MODULATION OF THE MONOSYNAPTIC REFLEX POTENTIALSIN THE DECEREBRATED RATS UNDER THE INFLUENCE OF HYDROXYTRYPTOPHAN.

We studied the serotonin effect on monosynaptic reflex potentials (MSR) of spinal motorneurons in the decerebrated rats in control and after intraperitoneal administration of serotonin precursor ­ 5-Hydroxytryptophan (5-HTP). MSR of motorneurons in the lumbar spinal cord were registered using electrical stimulation of dorsal root of the 5th lumbar section. During stimulation physiological saline or 5-hydroxytryptophan was injected intraperitoneally. In comparison with average amplitude of the control MSR there were registered significant increase in amplitudes of the MSR (169% and +172%, P <0,001) in animals with injection 5-HTP. These data suggest that serotonin release after 5-HTP administration leads to activation of motorneurons in the lumbar spinal cord. The mechanism of this activation may be related to the weakening of the inhibitory control of interneurons in the transmission pathways of the excitatory influences from muscle afferent to motorneurons and to the postural (antigravity) reflex reactions which necessary for the initiation of locomotion.

Subthreshold activation of spinal motoneurones in the stretch reflex: experimental data and modeling.

Responses of gastrocnemius-soleus motoneurones to stretches of the homonymous muscles were recorded intrasomatically in decerebrate cats; changes of membrane potential (MP) were evoked by smoothed trapezoid stretches of the muscles. Amplitudes of separate excitatory postsynaptic potentials (EPSPs) were defined via differences between values of MP at the end and beginning of the positive derivative waves, which were also used as basic elements in the model of the excitatory postsynaptic currents (EPSCs). EPSCs were assumed to be transformed into EPSPs by low-pass filtering properties of the somatic membrane; parameters of the filtering were firstly defined from analysis of Ia EPSP in the same cell and then were applied in model P ( m0). The model showed unsatisfactory quality in tracking slow components of MP; to overcome the disadvantage there was proposed model P ( m1) based on addition to P ( m0) the difference between two low-pass filtered signals MP and P ( m0) (the cutoff frequency 10 or 20 Hz). An overestimation of EPSPs' amplitudes was corrected in model P ( m2). The mismatch in tracking slow changes of MP was assumed to be connected with summation of a great number of low-amplitude EPSPs generated at distal dendrites; information about waveform of separate EPSPs could disappear in this process. One can speculate that slow components of membrane depolarization at least partly are linked with the persistent inward currents in dendrites; variable and, sometimes, too fast decays in EPSPs seem to reflect inhibitory synaptic influences.

Modulation of the activity of midbrain central gray substance neurons by calcium channel agonists and antagonists in vitro.

Changes in the background impulse activity of midbrain central gray substance neurons have been studied on slice preparations from the rat midbrain upon application of calcium-free solution, an activator of calcium channels, BAY-K 8644 (10 nM), organic (verapamil, 40 microM; D600, 10 microM; nifedipine, 1-10 microM; amiloride, 1 microM) and inorganic (Co2+, 1.5 mM) calcium channel blockers. Besides BAY-K 8644, all the substances inhibited most of the neurons studied. Verapamil, BAY-K 8644 and Co2+ also revealed facilitatory effects. Facilitatory action of BAY-K was most effective in silent neurons and in those previously inhibited by amiloride. Latent period values of inhibition in calcium-free solution and upon application of organic and inorganic blockers have the following sequence: D600 > amiloride > verapamil > Co2+ > nifedipine > calcium-free solution. Maximum rise time had the following order: amiloride > D600 > nifedipine > verapamil > Co2+ > calcium-free solution. Complete suppression of the neuronal activity induced by amiloride lasted twice as long as that induced by calcium-free solution, Co2+ and nifedipine, and six times as long as verapamil-induced suppression. Preliminary application of calcium channel blockers reduced facilitatory and increased inhibitory effects of serotonin and substance P. Data obtained are discussed with the supposition in mind that inhibition of the function of calcium channels in central gray substance neurons could be one of the mechanisms underlying the analgesic effect of a series of neurotropic agents after their introduction into this structure.

