Retuning of segmental responses to peripheral stimulation in cats during fictitious locomotion

Segmental responses of the lumbosacral region of the spinal cord to peripheral afferent stimulation were studied in decorticated, immobilized cats before and during fictitious locomotion. The appearance of fictitious locomotion was accompanied by a tonic increase in the N₁-component of the dorsal cord potential and dorsal root potential. Against the background of this tonic increase, modulation of these responses depending on the phase of fictitious locomotion was observed. When the N₁-component and dorsal root potential were evoked at the end of the "extension" phase and at the beginning of the "flexion" phase their amplitude was greater, but when they were evoked at the end of the "flexion" phase and the beginning of the "extension" phase it was smaller. Polysynaptic and monosynaptic reflex response of motoneurons exhibited the same phase dependence during fictitious locomotion. The mechanisms and physiological importance of this retuning of segmental responses are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 283–291, May–June, 1981.     

Depolarization of primary afferents during fictitious scratching in thalamic cats

The dorsal cord and dorsal root potentials were recorded in immobilized thalamic cats during fictitious scratching evoked by mechanical stimulation of the ear. Depolarization of primary afferents was shown to be simulated by the central scratching generator. Antidromic spike discharges appeared at the peak of the primary afferent depolarization waves in certain afferent fibers. Similar discharges arise in the resting state in response to stimulation of limb mechanoreceptors. It is suggested that during real scratching primary afferent depolarization and antidromic spikes evoked by it may effectively modulate the level of the afferent flow to spinal neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 173–176, March–April, 1978.     

Active selection of afferent information as the basic principle of peripheral correction of the activity of spinal rhythmic movement generators

This paper summarizes information obtained in the experimental study of the dynamics of polarization of central primary afferent endings and modifications of segmental responses to afferent stimuli during fictitious locomotion and fictitious scratching in immobilized, decorticated, decerebrate, and spinal cats. Fictitious locomotion was accompanied by tonic hyperpolarization, fictitious scratching by tonic depolarization of central primary afferent endings. Against the background of these long-lasting changes in primary afferent depolarization, it exhibited periodic changes in the rhythm of efferent activity. Periodic changes of depolarization were virtually in phase in different ipsilateral segments of the lumbosacral enlargement. Data on groups of afferent fibers in whose central endings tonic and phasic changes of polarization took place. The appearance of fictitious locomotion was accompanied by a tonic increase, and of fictitious scratching by tonic inhibition of several evoked segmental responses. These tonic changes were a background against which segmental responses were modulated in step with the working rhythm of the locomotion and scratching generators. Many of the changes in evoked segmental responses were shown to be based on modulation of polarization of central endings of primary afferents by locomotion and scratching generators. It is concluded that active tonic and phase-dependent selection of incoming afferent information is effected through modulation of presynaptic inhibition of the generator. The role of this selection in peripheral collection of activity of locomotion and scratching generators is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 343–353, May–June, 1984.     

Inhibitory effect of dopamine on the transmission of excitation in isolated rat spinal cord

The effects of dopamine on ventral root potential produced by a single supramaximal dorsal root stimulation of the dorsal root was investigated during experiments on isolated superfused spinal cord segments from 10–16-day old rats. A reciprocal dose-dependent inhibition of the mono- and polysynaptic components of reflex response was also observed. Minimum effective concentration was 1×10^–8 M dopamine. Extent of reflex response increased in step with dopamine concentration, so that the amplitude of the monosynaptic component of ventral root potential was decreased by 20% and 87% of baseline level by the action of 10^–4 and 10^–3 M dopamine respectively on the cord. The amplitude of the polysynaptic component was thereby decreased by an average of 18% and 87%. Findings indicate that dopaminergic brainstem-spinal pathways contribute to the governing of impulse transmission in the segmental reflex arcs. Inhibition of dopaminergic synaptic transmission probably underlies the increase in latency already described in the literature, as well as the increase observed in the threshold of reflex motor response to nociceptive action following either stimulation of the dopaminergic brainstem structures or intravenous administration of dopamine agonists.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 616–621, September–October, 1986.     

