Biology subjects

Chandra, R.

Publications and source records attributed to Chandra, R..

13 recordsLinked to original sources

bioRxiv2025

Nicotinic Modulation of Fast-spiking Neurons in Rat Somatosensory Cortex Across Development

Signaling at nicotinic acetylcholine receptors (nAChRs) is vital for normal development of cerebral cortical circuits. These developing circuits are also shaped by fast-spiking (FS) inhibitory cortical neurons. While nicotinic dysfunction in FS neurons is implicated in a number of psychiatric and neurodevelopmental disorders, FS neurons are thought to not have nicotinic responses in adults. Here, we establish a timeline of FS neuron response to nicotine pre- and postsynaptically in primary somatosensory cortex in male and female rats. We found that nicotine increases the frequency of spontaneous synaptic inputs to FS neurons during the second postnatal week, and this effect persisted through development. In contrast, FS neurons in S1 had no postsynaptic responses to nicotine from as early as they can be reliably identified. This was not attributable to receptor desensitization, and we further revealed that FS neurons express abundant mRNA for several nAChR subunits, beginning early in development. To determine why FS neurons do not respond to nicotine, despite expressing these receptors, we probed for the expression of lynx1, a negative nicotinic modulator. Lynx1 mRNA was expressed in FS neurons from early development, with expression increasing dramatically during the second postnatal week. SIGNIFICANCE STATEMENTSignaling at nicotinic receptors is critical for development of cortical circuits. These circuits are also shaped by fast-spiking (FS) inhibitory neurons. We reveal how these developmental processes interact, by establishing a timeline of nicotinic effects on FS neurons in rats. We find that nicotine presynaptically regulates inputs to FS neurons from early development. However, FS neurons at all ages lack postsynaptic responses to nicotine, despite expressing nicotinic receptor mRNA. This might be due to the expression of lynx1, a negative nicotinic receptor modulator, which we identify in FS neurons as early as the first postnatal week. This work reveals novel aspects of development, relevant to both normal cortical development and the neuropsychiatric pathologies associated with abnormal FS neurons and nicotinic development.

neuroscience↗

bioRxiv2024

A Novel Combinatorial Approach Integrating Experimental and Computational Analysis of Antioxidant Activity: Evaluating Catechin and L-Ascorbic Acid in Serum

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality globally, with oxidative stress playing a pivotal role in its progression. Free radicals produced via oxidative stress contribute to lipid peroxidation, leading to subsequent inflammatory responses, which then result in atherosclerosis. Antioxidants inhibit these harmful effects through their reducing ability, thereby preventing oxidative damage. In this study, we introduce a with computational models simulating hydrophilic and hydrophobic serum environments. We optimized the Ferric Reducing Ability of Plasma (FRAP) assay at a microscale level to evaluate the antioxidant activity of L-ascorbic acid (vitamin C) and catechin, a phytochemical found in green tea, in normal and hypertriglyceridemic serum. Hypertriglyceridemic serum, characterized by increased hydrophobic lipid content, provides a model to examine the impact of serum triglycerides on antioxidant activity. Additionally, we employed computational models using the Gaussian software to simulate the hydrogen atom transfer (HAT) mechanism, calculating free energy changes and bond dissociation energy (BDE) to assess the antioxidant potency of the studied compounds in both hydrophilic and hydrophobic environments. The computational results align with the experimental finding offering a unique combinatorial approach to assess antioxidant activity in both normal and hypertriglyceridemic serum, with potential implications for clinical interventions.

biochemistry↗

bioRxiv2023

Gut mucosal cells transfer α-synuclein to the vagus nerve

Epidemiological and histopathological findings have raised the possibility that misfolded -synuclein protein might spread from the gut to the brain and increase the risk of Parkinsons disease (PD). While past experimental studies in mouse models have relied on gut injections of exogenous recombinant -synuclein fibrils to study gut to brain -synuclein transfer, the possible origins of misfolded -synuclein within the gut have remained elusive. We recently demonstrated that sensory cells of the gut mucosa express -synuclein. In this study, we employed mouse intestinal organoids expressing human -synuclein to observe the transfer of -synuclein protein from gut epithelial cells in organoids co-cultured with vagal nodose neurons that are otherwise devoid of -synuclein expression. In intact mice that express pathological human -synuclein, but no mouse -synuclein, -synuclein fibril templating activity emerges in -synuclein seeded fibril aggregation assays in tissues from the gut, vagus nerve, and dorsal motor nucleus. In newly engineered transgenic mice that restrict pathological human -synuclein expression to intestinal epithelial cells, -synuclein fibril-templating activity transfers to the vagus nerve and to the dorsal motor nucleus. Subdiaphragmatic vagotomy prior to the induction of -synuclein expression in the gut epithelial cells effectively protects the hindbrain from the emergence of -synuclein fibril templating activity. Overall, these findings highlight a novel potential non-neuronal source of fibrillar -synuclein protein that might arise in gut mucosal cells.