[Changes in background activity of periaqueductal gray neurons through application of serotonin or inhibition of its synthesis]. / Izmenenie fonovoi aktivnosti neironov tsentral'nogo serogo veshchestva pri podvedenii k nim serotonina ili blokade ego sinteza.

Application of serotonin (ST, 1.10(-4) M to periaqueductal grey neurons influenced background activity (BA) only in the third group of cells. In 45.5% of them ST evoked depression of BA. Through application of ST remarkable potentiation of BA inhibition evoked by locus coeruleus (LC), substantia nigra (SN) stimulation was found, but inhibitory affects of nucleus raphe magnus (NRM) were less intensive. After intraperitoneal injection of p-chlorophenylalanine the efficiency of NRM stimulation became lower, but influences of LC and SN on BA increased. The mechanisms of serotoninergic effects on BA of periaqueductal grey neurons are discussed.

[Modulation of periaqueductal gray neuronal activity by influences of brain stem monoaminergic structures]. / Moduliatsiia aktivnosti neironov tsentral'nogo cerogo veshchestva srednego mozga vliianiiami monoaminergicheskikh struktur stvola.

Studies of spontaneous firing (SF) in the midbrain periaqueductal gray (PAG) neurons before and after stimulation of nucleus raphe magnus, locus coeruleus and substantia nigra were performed on the rat anesthetized with Hexenal (200 mg/kg). Three types of neurons different in SF structure were found. Stimulation of indicated structures increased SF rate in 11-14.5% and decreased 31-47% of the studied neurons of the third group. Simultaneous stimulation of two structures did not induce a remarkable increase of SF rate. If one of two simultaneously stimulated structures suppressed SF the ultimate effect was, as a rule, depression of SF. Greatest suppression of SF was observed if stimulation of nucleus raphe magnus was induced. Role of PAG in organization of the brain stem component of antinociceptive mechanism is discussed.

[Experimental spinal cord contusion. I. An assessment of the state of the conductivity of different funiculi]. / Eksperimental'naia kontuziia spinnogo mozga. I. Otsenka sostoianiia provodimosti razlichnykh kanatikov.

Experiments were conducted on albino rats to study the changes of the amplitude and latency of maxima tract and synaptic components of the dorsal surface potential before and after spinal cord injury at the level of Th9. Dorsal surface potentials were recorded from L4 after stimulation in C2. The amplitude of tract and synaptic component maxima of the short latency potential were found to be considerably reduced after the injury. The latency of both components increased after the injury. The changes of the amplitude or latency of potentials evoked from different stimulated points of the cord were analysed. The possible mechanism of the revealed changes is discussed.

[Changes in the neuronal background activity of the central gray substance of the midbrain to motor cortex stimulation in rats]. / Izmenenie fonovoi aktivnosti neironov tsentral'nogo serogo veshchestva srednego mozga pri stimuliatsii motornoi kory u krys.

Motor cortex stimulation induced inhibition of the background activity (BA) in 47% periaqueductal gray neurons, excitation--in 20% and had no influence in 32% neurons. Most of the activated neurons (67%) had the 3d type of BA. Neurons with the 1st type of activity did not respond to the cortex stimulation.

[The effect of creatine phosphate on reflex transmission in the normal spinal cord and under hypoxic conditions]. / Vliianie kreatinfosfata na reflektornuiu peredachu v spinnom mozge v norme i v usloviiakh gipoksii.

The effect of phosphocreatine on reflex transmission in the spinal cord was studied in rats in vivo and in vitro. Low concentrations (10(-8)-10(-6) M) of phosphocreatine facilitated while high concentrations (10(-4)-10(-3) M) inhibited the amplitude of mono- and polysynaptic reflexes. It was found that phosphocreatine decreases the inhibiting action of hypoxia on test responses and accelerates restoration of the reflex transmission in the spinal cord.

