Biology subjects

Dagostin, A.

Publications and source records attributed to Dagostin, A..

5 recordsLinked to original sources

bioRxiv2025

Astrocyte gap junctions and Kir channels contribute to K+ buffering and regulate neuronal excitability

ABSRACTAstrocytes are connected in a functional syncytium via gap junctions, which is thought to contribute to maintenance of extracellular K+ homeostasis. The prevailing hypothesis is that K+ released during neuronal firing is taken up by astrocytes via Kir channels and then distributed among neighboring astrocytes via gap junctions. Previous reports examining the role of Kir channels and gap junctions have shown both hyperexcitability and depression when each mechanism is blocked. Here, we tested the effect of blocking Kir channels and gap junctions, both independently and simultaneously, on field activity of cortical slices in response to a 3 s, 20 Hz stimulation train. Independently blocking either Kir channels or gap junctions increased the amplitude of the first fEPSC (field excitatory post-synaptic current) in response to a stimulation train, followed by suppression of fEPSCs during sustained stimulation. Surprisingly, blocking both gap junctions and Kir channels enhanced the suppression of neuronal activity, resulting in a [~]75% decrease in fiber volley (pre-synaptic action potentials) amplitude in the first response, followed by a fast and strong suppression of sustained fEPSCs. Our results demonstrate that blocking Kir channels and gap junctions can increase the excitability of neurons when firing is sparse, but suppression results when the firing frequency is increased to cortical physiological ranges. This suggest that K+ buffering via Kir and gap junctions, likely mediated by astrocytes, together play a critical role in maintaining neuronal excitability, particularly during sustained activity.

neuroscience↗

bioRxiv2024

Synaptic facilitation enhances the reliability and precision of high frequency neurotransmission

The small and tortuous volume of synaptic clefts limits the diffusion of Ca2+ ions during high frequency spiking. Extracellular Ca2+ levels ([Ca2+]o) of 0.8 mM or lower have been measured or calculated for different synapses. Here, we recorded evoked postsynaptic potentials (EPSP) and action potentials (AP) from young adult male and female mouse auditory brainstem principal neurons to investigate the relationship between neurotransmission reliability, stimulation frequency and [Ca2+]o. In 0.8 mM [Ca2+]o, we observed AP failures during afferent fiber stimulation at 100 Hz. Surprisingly, AP failures, EPSP-AP latency and jitter were all greatly reduced when stimulation frequency was increased to 500 Hz. Analysis of the EPSP/AP waveform revealed marked facilitation at 500 Hz that was not present at 100 Hz. Raising [Ca2+]o to 1.2 mM or 2.0 mM reduced or eliminated facilitation and, in these conditions, stimulation at 500 Hz increased the number of AP failures. In 0.8 mM [Ca2+]o, afferent fiber stimulation over a broad range of frequencies from 10-1000 Hz produced three different types of spiking responses: Type I cells exhibited band-pass filtering, with best response at approximately 500 Hz, Type II cells exhibited low-pass filtering above 600 Hz, and Type III cells exhibited shallow band-pass filtering centered at approximately 300 Hz. To predict AP success or failure, we built a model based on three factors: size of the EPSP, membrane potential immediately prior to the synaptic event and the number of preceding failures. We conclude that synaptic facilitation can contribute positively to the maintenance of reliable and precise high frequency neurotransmission in the auditory brainstem. Significance StatementFacilitation of evoked postsynaptic currents is a common feature of synapses. The strength of facilitation and its role in reaching spike threshold depends on intrinsic properties of the synapse, stimulation frequency, and extracellular Ca2+ concentration ([Ca2+]o). Physiological levels of [Ca2+]o can vary from 0.8 to 1.2 mM depending on synaptic activity. In the mouse Medial Nucleus of the Trapezoid Body, synaptic facilitation is readily observable in slice experiments using relatively low (0.8 mM) [Ca2+]o, but is partially or completely obscured by short-term synaptic depression when [Ca2+]o is high (1.2 or 2.0 mM). Here we show that facilitation can rescue the reliability of high-frequency (500 Hz) action potential firing in low [Ca2+]o, resulting in band-pass filter transmission.

neuroscience↗

bioRxiv2021

Resurgent Na+ currents promote ultrafast spiking in projection neurons that drive fine motor control

