreased circuit hyperexcitability, but at the expense of increased pathological tau species. This study suggests early disease interventions targeting non-excitatory cell types may protect regions with early vulnerability to pathological symptoms of Alzheimers Disease and downstream cognitive decline.

neuroscience↗

bioRxiv2023

Hidden HCN channels permit pathway-specific synaptic amplification in L2/3 pyramidal neurons

Layer 2/3 pyramidal cells (L2/3 PCs) play a crucial role in cortical information transfer. Although the dendritic arbors of L2/3 PCs are impressive, they often lack the distinct anatomical compartments characteristic of deeper L5 PCs. For example, many L2/3 PCs do not display an apparent distal tuft region. However, L2/3 PCs receive inputs from both thalamic (bottom-up) and cortical (top-down) inputs, which preferentially synapse onto their proximal and distal dendrites, respectively. Nonuniform organization of channels and NMDA receptors in L2/3 dendrites could serve to independently modulate these information streams to affect learning and behavior, yet whether L2/3 PC dendrites possess this capability has not been established. Here we found a previously unappreciated, non-uniform HCN channel distribution in L2/3 PCs, allowing for pathway-specific gating of NMDA receptor recruitment at bottom-up (proximal) but not top-down (distal) synapses. HCN availability shifted depending on developmental stage and neuromodulation, suggesting that the gain of thalamic and cortical-cortical signals in L2/3 may be independently modified in vivo across different timescales.

neuroscience↗

bioRxiv2023

Classifier for the Rapid Simultaneous Determination of Sleep-Wake States and Seizures in Mice

Sleep-wake states bi-directionally interact with epilepsy and seizures, but the mechanisms are unknown. A barrier to comprehensive characterization and the study of mechanisms has been the difficulty of annotating large chronic recording datasets. To overcome this barrier, we sought to develop an automated method of classifying sleep-wake states, seizures, and the post-ictal state in mice ranging from controls to mice with severe epilepsy with accompanying background EEG abnormalities. We utilized a large dataset of recordings, including EMG, EEG, and hippocampal local field potentials, from control and intra-amygdala kainic acid-treated mice. We found that an existing sleep-wake classifier performed poorly, even after retraining. A support vector machine, relying on typically used scoring parameters, also performed below our benchmark. We then trained and evaluated several multi-layer neural network architectures and found that a bidirectional long short-term memory-based model performed best. This Sleep-Wake and Ictal State Classifier (SWISC) showed high agreement between ground-truth and classifier scores for all sleep and seizure states in an unseen and unlearned epileptic dataset (average agreement 96.41% {+/-} SD 3.80%), and saline animals (97.77% {+/-} 1.40%). Channel elimination and feature selection provided interpretability and demonstrated that SWISC was primarily dependent on hippocampal signals, yet still maintained good performance ([~]90% agreement) with EEG alone, thereby expanding the classifiers applicability to other epilepsy datasets. SWISC enables the efficient combined scoring of sleep-wake and seizure states in mouse models of epilepsy and healthy controls, facilitating comprehensive and mechanistic studies of sleep-wake and biological rhythms in epilepsy.

neuroscience↗

bioRxiv2023

A novel enhancer-AAV approach selectively targeting dentate granule cells

The mammalian brain contains the most diverse array of cell types of any organ, including dozens of neuronal subtypes with distinct anatomical and functional characteristics. The brain leverages these neuron-type-specializations to perform diverse circuit operations and thus execute different behaviors properly. Through the use of Cre lines, access to specific neuron types has steadily improved over past decades. Despite their extraordinary utility, development and cross-breeding of Cre lines is time-consuming and expensive, presenting a significant barrier to entry for many investigators. Furthermore, cell-based therapeutics developed in Cre mice are not clinically translatable. Recently, several AAV vectors utilizing neuron-type-specific regulatory transcriptional sequences (enhancer-AAVs) were developed which overcome these limitations. Using a publicly available RNAseq dataset, we evaluated the potential of several candidate enhancers for neuron-type-specific targeting in the hippocampus. Here we identified a promising enhancer-AAV for targeting dentate granule cells and validated its selectivity in wild-type adult mice.

neuroscience↗

bioRxiv2021

Biophysical Kv channel alterations dampen excitability of cortical PV interneurons and contribute to network hyperexcitability in early Alzheimer's