[The depression of the background neuronal activity of the midbrain central gray substance by stimulation of monoaminergic structures]. / Ugnetenie fonovoi aktivnosti neironov tsentral'nogo serogo veshchestva srednego mozga pri stimuliatsii monoaminergicheskikh struktur.

Three types of neurons which exhibit spontaneous firing were found in the midbrain periaqueductal grey. The stimulation of monoaminergic structures did not change the firing of the first and second types of neurons but suppressed the third one.

[Antidromic impulsation of the dorsal roots at the time of real locomotion in rats]. / Issledovanie antidromnoi impul'satsii dorsal'nykh koreshkov vo vremia real'noi lokomotsii krys.

The antidromic activity of dorsal roots during swimming and stepping of rats was studied. It consisted of phase-dependent and tonic components of antidromic potentials. The most pronounced correlation was found between the intensity of antidromic activity and afferent input while the relation between the antidromic activity and efferent output was less appreciable. Possible sources for the initiation of antidromic activity and the significance of presynaptic depolarization in the spinal reflex control are discussed.

[Modulation of the segmental reflex reactions during real locomotion in rats]. / Moduliatsiia segmentarnykh reflektornykh reaktsii vo vremia real'noi lokomotsii krys.

Studies of low- and high-threshold reflex reactions evoked by dorsal root stimulation in different phases of real locomotion (swimming) in rat were performed. The pronounced facilitation of low- and high-threshold muscle responses in the period of particular muscle activity and their extensive depression in the period coupled with antagonist muscle activity were revealed. The low-threshold stimulation did not change the temporal and amplitude parameters of locomotor movements, but high-threshold one influenced the amplitude and frequency of locomotor movements. The functional significance and possible mechanisms of modulation of the influence of peripheral afferents are discussed.

[Phase-dependent changes in the posterior root potentials during real locomotion in rats]. / Fazozavisimye izmeneniia zadnekoreshkovykh potentsialov vo vremia real'noi lokomotsii krys.

Dorsal root potentials (DRP) were studied during two kinds of the real locomotion (swimming and stepping) of rats. Two negative DRP waves were observed in one locomotor cycle. One wave coincided with stance on extension, while the other one--with swing phase. Dependence between the DRP amplitude and intensity of afferent input during the real locomotion and passive movements of hind limbs was established. It is concluded that wave-like changes of DRP in the real locomotion are mainly due to the influences from peripheral afferents.

[Kinematic analysis of the different types of locomotor movement in rats after deafferentation]. / Analiz kinematiki razlichnykh vidov lokomotornykh dvizhenii u krys posle deafferentatsii.

Comparative analysis of kinematics of rat hindlimb movements during different kind of locomotion (swimming, walking, hindlimb swimming but forelimb walking) was performed. After deafferentation an increase of the locomotor rhythm frequency and a decrease of the movement amplitude of hindlimb joints were common features for all kinds of the locomotion. This indicates that the above parameters of locomotor movements were formed by afferent influences. A decrease of the movement amplitude and of the EMG activity which were evoked after deafferentation were minimal for swimming and maximal for walking. The role of afferent influences in formation of different locomotion patterns is discussed.

[Reflex component of the swing phase: a comparative analysis of locomotion in intact and deafferentated rats]. / Reflektornyi komponent fazy perenosa: sravnitel'nyi analiz lokomot sii intaktnykh i deafferentirovannykh krys.

Comparative analysis of hindlimb biomechanics and EMG activity with different kinds of locomotion before and after bilateral LI-S2 spinal cord deafferentation were performed in rats. A delay of the onset and increase of duration of knee and ankle joint flexion, but not hip joint flexion were revealed after deafferentation. It was accompanied by reinforcing of the F-period of the swing phase which was more prominent during walking than swimming. The amplitude and duration of the muscle activity decreased, in particular, during the F-period of the swing phase. The role of afferent inflow in the formation of the F-phase of the locomotor cycle is discussed.

