Biology subjects

Alvanos, T.

Publications and source records attributed to Alvanos, T..

3 recordsLinked to original sources

bioRxiv2025

Neuromodulation of the endbulb of Held synapse in the cochlear nucleus

Synapses vary greatly in synaptic strength and plasticity, even within the same circuitry or set of pre- and postsynaptic neurons. Neuromodulation is a candidate mechanism to explain some of this variability. Neuromodulators such as monoamines can differentially regulate presynaptic function as well as neuronal excitability. Variability is found also for the large calyceal synapses of the auditory pathway that are endowed with high synaptic vesicle (SV) release probability (Pvr) and large postsynaptic currents enabling reliable and temporally precise transmission of auditory information. Here we investigated whether the calyceal endbulb of Held synapse formed by auditory nerve fibers onto bushy cells (BCs) in the anteroventral cochlear nucleus (AVCN) is modulated by norepinephrine (NE) and serotonin (5-HT). Using electron microscopy (EM) of the cochlear nucleus we found evidence for putative monoaminergic varicosities in both ventral and dorsal divisions. Immunostaining for vesicular 5-HT and NE transporters revealed NE-containing and 5-HT-containing varicosities in the AVCN, juxtaposed to both endbulbs and BCs. Furthermore, we detected immunofluorescence for 5-HT1B, 5-HT4, 5-H7 receptors (R) and 2C-adrenergic receptors (AR) in BCs. We used voltage-clamp recordings from mouse BCs in order to uncover potential presynaptic effects of neuromodulation, which revealed an increase in frequency of miniature excitatory postsynaptic currents (mEPSCs) upon application of NE but not 5-HT. Evoked synaptic transmission was unaffected by the application of either NE or 5-HT. Likewise, while studying the biophysical properties of the BCs, we did not observe effects of NE or 5-HT on low-voltage-activated K+ (K+LVA) and hyperpolarization-activated mixed cation (HCN) channels during application. In summary, we report evidence for the presence of monoaminergic innervation in the cochlear nucleus and for subtle functional NE-neuromodulation at the endbulb of Held synapse.

neuroscience↗

bioRxiv2023

Efficient and sustained optogenetic control of nervous and cardiac systems

Optogenetic control is used to manipulate the activity of specific cell types in vivo for a variety of biological and clinical applications. Here we report ChReef, an improved variant of the channelrhodopsin ChRmine. ChReef offers minimal photocurrent desensitization, a unitary conductance of 80 fS and closing kinetics of 30 ms, which together enable reliable optogenetic control of cells at low light levels with good temporal fidelity and sustained stimulation. We demonstrate efficient and reliable red-light pacing and depolarization-block of ChReef-expressing cardiomyocyte clusters. We used AAV-based gene transfer to express ChReef in retinal ganglion cells, where it restores visual function in blind mice with light sources as weak as an iPad screen. Toward optogenetic hearing restoration, ChReef enables stimulation of the auditory pathway in rodents and non-human primates with nano-Joule threshold, enabling efficient and frequency-specific stimulation by LED-based optical cochlear implants.

biophysics↗

bioRxiv2021

RIM-Binding Protein 2 organizes Ca2+ channel topography and regulates release probability and vesicle replenishment at a fast central synapse

RIM-Binding Protein 2 (RIM-BP2) is a multi-domain protein of the presynaptic active zone (AZ). By binding to Rab-interacting protein (RIM), bassoon and voltage-gated Ca{superscript 2} channels (CaV), it is considered to be a central organizer of the topography of CaV and release sites of synaptic vesicles (SVs) at the AZ. Here, we investigated the role of RIM-BP2 at the endbulb of Held synapse of auditory nerve fibers with bushy cells of the cochlear nucleus, a fast relay of the auditory pathway with high release probability. Disruption of RIM-BP2 lowered release probability altering short-term plasticity and reduced evoked excitatory postsynaptic currents (EPSCs). Analysis of SV pool dynamics during high frequency train stimulation indicated a reduction of SVs with high release probability but an overall normal size of the readily releasable SV pool (RRP). The Ca2+-dependent fast component of SV replenishment after RRP depletion was slowed. Ultrastructural analysis by super-resolution light and electron microscopy revealed an impaired topography of presynaptic CaV and a reduction of docked and membrane-proximal SVs at the AZ. We conclude that RIM-BP2 organizes the topography of CaV, and promotes SV tethering and docking. This way RIM-BP2 is critical for establishing a high initial release probability as required to reliably signal sound onset information that we found to be degraded in bushy cells of RIM-BP2-deficient mice in vivo. Significance StatementRIM-binding proteins (RIM-BPs) are key organizers of the active zone (AZ). Using a multidisciplinary approach to the calyceal endbulb of Held synapse that transmit auditory information at rates of up to hundreds of Hertz with sub-millisecond precision we demonstrate a requirement for RIM-BP2 for normal auditory signaling. Endbulb synapses lacking RIM-BP2 show a reduced release probability despite normal whole-terminal Ca2+ influx and abundance of the key priming protein Munc13-1, a reduced rate of SV replenishment, as well as an altered topography of CaV2.1 Ca2+ channels, and fewer docked and membrane proximal synaptic vesicles. This hampers transmission of sound onset information likely affecting downstream neural computations such as of sound localization.

neuroscience↗