Neirofiziologiia = Neurophysiology最新文献

Selective cholinomimetics and cholinolytics were employed to identify cholinoreceptors on the somatic membrane in Helix lucorum RPa3 and LPa3 neurons using recording of transmembrane ionic currents. Agonists of nicotinic and muscarinic cholinoreceptors evoked reversible activation and following nonreversible inhibition of receptors (except carbamylcholine). Selective cholinomimetics were connected with the same membrane sites that were activated by acetylcholine. Nicotinic and muscarinic cholinolytics decreased the amplitude of inward current induced by acetylcholine (scopolamine and platyphylline had no effect). It is concluded that somatic membrane of RPa3 and LPa3 Helix neurons contains nicotinic and muscarinic cholinoreceptors. These receptors have several pharmacological peculiarities as compared with those of the vertebrates. Muscarinic cholinoreceptors of RPa3 and LPa3 neurons must be included into a special subtype that differs from well-known M1 and M2 subtypes.

Variety of outward voltage-dependent currents in cultured frog myoblasts were registered by means of whole cell voltage clamp. Six types of potassium currents (Ik) which reach the peak value (-10 mV) in 5, 12, 20, 30, 50 ms (fast) and do not reach the maximum in 7 s (slow) were established. High sensitivity to low temperature (+5 degrees) was shown for channels of very fast and of slow non-inactivated Ik. The assumption is made that some of Ik--5, 20 and 30 ms to peak are especially characteristic of myoblasts fusion stage.

The factors determining the decay of multiquantal end plate currents (EPC) were studied in the diaphragm muscle of rat by the comparison of EPC and miniature EPC (MEPC) amplitude--temporal characteristics. The decay of EPC (quantal content 25-100) was 1.2 times slower than the decay of MEPC when AChE was active. The AChE inhibition by armine or neostigmine made this difference 10-100 times higher. In most synapses the decay of multiquantal EPC can be approximated by a sum of two or three exponents. It depended on the quantal content and 3-exponential EPC could be transformed in 2-exponential and later to monoexponential ones if increasing concentration of magnesium ions. A slow component of EPCs (but not of MEPC) decay was highly sensitive to concentration of magnesium ions and had 3 times higher dependence of the membrane potential value than that one of MEPC. The irreversible blocking of receptors by alpha-bungarotoxin (alpha-BuTX) accelerated the decay of MEPC but the decay of multiquantal EPC changed in two phases: it was prolonged at the beginning of alpha-BuTX action followed by its acceleration, but never the time of the decay of EPC had achieved the apparent open time of ACh-activated ionic channels. It is suggested that during the multiquantal EPC generation not only the synchronization of opening but the kinetic of ACh-activated channels is changed, probably by blocking of this channels by high concentrations of endogenous ACh.

Vibrational stimulation of cat's skin by the frequencies of 10, 30 and 50 per second evoked response of mechanoreceptors innervated with A beta and A delta-fibers, responding to each vibration stimulus. The higher vibrostimulation frequency, the more distinct changes appear in the "on"--and "off"--responses which are caused by a decreasing number of pulses for each vibration impact. The mechanoreceptors innervated with the C-fibers are not excited by these frequencies. After a preliminary vibrostimulation the part of mechanoreceptors innervated with C-fibers do not respond to the mechanical stimulus tested. The higher the frequency of preliminary vibrostimulation, the fewer receptors respond to the tested stimulus.

Background impulse activity (BIA) of separate fibres of dorsal roots of 5 lumbar segment of rats after one-sided cutting of the sciatic nerve which caused early enhancement of monosynaptic segmental reflexes (5 days after operation) has been recorded. It is revealed that afferent fibres with BIA are found more rarely on side of cutting than on the opposite side and frequency of background activity is lower than in the opposite root. It is concluded that development of spontaneous activity of the spinal ganglion neurons after cutting nerves does not ensure a higher BIA level in afferent fibres. The given phenomenon cannot be a reason of early enhancement of monosynaptic reflexes after the nerve cutting.

Neuronal responses of area 7 of the parietal associative cortex (PAC) to paired stimulation of the nLD and nLP thalamic nuclei were investigated by extra- and intracellular recording methods. It was found out that testing stimulation of the associative nuclei resulted in inhibition, facilitation or absence of clear neuronal responses. Inhibition was observed more often then other types of reactions. The intracellular recording has shown that inhibition of responses to testing stimuli developed during the initial phase of IPSP, while in the repolarization phase a facilitation was possible. The reversion of a Cl- -dependent component of IPSP did not lead to inhibition of responses to the testing stimulation in that period. It is suggested that inhibition of responses to the testing stimulus occurs in the presence of inward Cl- -dependent current, while facilitation of responses may be a result of activation of the late EPSPs.

The data about vestibular nuclear complex and vestibulospinal systems in the submammalian and mammalian vertebrates are offered in the review. Information presented in the world literature concerning the vestibular nuclei topography, structure, fibre connections and influences on the spinal cord and skeletal muscles is summarized. The current conceptions of the structural and functional specificity of different vestibulospinal systems are considered.

Localization sites of neurons in the dorsal motor nucleus of cat vagus innervating the duodenal-jejunal region and upper part of the jejunum were investigated using the technique of the retrograde axonal transport of horseradish peroxidase. Most part of the neurons was located within the ventrolateral area of the nucleus from +1.0 to +2.7 mm (according to obex). Morphological features of the ganglion nodosum neurons which organize afferent innervation of the intestine were analyzed. It has been shown that the maximal amount of such neurons is concentrated in the medium and caudal parts of the ganglion.

Main mechanisms of muscle contraction control: recruiting of motor units and changes of their firing rate are discussed in the review. Relative contribution of these mechanisms at different types of muscular activity (tonic contraction, vibration reflex, locomotion) is considered.

Vitamin B6 has been studied for the mechanism of its effect on acetylcholine-induced sodium-potassium and chloride currents in E16 neuron of isolated brain of the snail Helix pomatia. The results indicate that the effect of vitamin B6 on acetylcholine-induced currents in postsynaptic neuron E16 is mediated via changes in gamma-aminobutyric acid (GABA) release from a presynaptic neuron and subsequent GABA-induced and cAMP-dependent processes in E16 neuron. It is suggested that effects of vitamin and antivitamin B6 on axons of a presynaptic neuron or neurons may be connected with regulation of GABA synthesis from glutamate catalyzed by the pyridoxal-phosphate-containing enzyme.