[Phase-modulated antidromic action potentials in the dorsal root of the rat during locomotion]. / Faznomodulirovannye antidromnye potentsialy deistviia v dorsal'nom koreshke krysy vo vremia lokomotsii.

Discharges of antidromic spike potentials (ASP) were recorded from the rat dorsal root during locomotion. Tonic and phasic components were revealed in discharges of ASP. The phase-dependent modulation of phasic component was observed during locomotion. The role of ASP as a possible mechanism for restriction of afferent input was discussed.

[Uncoupling of modulation of the afferent flow and phasic activity of muscles during a period of unstable locomotion in the rat]. / Nesopriazhennost' moduliatsii afferentnogo pritoka i faznoi aktivnosti myshts v period nestabil'noi lokomotsii u krys.

During unstable locomotion which is characterised by irregular, low-amplitude movements different types of uncoupling between modulation of the amplitude and temporal characteristics of the afferent influx and efferent activity were revealed.

[Comparative analysis of the kinematics of hindlimb movements in different forms of locomotion in the rat]. / Sravnitel'nyi analiz kinematiki dvizhenii zadnei konechnostei krysy pri razlichnykh vidakh lokomotsii.

Changes in the locomotor cycles and joint angles during walking and swimming were comparatively analyzed in rats. Differences in hindlimb movements with or without participation of the forelimb were shown as well as differences between swing phases during walking and swimming. The role of central spinal processes and effects of peripheral afferents in organization of the different kind of locomotions is discussed.

[Various locomotor movements in the rat]. / Issledovanie razlichnykh lokomotornykh dvizhenii u krys.

The kinematics of movements and EMG activity of the hindlimb were investigated in rats during swimming and walking. It was shown that changes in loading on the limbs were the main factor modifying the frequency, amplitude, configuration, swing time and footing time of the studied movements.

[Neuronal organization of coeruleo-spinal connections in the cat]. / Neironnaia organizatsiia tseruleo-spinal'nykh sviazei u koshki.

Electrical stimulation of locus coeruleus in anesthetized cats was accompanied by a decrease in the inhibitory action of flexor reflex afferents (FRA) on extensor motoneurons. No changes in excitatory reactions of spinal motoneurons were observed. Microinjections of aspartic acid or chlorpromazine depressed FRA inhibitory action; injection of procaine and noradrenaline potentiated this action. The responses of differente spinal interneurons during activation of locus coeruleus were also studied. A conclusion is made that the inhibitory action of FRA is depressed by coeruleo-spinal influences on the level of the last-order inhibitory interneuron of the FRA system.

[Changes in inhibitory responses in the spinal cord of the cat induced by stimulation of suprasegmental structures during rhythmic stimulation of the locus coeruleus]. / Izmeneniia tormoziashchikh reaktii v spinnom mozge koshki, vyzvannykh stimuliatsiei nadsegmentarnykh struktur, pri ritmicheskom razdrazhenii golubogo piatna.

Effects of rhythmic locus coeruleus stimulation on spinal reactions evoked by cortico-, reticulo- and vestibulospinal influences were studied in anesthetized decerebellized cats. Two-component inhibitory reactions in extensor and excitatory-inhibitory reactions in flexor motoneurons were found after the stimulation of the motor cortex or the medullary reticular formation. The locus coeruleus stimulation depressed the late component of responses in both group of motoneurons but had a less influence on the early inhibitory and excitatory components. No changes were observed in reactions evoked by vestibulospinal influences in the extensor and flexor motoneurons. Mechanisms of descending influences of locus coeruleus on spinal reactions evoked by primary afferents and supraspinal structures are discussed.