Spike Transmission Delay at the Calyx of Held In Vivo: Rate Dependence, Phenomenological Modeling, and Relevance for Sound Localization

Transmission at central synapses exhibits rapid changes in response amplitude under different patterns of stimulation. Whether the delay associated with the transmission of action potentials is similarly modifiable is important for temporally precise computations. We address this question at the calyx of Held of the medial nucleus of the trapezoid body (MNTB) in Mongolian gerbils in vivo using extracellular recordings. Here the pre- and postsynaptic activity can be observed simultaneously, allowing the definition of an action potential transmission delay (ATD) from the pre- to the postsynaptic side. We find the ATD to increase as a function of spike rate (10–40%). The temporal dynamics of the ATD increase exhibit an exponential shape with activity-dependent time constants (∼15–25 ms). Recovery dynamics of ATD were mono- (20–70 ms) or biexponential with fast (3–20 ms) and slow time constants (50–500 ms). Using a phenomenological model to capture ATD dynamics, we estimated ΔATD = 5–30 μs per transmitted action potential. Using vocalizations and cage noise stimuli, we confirm that substantial changes in ATD occur in natural situations. Because the ATD changes cover the behaviorally relevant range of interaural time differences in gerbils, these results could provide constraints for models of sound localization.

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Action potential evoked transmitter release in central synapses: insights from the developing calyx of Held

Molecular Brain ◽

10.1186/1756-6606-2-36 ◽

2009 ◽

Vol 2 (1) ◽

pp. 36 ◽

Cited By ~ 35

Author(s):

Lu-Yang Wang ◽

Michael J Fedchyshyn ◽

Yi-Mei Yang

Keyword(s):

Action Potential ◽

Transmitter Release ◽

Calyx Of Held ◽

Central Synapses ◽

Evoked Transmitter Release

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Resistance to action potential depression of a rat axon terminal in vivo

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1619433114 ◽

2017 ◽

Vol 114 (16) ◽

pp. 4249-4254 ◽

Cited By ~ 15

Author(s):

Martijn C. Sierksma ◽

J. Gerard G. Borst

Keyword(s):

Membrane Potential ◽

Action Potential ◽

Auditory Brainstem ◽

Strong Impact ◽

Fast Recovery ◽

Calyx Of Held ◽

Onset Potential ◽

Rat Pups ◽

The Central Nervous System

The shape of the presynaptic action potential (AP) has a strong impact on neurotransmitter release. Because of the small size of most terminals in the central nervous system, little is known about the regulation of their AP shape during natural firing patterns in vivo. The calyx of Held is a giant axosomatic terminal in the auditory brainstem, whose biophysical properties have been well studied in slices. Here, we made whole-cell recordings from calyceal terminals in newborn rat pups. The calyx showed a characteristic burst firing pattern, which has previously been shown to originate from the cochlea. Surprisingly, even for frequencies over 200 Hz, the AP showed little or no depression. Current injections showed that the rate of rise of the AP depended strongly on its onset potential, and that the membrane potential after the AP (Vafter) was close to the value at which no depression would occur during high-frequency activity. Immunolabeling revealed that Nav1.6 is already present at the calyx shortly after its formation, which was in line with the fast recovery from AP depression that we observed in slice recordings. Our findings thus indicate that fast recovery from depression and an inter-AP membrane potential that minimizes changes on the next AP in vivo, together enable high timing precision of the calyx of Held already shortly after its formation.

