Biology subjects

Sylantyev, S.

Publications and source records attributed to Sylantyev, S..

6 recordsLinked to original sources

bioRxiv2023

A brainstem to hypothalamic arcuate nucleus GABAergic circuit drives feeding

The obesity epidemic is principally driven by the consumption of more calories than the body requires. It is therefore essential that the mechanisms underpinning feeding behavior are defined. The brainstem nucleus of the solitary tract (NTS) receives direct information from the digestive system and projects to second order regions in the brain. Though {gamma}-Aminobutyric acid is widely expressed in the NTS (GABANTS), its function has not been defined. Characterization of GABA cells using single nucleus RNA sequencing (Nuc-Seq) identified at least 19 clusters. Here we provide insight into the function of GABANTS cells, revealing that selective activation of GABANTS neurons significantly controls food intake and body weight. Optogenetic interrogation of GABANTS circuitry identified GABANTS[->]arcuate nucleus of the hypothalamus (ARC) projections as appetite suppressive without creating aversion. Electrophysiological analysis revealed GABANTS[->]ARC stimulation inhibits hunger promoting agouti-related protein/neuropeptide Y (AgRP/NPY) neurons via GABA release. Adopting an intersectional genetics strategy, we clarify that the GABANTS[->]ARC circuit induces satiety. These data identify GABANTS as a new modulator of feeding behavior, body weight and controller of orexigenic AgRP/NPY activity, thereby providing insight into the neural underpinnings of obesity. HighlightsO_LINucleus of the solitary tract (NTS) GABA neurons are responsive to nutritional status. C_LIO_LIChemogenetic GABANTS neuron activation reduces food intake and body weight. C_LIO_LIGABANTS projections to the hypothalamic arcuate nucleus (ARC) promote satiety. C_LIO_LIOptogenetic GABANTS[->]ARC stimulation inhibits orexigenic AgRP/NPY neurons. C_LI In BriefMartinez de Morentin et al. identify GABAergic neurons in the nucleus of the solitary tract as a new player in the circuit governing feeding behavior and body weight.

neuroscience↗

bioRxiv2022

Protein aggregation and calcium dysregulation are the earliest hallmarks of synucleinopathy in human midbrain dopaminergic neurons

Mutations in the SNCA gene cause autosomal dominant Parkinsons disease (PD), with progressive loss of dopaminergic neurons in the substantia nigra, and accumulation of aggregates of -synuclein. However, the sequence of molecular events that proceed from the SNCA mutation during development, to its end stage pathology is unknown. Utilising human induced pluripotent stem cells (hiPSCs) with SNCA mutations, we resolved the temporal sequence of pathophysiological events that occur during neuronal differentiation in order to discover the early, and likely causative, events in synucleinopathies. We adapted a small molecule-based protocol that generates highly enriched midbrain dopaminergic (mDA) neurons (>80%). We characterised their molecular identity using single-cell RNA sequencing and their functional identity through the synthesis and secretion of dopamine, the ability to generate action potentials, and form functional synapses and networks. RNA velocity analyses confirmed the developmental transcriptomic trajectory of midbrain neural precursors into mDA neurons using our approach, and identified key driver genes in mDA neuronal development. To characterise the synucleinopathy, we adopted super-resolution methods to determine the number, size and structure of aggregates in SNCA-mutant mDA neurons. At one week of differentiation, prior to maturation to mDA neurons of molecular and functional identity, we demonstrate the formation of small aggregates; specifically, {beta}-sheet rich oligomeric aggregates, in SNCA-mutant midbrain immature neurons. The aggregation progresses over time to accumulate phosphorylated aggregates, and later fibrillar aggregates. When the midbrain neurons were functional, we observed evidence of impaired physiological calcium signalling, with raised basal calcium, and impairments in cytosolic and mitochondrial calcium efflux. Once midbrain identity fully developed, SNCA-mutant neurons exhibited bioenergetic impairments, mitochondrial dysfunction and oxidative stress. During the maturation of mDA neurons, upregulation of mitophagy and autophagy occured, and ultimately these multiple cellular stresses lead to an increase in cell death by six weeks post-differentiation. Our differentiation paradigm generates an efficient model for studying disease mechanisms in PD, and highlights that protein misfolding to generate intraneuronal oligomers is one of the earliest critical events driving disease in human neurons, rather than a late-stage hallmark of the disease.

neuroscience↗

bioRxiv2022

Blood cells communicate remotely via an NMDA receptor-mediated glutamatergic chain-reaction

