Biomedical subjects

J D Brooke

Publications and source records attributed to J D Brooke.

At least 37 records · Page 2Linked to original sources

PubMed1996

Mechanisms within the spinal cord are involved in the movement-induced attenuation of an H reflex in the dog.

1. H reflexes were elicited in the second interosseous muscle of the hindpaw of the anesthetized dog during passive rotation of the shank about the ipsilateral or contralateral knee. Reflexes sampled at four points in the cycle of movement were compared with stationary controls. For both the ipsilateral and contralateral limb manipulations, reflexes were significantly reduced (P < 0.05) across the cycle of movement. Position-related modulation of the reflex amplitude was not detected (P > 0.05) in either instance. 2. The experiments were then repeated after the spinal transection of each animal at the level of T13. Passive rotation about either the ipsilateral or contralateral knee significantly attenuated (P < 0.05) the H reflex across a cycle of movement in the spinal dog. There was little difference in the amount of inhibition produced by the movement between the intact and spinal animals. On average, the reflex was attenuated 29 +/- 2.4% (mean +/- SE) in the intact animals and 32 +/- 2.1% in the spinal animals. 3. It is concluded that passive rotation about the knee of either leg leads to suppression of the H reflex of the second interosseous muscle both in the ipsilateral, moving leg and the contralateral, stationary one. This reflex suppression occurs across the cycle of movement. The mediating circuitry lies within the spinal cord, caudal to T13.

Animals↗

PubMed1995

Movement-induced depression of soleus H reflexes is consistent in humans over the range of excitatory afferents involved.

The presumption that the H reflex arises exclusively from Ia afferent discharge has been challenged. If the reflex is comprised of many afferent responses, then movement-induced H reflex inhibition witnessed at one point in the recruitment curve may be quite different from the inhibition at another point in the curve. H reflex recruitment curves were constructed for three subjects during passive pedalling, isolated knee rotation and isolated hip rotation. Compared to control recruitment curves, these curves were reduced across the full spectrum of stimulus intensities. This suggests one of two possibilities: (1) all afferents contributing to the H reflex are subject to the same source and modality of inhibition; or (2) there is only one afferent type contributing to the reflex.

Adult↗

PubMed1995

Long-lasting conditioning of the human soleus H reflex following quadriceps tendon tap.

Percussion of the quadriceps tendon was used to test the hypothesis that knee extensor muscle spindle discharge initiates down-regulation of the gain of the soleus H reflex. Seven subjects participated. Soleus H reflex magnitude was observed for up to 15 s, following conditioning tendon taps of 60 N or 80 N force and 10 ms duration, with the knee at 60 degrees or 90 degrees of flexion. The tap elicited quadriceps stretch reflexes in four subjects, with a mean latency of 42 ms. The major component of the conditioning of the soleus H reflex was significant attenuation of magnitude by 30-90% of controls, starting as early as 36 ms post-percussion and lasting as long as 3-8 s. The attenuation of reflex magnitude was evident, whichever combination of duration and force of tap was used. Preceding and/or following this inhibition, there was mild facilitation. Static stretch of quadriceps also significantly reduced soleus H reflex magnitude. These results support the spindle receptor origin for the gain attenuation seen during movement. The time course of the gain attenuation suggests a spinal route, by which the spindle discharge of the heteronymous extensor muscles initiates presynaptic inhibition of transmission through the reflex pathway.

Adult↗

PubMed1995

Mechanisms within the human spinal cord suppress fast reflexes to control the movement of the legs.

Passive locomotor-like movement induces depression of the gain of a fast conducting spinal sensorimotor path in humans. It was hypothesized that this gain control is mediated through a spinal circuit. In the first experiment, passive pedalling motion was rapidly initiated in eight able bodied subjects. Soleus H-reflexes (used to reveal the gain of the short latency stretch reflex) were recorded over the first 250 ms after the movement started. Significant depression in H-reflex magnitude was observed by 50 ms after the onset of movement. On the basis of the timing, this gain attenuation was likely mediated through a spinal circuit. In a second experiment we tested chronic quadriplegics with clinically complete lesions of the spinal cord. Of five subjects tested, three expressed the reflex and all three showed significant inhibition with passive pedalling movement (mean depression was to 39% of controls). Both the rapid onset of the gain change (Expt. 1) and the presence of movement-induced inhibition in individuals with spinal lesions (Expt. 2) provide evidence that this component of human locomotor control is located in the spinal cord. The initiating source is probably somatosensory receptor discharge due to the movement.

H-Reflex↗

PubMed1995

Long-lasting inhibition of the human soleus H reflex pathway after passive movement.

