Hunting for origins of migraine pain: cluster analysis of spontaneous and capsaicin-induced firing in meningeal trigeminal nerve fibers.

Trigeminal nerves in meninges are implicated in generation of nociceptive firing underlying migraine pain. However, the neurochemical mechanisms of nociceptive firing in meningeal trigeminal nerves are little understood. In this study, using suction electrode recordings from peripheral branches of the trigeminal nerve in isolated rat meninges, we analyzed spontaneous and capsaicin-induced orthodromic spiking activity. In control, biphasic single spikes with variable amplitude and shapes were observed. Application of the transient receptor potential vanilloid 1 (TRPV1) agonist capsaicin to meninges dramatically increased firing whereas the amplitudes and shapes of spikes remained essentially unchanged. This effect was antagonized by the specific TRPV1 antagonist capsazepine. Using the clustering approach, several groups of uniform spikes (clusters) were identified. The clustering approach combined with capsaicin application allowed us to detect and to distinguish "responder" (65%) from "non-responder" clusters (35%). Notably, responders fired spikes at frequencies exceeding 10 Hz, high enough to provide postsynaptic temporal summation of excitation at brainstem and spinal cord level. Almost all spikes were suppressed by tetrodotoxin (TTX) suggesting an involvement of the TTX-sensitive sodium channels in nociceptive signaling at the peripheral branches of trigeminal neurons. Our analysis also identified transient (desensitizing) and long-lasting (slowly desensitizing) responses to the continuous application of capsaicin. Thus, the persistent activation of nociceptors in capsaicin-sensitive nerve fibers shown here may be involved in trigeminal pain signaling and plasticity along with the release of migraine-related neuropeptides from TRPV1 positive neurons. Furthermore, cluster analysis could be widely used to characterize the temporal and neurochemical profiles of other pain transducers likely implicated in migraine.

[Ionotropic receptors of acetylcholine and ATP: the mechanisms of inhibition].

In this review two kinds of receptors connected with ionic channels are analyzed. First kind is the receptor whose channel can be open with acetylcholine; they a named ionotropic cholinoreceptors (AChRn). The second kind is the receptor whose channel can be open with extracellular ATP. They a named ionotropic purinoreceptors and are designated P2X. Mathematical modelling of the kinetics of interactions with agonists and inhibitors of cholinergic and purine receptors has shown that each of the investigated mechanisms of inhibition of postsynaptic currents (competitive block, channel block, allosteric modulation and acceleration of desensitization) has different influence on the basic characteristics of postsynaptic currents. For unambiguous classification of inhibitory substances according to the molecular mechanisms of their action it is necessary to consider: a trend and size of change under inhibitory action of a decay time constant of the agonist-induced currents; dependence of development of changes and of speed of washing out of substance's effect from duration of its action, from number of activations of receptors and its frequency.

The mechanisms of inhibition of frog endplate currents with homologous derivatives of the 1,1-dimethyl-3-oxybutyl phosphonic acid.

The mode of inhibition of endplate currents by four esters of 1,1-dimethyl-3-oxybutyl phosphonic acid with different lipophilicities and molecule lengths were estimated by mathematical modeling based on previous electrophysiological data supplemented by several experiments with rhythmic stimulation. The aim was to discriminate between their receptor and non-receptor effects. It was shown that all esters have a two-component mechanism of depression: inhibition of the receptor open channel and allosteric modulation of the receptor-channel complex. The ratio of both functional components depends on the length and lipophilicity of the esters. Short and less lipophilic esters mostly act as open channel inhibitors and the rate of inhibition substantially depends on the rate of stimulation, i. e. probability of the receptor-channel opening. As the length of the ester radicals and their lipophilicity increased, these compounds were more active as allosteric receptor inhibitors, probably hindering the function of nAChRs from the lipid annulus.

The inhibitory action of the antimigraine nonsteroidal anti-inflammatory drug naproxen on P2X3 receptor-mediated responses in rat trigeminal neurons.

Enhanced nociceptive firing in trigeminal ganglion neurons is a likely reason for migraine pain. In experimental migraine-like conditions induced by the calcitonin gene-related peptide (CGRP), P2X3 receptors abundantly expressed in trigeminal neurons are highly responsive to the excitatory action of extracellular ATP. In this study, we tested whether naproxen, a common antimigraine medicine, could affect the function of P2X3 receptors in the presence or absence of the algogen nerve growth factor (NGF), the level of which is elevated in patients with chronic migraine. We used calcium imaging and patch clamp recordings from rat trigeminal neurons, which were activated by a relative specific P2X3 agonist α,ß-meATP or by high potassium-induced depolarization. In the absence of NGF, naproxen dose-dependently (0.1-1 mM) reduced intracellular calcium transients elicited by α,ß-meATP. Naproxen also led to a slight, but significant, reduction in calcium transients induced by potassium ions, indicating the involvement of voltage-gated calcium channels. The inhibitory action of 1 mM naproxen was enhanced after NGF pretreatment, suggesting that P2X3 receptors in sensitized neurons are more susceptible to inhibition by high doses of this nonsteroidal anti-inflammatory drug (NSAID). Using patch clamp recordings from HEK293 cells expressing P2X3 receptors, we tested the direct action of naproxen on P2X3 receptor-mediated membrane currents. In clinically relevant concentrations of 0.5 mM, naproxen produced a use-dependent blocking effect on ATP receptors. Kinetic analysis suggests that naproxen inhibited P2X3 receptors via facilitation of fast desensitization, which determines current decay in the continuous presence of the agonist. In summary, we present a novel fast mechanism for the antimigraine action of naproxen, which can act in synergy with the cyclooxygenase inhibition to attenuate headaches.