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Structure-function relation of the developing calyx of Held synapse in vivo

10.1101/2020.01.07.893685 ◽

2020 ◽

Author(s):

Martijn C. Sierksma ◽

Johan A. Slotman ◽

Adriaan B. Houtsmuller ◽

J. Gerard G. Borst

Keyword(s):

Structure Function ◽

Glutamate Transporters ◽

Synaptic Strength ◽

Target Cells ◽

List Type ◽

Calyx Of Held ◽

Synaptic Terminals ◽

Medial Nucleus ◽

Vesicular Glutamate Transporters

AbstractIn adult rodents, a principal neuron in the medial nucleus of the trapezoid (MNTB) is generally contacted by a single, giant axosomatic terminal called the calyx of Held. How this one-on-one relation is established is still unknown, but anatomical evidence suggests that during development principal neurons are innervated by multiple calyces, which may indicate calyceal competition. However, in vivo electrophysiological recordings from principal neurons indicated that only a single strong synaptic connection forms per cell. To test whether a mismatch exists between synaptic strength and terminal size, we compared the strength of synaptic inputs with the morphology of the synaptic terminals. In vivo whole-cell recordings of the MNTB neurons from newborn Wistar rats of either sex were made while stimulating their afferent axons, allowing us to identify multiple inputs. The strength of the strongest input increased to calyceal levels in a few days across cells, while the strength of the second strongest input was stable. The recorded cells were subsequently immunolabeled for vesicular glutamate transporters (VGluT) to reveal axosomatic terminals with structured-illumination microscopy. Synaptic strength of the strongest input was correlated with the contact area of the largest VGluT cluster at the soma (r = 0.8), and no indication of a mismatch between structure and strength was observed. Together, our data agree with a developmental scheme in which one input strengthens and becomes the calyx of Held, but not with multi-calyceal competition.Key points summaryDuring development the giant, auditory calyx of Held forms a one-to-one connection with a principal neuron of the medial nucleus of the trapezoid body.While anatomical studies described that most of the target cells are temporarily contacted by multiple calyces, multi-calyceal innervation was only sporadically observed in in vivo recordings, suggesting a structure-function discrepancy.We correlated synaptic strength of inputs, identified in in vivo recordings, with post hoc labeling of the recorded neuron and synaptic terminals containing vesicular glutamate transporters (VGluT).During development only one input increased to the level of the calyx of Held synapse, and its strength correlated with the large VGluT cluster contacting the postsynaptic soma.As neither competing strong inputs nor multiple large VGluT clusters on a single cell were observed, our findings did not indicate a structure-function discrepancy.

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Synaptic Transmission at the Calyx of Held Under In Vivo–Like Activity Levels

Journal of Neurophysiology ◽

10.1152/jn.00355.2007 ◽

2007 ◽

Vol 98 (2) ◽

pp. 807-820 ◽

Cited By ~ 78

Author(s):

Joachim Hermann ◽

Michael Pecka ◽

Henrique von Gersdorff ◽

Benedikt Grothe ◽

Achim Klug

Keyword(s):

Synaptic Transmission ◽

Brain Stem ◽

Spontaneous Activity ◽

Afferent Fiber ◽

High Frequency Stimulation ◽

Mongolian Gerbils ◽

Calyx Of Held ◽

Sensory Stimuli

One of the hallmarks of auditory neurons in vivo is spontaneous activity that occurs even in the absence of any sensory stimuli. Sound-evoked bursts of discharges are thus embedded within this background of random firing. The calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB) has been characterized in vitro as a fast relay that reliably fires at high stimulus frequencies (≤800 Hz). However, inherently due to the preparation method, spontaneous activity is absent in studies using brain stem slices. Here we first determine in vivo spontaneous firing rates of MNTB principal cells from Mongolian gerbils and then reintroduce this random firing to in vitro gerbil brain stem synapses at near-physiological temperature. After conditioning synapses with afferent fiber stimulation for 2 min at Poisson averaged rates of 20, 40, and 60 Hz, we observed a number of differences in the properties of synaptic transmission between conditioned and unconditioned synapses. Foremost, we observed reduced steady-state EPSC amplitudes that depressed even further during an embedded short-stimulation train of 100, 300, or 600 Hz (a protocol that thus simulates in vitro what probably occurs at the in vivo MNTB after a short sound stimulus in a silent background). Accordingly, current-clamp, dynamic-clamp, and loose-patch recordings revealed a number of action potential failures at the postsynaptic cell during high-frequency–stimulation trains, although the initial onset of evoked activity was still transmitted with higher fidelity. We thus propose that some in vivo auditory synapses are in a tonic state of reduced EPSC amplitudes as a consequence of high spontaneous spiking and this in vivo–like conditioning has important consequences for the encoding of signals throughout the auditory pathway.