Human soleus H reflexes are attenuated during passive pedalling movements. This depression occurs within 70 ms of movement onset. We hypothesized that the reflex gain would return to control values with a similar brevity following movement. However, H reflexes sampled following a slow (10 rpm) passive pedalling movement of a single leg remained below control values for the duration of a 200 ms collection period, for all four pedal positions tested. The extent of the attenuation after movement was position dependent in a manner similar to that observed during movement. This position effect was more precisely defined by sampling reflexes 200 ms post-movement at 10 pedal crank positions. Also, the full course of reflex recovery was investigated by sampling up to 8 s post-movement at four pedal positions. Reflex gain remained reduced 1-4 s post-movement, in a position dependent manner. There was a subsequent facilitation of the reflex. Thus, following a locomotor-like movement there is sustained attenuation of the soleus H reflex. The early post-movement period is likely the continued expression of movement-induced reflex inhibition while the later period may arise from descending influences consequent to the termination of movement. Presynaptic inhibition is implicated, as reflexes still showed the gain modulation when sampled while soleus was tonically contracted, both following and during the passive movement.

Adult↗

PubMed1995

The relationship between the kinematics of passive movement, the stretch of extensor muscles of the leg and the change induced in the gain of the soleus H reflex in humans.

The gain of the H reflex attenuates during passive stepping and pedalling movements of the leg. We hypothesized that the kinematics of the movement indirectly reflect the receptor origin of this attenuation. In the first experiment, H reflexes were evoked in soleus at 26 points in the cycle of slow, passive pedalling movement of the leg and at 13 points with the leg static (the ankle was always immobilized). Maximum inhibition occurred as the leg moved through its most flexed position (P < 0.05). Inhibition observed in the static leg was also strongest at this position (P < 0.05). The increase in inhibition was gradual during flexion movement, with rapid reversal of this increase during extension. In the second experiment, the length of stretch of the vasti muscles was modelled. Variable pedal crank lengths and revolutions per minute (rpm) altered leg joint displacements and angular velocities. Equivalent rates of stretch of the vasti, achieved through different combinations of joint displacements and velocities, elicited equivalent attenuations of mean reflex magnitudes in the flexed leg. Reflex gain exponentially related to rate of stretch (R2 = 0.98 P < 0.01). The results imply that gain attenuation of this spinal sensorimotor path arises from spindle discharge in heteronymous extensor muscles of knee and/or hip, concomitant with movement.

Adult↗

PubMed1995

Amplitude modulation of the soleus H reflex in the human during active and passive stepping movements.

1. It was hypothesized that passive movement of either the whole leg or its separate segments, in a manner mimicking human gait, leads to attenuation of the soleus H reflex. It was further hypothesized that this attenuation arises from presynaptic effects. Reflex amplitudes were observed in humans during natural bipedal and unipedal stepping on the spot, during passive stepping, during passive movement of the lower limb segments about the hip, knee, and ankle individually in a stepping fashion, and during passive movement with tonic contraction of the soleus muscle. 2. In natural stepping at a cadence of 54 steps/min, the reflex means were substantially depressed in the swing phase (P < 0.01). (Means, standing control 90.1%, unipedal 8.3%, bipedal 6.9%, of maximum M wave.) During the stance phase, reflex magnitudes were mildly and significantly elevated in four of six subjects, compared with standing controls (P < 0.05). 3. For passive stepping, subjects were dorsally tilted 20 and 90 degrees (lying supine) from the vertical position, to obtain quiet electromyograms (EMGs) in the postural muscles. Recorded during natural stepping, the right leg was manipulated to match the electrogoniometer traces of the three major joints. 4. At 20 degrees of tilt of the body, mean H reflexes were significantly lower, by 26.4%, compared with the supine position (P < 0.05). During passive stepping movement of the leg at 54 steps/min, the reflex was profoundly attenuated over the entire cycle (P < 0.01). The significantly attenuated reflexes during active stepping and during passive stepping movement of the whole leg were not significantly different at the point where the limb approached full flexion in the swing phase (P > 0.48). This was the case for measurements made at either body position, 20 degrees dorsal tilt or supine. 5. Passive flexion-extension, around either the hip or the knee, significantly inhibited the mean reflex magnitude close to full flexion, at either body position (P < 0.01). Such movement around the ankle resulted in significant inhibition of the reflex in two of the four subjects (P < 0.05). The numeric sum of the reflex depression arising from the flexion-extension of the individual joints was greater than that arising from movement of the whole limb. 6. With the ankle braced, the significant reflex attenuation remained when a tonic isometric contraction of the soleus muscle was introduced. This suggests premotoneuronal mechanisms for the inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1995

Inhibition of canine H reflexes during locomotor-like rotation about the knee arises from muscle mechanoreceptors in quadriceps.