In Alzheimers disease (AD), a multitude of genetic risk factors and early biomarkers are known. Nevertheless, the causal factors responsible for initiating cognitive decline in AD remain controversial. Toxic plaques and tangles correlate with progressive neuropathology, yet disruptions in circuit activity emerge before their deposition in AD models and patients. Parvalbumin (PV) interneurons are potential candidates for dysregulating cortical excitability, as they display altered AP firing before neighboring excitatory neurons in prodromal AD. Here we report a novel mechanism responsible for PV hypoexcitability in young adult familial AD mice. We found that biophysical modulation of K+ channels, but not changes in mRNA expression, are responsible for dampened excitability. These K+ conductances could efficiently regulate near-threshold AP firing, resulting in gamma-frequency specific network hyperexcitability. Our findings suggest that posttranslational modulation of ion channels can reshape cortical network activity prior to changes in their gene expression in early AD.

neuroscience↗

bioRxiv2021

Cell type-specific biotin labeling in vivo resolves regional neuronal proteomic differences in mouse brain

Isolation and proteomic profiling of brain cell types, particularly neurons, pose several technical challenges which limit our ability to resolve distinct cellular phenotypes in neurological diseases. Therefore, we generated a novel mouse line that enables cell type-specific expression of a biotin ligase, TurboID, via Cre-lox strategy for in vivo proximity-dependent biotinylation of proteins. Using adenoviral-based and transgenic approaches, we show striking protein biotinylation in neuronal cell bodies and axons throughout the mouse brain. We quantified more than 2,000 neuron-derived proteins following enrichment that mapped to numerous subcellular compartments. Synaptic, transmembrane transporters, ion channel subunits, and disease-relevant druggable targets were among the most significantly enriched proteins. Remarkably, we resolved brain region-specific proteomic profiles of Camk2a neurons with distinct functional molecular signatures and disease associations that may underlie regional neuronal vulnerability. Leveraging the neuronal specificity of this in vivo biotinylation strategy, we used an antibody-based approach to uncover regionally unique patterns of neuron-derived signaling phospho-proteins and cytokines, particularly in the cortex and cerebellum. Our work provides a proteomic framework to investigate cell type-specific mechanisms driving physiological and pathological states of the brain as well as complex tissues beyond the brain.

neuroscience↗

bioRxiv2021

Ultrafast large-scale simulations of biophysically realistic neurons using deep learning

Understanding the activity of the mammalian brain requires an integrative knowledge of circuits at distinct scales, ranging from ion channel gating to circuit connectomics. To understand how multiple parameters contribute synergistically to circuit behavior, neuronal computational models are regularly employed. However, traditional models containing anatomically and biophysically realistic neurons are computationally demanding even when scaled to model local circuits. To overcome this limitation, we trained several artificial neural net (ANN) architectures to model the activity of realistic, multicompartmental neurons. We identified a single ANN that accurately predicted both subthreshold and action potential firing and correctly generalized its responses to previously unobserved synaptic input. When scaled, processing times were orders of magnitude faster compared with traditional approaches, allowing for rapid parameter-space mapping in a circuit model of Rett syndrome. Thus, we present a novel ANN approach that allows for rapid, detailed network experiments using inexpensive, readily available computational resources.

neuroscience↗

bioRxiv2019

Functional specification of CCK+ interneurons by alternative isoforms of Kv4.3 auxiliary subunits

CCK-expressing interneurons (CCK+INs) are crucial for controlling hippocampal activity. We found two firing phenotypes of CCK+INs in rat CA3 area; either possessing a previously undetected membrane potential-dependent firing or regular firing phenotype, due to different low-voltage-activated potassium currents. These different excitability properties destine the two types for distinct functions, because the former is essentially silenced during realistic 8-15 Hz oscillations. The general excitability, morphology and gene-profiles of the two types were surprisingly similar. Even the expression of Kv4.3 channels were comparable, despite evidences showing that Kv4.3-mediated currents underlie the distinct firing properties. Instead, the firing phenotypes were correlated with the presence of distinct isoforms of Kv4 auxiliary subunits (KChIP1 vs. KChIP4e and DPP6S). Our results reveal the underlying mechanisms of two previously unknown types of CCK+INs and demonstrate that alternative splicing of few genes, which may be viewed as a minor event in the cells whole transcriptome, can underlie distinct cell-type identity.

neuroscience↗