Hydrodynamic flow in a synaptic cleft during exocytosis.

It is shown that exocytosis in a chemical synapse may be accompanied by "microjet" formation due to the overpressure that exists in the vesicles. This mechanism may take place either at complete fusion of a vesicle with the presynaptic membrane or in the so-called kiss-and-run mode of neurotransmitter release. A simple hydrodynamic model of the viscous incompressible flow arising in the synaptic cleft is suggested. The occurrence of hydrodynamic flow (microjet) leads to more efficient transport of neurotransmitter than in the case of classical diffusive transport.

Mechanisms of the inhibition of endplate acetylcholine receptors by antiseptic chlorhexidine (experiments and models).

Mechanisms of the inhibition of evoked multiquantal endplate currents (EPC) by chlorhexidine (CHX) were studied in electrophysiological experiments and by mathematical modeling to discriminate between possible channel, receptor, and non-receptor effects of this common antiseptic drug. Experiments were carried out on the isolated neuromuscular preparation of the cut m. sartorius of the frog Rana ridibunda. The nerve-stimulation-evoked endplate currents were measured by standard double microelectrode technique. For the mathematical simulation, a method based on the solution of a system of ordinary differential equations was used. CHX in milimolar concentrations suppressed the amplitude and shortened the evoked EPC. Recovery of the EPC amplitude was very slow, and EPC shortening persisted during 30-40 min washout of the drug. There is no indication that CHX competes for acetylcholine or carbachol binding site(s). A comparison of the experimental data with mathematical simulation made it possible to construct a reliable kinetic scheme, which describes the action of CHX. CHX induces a combined slow blockade of the open ionic channel and long-lasting allosteric inhibition of the nicotinic acetylcholine receptor. The very slow washout of the drug in terms of EPC amplitude and virtually no recovery of the shortened EPC time course might substantiate certain caution to avoid unintentional high-dose application during its antibacterial application.

Model of concentration changes across the synaptic cleft during a single quantum release.

A model of concentration changes across the synaptic cleft during a single quantum release is presented that can be used for description and characterization of the kinetic in postsynaptic current development under the influence of different antagonists, modulators, desensitization promoters or complex channel blockers. The model enables the calculation of the relative number of open channels as a function of time for two standard cases - when acetylcholinesterase (AChE) is either active or inhibited. One outcome of the present model is that the variable part of AChE activity is zero at the moment of acetylcholine (Ach) release and then increases. This is in contrast to common view that the activity of AChE at the initial moment of release of quanta is maximal and decreases over the time course of quantum action. However, the model explains why non-quantal ACh leakage from the nerve terminal creating a concentration of approximately 10(-8) mol.l(-1) in the cleft can escape hydrolysis by intrasynaptically located cholinesterase and reach the subsynaptic membrane. The model can also be used for theoretical considerations of time and amplitude changes during repetitive nerve-evoke quanta release.

Mechanisms of the effect of 1,1-dimethyl-3-hydroxybutyl phosphonic acid derivatives on synaptic transmission in neuromuscular junction.

We studied the effect of homologues derivatives of 1,1-dimethyl-3-hydroxybutyl phosphonic acid on synaptic transmission in frog neuromuscular junction. Here we reviewed general mechanisms of inhibition of the postsynaptic current.

[Dependence of the concentration of the demi-maximal action of a channel blocker on the agonist concentration].

Based on the analysis of kinetic scheme of blocking of open channels at any number of blocker binding sites, the dependence of current on blocker concentration was found. A variant of this dependence for a trapping blocker was also found. The restrictions of the applicability of the Hill equation and the necessity of taking into account the dependence of the concentration of demi-maximal blocker action (IC50) on the concentration of agonist were shown.

[Study of giant depolarizing activity in the neonatal hippocampal neurones]. / Issledovanie mekhanizma vozniknoveniya gigantskikh depoliariziruiushchikh potentsialov v neironakh gippokampa novorozhdennykh krys.

Spontaneous oscillatory activity is a general feature of developing neural networks. Early in postnatal development, spontaneous network-driven events, termed giant depolarizing potentials (GDPs), occur synchronously over the entire hippocampus. By performing simulation of hippocampal network with using physiology parameters of the neurons and its network from the present experiments and literature dates, we investigated the participation of the different components of network in the generation of GDPs. Comparing the results of the model and in vitro experiments we conclude that are necessary for the GDP generation involvement the activation of GABAergic, glutamatergic inputs and perhaps gap junction.