1. H reflexes were elicited in the small muscles of the foot in the canine and human during passive locomotor-like rotation of the shank about the ipsilateral knee. The movement-induced effect was similar in the two species. In the anesthetized dog, the reflex gain was reduced by 36 +/- 8.4% (mean +/- SE) on average, compared with appropriate stationary controls. Reflexes in the human were reduced during movement to 45 +/- 3.5% of their stationary control values. 2. H reflexes were elicited in the anesthetized dog during passive locomotor-like rotation about the knee and were compared with reflexes obtained with the limb stationary. Populations of mechanoreceptors were then systematically removed to ascertain which group or groups provided the sensory input that leads to the decrease in reflex gain during movement. We hypothesized that the majority of the reflex attenuation could be attributed to muscle mechanoreceptors. 3. Reflexes continued to be significantly reduced (P < 0.05) during passive movement about the knee until the muscle mechanoreceptors of the quadriceps muscle group were deactivated. The removal of input from joint receptors or cutaneous receptors did not eliminate the gain reduction induced by the passive movement. 4. It is concluded that muscle mechanoreceptors of the quadriceps muscle group provide an inhibitory input to the H reflex pathway of the dog plantar muscle when the knee is passively moved in a locomotor-like fashion. This source of inhibition likely also contributes to the soleus H reflex gain reduction in humans.

Animals↗

PubMed1993

Contralateral inhibition of soleus H reflexes with different velocities of passive movement of the opposite leg.

The research question was, do events arising from rhythmic passive movement of the human leg lead to inhibition of the H reflex pathway in the stationary leg contralateral to that movement? Further, as the angular velocity of the passive movement increases, does the contralateral reflex inhibition also increase? Stable stimulation of the tibial nerve elicited H reflexes in the EMG of soleus. Trials involved the stimulated or the contralateral leg being rotated passively in a pedalling motion, at various velocities. The controls were made with the subjects seated and relaxed. The results showed that reflex magnitudes were significantly depressed when the test limb was passively rotated at 60 rpm. in comparison to the seated control trials. Rotation of the opposite limb depressed reflex magnitudes in the test limb, which was stationary. This contralateral inhibition increased, (mean reflex magnitudes of 62.68%, 41.04%, 16.65% and 9.58% of peak-to-peak Mmax), as the velocity of rotation of the opposite limb increased (10, 30, 60, 90 rpm, respectively) (P < 0.01). The effect of movement velocity was interpreted as the result of altered sensory receptor discharge arising from the passive movement. It is concluded that contralateral sensory activity contributes to the movement-elicited afferent discharge which tunes the spinal somatosensory-motor mechanisms for human locomotion.

Adult↗

PubMed1993

The independence of premovement H reflex gain and kinesthetic requirements for task performance.

The gain of the H reflex pathway is extensively altered prior to a voluntary contraction. We hypothesized that this gain change is modulated for the kinesthetic requirements of the ensuing task. The experiment involved a simple reaction time task, in which soleus H reflexes were evoked during the final 100 msec before the electromyographic activity for simple ankle movements of low, medium and high requirement for accurate positioning of the foot. The latter two conditions involved tracking and perturbed tracking, respectively. Subjects were required to respond with a non-ballistic movement. Over the 6 subjects and tasks, before plantar flexion, mean reflex magnitudes significantly increased (P < 0.05; to 160% of control, S.D. 60%). Before dorsiflexion they decreased (to 87% of control, S.D. 10%). However, the two accuracy requirements did not significantly alter the soleus H reflex changes, before either plantar flexion or dorsiflexion (P > 0.05). We conclude that the premovement gating of the spinal route from Ia afferents to the autogenic soleus muscle is independent of the changes in the presently tested types of kinesthetic requirements for movement.

Adult↗

PubMed1993

Interaction of reciprocally induced inhibition and premotor facilitation of soleus H reflexes in humans.

During contraction of the soleus muscle, H reflex magnitude is facilitated and vibration induced, late reciprocal inhibition of H reflex magnitude is reduced. The current study investigated whether reduction of electrically evoked late reciprocal inhibition also occurs in the period immediately before movement. H reflexes were facilitated immediately prior to unconditioned plantar flexion movements and conditioning stimuli to the common peroneal nerve produced long-lasting inhibition of the H reflex in 5 subjects. Conditioning stimuli applied during premotor facilitation lead to a significant inhibition of the facilitated H reflex (P < 0.05) in 3 of the 5 subjects. The level of this inhibition was not reduced from that seen with conditioning stimuli alone. These observations suggest that peripherally induced, long-lasting inhibition from the antagonist nerve can alter the excitability of the motoneuronal pool immediately before movement in humans.

