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Biomedical subjects

P Wand

Publications and source records attributed to P Wand.

36 records · Page 2Linked to original sources
PubMed1979

Muscle spindle discharge in normal and obstructed movements.

1. The discharge activity of muscle spindle endings located in tail and hind limb muscles was recorded during voluntary movements in the cat. 2. During active shortening of the receptor-bearing muscles, both primary and secondary endings tended to fall silent. This was more pronounced, the higher the rate of muscle shortening. We suggest that in unobstructed movements in which muscle velocities exceed 0.2 resting lengths per second (lr/sec), the firing patterns of spindle afferents are dominated by their responses to the length variations. At velocities lower than 0.2 lr/sec, fusimotor action may predominate. 3. When active muscle shortening was unexpectedly halted, both primary and secondary endings resumed firing, but the increases in discharge rate were not as abrupt as might have been expected had there been strong co-activation of fusimotor and skeletomotor neurones. Rather, for the types of movements studied, fusimotor action appears to have been quite modest.

Action Potentials↗
PubMed1977

Effects of 1,3-dimethyl-5-aminoadamantane hydrochloride (DMAA) on the stretch-induced reflex tension of flexor muscles and the excitability of the gamma-loop in decerebrate and spinal cats.

The effects of 10 mg/kg i.v. 1,3-dimethyl-5-aminoadamantane hydrochloride (memantine, DMAA) on the stretch-induced reflex tension of flexor muscles extensor digitorum longus and tibialis anterior (EDL/TA) and on the excitability of the neurons relaying transmission in the gamma-loop have been investigated in decerebrate and spinal cats. DMAA essentially reduced the relfex excitability of flexors EDL/TA induced by fusimotor activity in the decerebrate preparation. The drug did not stimulate the reflex activity in acute spinal cats. In the concentration used, DMAA suppressed largely the transmission of the fusimotor reflex in the decerebrate as well as in the spinal preparation, although in spinal cats DMAA increased the average firing rate of muscle spindle primaries originating from EDL/TA muscles. The possible mechanism of action of the compound on dopaminergic and serotonergic systems as well as its basic effects on neuronal membranes is discussed.

Amantadine↗
PubMed1976

The response of alpha-motoneurons of different size to stretch and vibration of extensor muscles after injection of 5-hydroxytryptophan in spinal cats.

1. Vibration of the GS muscle at 100/sec, and the peak-to-peak amplitude of about 100 mu, produced slight reflex activity of homonymous and heteronymous alpha-motoneurons in the spinal, unanesthetized cat. 2. Intravenous injection of the 5-HT precursor 5-HTP (25 mg/kg, L-form) performed in the spinal preparation facilitated the responses of single extensor alpha-motoneurons to both vibration and stretch of the corresponding muscle. The 5-HT antagonist methysergide (0-5 mg/kg i. v.) blocked almost completely the facilitation of the vibration and stretch induced motoneuronal discharges produced by 5-HTP in the spinal cat, indicating that the facilitation was 5-HT specific. 4. A comparison of the types of alpha-motoneurons participating in the reflex responses elicited by the different stimuli in the spinal cat following injection of 5-HTP showed that both small-tonic and large-phasic alpha-motoneurons take part in both stretch and vibration reflexes. 5. It is concluded that the alpha-motoneuron pool of the GS muscle represents an homogenous population, no matter what kind of synaptic drive is used for its activation, and that the susceptibility of a motoneuron to discharge depends on the amount of the afferent excitatory input rather than on the modalities of sensory stimulation.

5-Hydroxytryptophan↗
PubMed1975

The proprioceptive activation of stretch tension in pretibial flexor muscles induced by stimulation of antagonistic muscle afferents.

1. The effect of tetanic stimulation of ipsilateral group I afferents from the GS muscle on a synchronous stretch of the flexor EDL/TA muscles has been investigated in precollicular decerebrate cats. 2. The stretch-induced tension of the EDL/TA muscles increases remarkably during simultaneous stimulation of the GS nerve with maximal intensities corresponding to 1.5 times the threshold for the group 1 afferents. This increas appears above all in the dynamic part of stretch. 3. Under our experimental conditions there is no activation fo flexor-alpha-motoneurones during tetanic stimulation of the GS afferents without muscle stretch, as measured by the resting tension of the EDL/TA muscles. 4. Desptie an increase in the stretch-induced tension during fusimotor stimulation of antagonistic group I afferents, a transmission loss in the excitation via the psi-loop to the flexor-alpha-motoneurones occurs. This could be demonstrated by the ratio: increase in the tension T /increase in the number of Ia spikes. This is explained by snychronous convergence of the discharges of Ia inhibitory interneurones to the flexor-alpha-motoneurones. 5. The system studied demonstrates an input-output relation of the stretch reflex during conditions in which both reciprocal inhibition and autogenetic excitation via the psi-loop occur. It appears however, that the reciprocal inhibition is partly overwhelmed by the autogenetic excitation which results from the increase in the Ia discharge rate during fusimotor reflex. 6. It is postulated that static rather than dynamic psi-moto-neurones are involved in the investigated reflex arc.

Action Potentials↗
PubMed1975

Response of Renshaw cells to sinusoidal stretch of hindlimb extensor muscles.

