Synaptic Transmission
This complex process is vital for the communication between neurons and plays a crucial role in neural function.
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In the following we consider four different implementations of the active controllers fP and fD and analyze the corresponding properties and performance. In Models 1 and 2 the active feedback is linear and continuous in time. In Models 3 and 4 the active feedback is non-linear and intermittent.
Briefly, in this model a synapse contains a finite amount of ‘resources’, which can be divided in three fractions: recovered (x), active (y), and inactive (z), in a dynamical relation to each other. At the arrival of a spike (at time tsp), a fraction p of recovered resource is activated, quickly inactivated with a time constant τin and then recovered with a time constant τrec according to the following equations:
with x + y + z = 1 and y0 = z0 = 0, x0 = 1.
p indicates the effective use of the synaptic resources of the synapses and can be seen as the average release probability of a quantal model. During repeated stimulation p can increase due to facilitation. In particular, at the arrival of a spike (t = tisp) p is incremented by a factor U(1 − p−), where p− is the last pre-spike value of p, so that the post-spike value is p+ = p− + U(1 − p−). After the spike, instead, p decays to baseline with a time constant τfacil, (Tsodyks et al., 1998 (link)), so that in the interval between the arrival of two spikes, t ∈ (tisp, tjsp):
U determines the increase in the value of p with each spike and coincides with the value of p reached upon the arrival of the first spike, i.e., p0 = p(t1sp) = U. It is worth noting that p is incremented before x is converted to y.
The resulting excitatory post-synaptic current (EPSC) is proportional to the active resource:
where A is the absolute synaptic strength, corresponding to the maximum EPSC obtained by activating all the resources.
The values used for all parameters are discussed in the Results section. Since the findings in Abramov et al. (2009 (link)) are principally mediated by AMPA receptors, we did not explicitly include NMDA receptors in the CA1 neuron model.
To model the activation of a group of afferent fibers from CA3 pyramidal neurons through the Schaffer collaterals, ten synapses were distributed randomly on the apical trunk between 100 and 400 μm from the soma. Each synapse in the model represents the effect of a population of synapses activated in the oblique dendrites. A range of peak synaptic conductances (weights) was explored. All simulations were repeated 10 times redistributing synaptic location and weights. Results are expressed as mean ± SEM (standard error of the mean, SEM).
up to the first order of , where erf(x) is the error function and , , , and ξ is the Riemann zeta function. Normalization constant C is calculated from the .
The contribution of extremely strong excitatory synapses to output firing is approximated as the sum of the conditional firing probabilities over inputs to these synapses. In the effective-time-constant approximation, the effective amplitude of EPSP evoked by i-th synapse is where v is the membrane potential just before the arrival of presynaptic input and Ei is the EPSP amplitude measured from the resting potential. Because the conditional probability of having an output spike given the i-th input is equal to the area of the stationary density function satisfying , the conditional probability is equal to Then, by summing these contributions, we obtain the firing rate of the neuron as Finally, by substituting Pi of the strongest synapse into and using
Most recents protocols related to «Synaptic Transmission»
The structural connectivity (SC) for the DMF model used here was obtained by following the procedure described by Wang et al. (2019) (link) to derive a consensus structural connectivity matrix. A consensus matrix A was obtained separately for each group (healthy controls, MCS patients, UWS patients) as follows: for each pair of regions i and j, if more than half of subjects had non-zero connection i and j, Aij was set to the average across all subjects with non-zero connections between i and j. Otherwise, Aij was set to zero.
The DMF model has one free parameter, known as “global coupling” and denoted by G, which accounts for differences in transmission between brain regions, considering the effects of neurotransmission but also synaptic plasticity mechanisms. Thus, separately for each group, we used a model informed by that group's consensus connectome to generate 40 simulations for each value of G between 0.1 and 2.5, using increments of 0.1. Finally, we set the G parameter to the value just before the one at which the simulated firing of each model became unstable, reflecting a near-critical regime.