Activity of propriospinal neurons during the scratch reflex in cats

Fictitious scratching, i.e., rhythmic activity of hind-limb motoneurons at the characteristic scratching frequency, was evoked by tactile stimulation of the ear in thalamic cats immobilized with flaxedil. Activity of propriospinal neurons in segments C₁, C₂, and T₄–T₇ was recorded extracellularly. The neurons were identified by their antidromic response to stimulation of their axons in segment L₁. Most neurons did not respond to stimulation of the ear. Some neurons, however, were activated during fictitious scratching. Neurons of the cervical segments responded not only to stimulation of the ear, but also to tactile stimulation of the forelimbs and also to passive movements of those limbs. Neurons of the thoracic segments were activated only by stimulation of the ipsilateral ear; these neurons were inhibited by stimulation of the contralateral ear. The role of the propriospinal neurons in the activation of the spinal mechanisms of scratching is discussed.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 504–511, September–October, 1977.     

Changes in segmental reflex responses during stimulation of locus coeruleus and potentiation of the action of catecholamines

Repetitive stimulation of the locus coeruleus (up to 150 µA in strength) was accompanied by marked weakening of the inhibitory action of flexor reflex afferents and of the reciprocal inhibitory action on extensor motoneurons. Meanwhile stimulation of this sort had no significant effect on direct inhibition of flexor and extensor motoneurons, on the facilitatory action of flexor reflex afferents and the reciprocal inhibitory action on flexor motoneurons and also on dorsal root potentials. Intravenously injected pyrogallol had a similar action, but its effect was much weaker after spinalization of the animals or blocking of spinal cord conduction by cold. Enhancement of the monosynaptic reflex, which also was observed after injection of pyrogallol, was characterized by different temporal parameters; the intensity of this effect was unaffected both by spinalization and by cold block. These data, and also the results of experiments with partial divisions of the spinal cord, suggest that the effects of stimulation of the locus coeruleus are the result of activity of a descending coerulo-spinal tract, running in the ventral quadrant of the spinal cord.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 39–47, January–February, 1981.     

Inhibition of spinal reflex responses in the last period of embryogenesis

Some characteristics of spinal reflex reaction inhibition were studied in cat fetuses during the last three weeks of antenatal development. The experiments were conducted on fetuses with intact placental circulation. Restoration of the excitability of the spinal reflex arcs was very slow after stimulation of the dorsal root by a single stimulus. In embryos studied 20 days before birth the full inhibition of reflex responses lasted about 500 msec. Even 2–3 sec after a single stimulation of the afferent fibers the amplitude of the reflex response to the second stimulus was only 30–40% of the control value. It was determined that such long postactivation depression is unrelated to refractoriness or antidromic inhibition. The presence of a prolonged intense depolarization of afferent terminal fibers at these stages suggests a presynaptic inhibition as one of the most probable reasons for the prolonged postactivation depression. Another important factor in the appearance of postactivation depression is probably the morphologic and functional immaturity of synaptic structures. A reciprocal inhibition was observed in cat fetuses on the 10–12th antenatal day. On the basis of these data it is suggested that in embryogenesis presynaptic inhibition considerably precedes that of postsynaptic fibers.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 68–75, January–February, 1971.     

Activity of lumbosacral interneurons during fictitious scratching

Activity of lumbosacral spinal interneurons was studied during fictitious scratching in decerebrate, immobilized cats. Neurons whose activity changed during fictitious scratching were located in the substantia intermedia lateralis and ventral horn. Among these neurons cells were distinguished whose activity was modulated in rhythm with motor discharges to different muscles (61.6%) and cells which were activated tonically (21.4%) or inhibited tonically (17%). By correlation of activity with discharges to corresponding muscles the rhythmically activated neurons were divided into "aiming" (36.6%) and "scratching" (25%). Neurons whose activity was unchanged during fictitious scratching also were observed. These cells were located mainly in the more dorsal regions of gray matter. Neurons to which wide convergence of excitatory influences from high-threshold cutaneous and muscular afferents was observed were mainly placed in the "aiming" group. "Scratching" neurons, compared with "aiming," more often received inputs only from low-threshold cutaneous or high-threshold muscular afferents. Group Ia interneurons were activated in phase with the corresponding motoneurons. Passive displacement of the limb in a forward direction predominantly inhibited spike activity of the "aiming" and potentiated activity of the "scratching" neurons. The neuronal organization of the spinal scratch generator is discussed on the basis of the results.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 57–66, January–February, 1981.     