1. Renshaw cells responding disynaptically to electrically induced group I volleys in the intact gastrocnemius-soleus (GS) nerve, were submitted to small-amplitude, high-frequency vibration applied longitudinally to the deefferented GS muscle in precollicular decerebrate cats. 2. Vibration of the GS muscle at 200/sec, 180 mu peak-to-peak amplitude for 80-100 msec produced a sudden increase in the discharge rate of Renshaw cells, which gradually decreased within 25-50 msec to reach a steady level higher than that recorded in the absence of vibration. 3. Excitation of Renshaw cells appeared at a threshold amplitude of vibration (at 200-250/sec) of 5-20 mu and increased to a maximum value for amplitudes of about 70-80 mu, i.e., when all the primary endings of the spindles from the GS muscle had been driven by the stimulus. Recruitment of the secondary endings of the muscle spindles, due to large amplitude muscle vibration, did not modify the response of the Renshaw cells to the mechanically induced group Ia volleys. 4. These findings were obtained with the GS muscle pulled at 8 mm of initial extension. A threshold response of Renshaw cells to vibration appeared at 4 mm of static stretch, while maximal responses occurred at 8 mm. No further increase and actually a slight decrease in the response appeared for initial extensions of the muscle of 10-12 mm. 5. For a given vibration amplitude, the response of the Renshaw cells increased with increasing frequencies of vibration to reach the maximum at frequencies of 150-250/sec. Bursts of Renshaw cell discharges synchronous to each stroke of vibrator occurred only for low frequencies of stimulation (less than 25/sec). 6. It is concluded that vibration of the GS muscle represents a very effective method in exciting the Renshaw cells and that this response depends upon selective stimulation of homonymous motoneurons monosynaptically excited by the orthodromic volleys originating from the primary endings of the corresponding muscle spindles.

Action Potentials↗
PubMed1975

The relative sensitivity of Renshaw cells to orthodromic group Ia volleys caused by static stretch and vibrations of extensor muscles.

1. Activity of Renshaw cells monosynaptically excited by ventral root stimulation and disynaptically excited by electric stimulation of the group Ia afferents in the gastrocnemius-soleus (GS) nerve, was recorded in precollicular decerebrate cats. The response of these units to prolonged vibration applied longitudinally to the deefferented GS muscle was then compared with that elicited by static stretch of the homonymous muscle, for comparable frequencies of discharge of the group Ia afferents. 2. Small-amplitude vibration of the GS muscle at 200/sec for one second produced a sudden increase in the discharge rate of Renshaw cells, which gradually decreased within the first 100 msec of vibration to reach steady albeit lower level than that obtained during the first part of vibration. The response of the Renshaw cells during the first 100 msec of vibration (phasic response) and that elicited during the last 500 msec of vibration (tonic response) were evaluated for different frequencies of sinusoidal stretch. The mean increase in the firing frequency per imp./sec in the Ia afferents was also calculated using the total one-second period. 3. The response of Renshaw cells to muscle vibration increased with the frequency of vibration and, over the value of 10/sec, appeared to be linearly related to the frequency of the input, at least up to the frequency of 150/sec. Since vibration was of sufficient amplitude to produce driving of all the primary endings of muscle spindles, the responses were expressed as mean increases in the discharge rate of Renshaw cells per average impulse/sec in the Ia afferents. The discharge of the Renshaw cell increased on the average by 2.90 and 1.08 imp./sec per each imp./sec in the Ia afferents during the phasic and the tonic component of the response respectively, while the response calculated during the whole period of vibration corresponded on the average to 1.45 imp./sec per each imp./sec in the Ia afferents. 4. The Renshaw cells tested above responded also with increasing frequencies of discharge to increasing levels of static extension of the GS muscle. In particular the discharge frequency of Renshaw cells was on the average linearly related to muscle extension, at least for values ranging from 0 to 8 mm. The mean increase in discharge rate as a function of the static extension corresponded on the average to 0.89 imp./sec/mm. Since the discharge rate of the primary endings of muscle spindles recorded from the deefferented GS muscle increased by 2.62 imp./sec/mm, it appears that the mean increase in the discharge rate of Renshaw cells as a function of static extension corresponded to 0.34 imp./sec per each imp./sec in the Ia afferents.

Action Potentials↗
PubMed1975

The sensitivity of Renshaw cells to velocity of sinusoidal stretches of the triceps surae muscle.

1. The electrical activity of Renshaw cells monosynaptically excited by ventral root stimulation and disynaptically excited by electric stimulation of the group I afferents in the GS nerve has been recorded and their response to individual sinusoidal stretches of the deefferented GS muscle tested for different amplitudes and durations of the stimulus. 2. The experimental data indicate that the Rensahw cell responses are not only length dependent but also rate dependent. This finding indicates that the same Renshaw cells receive recurrent collaterals of both tonic and phasic motoneurons. 3. The observation that the discharge of Renshaw cells is particularly sensitive to the velocity of stretch suggests that the recurrent collaterals of large phasic motoneurons, which are recruited during high velocity stretches, exert a stronger excitatory action on Renshaw cells than do axon collaterals of the smaller tonic motoneurons, which are selectively stimulated during low velocity stretches.

Action Potentials↗