Subsequently, for each group, 40 further simulations were obtained from the corresponding DMF model with the optimal G parameter. A Balloon-Windkessel hemodynamic model (Friston et al., 2003 (link)) was then used to turn simulated regional neuronal activity into simulated regional BOLD signal. Finally, simulated regional BOLD signal was bandpass filtered in the same range as the empirical data (0.008–0.09 Hz, or 0.04–0.07 Hz for the intrinsic ignition analysis).
As an alternative way of finding the most suitable value of G for the simulation of each condition, we adopted the approach previously described (Deco et al., 2018 (link); Hansen et al., 2015 (link); Herzog et al., 2020 (link); Luppi et al., 2022b (link)) which aims to obtain the best match between empirical and simulated functional connectivity dynamics. First, we quantified empirical functional connectivity dynamics (FCD) in terms of Pearson correlation between regional BOLD timeseries, computed within a sliding window of 30 TRs with increments of 3 TRs (Deco et al., 2018 (link); Hansen et al., 2015 (link); Herzog et al., 2020 (link); Luppi et al., 2022b (link)). Subsequently, the resulting matrices of functional connectivity at times tx and ty were themselves correlated, for each pair of timepoints tx and ty, thereby obtaining an FCD matrix of time-versus-time correlations. Thus, each entry in the FCD matrix represents the similarity between functional connectivity patterns at different points in time. This procedure was repeated for each subject of each group (controls, MCS, and UWS). For each simulation at each value of G, we used the Kolmogorov-Smirnov distance to compare the histograms of empirical (group-wise) and simulated FCD values (obtained from the upper triangular FCD matrix). Finally, we set the model's G parameter to the value that was observed to minimize the mean KS distance - corresponding to the model that is best capable of simulating the temporal dynamics of resting-state brain functional connectivity observed in the corresponding group (Figure S8). After having found the value of G for each condition, simulated BOLD signals were obtained as described above. This same procedure was also used for fitting the DMF model based on each individual's structural connectome, simulating BOLD signals to fit their own empirical FCD.
Recordings were performed in the same solution in a submerged chamber that was continuously superfused with carbogen-bubbled ACSF (1.2 ml/min) at 32 °C. Recordings of field excitatory postsynaptic potentials (fEPSPs) were performed in CA1a and CA1c with a glass pipette filled with ACSF to activate synapses in the CA1b stratum radiatum. The resistance of the pipette was 1–4 MΩ. Stimulation pulses were applied to Schaffer collaterals via a monopolar, electrolytically sharpened and lacquer-coated stainless-steel electrode located approximately 300 mm closer to the CA3 subfield than to the recording electrode. Basal synaptic transmission was monitored at 0.05 Hz and collected at 3 pulses/min. The spaced LTP protocol was performed as previously described (Kramár et al., 2012). LTP was induced by applying 5xTBS with an interval of 20 s. One TBS consisted of a single train of ten bursts (four pulses at 100 Hz) separated by 200 ms and the width of the single pulses was 0.2 ms. To induce spaced LTP, we applied two trains of TBS (TBS1/TBS2) separated by 1 h. The stimulation strength was set to provide baseline fEPSPs with slopes of approximately 50% of the subthreshold maximum. The data were recorded at a sampling rate of 10 kHz and then filtered (0–5 kHz) and analyzed using IntraCell software (custom-made, LIN Magdeburg, Germany).
One hemidiaphragm was used as a treatment, and the other served as its paired untreated control. All treatments were performed ex vivo. Muscles were stimulated through the phrenic nerve at 1 Hz, which allows the maintenance of different tonic functions without depleting synaptic vesicles, for 30 min using the A-M Systems 2100 isolated pulse generator (A-M System) as in previous studies [38 (link)–40 (link)]. We designed a protocol of stimulation that preserves the nerve stimulation and the associated neurotransmission mechanism. This method prevents other mechanisms associated with non-nerve-induced (direct) muscle contraction [46 –48 (link)]. To verify muscle contraction, a visual checking was done. Two main experiments were performed to distinguish the effects of synaptic activity from those of muscle activity (Fig.
Presynaptic stimulation (Ctrl versus ES): to show the impact of the synaptic activity, we compared presynaptically stimulated muscles whose contraction was blocked by μ-CgTx-GIIIB with nonstimulated muscles also incubated with μ-CgTx-GIIIB to control for nonspecific effects of the blocker.
