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PubMed1975

Cortical and long spinal actions on lumbosacral motoneurones in the cat.

1. The effects of stimulating forelimb afferents on various ipsilateral motoneurones of the hind limb have been compared with those of volleys set up in the contralateral pericruciate cortex in cats anaesthetized with chloralose. 2. With intact neuraxis, brachial plexus volleys evoke discharge of flexor and extensor motoneurones; short cortical tetani also elicit discharge mainly of flexor motoneurons. After a pyramid-sparing brainstem lesion, little or no firing is evoked by either input. 3. Monosynaptic reflex testing and intracellular recording reveal subthreshold actions on hind-limb motoneurones, inhibition of FDHL and later facilitation of extensors and flexors by forelimb volleys, facilitation of flexors and extensors together with inconstant inhibition of the latter, by cortical stimulation. 4. Interruption of medullary extrapyramidal paths greatly reduces intensity and duration of facilitation from the forelimb, and largely removes cortically evoked extensor facilitation. Inhibition of FDHL from forelimb and cortex is unchanged; cortical volleys continue to facilitate flexors, and have mainly inhibitory action on extensors in these 'pyramidal' preparations. 5. Hyperpolarization of FDHL motoneurones occurs in response to forelimb and cortical volleys, of time course corresponding to depression of test reflexes. Spinal pathways responsible for the two inhibitory actions are independent, and unless each is very strong, their separate actions summate when elicited together. 6. Receptive field for FDHL inhibition from the forelimb is located distally in the forepaw, and its receptors are largely served by cutaneous fibres of low threshold; some Group II fibres in distal muscle nerves also contribute. Receptive field for facilitation embraces the whole limb, and the executant afferent fibres are of higher threshold. 7. Natural stimulation of the forelimb can evoke the long spinal actions, vibration or light pressure on the forepaw eliciting FDHL inhibition, and strong pinching evoking the more general facilitation. Possible functional roles of these actions in the intact animal are discussed.

Animals↗

PubMed1978

Mechanism of the vibration paradox: excitatory and inhibitory effects of tendon vibration on single soleus muscle motor units in man.

1. The parameters of presynaptic inhibition of the Ia spindle afferents from soleus muscle by vibration have been investigated. The inhibitory effects increase with the amplitude of vibration, but decrease when the vibration frequency is increased.2. The monosynaptic reflex threshold of twenty-one single soleus motor units activated in the H (Hoffmann) reflex by a single electrical stimulus to the posterior tibial nerve was estimated quantitatively and expressed in relation to the size of the simultaneously recorded H reflex.3. A parametric study of the effects of various Achilles tendon vibrations on the reflex threshold of the single soleus motor units indicated that their order of derecruitment is concordant with their rank order for activation in the phasic reflexes of the soleus. The last recruited motoneurones are the most susceptible to being silenced by steady vibration.4. Muscle vibration progressively recruits single motor units according to the motoneurone size principle through polysynaptic proprioceptive pathways. However the presynaptic inhibition of Ia spindle afferents simultaneously induced by the vibration works in reverse on the same rank order of motoneurones of the soleus spinal pool, thereby limiting the polysynaptic recruitment of units in the tonic vibration reflex while depressing the autogenic phasic proprioceptive reflexes. These mechanisms elucidate the so-called vibration paradox and extend the size principle of Henneman to presynaptic inhibitory effects.

Achilles Tendon↗

PubMed1979

Recurrent inhibition and afterhyperpolarization following motoneuronal discharge in the cat.

1. The relation between the size of a monosynaptic reflex (varying from the smallest values to the maximal motor response) and the output from Renshaw cells was investigated. This relation was extremely variable from one Renshaw cell to another. However, a linear relation between the reflex size and the early discharge emerged when the responses of all the Renshaw cells were averaged or when the summed activity of a pool of Renshaw cells was estimated by recording the recurrent inhibition in their target motoneurones. It was concluded that the lowest threshold motoneurones were efficient in producing recurrent inhibition. 2. In motoneurones, recorded intracellularly, the size of the depression caused by the afterhyperpolarization was compared to the maximum autogenetic recurrent inhibition. Under the particular experimental conditions used to mimic human experiments (Hultborn & Pierrot-Deseilligny, 1979a), it was found that recurrent inhibition had the same order of magnitude as the depression caused by afterhyperpolarization. 3. The additional depression caused by the summation of afterhyperpolarizations of two consecutive spikes was measured. It was shown that a summation of importance equal to the maximum autogenic recurrent inhibition required a mean interspike interval of 25 msec.