Neutrophils are white blood cells that are critical to the acute inflammatory and adaptive immune responses. Their swarming-pattern behaviour is controlled by multiple cellular cascades involving calcium-dependent release of various signalling molecules. Previous studies have reported that neutrophils express glutamate receptors and can release glutamate but evidence of direct neutrophil-neutrophil communication has been elusive. Here, we hold semi-suspended cultured human neutrophils in patch-clamp whole-cell mode to find that calcium mobilisation induced by stimulating one neutrophil can trigger an NMDA receptor-driven membrane current and calcium signal in neighbouring neutrophils. We employ an enzymatic-based imaging assay to image, in real time, glutamate release from neutrophils induced by glutamate released from their neighbours. These observations provide direct evidence for a positive-feedback inter-neutrophil communication that could contribute to mechanisms regulating communal neutrophil behaviour.

cell biology↗

bioRxiv2021

Extrasynaptic GABA waves underlie epileptiform rhythms in the hippocampal network

Mechanisms that entrain and drive rhythmic epileptiform discharges remain debated. Traditionally, this quest has been focusing on interneuronal networks driven by GABAergic connections that activate synaptic or extrasynaptic receptors. However, synchronised interneuronal discharges could also trigger a transient elevation of extracellular GABA across the tissue volume, thus raising tonic GABAA receptor conductance (Gtonic) in multiple cells. Here, we use patch-clamp GABA sniffer and optical GABA sensor to show that periodic epileptiform discharges are preceded by region-wide, rising waves of extracellular GABA. Neural network simulations that incorporate volume-transmitted GABA signals point to mechanistic principles underpinning this relationship. We validate this hypothesis using simultaneous patch-clamp recordings from multiple nerve cells, selective optogenetic stimulation of fast-spiking interneurons. Critically, we manipulate GABA uptake to suppress extracellular GABA waves but not synaptic GABAergic transmission, which shows a clear effect on rhythm generation. Our findings thus unveil a key role of extrasynaptic, volume-transmitted GABA actions in pacing regenerative rhythmic activity in brain networks.

neuroscience↗

bioRxiv2020

Highly enriched hiPSC-derived midbrain dopaminergic neurons robustly models Parkinson's disease.

The development of human induced pluripotent stem cells (hiPSC) has greatly aided our ability to model neurodegenerative diseases. However, generation of midbrain dopaminergic (mDA) neurons is a major challenge and protocols are variable. Here, we developed a method to differentiate hiPSCs into enriched populations (>80%) of mDA neurons using only small molecules. We confirmed the identity of the mDA neurons using single-cell RNA-sequencing and detection of classical markers. Single-cell live imaging demonstrated neuronal calcium signalling and functional dopamine transport. Electrophysiology measures highlighted the ability to form synapses and networks in culture. Patient-specific hiPSC lines differentiated to produce functional mDA neurons that exhibit the hallmarks of synucleinopathy including: aggregate formation, oxidative stress as well as mitochondrial dysfunction and impaired lysosomal dynamics. In summary, we establish a robust differentiation paradigm to generate enriched mDA neurons from hiPSCs, which can be used to faithfully model key aspects of Parkinsons disease (PD), providing the potential to further elucidate molecular mechanisms contributing to disease development.

neuroscience↗

bioRxiv2020

Extracellular GABA waves regulate coincidence detection in excitatory circuits

Coincidence detection of excitatory inputs by principal neurons underpins the rules of signal integration and Hebbian plasticity in the brain. In the hippocampal circuitry, detection fidelity is thought to depend on the GABAergic synaptic input through a feed-forward inhibitory circuit also involving the hyperpolarization-activated Ih current. However, afferent connections often bypass feed-forward circuitry, suggesting that a different GABAergic mechanism might control coincidence detection in such cases. To test whether fluctuations in the extracellular GABA concentration [GABA] could play a regulatory role here, we use a GABA sniffer patch in acute hippocampal slices of the rat and document strong dependence of [GABA] on network activity. We find that blocking GABAergic signalling strongly reduces the coincidence detection window of direct excitatory inputs to pyramidal cells whereas increasing [GABA] through GABA uptake blockade expands it. The underlying mechanism involves membrane-shunting tonic GABAA receptor current; it does not have to rely on Ih but depends strongly on the neuronal GABA transporter GAT-1. We use dendrite-soma dual patch-clamp recordings to show that the strong effect of membrane shunting on coincidence detection relies on nonlinear amplification of changes in the decay of dendritic synaptic currents when they reach the soma. Our results suggest that, by dynamically regulating extracellular GABA, brain network activity can optimise signal integration rules in local excitatory circuits.

neuroscience↗