Role of propriospinal neurons in inhibition of the afferent flow

The effects of stimulation of the dorsal funiculus on dorsal surface potentials (DSPs) of the spinal cord evoked by stimulation of a peripheral nerve and on antidromic action potentials (AAPs) evoked by stimulation of terminal branches of primary afferent fibers and recorded from the afferent nerve or dorsal root, were investigated in acute experiments on spinal cats and on cats anesthetized with pentobarbital and chloralose. Stimulation of the dorsal funiculus led to biphasic inhibition of the N₁-component of the DSP with maxima at the 15th–30th and 60th–80th milliseconds between the conditioning and testing stimuli. Maximal reinforcement of the AAP was found with these intervals. Bilateral division of the dorsal funiculi between the point of application of the conditioning stimuli and the point of recording the DSP abolished the first wave of inhibition of the DSP and the reinforcement of the AAP. After total transection of the cord above the site of conditioning stimulation the picture was unchanged. It is concluded that the initial changes in DSP and AAP are due to activation of the presynaptic inhibition mechanism by antidromic impulses traveling along nerve fibers running in the dorsal funiculus. Repeated inhibition of the DSP, like reinforcement of the AAP, can possibly be attributed to activation of similar inhibitory mechanisms through the propriospinal neurons of the spinal cord.Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 401–405, July–August, 1973.     

On mechanisms of depression in pathways of presynaptic inhibition

We investigated inhibition of the N₁-component of the spinal cord dorsal potential (CDP) evoked by experimental stimulation of the n. peroneus in spinal cats. Stimulation was carried out following two conditioning stimuli administered at different time intervals to the same or different cutaneous nerves. The interval between the last conditioning stimulus and the experimental one remained constant (20 msec). It is demonstrated that there is no dependence between weakening of inhibitory action of the second conditioning stimulus and inhibition of the dorsal horn interneurons excited by it that generate the N₁-component of the CDP. It is hypothesized that mechanisms which act on the principle of negative feedback are present in the vincinity of the synaptic junctions of cutaneous afferent fibers with neurons of the substantia gelationsa, and that these mechanisms restrict the development of presynaptic inhibition during inflow of a series of afferent impulses into the cord.Dnepropetrovsk State University. Translated from Neirofiziologia, Vol. 1, No. 3, pp. 253–261, November–December, 1969.     

Activity of propriospinal neurons in segments C3 and C4 during fictitious locomotion in cats

Activity of propriospinal neurons in segments C3 and C4 was recorded in immobilized decerebrate cats, whose spinal cord was divided at the lower thoracic level, during locomotor activity of neuronal mechanisms controlling the forelimbs (fictitious locomotion of the forelimbs). Neurons were identified according to antidromic responses to stimulation of the lateral column of the spinal cord at level C6. Antidromic responses also appeared in 70% of these neurons to stimulation of the medullary lateral reticular nucleus. During fictitious locomotion, i.e., in the absence of afferent signals from the limb receptors, rhythmic modulation of the discharge of most neurons was observed, correlating with activity of motoneurons. If the rostral region of the cervical enlargement of the spinal cord was cooled, causing generation of the locomotor rhythm to cease, rhythmic activity of propriospinal neurons in segments C3 and C4 also ceased. The main source of modulation of activity of propriospinal neurons in segments C3 and C4 is thus the central spinal mechanisms controlling activity of the forelimbs.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow University. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 320–326, May–June, 1985.     

Effect of peripheral heating and cooling on spinal reflex activity

The effects of heating and cooling the skin of the thigh and leg on the character of changes in monosynaptic and polysynaptic reflexes and of the first negative wave (N_`) of the dorsal cord potential was studied in acute experiments on lightly anesthetized cats. During cooling of the skin the amplitude of the monosynaptic reflex and N₁-wave was increased while the polysynaptic reflex was inhibited; during heating the amplitude of the monosynaptic reflex and N₁-wave was reduced while the polysynaptic reflex was increased. After de-efferentation the cooling effect was reduced, and after division of the spinal cord responses to cooling of the skin were considerably inhibited. The mechanism of the selective action of cooling and heating of the skin on monosynaptic and polysynaptic reflexes are discussed.Institute of Physiology, Academy of Sciences of the Kazakh SSR, Alma-Ata. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 181–185, March–April, 1973.     