Animals↗

PubMed1983

GABA-mediated responses are not selectively depressed by 3-mercaptopropionic acid in the spinal cord.

The competitive inhibitor of glutamic acid decarboxylase (GAD), 3-mercaptopropionic acid (MPA), causes depletion of gamma-aminobutyric acid and convulsions. We expected it to be a superior GABA depleting agent for in vivo experiments to the frequently used semicarbazide. The dorsal root potentials (DRP) and monosynaptic reflex responses (MSR) evoked by adjacent dorsal root and peripheral nerve stimulation, respectively, were recorded in spinal unanaesthetized cats. MPA (100-200 mg/kg) caused a gradual decrease in DRP, reaching a peak in about 40 min after drug administration. This was usually associated with convulsive activity. Postsynaptic direct inhibition was not substantially affected. However, the MSR was consistently decreased, within 10 min after injection of MPA. It is concluded that MPA is not a suitable tool, at least in the spinal cord, for the selective reduction of GABAergic transmission.

3-Mercaptopropionic Acid↗

PubMed1997

Electrophysiological properties of lumbar motoneurons in the alpha-chloralose-anesthetized cat during carbachol-induced motor inhibition.

The present study was undertaken 1) to examine the neuronal mechanisms responsible for the inhibition of spinal cord motoneurons that occurs in alpha-chloralose-anesthetized cats following the microinjection of carbachol into the nucleus pontis oralis (NPO), and 2) to determine whether the inhibitory mechanisms are the same as those that are responsible for the postsynaptic inhibition of motoneurons that is present during naturally occurring active sleep. Accordingly, the basic electrophysiological properties of lumbar motoneurons were examined, with the use of intracellular recording techniques, in cats anesthetized with alpha-chloralose and compared with those present during naturally occurring active sleep. The intrapontine administration of carbachol resulted in a sustained reduction in the amplitude of the spinal cord Ia monosynaptic reflex. Discrete large-amplitude inhibitory postsynaptic potentials (IPSPs), which are only present during the state of active sleep in the chronic cat, were also observed in high-gain recordings from lumbar motoneurons after the injection of carbachol. During carbachol-induced motor inhibition, lumbar motoneurons exhibited a statistically significant decrease in input resistance, membrane time constant and a reduction in the amplitude of the action potential's afterhyperpolarization. In addition, there was a statistically significant increase in rheobase and in the delay between the initial-segment (IS) and somadendritic (SD) portions of the action potential (IS-SD delay). There was a significant increase in the mean motoneuron resting membrane potential (i.e., hyperpolarization). The preceding changes in the electrophysiological properties of motoneurons, as well as the development of discrete IPSPs, indicate that lumbar motoneurons are postsynaptically inhibited after the intrapontine administration of carbachol in cats that are anesthetized with alpha-chloralose. These changes in the electrophysiological properties of lumbar motoneurons were found to be comparable with those that take place during the atonia of active (rapid-eye-movement) sleep in chronic cats. The present results support the conclusion that the neural system that is responsible for motor inhibition during naturally occurring active sleep can also be activated in alpha-chloralose-anesthetized cats following the injection of carbachol into the NPO.

Action Potentials↗

PubMed1977

Rapid eye movement sleep, motoneurone inhibition, and apneic spells in preterm infants.

Not principally different from the results obtained in more mature subjects, monosynaptic reflex excitability of spinal motoneurones in preterm infants decreases during active sleep. However, in preterm infants the electric reflex response is not abolished, and is not even continuously depressed during the entire active sleep period. Spinal motoneurone inhibition is demonstrable only during certain periods of active sleep, and it is during this state of decreased spinal motoneurone excitability when apneic spells predominantly occur.