[The reconstruction of the dynamics of acetylcholine concentration in synaptic cleft in response to a monoquantum signal]. / Rekonstruktsiia dinamiki izmeneniia kontsentratsii atsetilkholina v sinapticheskoi shcheli pri odnokvantovom signale.

By using the experimental data and the model of cholinereceptor activation kinetics in frog nervous-muscular junction, the function of acetylcholine release from the nervous terminal and the function of acetylcholinesterase activity in synaptic cleft were reproduced and approximated. These functions can be used in modeling the influence of blockers and other biogenic postsynaptic modulators on synaptic transfer.

Serotonin modulates neuromuscular transmission in frogs.

The effect of 5-hydroxytryptamine (serotonin) on neuromuscular transmission in frog skeletal muscle was studied using voltage clamp technique. Serotonin produced no effect on end-plate currents during low frequency electrical stimulation of the motor nerve, but increased the amplitude depression of multiquantal currents during high-frequency stimulation similar to motor commands fired by motoneurons. It was shown that the inhibitory effect of serotonin on neuromuscular transmission is determined by slow potential-dependent block of open ionic channels in the postsynaptic membrane accumulating during rhythmic activation of the synapse.

Rapid relief of block by mecamylamine of neuronal nicotinic acetylcholine receptors of rat chromaffin cells in vitro: an electrophysiological and modeling study.

The mechanism responsible for the blocking action of mecamylamine on neuronal nicotinic acetylcholine receptors (nAChRs) was studied on rat isolated chromaffin cells recorded under whole-cell patch clamp. Mecamylamine strongly depressed (IC(50) = 0.34 microM) inward currents elicited by short pulses of nicotine, an effect slowly reversible on wash. The mecamylamine block was voltage-dependent and promptly relieved by a protocol combining membrane depolarization with a nicotine pulse. Either depolarization or nicotine pulses were insufficient per se to elicit block relief. Block relief was transient; response depression returned in a use-dependent manner. Exposure to mecamylamine failed to block nAChRs if they were not activated by nicotine or if they were activated at positive membrane potentials. These data suggest that mecamylamine could not interact with receptors either at rest or at depolarized level. Other nicotinic antagonists like dihydro-beta-erythroidine or tubocurarine did not share this action of mecamylamine although proadifen partly mimicked it. Mecamylamine is suggested to penetrate and block open nAChRs that would subsequently close and trap this antagonist. Computer modeling indicated that the mechanism of mecamylamine blocking action could be described by assuming that 1) mecamylamine-blocked receptors possessed a much slower, voltage-dependent isomerization rate, 2) the rate constant for mecamylamine unbinding was large and poorly voltage dependent. Hence, channel reopening plus depolarization allowed mecamylamine escape and block relief. In the presence of mecamylamine, therefore, nAChRs acquire the new property of operating as coincidence detectors for concomitant changes in membrane potential and receptor occupancy.

[Modeling of the two wave response of ATP receptors to jumps of the agonist concentration in pheochromocytoma cells]. / Modelirovanie dvukh voln otveta ATP-retseptorov kletok feokhromotsitomy na skachok kontsentratsii agonista.

A model for the kinetics of conformational transitions of ionotropic ATP receptors in pheochromocytoma cells was elaborated. The contribution of the states of ionotropic receptors (upon the blockage of the "open" channel state) to the kinetics of postsynaptic currents was estimated at mediator concentrations studied. The model enables one to determine the contribution of various conformational states of the receptor, in particular in the "closed" state, to the dynamics of ionic current that is registered upon stimulation of ATP receptors. It is shown that after the cessation of the agonist application, a secondary current wave can arise. The rate constants for conformational transitions of ATP receptors were determined.

Mechanism of organization of different types of directed movements.

This article considers the mechanism for construction of movements in biological systems as a means of reducing excess degrees of freedom of a motor organ. It is suggested that each type of excess of degrees of freedom is reduced by one of the hierarchically coordinated systems of motor control. Detailed consideration is given to mechanisms for reducing the dynamic excess of a motor organ, the kinematic excess associated with polyarticular motor organs, and the kinematic excess of the desired trajectory. A functional scheme is developed for a motor control system which reduces these excess degrees of freedom, and the control processes for various types of movement were studied by computer modeling.

[The mechanism of the organization of the types of goal-directed movements]. / Mekhanizm organizatsii nekotorykh tipov tselenapravlennykh dvizhenii.

A possible organization of motor control during moving from a distant point to a purposive one is considered as a way of reduction of three excessive degrees of freedom at hierarchically coordinated levels of motor control. Computer simulation of such movement organization showed its insensitivity to dynamic noise, fluctuations in driving parameters, deviations, delays, and "clutches" of separate joints.