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Multiple Large Inputs to Principal Cells in the Mouse Medial Nucleus of the Trapezoid Body

Journal of Neurophysiology ◽

10.1152/jn.00927.2003 ◽

2004 ◽

Vol 92 (1) ◽

pp. 545-552 ◽

Cited By ~ 19

Author(s):

Jeremy B. Bergsman ◽

Pietro De Camilli ◽

David A. McCormick

Keyword(s):

Sound Localization ◽

Excitatory Input ◽

Nerve Terminals ◽

Calyx Of Held ◽

Anatomical Studies ◽

Principal Cells ◽

Medial Nucleus ◽

Central Synapse ◽

Auditory Brain Stem ◽

Trapezoid Body

The calyx of Held is a giant nerve terminal that forms a synapse directly onto the principal cells of the medial nucleus of the trapezoid body (MNTB) in the mammalian auditory brain stem. This central synapse, which is involved in sound localization, has become widely used for studying synaptic transmission. Anatomical studies of this nucleus have indicated that each principal cell is innervated by only one calyx. Here we use previously established electrophysiological criteria of excitatory postsynaptic current amplitude, kinetics, and transmitter type, as well as other characteristics commonly reported for this synapse, to examine the input properties of principal neurons. Our findings indicate that some principal cells receive more than one strong excitatory input. These inputs meet previously established electrophysiological criteria for identification as calyceal nerve terminals. Implications for the execution and analysis of experiments to avoid errors due to such multiple inputs are discussed.

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Using ephaptic coupling to estimate the synaptic cleft resistivity of the calyx of Held synapse

PLoS Computational Biology ◽

10.1371/journal.pcbi.1009527 ◽

2021 ◽

Vol 17 (10) ◽

pp. e1009527

Author(s):

Martijn C. Sierksma ◽

J. Gerard G. Borst

Keyword(s):

Action Potential ◽

Synaptic Cleft ◽

Calcium Currents ◽

Fourth Power ◽

Scale Invariant ◽

Calyx Of Held ◽

Presynaptic Action ◽

Medial Nucleus ◽

Presynaptic Calcium ◽

Ephaptic Coupling

At synapses, the pre- and postsynaptic cells get so close that currents entering the cleft do not flow exclusively along its conductance, gcl. A prominent example is found in the calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB), where the presynaptic action potential can be recorded in the postsynaptic cell in the form of a prespike. Here, we developed a theoretical framework for ephaptic coupling via the synaptic cleft, and we tested its predictions using the MNTB prespike recorded in voltage-clamp. The shape of the prespike is predicted to resemble either the first or the second derivative of the inverted presynaptic action potential if cleft currents dissipate either mostly capacitively or resistively, respectively. We found that the resistive dissipation scenario provided a better description of the prespike shape. Its size is predicted to scale with the fourth power of the radius of the synapse, explaining why intracellularly recorded prespikes are uncommon in the central nervous system. We show that presynaptic calcium currents also contribute to the prespike shape. This calcium prespike resembled the first derivative of the inverted calcium current, again as predicted by the resistive dissipation scenario. Using this calcium prespike, we obtained an estimate for gcl of ~1 μS. We demonstrate that, for a circular synapse geometry, such as in conventional boutons or the immature calyx of Held, gcl is scale-invariant and only defined by extracellular resistivity, which was ~75 Ωcm, and by cleft height. During development the calyx of Held develops fenestrations. We show that these fenestrations effectively minimize the cleft potentials generated by the adult action potential, which might otherwise interfere with calcium channel opening. We thus provide a quantitative account of the dissipation of currents by the synaptic cleft, which can be readily extrapolated to conventional, bouton-like synapses.