Apnea↗

PubMed1980

Jaw muscle activity during chin-tapping.

Electromyographic (EMG) activity was recorded from the masseter, the anterior temporal and the anterior digastric muscle on the right side of ten dental students when taps were administered upwards or downwards to the chin. The experiment was performed both with relaxed jaw muscles and with contracting depressor muscles. Pairs of intracutaneous platinum hook electrodes were used for the masseter and temporal muscles while concentric needle electrodes were inserted into the anterior digastric muscles. The mean latency of the jaw-jerk elicited in the relaxed masseter muscle when tapping downwards on the chin was 7.8 msec and in the temporal muscle 8.4 msec. The corresponding values of the latency during jaw opening against resistance from the investigator's finger was 8.2 msec and 9.0 msec. During upward tapping on the chin recordings from the anterior digastric muscle showed obvious changes in EMG activity, the latency ranging from 13 to 34 msec. Thus, compared to the latency of the jaw-jerk in the masseter and temporal muscles, which contain numerous muscle spindles, recordings from the anterior digastric muscle, where muscle spindles are thought to be either lacking or few in number, showed no signs of a monosynaptic reflex.

Adult↗

PubMed1996

[Depression of reciprocal Ia inhibition of crural motoneurons during rhythmical jaw movement in rabbit].

The purpose of this study was to investigate how the reciprocal inhibition of the ankle-flexor motoneuron by the ankle-extensor spindle afferents is altered during cortically-induced rhythmical jaw movement (RJM) in urethane-anesthetized rabbit. The monosynaptic reflex (MSR) was induced by test shock of the common peroneal nerve (CPN) and recorded from a distal point of the nerve. The conditioning shock applied to the tibial nerve (TN) at the intensity below 1.2 times the threshold caused a significant inhibition of the MSR in the CPN. The inhibition tended to slightly decrease with an increase in amplitude of the test MSR with either application of stronger test shock or during RJM. The decrease of the reciprocal inhibition significantly exceeded the degree that can be ascribed to the increase of the amplitude of the MSR during RJM. The reciprocal inhibition was significantly reduced during fictive as well as actual RJM. It was concluded that (1) the reciprocal Ia inhibition of the crural motoneurons in the rabbit is reduced with RJM and (2) the intraoral sensory input is not essential for this reduction. This study indicated that the oral motor activity generally exerts a strong influence on the bodily motor function.

Animals↗

PubMedDate not supplied

[Status of the spinal inhibitory reactions in humans subjected to hyperbaric oxygenation].

The state of human spinal inhibition responses under normo- and hyperbaric pressure (6.5 ata) was comparatively studied. The paired stimulation method has been used to estimate resetting of tested monosynaptic reflex in the 20-900 ms interval of paired stimulation at rest or against the background of supraspinal modulation of spinal reflective processes (Jendrassik manoeuvre, voluntary plantar flexion) were studied. The depression of inhibition reactions under hyperbaric pressure identical to that during the supraspinal modulation under normobaric conditions is shown. It is supposed that these influences on spinal reflection processes are caused by the same neuronal mechanism.

Atmosphere Exposure Chambers↗

PubMed1977

Motoneuron excitability in psychiatric patients.

The excitability at the alpha-motoneuron pool was studied by measuring the spinal monosynaptic reflex responses of soleus muscle to paired stimuli in psychiatric patients and controls. Patients showed significant alterations in the recovery of excitability when compared with normal volunteers. Specifically, the value for the peak of "secondary facilitation" was reduced in 5 of 8 chronic schizophrenic patients, while the following trough in the recovery cycle was reduced in 9 of 18 acutely schizophrenic patients. Drug effects were studied in 10 patients. Phenothiazine antipsychotic medication tended to enhance recovery of excitability. Patients of all types showed alterations of excitability. The altered excitability may relfect one aspect of a widespread abnormality of CNS function or may be a specific response to a supraspinal defect in neurophysiological activity in psychotic patients.

Affective Disorders, Psychotic↗

PubMed1986

Changes in the firing of single motor units before and after voluntary movement.