The underlying mechanisms that promote precise spiking in upper motor neurons controlling fine motor skills are not well understood. Here we report that projection neurons in the adult zebra finch song nucleus RA display: 1) robust high-frequency firing, 2) ultra-short half-width spike waveforms, 3) superfast Na+ current inactivation kinetics and 4) large resurgent Na+ currents (INaR). These spiking properties closely resemble those of specialized pyramidal neurons in mammalian motor cortex and are well suited for precise temporal coding. They emerge during the critical period for vocal learning in males but not females, coinciding with a complete switch of modulatory Na+ channel subunit expression from Nav{beta}3 to Nav{beta}4. Dynamic clamping and dialysis of Nav{beta}4s C-terminal peptide into juvenile RA neurons provide evidence that this subunit, and its associated INaR, promote neuronal excitability. We propose that Nav{beta}4 underpins INaR that facilitates precise, prolonged, and reliable high-frequency firing in upper motor neurons.

neuroscience↗

bioRxiv2021

Neuroimmune-glial cells interactions elevate the kynurenine metabolic pathway to sustain neuropathic pain

Neuropathic pain is triggered by injury to the somatosensory system, and is one of the most important types of chronic pain. Nevertheless, critical pathophysiological mechanisms that maintain neuropathic pain are poorly understood. Here, we show that neuropathic pain is abrogated when the kynurenine metabolic pathway (KYNPATH) initiated by the enzyme indoleamine 2,3-dioxygenase (IDO) is ablated pharmacologically or genetically. Mechanistically, it was found that IDO upregulation in dendritic cells that accumulate in the dorsal root leptomeninges led to increased levels of kynurenine (Kyn) in the spinal cord, where Kyn is metabolized by astrocytes-expressed kynurenine-3-monooxygenase into a pro-nociceptive metabolite 3-hydroxykynurenine. In conclusion, these data reveal a novel role for KYNPATH as an important factor maintaining neuropathic pain during neuroimmune-glia cells interactions. This novel paradigm offers potential new targets for drug development against this type of chronic pain.

neuroscience↗

bioRxiv2019

Dendritic speeding of synaptic potentials in an auditory brainstem principal neuron

Principal cells of the medial nucleus of the trapezoid body (MNTB) in the mammalian auditory brainstem receive most of their strong synaptic inputs directly on the cell soma. However, these neurons also grow extensive dendrites during the first four postnatal weeks. What are the functional roles of these dendrites? We studied the morphology and growth of the dendrites in the mouse MNTB using both electron microscopy and confocal fluorescence imaging from postnatal day 9 (P9; pre-hearing) to P30. The soma of principal cells sprouted 1 to 3 thin dendrites (diameter ~ 1.5 microns) by P21 to P30. Each dendrite bifurcated into 2-3 branches and spanned an overall distance of about 80 to 200 microns. By contrast, at P9-11 the soma had 1 to 2 dendrites that extended for only 25 microns on average. Patch clamp experiments revealed that the growth of dendrites during development correlates with a progressive decrease in the input resistance, whereas acute removal of dendrites during brain slicing leads to higher input resistances. Accordingly, recordings of excitatory postsynaptic potentials (EPSPs) evoked by afferent fiber stimulation show that EPSP decay is faster in P21-24 neurons with intact dendrites than in neurons without dendrites. This dendritic speeding of the EPSP reduces the decay time constant 5-fold, which will impact significantly synaptic current summation and the ability to fire high-frequency spike trains. These data suggest a novel role for dendrites in auditory brainstem neurons: the speeding of EPSPs for faster and more precise output signal transfer.\n\nSignificance StatementAuditory circuits that compute sound localization express different types of specialized synapses. Some are capable of fast, precise and sustained synaptic transmission. As the paradigm example, principal cells of the MNTB receive a single calyx-type nerve terminal on their soma and this large excitatory synapse produces fast and brief supra-threshold EPSPs that can trigger trains of high frequency spikes. However, these neurons also extend thin and long dendrites with unknown function. We examined the relationship between dendritic morphology, passive electrical properties and EPSP waveform. We found that more mature neurons with intact dendrites have lower input resistances and short EPSP waveforms, ideally suited for conveying precise timing information, whereas immature neurons with shorter dendrites and higher input resistance have longer lasting EPSPs.

neuroscience↗