Contraction (ES versus ES + C): to estimate the effect of nerve-induced muscle contraction, we compared stimulated/contracting muscles with stimulated/noncontracting muscles whose contraction was blocked by μ-CgTx-GIII. By comparing the presynaptic stimulation with or without postsynaptic activity, we separate the effect of contraction. However, one should consider that postsynaptic contraction experiments also contain presynaptic activity.
Design of experimental treatment for the study of effects of presynaptic activity and nerve-induced muscle contraction. μ-CgTx-GIIIB, μ-conotoxin GIIIB
Furthermore, to assess the effect of PKA blocking, three different experiments have been performed:
To estimate the effect of PKA inhibition under synaptic activity, we compared presynaptically stimulated muscles whose contraction was blocked by μ-CgTx-GIIIB with and without H-89: ES versus ES + H-89.
To show the impact of the PKA inhibition under muscle contraction, we compared stimulating and contracting muscles with and without H-89: (ES + C) versus (ES + C) + H-89.
To demonstrate if degradation or redistribution along the axon is involved, the diaphragm muscle was dissected with special care to preserve phrenic nerve connectivity. We compared stimulating and contracting muscles with and without protease inhibitor (Prot.Inh.) cocktail 1% (10 μl/ml; Sigma, Saint Louis, MO, USA): (ES + C) versus (ES + C) + Prot.Inh.
CBD (Cayman Chemical, Ann Arbor, MI) was diluted with 0.05% methanol and sterile saline. CBD, one of the major compounds present in the marijuana (C. sativa) plant, has some medicinal properties; however, its mechanism is not well known (Andreza et al. 2016 (link); Jeong et al. 2019 (link)).
Ropinirole hydrochloride (ROP; KYOWA Pharmaceutical Industry Co., Ltd, Osaka, Japan) was diluted with 0.05% dimethyl sulfoxide (DMSO; Dojindo Laboratories, Kumamoto, Japan) and sterile saline. The drug is a novel non-ergoline dopamine agonist, has selective affinity for dopamine D2 receptors, and is indicated for the treatment of early and advanced Parkinson’s disease (Pahwa et al. 2004 (link)).
We generated the input–output curve (I–O curve) by gradually increasing the intensity of the stimulation in the DG area before recording LTP, and the field excitatory postsynaptic potential (fEPSP) was evoked and recorded via electrical stimulation with a wave width of 0.6 ms and frequency of 0.067 Hz. The rising slope of the fEPSP in each mouse was obtained to evaluate the basic function of synaptic transmission. The electrical stimulation intensity that induced 30% of the maximum amplitude of the fEPSP was set as the stimulus intensity for the baseline fEPSP recording. After 15 min of stable baseline recording, high-frequency stimuli (HFS) (100 Hz; 100 trains; 1 s) were delivered to induce LTP. Then, fEPSPs were continuously monitored for 90 min. The fEPSPs were recorded using Clampex 10.2 software and analyzed using Clampfit 10.2 software (Molecular Devices Corporation, California, USA). The obtained data are presented as the percentage of the population spike (PS) amplitude of fEPSPs to the baseline and expressed as the mean ± standard error (SE).
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More about "Synaptic Transmission"
This complex process is vital for the proper functioning of the nervous system.
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This cutting-edge tool allows researchers to easily locate the best protocols from literature, preprints, and patents, using intelligent search and comparison capabilities.
By harnessing the power of AI, PubCompare.ai helps identify the optimal products and protocols to drive synaptic transmission research forward.
Key aspects of synaptic transmission include neurotransmitter release, receptor activation, and signal propagation.
Commonly used tools and techniques in this field include the PClamp 10 software, Multiclamp 700B amplifier, and various pharmacological agents like Picrotoxin, 4-aminopyridine (4-AP), Kynurenic acid, Gabazine, and SR95531.
Researchers can utilize these resources, along with the PubCompare.ai platform, to streamline their synaptic transmission experiments, optimize experimental protocols, and ultimately accelerate their discoveries in this critical area of neuroscience.
Experience the power of intelligent protocol optimization today and unlock new insights into the complex world of synaptic transmission.