neuroscience↗

bioRxiv2022

Inducible CRISPR epigenome systems mimic cocaine induced bidirectional regulation of Nab2 and Egr3

Substance use disorder is a debilitating chronic disease and a leading cause of disability around the world. The nucleus accumbens (NAc) is a major brain hub that mediates reward behavior. Studies demonstrate exposure to cocaine is associated with molecular and functional imbalance in two NAc medium spiny neuron subtypes (MSNs), dopamine receptor 1 and 2 enriched D1-MSNs and D2-MSNs. Our previous reports showed that repeated cocaine exposure induced transcription factor early growth response 3 (Egr3) mRNA in NAc D1-MSNs, while reducing it in D2-MSNs. Here, we report our findings of repeated cocaine exposure inducing cell subtype specific bidirectional expression of the Egr3 corepressor NGFI-A-binding protein 2 (Nab2). Using CRISPR activation and interference (CRISPRa and CRISPRi) tools combined with Nab2 or Egr3 targeted sgRNAs, we mimicked these bidirectional changes in Neuro2a cells. Furthermore, we investigated D1-MSN and D2-MSN subtype specific expressional changes of histone lysine demethylases Kdm1a, Kdm6a and Kdm5c in NAc after repeated cocaine exposure. Since Kdm1a showed bidirectional expression patterns in D1-MSNs and D2-MSNs, like Egr3, we developed a light inducible Opto-CRISPR-KDM1a system. We were able to downregulate Egr3 and Nab2 transcripts and cause bidirectional expression changes in D1-MSNs and D2-MSNs similar to cocaine exposure in Neuro2A cells. In contrast, our Opto-CRISPR-p300 activation system induced the Egr3 and Nab2 transcripts and caused bidirectional transcription regulations in D1-MSNs and D2-MSNs. Our study sheds light on the expression patterns of Nab2 and Egr3 in specific NAc MSN subtypes in cocaine action and uses CRISPR tools to further mimic these expression patterns.

neuroscience↗

bioRxiv2022

Specific sensory neurons and insulin-like peptides modulate food type-dependent oogenesis and fertilization in Caenorhabditis elegans

AbstractAn animals responses to environmental cues are critical for its reproductive program. Thus, a mechanism that allows the animal to sense and adjust to its environment should make for a more efficient reproductive physiology. Here we demonstrate that in Caenorhabditis elegans specific sensory neurons influence onset of oogenesis through insulin signaling in response to food-derived cues. The chemosensory neurons ASJ modulate oogenesis onset through the insulin-like peptide (ILP) INS-6. In contrast, other sensory neurons, the olfactory neurons AWA, regulate food type-dependent differences in C. elegans fertilization rates, but not onset of oogenesis. AWA modulates fertilization rates at least partly in parallel to insulin receptor signaling, since the insulin receptor DAF-2 regulates fertilization independently of food type, which requires ILPs other than INS-6. Together our findings suggest that optimal reproduction requires the integration of diverse food-derived inputs through multiple neuronal signals acting on the C. elegans germline.

developmental biology↗

bioRxiv2022

Negative emotional behavior during fentanyl abstinence is mediated by adaptations in nucleus accumbens neuron subtypes

Opioid discontinuation generates a withdrawal syndrome marked by a negative emotional state. Increased anxiety and dysphoria during opioid discontinuation are a significant barrier to achieving long-term abstinence in opioid-dependent individuals. Adaptations in brain-reward circuitry are implicated in the opioid abstinence syndrome, but current knowledge is limited to changes following natural and semi-synthetic opioids. Here we report abstinence from the synthetic opioid fentanyl engenders structural, functional, and molecular plasticity in nucleus accumbens neuron subtypes (MSNs) that mediate negative emotional behaviors. We show fentanyl abstinence causes dendritic atrophy and increased excitatory drive exclusive to D1-receptor containing MSNs. Using subtype specific RNAseq and Weighted Gene Co-Expression Network Analysis, we identified molecular signatures of fentanyl abstinence in MSN subtypes. We found a network of co-expressed genes downregulated selectively in D1-MSNs, and transcriptionally co-regulated by E2F1. We show targeting abstinence-induced molecular changes protects D1-MSNs from maladaptive plasticity and alleviates negative emotional behaviors after fentanyl abstinence.