Segmental inhibitory response in the frog spinal cord during orthodromic motoneuron activation

Different types of reflex discharges were produced in various preparations by stimulating the dorsal root of isolated frog spinal cord. These ranged from multiphasic low-amplitude waves to distinctly synchronized monosynaptic response. The discharges were followed by facilitation in the former and deep, protracted inhibition of response to test dorsal root stimulation in the latter. When interstimulus intervals measured 40–50 msec, inhibitory action was less pronounced than at shorter (15–30 msec) or longer (60–100 msec) intervals, thus indicating that at least two types of inhibition were at work, one at an earlier and the other at a later stage. Strychnine at a concentration of 10^–5 M effectively reinforced the former and blocked the latter, while 10^–4 M d-tubocurarine attenuated both types of inhibition substantially. It is concluded that inhibition of response occurs mainly as a result of recurrent activation of inhibitory systems via recurrent motoneuron axon collaterals when frog spinal cord afferents are excited. Intensity of the later (presynaptic) and earlier (postsynaptic) inhibition of reflex transmission is determined by the degree of synchrony in motoneuronal discharge in response to orthodromic stimulation.Institute of Medical Radiology, Academy of Medical Sciences of the USSR, Obninsk, Kaluga Oblast. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 343–350, May–June, 1987.     

Interaction between responses evoked by acoustic and somatosensory stimuli in neurons of the magnocellular part of the medial geniculate body

Interaction between responses to acoustic clicks and to electrodermal stimulation of the contralateral forelimb was investigated in 78 neurons in the magnocellular part of the medial geniculate body of curarized cats. Of this number, 33 neurons responded by discharges both to clicks and to electrodermal stimulation, 25 responded to clicks only, and 20 to electrodermal stimulation only, or to stimulation of the dorsal funiculus of the spinal cord. Conditioning stimulation evoked inhibition of the response to the testing stimulus in 32 of 33 neurons responding by spike discharges to both clicks and electrodermal stimulation. Electrodermal stimulation inhibited responses to clicks in all the neurons tested which responded only to clicks, whereas clicks evoked inhibition of responses to electrodermal stimulation (or to stimulation of the dorsal funiculus) in only four of the 20 neurons which responded to these types of stimulation only. It is suggested that inhibition of excitability arising in neurons of the magnocellular part of the medial geniculate body during interaction between auditory and somatosensory afferent volleys is based on postsynaptic inhibition.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 368–374, July–August, 1980.     

Scratch reflex evoked by strychnine applied to the spinal cord

Effective facilitation of the scratch reflex was observed in experiments on recently decerebrated and spinal cats in response to application of strychnine solution to the dorsal surface of the spinal cord. The receptive fields of the scratch reflex in this case depended on the segments to which the strychnine was applied. The receptive fields of a scratch reflex evoked by D-tubocurarine coincided with those of the intact adult animals, but the receptive fields for strychnine application were wider and corresponded to those of the scratch reflex in kittens [1, 10]. It is suggested that strychnine application abolishes the inhibition of the afferent inputs of the scratch reflex in the lower cervical segments of the spinal cord which has developed during ontogeny.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 622–625, November–December, 1978.     

Gentle Mechanical Skin Stimulation Inhibits Micturition Contractions via the Spinal Opioidergic System and by Decreasing Both Ascending and Descending Transmissions of the Micturition Reflex in the Spinal Cord

Recently, we found that gentle mechanical skin stimulation inhibits the micturition reflex in anesthetized rats. However, the central mechanisms underlying this inhibition have not been determined. This study aimed to clarify the central neural mechanisms underlying this inhibitory effect. In urethane-anesthetized rats, cutaneous stimuli were applied for 1 min to the skin of the perineum using an elastic polymer roller with a smooth, soft surface. Inhibition of rhythmic micturition contractions by perineal stimulation was abolished by naloxone, an antagonist of opioidergic receptors, administered into the intrathecal space of the lumbosacral spinal cord at doses of 2–20 μg but was not affected by the same doses of naloxone administered into the subarachnoid space of the cisterna magna. Next, we examined whether perineal rolling stimulation inhibited the descending and ascending limbs of the micturition reflex. Perineal rolling stimulation inhibited bladder contractions induced by electrical stimulation of the pontine micturition center (PMC) or the descending tract of the micturition reflex pathway. It also inhibited the bladder distension-induced increase in the blood flow of the dorsal cord at L5–S1, reflecting the neural activity of this area, as well as pelvic afferent-evoked field potentials in the dorsal commissure at the lumbosacral level; these areas contain long ascending neurons to the PMC. Neuronal activities in this center were also inhibited by the rolling stimulation. These results suggest that the perineal rolling stimulation activates the spinal opioidergic system and inhibits both ascending and descending transmissions of the micturition reflex pathway in the spinal cord. These inhibitions would lead to the shutting down of positive feedback between the bladder and the PMC, resulting in inhibition of the micturition reflex. Based on the central neural mechanisms we show here, gentle perineal stimulation may be applicable to several different types of overactive bladder.     