Adult↗

PubMed1993

Locomotor-like rotation of either hip or knee inhibits soleus H reflexes in humans.

Human soleus H reflexes are depressed with passive movement of the leg. We investigated the limb segment origin of this inhibition. In the first experiment, H reflexes were evoked in four subjects during (1) passive pedaling movement of the test leg at 60 rpm; (2 and 3) pedaling-like flexion and extension of the hip and the knee of the test leg separately; and (4) stationary controls. In the second experiment, with the test leg stationary, the same series of movements occurred in the opposite leg. Rotation of the hip or the knee of the test leg significantly reduced mean reflex amplitudes (p < 0.01) to levels similar to those for whole-leg movement (mean H reflexes: stationary, 71%; test leg pedaling movement, 10%; knee rotation, 15%; hip rotation, 13% [all data are given as percentages of Mmax]). The angle of the stationary joint did not significantly affect the results. Rotation of the contralateral hip significantly reduced mean reflex magnitudes. Rotation of the contralateral knee had a similar effect in three of the four subjects. We infer that a delimited field of receptors induces the movement conditioning of both the ipsilateral and contralateral spinal paths. It appears that somatosensory receptor discharge from movement of the hip or knee of either leg induces inhibition as the foundation for the modulation of H reflexes observed during human movement.

Adult↗

PubMed1992

Movement features and H-reflex modulation. I. Pedalling versus matched controls.

Modulation of soleus H-reflex magnitude over a cycle of leg movement and the adjustment of controls to account for it were explored. During pedalling, H-reflex magnitudes in all nine subjects were highest in the power producing phase and lowest in recovery. Stimulation intensity was standardized. Compared to sitting, these reflexes were significantly depressed (P less than 0.05). The sitting condition was modified in one experiment, so that the angles of the limb joints and the contraction level of soleus were matched to their values, measured at 13 equi-spaced points, around the pedal cycle. This matching resulted in some modulation of the H-reflex around the pedal cycle, when sitting. When the contraction of tibialis anterior was added to these changes to the seated control, this modulation came closer to that seen during movement. Movement-specific modulation of the reflex was now harder to identify. These data raise the question of whether the three features presently used for matching are causative in the movement modulation of the soleus H-reflex and whether they represent effects arising from centrally descending or peripheral sources.

Adult↗

PubMed1992

Movement features and H-reflex modulation. II. Passive rotation, movement velocity and single leg movement.

Modulation of soleus H-reflex magnitudes during pedalling, and their approximation when seated with appropriate joint positions and contractile activity was demonstrated in the previous paper. The present study investigated the modulation of H-reflexes during (A) pedalling movement in the absence of contractile activity, (B) different movement velocities and (C) movement of a single limb. Using a customized tandem cycle ergometer, seated subjects with trunk supported relaxed their leg muscles and allowed their legs to be rotated. Their feet were supported on the pedals with the ankle braced. Reflexes were collected at four phases in the movement cycle (with some at 13 phases) and with speeds of 5-60 revolutions per min (cycle times from 12 to 1 s). The results showed that (i) reflex magnitude substantially decreased with limb rotation (P less than 0.05). The degree of inhibition was dependent on the phase position. (ii) Increasing speed of passive rotation increased the inhibition at all positions, but was most pronounced near the fullest flexion of hip and knee. When subjects actively pedalled, the relationship between speed and inhibition remained. (iii) When the contralateral leg was moved and the target leg was stationary, crossed projection of reflex inhibition was clear. (iv) The reflex gain measured during active pedalling of one leg was similar to that observed during two legged pedalling. Again, a crossed effect from the contralateral leg could be observed. We conclude that the net influence of discharge from movement-elicited afference is inhibitory on this reflex path and that the reflex modulation during pedalling arises from overlaid sources.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Modulation of human short latency reflexes between standing and walking.

