Neirofiziologiia = Neurophysiology最新文献

Sodium succinate has been studied for its influence on the efficiency of glutamate transmission in the Schaffer collateral synapses and duration of its potentiation state caused by high-frequency stimulation in surviving hippocampal slices. It is shown that administration of sodium succinate (50 mg/kg i. p.) to rats 30 min prior to decapitation stabilizes glutamate transmission in field CA1 of the rat hippocampal slices and increases duration of its potentiation state.

In isolated snail neurones the level of cyclic AMP was increased either by intracellular injection of cAMP or by extracellular application of dibutyryl-cAMP and the change of high-threshold calcium current (ICa) decay was investigated. In 20 from 38 neurones it was obtained that both fast and slow phases of ICa decay were accelerated 2-2.5 times as affected by cAMP. The effect did not depend on the test-pulse potential and was displayed on the IBa. In the double-pulse experiments it was shown that cAMP enhanced the influence of depolarized prepulses (Vc) on the ICa tested (It). Analysis of the It-Vc curve showed that cAMP enhanced both Ca(2+)-dependent and voltage-dependent inactivation of ICa. The experiments where the intervals between Vc and Vt varied have shown that cAMP slowed down the rate of Ca(2+)-channels recovery from inactivation. The results suggest that cAMP increases the affinity of the Ca(2+)-channel inactivating substrate for Ca(2+)-ions.

The new technique has been used to realize paired short-term application of glutamate to whole dialyzed neuron. Desensitization of receptors via first application of glutamate resulted in incomplete recovery of the current evoked by the second application if interval between both applications was less than 160 ms. The recovery time constant of the current was found to be 44 ms at single exponential approximation. It is close to the mean desensitization time constant of the current evoked by single prolonged application of glutamate. Rhythmic application of glutamate resulted in a rapid fall of the mean current amplitude at frequencies over 10 Hz. Data obtained by the authors confirm the known concept of desensitization of non-NMDA receptors as a relatively slow conformation of the receptor-channel complex.

Amplitude of the L5 segmental reflex responses 20 min. before and after intraperitoneal introduction of obsidan, clopheline and finoptine was recorded in experiments on spinalized and thyroxinized rats which 3 weeks before have endured transection of the sciatic nerve. It is demonstrated that obsidan does not change the amplitude of the monosynaptic reflex responses of the ventral root restored under the effect of thyroxine at the operated side, while clopheline and finoptine mainly reduce it.

Impulse activity of single afferent fibres of the spinal cord dorsal roots of cats was investigated under local mechanical, heat and cold influence on receptive fields of their skin. These influences did not change the frequency of impulsation, but changed redistribution of interimpulse intervals. It is supposed that formation of polyfunctional properties of single afferent fibres is realized due to their polychannel information.

Cutaneous C-fibre polymodal mechano-heat (CMH) sensory units of narcotized cats have been studied for their responses to the close-arterial injection of potassium, acetylcholine and methacholine to the saphenous artery in subnoxious and noxious concentrations. Subnoxious chemical stimulation has induced low-frequency excitation of CMH units. The parameters of CMH units firing during subnoxious and noxious chemical stimulation may be used for estimation of effects of local anesthetics. To achieve local anesthesia it is sufficient to inhibit only high frequency responses in CMH units without a complete block of these sensors. With that end in view the use-dependent blockers of nerve excitation are suggested. The use-dependent inhibition of CMH units was found during mechanical stimulation under the action of lidocaine or n-propylajmaline. The mathematical model of C-fibre has demonstrated the key role of slow changes of membrane ionic permeabilities in determining the firing rate elicited by chemical stimulation.

It was shown in experiments on anesthetized cats that motor cortex (MC) stimulated by single current pulse caused formation of the lateral geniculate nucleus (LGN) response. It was established that changes in formation of LGN response evoked by contralateral superior colliculus (SC) stimulation were observed by condition of the precedence of LGN response evoked by stimulation of the MC. The expressiveness level of that decrease depended on intervals between conditioning cortical and testing tectal stimuli. At the same time the stimulation of the MC by single current pulse caused no changes in formation of the visual evoked potential of LGN. However, a significant decrease of the visual response of that part of the SC which stimulation caused formation of the LGN response was observed under the same conditions. The obtained data permit supposing that MC checks realization of the tectal influences on the LGN function on the tectal level. It is assumed that realization of the effect of the saccadic suppression of the LGN function in which accomplishment, as it was supposed earlier, the SC took part, was controlled by the MC phasic influence.

Intracellular responses of neurons of the suprasylvian gyrus to the intracortical stimulation (ICS) before and after superficial application of strychnine were investigated in experiments on immobilized and unanaesthetized cats. The normal cortex neurons reacted to ICS by monosynaptic EPSPs followed by IPSPs. Strychnine application triggered the epileptiform activity and appearance in neurons of paroxysmal depolarization shifts of the membrane potential (MP) which were replaced by hyperpolarization potentials. An increase and summation of the latter elicited the MP enlargement and either reduction or suppression of background spike activity. Intracellular injections of EGTA blocking the membrane calcium-dependent potassium conductivity (gK(Ca)) have eliminated the hyperpolarization potentials. Development of epileptiform activity was accompanied by depression of IPSPs and increase of the monosynaptic EPSPs. The contribution of gK(Ca) and of postsynaptic inhibition to the epileptogenesis is discussed.

Microcirculation disorders may cause functional deviation in gray matter cells of the spinal cord. One of the setting moments of the disorders is the subluxation of a vertebra as a result of the disturbance in carrying ability of the spinal disc in case of spinal osteochondrosis. In this position the soft tissues of the spinal motional well innervated segment are stretched, which induces irritation in the segmental part of the spinal cord including vegetative nervous structures. Subluxation of a vertebra causes changes in the structures and in the microcirculation vessels which grow simultaneously and this permits supposing their interrelation.