Reordering of scratch generator efferent activity produced by stimulating hindlimb skin afferents in decerebrate immobilized cat

Reordering of the parameters of motor activity produced in the scratch generator by regular electrical stimulation of the ipsilateral hindlimb muscle nerve during different limb positions was investigated in decerebrate immobilized cats. Brief short latency inhibition of currently occurring motor activity was produced in response to stimulation, which did not cause an overall shift in the relationship between the intensity of aiming and scratching motion. Changes in cycle duration and intensity of these activities were phase-locked. Speculations were made on the functional role of the phase-locked nature of motor activity remodeling. The possible existence within the scratch generator of a model of the afferent inflow entering the spinal cord during true scratching is suggested.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 382–390, May–June, 1987.     

Functional organization of mechanisms of presynaptic inhibition induced by stimulation of cutaneous afferents

Changes in the N₁-component and P-phase of the dorsal surface potential (DSP) of the spinal cord evoked by test stimulation of the posterior tibial nerve after conditioning stimulation of the sural nerve were investigated in anesthetized cats. The test responses were inhibited if stimulation was applied at short intervals. They then recovered to some extent, but after 1.8–2.2 msec, a further prolonged period of inhibition began. The initial inhibition was connected with occlusion of synaptic action, and the subsequent prolonged inhibition with the development of presynaptic inhibition. The latent periods of prolonged inhibition of the N₁-component and P-phase of the DSP (2 msec) were almost exactly identical, and the curves showing the diminution of the initial occlusion of these components were very similar. The results demonstrate that presynaptic inhibition of the interneurons generating the N₁-component of the DSP and of cells of the substantia gelatinosa which participate in depolarization of the presynaptic terminals of the cutaneous afferents is due to the action of depolarizing systems with similar temporal characteristics.Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 510–515, September–October, 1972.     

Cholinergic modulation of the synaptic transmission in the frog spinal cord

It was found during experiments on isolated frog spinal cord involving extracellular recording from the dorsal roots (sucrose bridging) and intracellular recording from motoneurons by microelectrodes that 10 mM of the M-cholinomimetic arecoline produces motoneuronal depolarization which is matched by depolarizing electronic ventral root potentials and a rise in motoneuronal input resistance. Arecoline changes synaptic transmission by increasing the amplitude of postsynaptic potentials during intracellular recording and that of motoneuronal reflex discharges in the ventral roots but reduces the duration of dorsal root potentials. In the presence of arecoline, L-glutamate-induced motoneuronal response increases. Facilitation of synaptic transmission produced by arecoline in the spinal cord is bound up with cholinergic M₂- activation, since it is suppressed by atropine but not by low concentrations of pirenzipine; it is also coupled with a reduction in adenylcyclase activity. When motoneuronal postsynaptic response has been suppressed, as in the case of surplus calcium or theophylline, arecoline produces an inhibitory effect on the amplitude of motoneuronal monosynaptic reflex discharges which is suppressed by pirenzipine at a concentration of 1×10^–7 M. This would indicate the presence at the primary afferent terminals of presynaptic cholinergic M₁ receptors which mediate its inhibition of impulses of transmitter release. This effect is independent of changes in cyclic nucleotide concentration.A. M. Gorkii Medical Institute, Donetsk. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 399–405, May–June, 1987.     

Responses of upper cervical spinal neurons in cats to stimulation of the brain-stem locomotor region at different frequencies

Synaptic responses of neurons in segments C₂ and C₃ to stimulation of locomotor points in the medulla or midbrain were recorded extracellularly in mesencephalic cats. Neurons generating responses with an index of 0.4–0.6 to stimulation with a frequency of 2 Hz maintained this same index at frequencies of 20–60 Hz. The discharge index of many neurons during stimulation at 2 Hz was low, and it increased to 0.4–0.6 when high-frequency stimulation was used. More than half of the cells were excited by stimulation of both ipsilateral and contralateral locomotor points; one-quarter of the neurons responded to stimulation of locomotor points in both medulla and midbrain. The cells studied were located 1.8–4.2 mm from the dorsal surface of the spinal cord. The mean latencies of responses with an index of not less than 0.5 lay within the range 2–30 msec, with a mode of 2–8 msec. Considerable fluctuations of latent period were observed for long-latency responses. The possibility that the neurons studied may participate in the transmission of activity from the locomotor region of the brain stem to stepping generators in the spinal cord is discussed.Institute for Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 355–361, July–August, 1983.