The changes in the firing of single motor units (MUs), i.e. the probability for the appearance of an impulse and the instantaneous firing frequency, from m. tibialis anterior and m. triceps surae, were investigated when the respective muscle was agonist or antagonist of the movement, as well as when the movement was performed by the contralateral leg. The changes in MU firing show that the excitability of the alpha-motoneurones is changed 25-45 ms before the front of the ipsilateral voluntary electromyogram. The excitability is increased when the muscle is agonist of the movement, and decreased when it is antagonist. The period of changed MU firing, found by us, corresponds to the duration of the period of increased monosynaptic reflex excitability, preceding the voluntary motor activity (Gerilovsky et al., 1982). Therefore, there are no grounds for assuming that the mechanisms causing these changes differ in the two cases. The results obtained show that the observed changes are specific: they are connected with the organization of the voluntary movement and they do not occur in movement involving the contralateral leg to the MU investigated.

Action Potentials↗

PubMedDate not supplied

[Jendrassik's maneuver for determination of efferent conduction in spinal cord injuries].

The effect of Jendrassik's manoeuvre on test H-responses of the gastrocnemius muscle was studied in 40 patients with trauma of the spinal cord and in 6 healthy individuals. In healthy individuals Jendrassik's manoeuvre led to a decrease of the amplitude of H-responses by 1.6-2.5 times (2.1 times on the average). The H-responses were also inhibited (by 1.3-2.0 times, 1.7 times on the average) in 7 patients in whom movements of the lower limbs were partly maintained. In 15 of 33 patients with lower limb paraplegia the H-responses were inhibited (by 1.2-2.4 times, 1.5 times on the average); Jendrassik's manoeuvre produced no effect in the other 18 patients of this group. It is concluded that the quantitative index of the effect of Jendrassik's manoeuvre on test monosynaptic reflexes of the lower limb muscles can be used for evaluating the maintenance of conductivity along the efferent conduction pathways of the spinal cord.

Adult↗

PubMed1979

[New evidence of depression of depolarization of primary afferents with ammonium ions].

Perfusion of the central canal of the lumbar segment of the spinal cord with artificial cerebrospinal fluid (CSF) supplemented with ammonium ions induced in cats depression of slow negative electrotonic potentials of dorsal roots (PDR). PDR depression developed simultaneously with postsynaptic depression of the inhibition of monosynaptic reflexes, however it was not related to the depression of mono- or polysynaptic reflex discharges. Further perfusion of the central canal with normal CSF resulted in a complete restoration of the PDR as well as inhibition of control reflexes. It is suggested that PDR depression with ammonium ions could be the result of the blocking of the chloric pump acting the afferent terminals and creating electromotive power for outward transmembranous chloric current producing depolarization of the afferent fibres.

Action Potentials↗

PubMed1979

[Maturation of nerve conduction velocity from birth to 5 years of age].

The Hoffmann monosynaptic reflex was recorded in the soleus muscle in 105 healthy children aged between 2 days and 5 years. From this the nerve conduction velocity in the proximal segment of the sciatic nerve was calculated. The tibial nerve conduction velocity (motor) was also measured in 59 of these children. The conduction velocity in the proximal and distal parts of the nerve develop in parallel and in an exponential manner but the conduction velocity in the reflex arc (afferent and efferent) is always faster than the motor conduction. Conduction time slightly but significantly decreases during the first year despite the increase in length of the nerve. Thereafter the conduction time slowly increases and by 5 years the values are similar to those in the neonatal period.

Aging↗

PubMed1981

Group Ia primary afferent terminal defect in cats with acrylamide neuropathy.