neuroscience↗

bioRxiv2021

Distinct properties in ventral pallidum projection neuron subtypes

The ventral pallidum (VP) is central to reward seeking and withdrawal from drugs of abuse. A characteristic of the VP is the diversity of its projection targets. Yet, it remains unknown whether different VP projections also differ in other aspects, such as their transcriptome, physiology and relevance to drug reward. In this study we perform a multimodal dissection of four major projections of the VP - to the lateral hypothalamus (VP[->]LH), ventral tegmental area (VP[->]VTA), lateral habenula (VP[->]LHb) and mediodorsal thalamus (VP[->]MDT) - with physiological, anatomical, genetic and behavioral tools and show significant differences between projections in all aspects. Specifically, the VP[->]LH and VP[->]VTA projections show minimal overlap and stand out as having opposite properties - VP[->]LH neurons show higher excitability compared to VP[->]VTA neurons, different pattern of inputs and differentially expressed genes. Moreover, inhibition of VP[->]LH projections diminishes, while inhibition of VP[->]VTA enhances cocaine preference after cocaine withdrawal. This demonstrates that VP projections are heterogenous neuron populations with different roles in cocaine withdrawal.

neuroscience↗

bioRxiv2021

Transcriptome profiling of the ventral pallidum reveals a role for pallido-thalamic neurons in cocaine reward

Psychostimulant exposure alters the activity of ventral pallidum (VP) projection-neurons. However, the molecular underpinnings of these circuit dysfunctions are unclear. We used RNA- sequencing to reveal alterations in the transcriptional landscape of the VP that are induced by cocaine self-administration in mice. We then probed gene expression in select VP neuronal subpopulations to isolate a circuit associated with cocaine intake. Finally, we used both overexpression and CRISPR-mediated knockdown to test the role of a gene target on cocaine- mediated behaviors as well as dendritic spine density. Our results showed that a large proportion (55%) of genes associated with structural plasticity were changed 24 hours following cocaine intake. Among them, the transcription factor Nr4a1 (Nuclear receptor subfamily 4, group A, member 1, or Nur77) showed high expression levels. We found that the VP to mediodorsal thalamus (VP[->]MDT) projection neurons specifically were recapitulating this increase in Nr4a1 expression. Overexpressing Nr4a1 in VP[->]MDT neurons enhanced drug-seeking and drug- induced reinstatement, while Nr4a1 knock down prevented self-administration acquisition and subsequent cocaine-mediated behaviors. Moreover, we showed that Nr4a1 negatively regulated spine dynamics in this specific cell subpopulation. Together, our study identifies for the first time the transcriptional mechanisms occurring in VP in drug exposure. Our study provides further understanding on the role of Nr4a1 in cocaine-related behaviors and identifies the crucial role of the VP[->]MDT circuit in drug intake and relapse-like behaviors.

neuroscience↗

bioRxiv2020

Sleep is required for odor exposure to consolidate memory and remodel olfactory synapses.

Animals with complex nervous systems demand sleep for memory consolidation and synaptic remodeling. Here we show that though the Caenorhabditis elegans nervous system has a limited number of neurons, sleep is necessary for both processes. In addition, it is unclear in any system if sleep collaborates with experience to alter synapses between specific neurons and whether this ultimately affects behavior. C. elegans neurons have defined connections and well-described contributions to behavior. We show that spaced odor-training and post-training sleep induce long-term memory. Memory consolidation, but not acquisition, requires a pair of interneurons, the AIYs, which play a role in odor-seeking behavior. In worms that consolidate memory, both sleep and odor conditioning are required to diminish inhibitory synaptic connections between the AWC chemosensory neurons and the AIYs. Thus, we demonstrate in a living organism that sleep is required for events immediately after training that drive memory consolidation and alter synaptic structures.

neuroscience↗

bioRxiv2020

Cocaine-induced neuron subtype mitochondrial dynamics through Egr3 transcriptional regulation

Mitochondrial function is required for brain energy homeostasis and neuroadaptation. Recent studies demonstrate that cocaine affects mitochondrial dynamics and morphological characteristics within the nucleus accumbens (NAc). Further, mitochondria are differentially regulated by cocaine in dopamine receptor-1 containing medium spiny neurons (D1-MSNs) vs dopamine receptor-2 (D2)-MSNs. However, there is little understanding into cocaine-induced transcriptional mechanisms and their role in regulating mitochondrial processes. Here, we demonstrate that cocaine enhances binding of the transcription factor, early growth response factor 3 (Egr3), to nuclear genes involved in mitochondrial function and dynamics. Moreover, cocaine exposure regulates mRNA of these mitochondria-associated nuclear genes in both contingent or noncontingent cocaine administration and in both rodent models and human postmortem tissue. Interestingly, several mitochondrial nuclear genes showed distinct profiles of expression in D1-MSNs vs D2-MSNs, with cocaine exposure generally increasing mitochondrial-associated nuclear gene expression in D1-MSNs vs suppression in D2-MSNs. We further show that blunting Egr3 expression in D1-MSNs blocks cocaine-enhancement of the mitochondrial-associated transcriptional coactivator, peroxisome proliferator-activated receptor gamma coactivator (PGC1), and the mitochondrial fission molecule, dynamin related protein 1 (Drp1). Finally, reduction of D1-MSN Egr3 expression attenuates cocaine-induced enhancement of small-sized mitochondria, causally demonstrating that Egr3 regulates mitochondrial morphological adaptations. Collectively, these studies demonstrate cocaine exposure impacts mitochondrial dynamics and morphology by Egr3 transcriptional regulation of mitochondria-related nuclear gene transcripts; indicating roles for these molecular mechanisms in neuronal function and plasticity occurring with cocaine exposure.