Inhibition of the magnitude of soleus muscle homonymous (H) reflexes occurs in humans when walking, compared to standing. The current study asked, (1) was the task modulation of Ia reflexes limited to soleus muscle, (2) was there support for attributing a presynaptic source to the inhibition in humans and (3) did an oligosynaptic short latency reflex show similar task modulation? In 3 subjects, H reflexes were evoked in vastus medialis and soleus, at 4 levels of contraction in the target muscle, with constant stimulus intensity when walking and standing. The reflex magnitudes in both muscles were significantly inhibited during the contractions for walking, compared to standing. Such inhibition also occurred in H reflexes of tibialis anterior muscle. An excitatory oligosynaptic reflex was then evoked in vastus medialis, through low intensity stimulation of the common peroneal nerve during walking and standing. The mean amplitudes of this reflex were not significantly different (P less than 0.05) between the two conditions, at any contraction level. The depression of quadriceps H reflexes, compared to the oligosynaptic reflexes through the same quadriceps motoneuronal pool in the same task, strongly suggested that the inhibition of H reflexes arose at other sites besides the motoneuronal cell body and proximal dendrites. We conclude that Ia H reflexes of various leg muscles of humans are inhibited when walking but that this does not generalize to the oligosynaptic short latency reflex between the anterior shank and thigh.

Adult↗

PubMed1990

Vibration insensitivity of a short latency reflex linking the lower leg and the active knee extensor muscles in humans.

The study indirectly investigated the afferent source of a human lower limb reflex that spans two joints and may link limb muscular activity during movement. Low threshold (motor nerve threshold (MT) to 1.6 MT) single, 1 msec, pulses were delivered to the common peroneal nerve at caput fibula. Heteronymous excitatory responses were observed in the elctromyogram of the knee extensor muscle vastus medialis (VM), when the latter was prior contracted. The briefest latency for the VM reflex was 24.2 msec. The distal belly and tendon of the tibialis anterior muscle were vibrated for 20 min at a frequency of 105 Hz, amplitude 1-2 mm, to inhibit the reflex potential evoked by group Ia afferent fibres from that muscle. This significantly reduced the amplitude of the group Ia mediated Hoffmann (H) reflex in TA. Such vibration did not depress the amplitude of the heteronymous reflex to VM, when initially the latter was at peak amplitude or at its mid-range for amplitude. Reflex latency, threshold, and stimulation current for peak expression suggested that group II fibres were unlikely to be the major initiators of the reflex. The results support the view that this human reflex is primarily Ib mediated.

Action Potentials↗

PubMed1990

Movement modulation of a short latency reflex linking the lower leg and the knee extensor muscles in humans.

Movement modulation of a heteronymous short latency spinal reflex was investigated with transcutaneous, low threshold, stimuli to the common peroneal nerve, during leg pedalling in humans. Electromyographic (EMG) electrodes on the skin over the quadriceps muscles revealed an excitatory response at a minimum latency of 22.8 msec. Samples were obtained at 5 phases in the cycle of pedal crank rotation, and for stimulus intensities to evoke both maximal, and submaximal, reflexes in quadriceps. Over the pedal cycle, the peak-to-peak magnitude of the reflex, in the 3 quadriceps muscles studied, was deeply modulated, including an areflexive phase. The reflex magnitude was linearly dependent on the ongoing EMG activity in quadriceps. It could be fully re-initiated if contractions were produced out of phase in pedalling. The slopes of the regression lines of reflex magnitude (as % maximum reflex) on contraction level (% maximum voluntary contraction) when pedalling (1.05 (r = 0.86, P less than 0.01], and with isometric contractions in the same subjects seated (1.03 (r = 0.69, P less than 0.01], were very similar, with similar thresholds. This contrasts with the inhibition of soleus H reflexes during human gait. The present heteronymous reflex, acting between limb segments, is modulated coincident with ongoing contraction level in the target muscle.

Adult↗

PubMed1989

Papillary mesenchymal bodies: a histologic finding useful in differentiating trichoepitheliomas from basal cell carcinomas.

To distinguish a basal cell carcinoma (BCC) from a trichoepithelioma can be difficult even for an experienced dermatopathologist. Previously reported differentiating histologic features are relative criteria that may be shared by both tumors. In a review of 30 consecutive cases each of trichoepitheliomas, keratotic BCC, and routine BCC, classic criteria were compared with papillary mesenchymal body formation. Papillary mesenchymal bodies are distinct fibroblastic aggregations that represent abortive attempts to form the papillary mesenchyme responsible for hair induction. Papillary mesenchymal bodies were observed in 93% of all trichoepitheliomas, 7% of all keratotic BCC, and 0% of all routine BCC. Hair bulb formation was observed in 30% of trichoepitheliomas and in none of the BCC. We conclude that papillary mesenchymal body formation is an easily recognizable histologic criterion that is more reliable in differentiating these two tumors than standard criteria, including epidermal connections, keratinization, calcification, foreign body reaction, fibrosis, stromal retraction, tumor mucin, ulceration, frondlike epithelial pattern, and the inflammatory response.

Basal Cell Carcinoma↗