Group la primary afferent terminal (PAT) function was assessed in cats with acrylamide neuropathy. Spinal monosynaptic input-output relationships, critical input, the ability to maintain repetitive discharge at low frequencies, and apparent transmitter turnover parameters were determined in animals with subthreshold, moderate and severe degrees of acrylamide neuropathy (75, 150, and 300 mg/kg, respectively. The monosynaptic pathways of the soleus and medial gastrocnemius motoneuron pools were elicited by stimulation of their respective muscle nerves. The threshold for activation of the monosynaptic reflex (MSR) evoked by both SOL and MG nerves was increased 50% (critical input), regardless of dose regimen. Repetitive stimulation of the MSR at low frequencies (2-10 Hz) produces a slow decline in amplitude until it reaches a plateau. The height of the plateau attained in neuropathic cats was considerably lower than the controls. Determination of apparent transmitter turnover parameters in neuropathic cats showed that the constant fraction of neurotransmitter released from group la PAT remained the same while the rate of replenishment of transmitter available for release was attenuated in both SOL-VR and MG-VR pathways. The increase in the critical input and decrease in the rate of replenishment points up a functional defect in a group la PAT in cats with acrylamide neuropathy.

Acrylamide↗

PubMedDate not supplied

[Studies of efferent conductivity along the spinal cord after traumatic injury].

Study of the audiospinal effect on the monosynaptic reflex in healthy individuals showed that sound stimulations increased the amplitude of the H-reflex response. Intensification of the H-response was evidence of functioning efferent conduction along the spinal cord pathways. This provided the basis for using the audiospinal effect for testing the functional condition of the efferent spinal pathways in patients with traumatic lesion of the spinal cord. Twenty two patients with spinal cord injury were examined. Sound stimulation increased the H-response amplitude in 9 patients with paraparesis and in 6 patients with paraplegia. In the other 7 patients with lower limb paraplegia the H-response was not intensified by sound stimulation. This was evidence of disturbed efferent conduction along the spinal cord, which corresponded clinically to total impairment of all conduction functions of the spinal cord for a long time after the trauma.

Acoustic Stimulation↗

PubMed1995

Descending noradrenergic neurones tonically suppress spinal presynaptic inhibition in rats.

We investigated the tonic depressant effect of descending noradrenergic neurones on spinal presynaptic inhibition. Presynaptic inhibition was measured in terms of the decrease in the amplitude of the monosynaptic reflex (MSR) evoked by conditioning stimulation of the adjacent dorsal root. This reduction in the MSR by conditioning stimulation was accompanied by primary afferent depolarization and was inhibited by the GABAA antagonist bicuculline, but not by the glycine antagonist strychnine. This presynaptic inhibition was much greater in spinalized rats than in intact rats, and was potentiated by the depletion of noradrenaline in the spinal cord in intact rats. These results suggest that presynaptic inhibition evoked by stimulation of the adjacent dorsal root seems to be tonically suppressed by descending noradrenergic neurones.

Afferent Pathways↗

PubMed1997

Ethanol as a general anesthetic: actions in spinal cord.

Ethanol, usually studied in relation to intoxication, is also capable of producing general anesthesia. The most common standard of anesthetic potency is the concentration which produces immobility in response to a noxious stimulus. This concentration will be referred to as the anesthetic concentration. Immobilization is a spinal effect. Ethanol effects were studied in spinal cord from 2-7-day-old rats at concentrations which included the anesthetic concentration in both adult rats (97 mM) and 6-7-day-old rats (235 mM). At neonatal but not adult anesthetic concentrations, ethanol depressed monosynaptic reflex amplitude (mediated by glutamate AMPA receptors + compound action potential). At both neonatal and adult anesthetic concentrations ethanol reversibly depressed the population excitatory postsynaptic potential (pEPSP) (glutamate AMPA and NMDA receptors), the slow ventral root potential (NMDA + metabotropic receptors), and the dorsal root potential (GABA(A) receptors, via glutamate-excited interneurons). Effects were greater on NMDA receptor-mediated components than on AMPA-receptor-mediated components of the pEPSP and greater on NMDA than on metabotropic receptor-mediated components of the slow ventral root potential. The profile of ethanol effects on spinal cord resembles that of inhalation general anesthetics. The results show that both AMPA and NMDA receptor-mediated transmission are sensitive to ethanol and that enhancement of GABAergic neurotransmission is overridden by depression of excitation to the interneurons. They provide no obvious explanation for ethanol's lower general anesthetic potency in the neonate.

6-Cyano-7-nitroquinoxaline-2,3-dione↗