neuroscience↗

bioRxiv2019

Individual differences in stereotypy and neuron subtype translatome with TrkB deletion

Motor stereotypies occurring in early-onset neuropsychiatric diseases are associated with dysregulated basal ganglia direct-pathway activity. Disruptions in network connectivity through impaired neuronal structure have been implicated in both rodents and humans. However, the neurobiological mechanisms leading to direct-pathway neuron disconnectivity in stereotypy remain poorly understood. We have a mouse line with Tropomyosin receptor kinase B (TrkB) receptor deletion from D1-expressing cells (D1-Cre-flTrkB) in which a subset of animals shows repetitive rotations and head tics with juvenile onset. Here we demonstrate these behaviors may be associated with abnormal direct-pathway activity by reducing rotations using chemogenetic inhibition of dorsal striatum D1-medium spiny neurons (D1-MSNs) in both juvenile and young adult mice. Taking advantage of phenotypical differences in animals with similar genotype, we then interrogated the D1-MSN specific translatome associated with repetitive behavior by using RNA-sequencing of ribosome-associated mRNA. Detailed translatome analysis followed by multiplexed gene expression assessment revealed profound alterations in neuronal projection and synaptic structure related genes in stereotypy mice. Examination of neuronal morphology demonstrated dendritic atrophy and dendritic spine loss in dorsal striatum D1-MSNs from mice with repetitive behavior. Together, our results uncover phenotype-specific molecular alterations in D1-MSNs that relate to morphological adaptations in mice displaying stereotypy behavior.

neuroscience↗

bioRxiv2019

Axonal transport of an insulin-like peptide mRNA promotes stress recovery in C. elegans

Aberrations in insulin or insulin-like peptide (ILP) signaling in the brain causes many neurological diseases. Here we report that mRNAs of specific ILPs are surprisingly mobilized to the axons of C. elegans during stress. Transport of the ILP ins-6 mRNA to axons facilitates recovery from stress, whereas loss of axonal mRNA delays recovery. In addition, the axonal traffic of ins-6 mRNA is regulated by at least two opposing signals: one that depends on the insulin receptor DAF-2 and a kinesin-2 motor; and a second signal that is independent of DAF-2, but involves a kinesin-3 motor. While Golgi bodies that package nascent peptides, like ILPs, have not been previously found in C. elegans axons, we show that axons of stressed C. elegans have increased Golgi ready to package peptides for secretion. Thus, our findings present a mechanism that facilitates an animals rapid recovery from stress through axonal ILP mRNA mobilization.

neuroscience↗

bioRxiv2018

Biology and Bias in Cell Type-Specific RNAseq of Nucleus Accumbens Medium Spiny Neurons

Isolation of cell populations is untangling complex biological interactions, but studies comparing methodologies lack in vivo complexity and draw limited conclusions about the types of transcripts identified by each technique. Furthermore, few studies compare FACS-based techniques to ribosomal affinity purification, and none do so genome-wide. We addressed this gap by systematically comparing nuclear-FACS, whole cell-FACS, and RiboTag affinity purification in the context of D1 or D2 dopamine receptor-expressing medium spiny neuron (MSN) subtypes of the nucleus accumbens (NAc), a key brain reward region. We find that nuclear-FACS-seq generates a substantially longer list of differentially expressed genes between these cell types, and a significantly larger number of neuropsychiatric GWAS hits than the other two methods. RiboTag-seq has much lower coverage of the transcriptome than the other methods, but very efficiently distinguishes D1- and D2-MSNs. We also demonstrate differences between D1- and D2-MSNs with respect to RNA localization, suggesting fundamental cell type differences in mechanisms of transcriptional regulation and subcellular transport of RNAs. Together, these findings guide the field in selecting the RNAseq method that best suits the scientific questions under investigation.

neuroscience↗