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Kinetic structure of recycling vesicle pool at the Calyx of Held synapse under in vivo-like activities

10.1101/2021.03.03.433702 ◽

2021 ◽

Author(s):

Zili Liu ◽

Ying Zhu ◽

Yubing Hu ◽

Jianyuan Sun

Keyword(s):

Synaptic Transmission ◽

Neuronal Activity ◽

Capacitance Measurement ◽

Calyx Of Held ◽

Physiological Temperature ◽

Vesicle Recycling ◽

Central Synapses ◽

Vesicle Pool ◽

The Impact

AbstractSynaptic transmission at mammalian central synapses has ongoing background activity at physiological temperature. The recycling vesicle pool, with proper kinetics, ensures sustained synaptic transmission. However, the kinetic structure of recycling vesicle pool has never been quantitatively analyzed before, and most studies were performed at room temperature and under resting conditions. With the combination of presynaptic capacitance measurement and postsynaptic EPSC recording on calyx of Held synapses at physiological temperature, we studied vesicle recycling under sustained presynaptic stimulation. The kinetics of vesicle reuse was revealed by impeding transmitter refilling with folimycin. We kinetically dissected the recycling vesicle pool as sequentially connected sub-pools and depicted the complete kinetic structure. The sizes and transition rates among these sub-pools were dynamically regulated by neuronal activity, in order to ensure efficient synaptic transmission. Our work highlights the impact of the vesicle recycling machinery on stable and reliable synaptic transmission under variable levels of neuronal activity.Impact statementThe recycling pool of vesicles are kinetically dissected as four populated pools ensuring stable and reliable synaptic transmission

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Faculty Opinions recommendation of In vivo coincidence detection in mammalian sound localization generates phase delays.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.725346898.793506404 ◽

2015 ◽

Author(s):

Alan Palmer ◽

Christian John Sumner

Keyword(s):

Sound Localization ◽

Coincidence Detection

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AZP2006, a new promising treatment for Alzheimer’s and related diseases

Scientific Reports ◽

10.1038/s41598-021-94708-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

N. Callizot ◽

C. Estrella ◽

S. Burlet ◽

A. Henriques ◽

C. Brantis ◽

...

Keyword(s):

Therapeutic Application ◽

Neuroprotective Effects ◽

Beneficial Effects ◽

Potential Therapeutic Application ◽

Promising Treatment ◽

Central Synapses ◽

First Time ◽

Pgrn Level

AbstractProgranulin (PGRN) is a protein with multiple functions including the regulation of neuroinflammation, neuronal survival, neurite and synapsis growth. Although the mechanisms of action of PGRN are currently unknown, its potential therapeutic application in treating neurodegenerative diseases is huge. Thus, strategies to increase PGRN levels in patients could provide an effective treatment. In the present study, we investigated the effects of AZP2006, a lysotropic molecule now in phase 2a clinical trial in Progressive Supranuclear Palsy patients, for its ability to increase PGRN level and promote neuroprotection. We showed for the first time the in vitro and in vivo neuroprotective effects of AZP2006 in neurons injured with Aβ1–42 and in two different pathological animal models of Alzheimer’s disease (AD) and aging. Thus, the chronic treatment with AZP2006 was shown to reduce the loss of central synapses and neurons but also to dramatically decrease the massive neuroinflammation associated with the animal pathology. A deeper investigation showed that the beneficial effects of AZP2006 were associated with PGRN production. Also, AZP2006 binds to PSAP (the cofactor of PGRN) and inhibits TLR9 receptors normally responsible for proinflammation when activated. Altogether, these results showed the high potential of AZP2006 as a new putative treatment for AD and related diseases.

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