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V J Wilson

Publications and source records attributed to V J Wilson.

At least 55 records · Page 3Linked to original sources
PubMed1987

Modulation by eye position of neck muscle contraction evoked by electrical labyrinthine stimulation in the alert cat.

Modulation of vestibulo-spinal reflexes by gaze is a model system for studying interactions between voluntary and reflex motor activity. In the alert cat, the EMG of Splenius and Obliquus capitis muscles increases with ipsilateral gaze eccentricity during spontaneous eye movements. Labyrinth stimulation by current pulses evokes EMGs with latencies consistent with a three neuron vestibulocollic pathway. The amplitude of evoked activity increases with eye position. The directions in which eye movements increase EMG was usually the same for both spontaneous and induced EMG activity, namely, horizontal and ipsilateral. However, sometimes the increase in spontaneous EMG occurred with horizontal eye position, whereas the induced EMG changed with vertical eye position. Spontaneous and evoked EMG are then modulated by different eye position signals. Command signals reflecting eye position probably reach two different types of neurons in the vestibulo-collic pathway, most likely secondary vestibular neurons and neck muscle motoneurons.

Animals↗
PubMed1987

Dynamics and directional sensitivity of neck muscle spindle responses to head rotation.

With the use of floating electrodes we recorded from the C2 dorsal root ganglion of decerebrate cats during sinusoidal and trapezoidal head rotation. Fifty-one spontaneously firing afferents were identified as muscle spindle endings. Some were identified by their excitatory response to injection of succinylcholine, others by the similarity of their behavior to that of endings excited by the drug. Because afferent input to the ganglion was restricted by sectioning most nerve trunks, most spindle endings were presumably located in ventral and ventrolateral perivertebral muscles. The firing of each spindle afferent was modulated most effectively by tilting the head in a specific direction; this direction was termed its response vector. Responses to sine waves and trapezoids were then studied with stimuli oriented as closely as possible to the vertical plane of this vector. Most spindle afferents could be classified in one of two categories. Those with high gain, pronounced nonlinearity, and high dynamic index were called type A. Those classified as type B had low gain, a fairly linear response, and low dynamic index. In response to small (0.5 degrees) stimuli, type A endings had phase leads of approximately 40 degrees at frequencies of sinusoidal stimulation of 0.02-0.1 Hz, increasing to approximately 80 degrees at 4 Hz; with larger (2.5 degrees) stimuli, phase was advanced by an additional 10-20 degrees at all frequencies. Phase of type B responses was less advanced than that of type A responses. Gain slopes of the two types of endings were similar. Bode plots of spindle afferents strongly resembled those of upper cervical neurons whose activity is modulated by head rotation. Each spindle afferent had a response vector whose direction remained stable with time, different frequencies of stimulation, and different stimulus amplitudes. The distribution of response vectors covered approximately 270 degrees, with a gap near nose down pitch. Changing initial head position usually had little effect on the direction of an afferent's response vector or on response dynamics. However, stimulation far from the best plane could transform a type A into a type B response. This raises the possibility that type B receptors could be type A receptors best stimulated by yaw and with only low sensitivity to stimulation in vertical planes. Type A receptors have all the properties of spindle primaries. The identification of type B receptors remains uncertain, because they may include secondary afferents as well as primaries stimulated far from their best three-dimensional vector.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Directional sensitivity of, and neck afferent input to, cervical and lumbar interneurons modulated by neck rotation.

In response to neck rotation of decerebrate, acutely labyrinthectomized cats, interneurons in C4 respond far more frequently to nose-up than to nose down pitch, whereas the reverse is true for interneurons in L3-L4. These directional sensitivities resemble the pattern of extensor excitation in the tonic neck reflex. C4 neurons receiving short latency excitation from the C2 dorsal root ganglion due to intraspinal pathways have a distribution of directional sensitivities to pitch stimuli that is similar to that of the whole population. The directional sensitivities of C4 neurons with late excitation, which may be due to supraspinal loops, are more broadly distributed.

Animals↗
PubMed1986

Spatial organization of neck and vestibular reflexes acting on the forelimbs of the decerebrate cat.

EMG recording was used to study the spatial organization of vestibular and tonic neck reflexes acting on forelimb and shoulder muscles of the decerebrate cat. Neck reflexes were studied in preparations with intact labyrinths as well as those with acute or chronic labyrinthectomies. Reflexes were described by response vectors whose orientation component is aligned with the optimal excitatory direction of tilt or head rotation. A muscle's vector orientation remained reasonably stable over a period of hours, although there was sometimes drift at the beginning or end of an experiment. Orientation of muscle response vectors did not change systematically with stimulus frequency of 0.05-2.0 Hz. For vestibular reflexes this is so, although their dynamics are consistent with convergent input from semicircular canals and otolith organs. Regardless of the preparation, a consistent reflex pattern emerged. Vestibular reflexes are characterized by response vector orientation near ear-down roll. Neck vector orientation lies in the opposite direction from the vestibular vector but typically lies further from the roll plane: Nose-up pitch is excitatory for the shoulder muscles supra- and infraspinatus, and for the medial and lateral heads of triceps, whereas nose-down pitch excites the long head of triceps. Our results generally agree with the pattern proposed by Roberts (28) for neck reflexes but disagree in part with his proposed pattern of vestibular reflexes; we did not see the expected consistent excitation by nose-down pitch.

Animals↗
PubMed1986

Responses of interneurons in the cat cervical cord to vestibular tilt stimulation.

The responses of interneurons in the cervical spinal cord of the decerebrate cat to whole-body tilt were studied with a goal of identifying spinal elements in the production of forelimb vestibular postural reflexes. Interneurons both in the cervical enlargement and at higher levels, from which propriospinal neurons have been identified, were examined, both in animals with intact labyrinths and in animals with nonfunctional semicircular canals (canal plugged). Most cervical interneurons responding to tilt respond best to rotations in vertical planes aligned within 30 degrees of the roll plane. Two to three times as many neurons are excited by side-up roll tilt as are excited by side-down roll. In cats with intact labyrinths, most responses have dynamics proportional either to (and in phase with) the position of the animal or to a sum of position and tilt velocity. This is consistent with input from both otolith organs and semicircular canals. In animals without functioning canals, the "velocity" response is absent. In a few cells (8 out of 76), a more complex response, characterized by an increasing gain and progressive phase lag, was observed. These response dynamics characterize the forelimb reflex in canal-plugged cats and have been previously observed in vestibular neurons in such preparations.

Animals↗
PubMed1985

Body position with respect to the head or body position in space is coded by lumbar interneurons.

In decerebrate cats, we have studied the response of neurons in the L3-L6 segments of the spinal cord to stimulation of neck and vestibular receptors. Neck receptors were stimulated by head rotation in labyrinthectomized cats or by body rotation with the head fixed in labyrinth-intact cats. Vestibular receptors were stimulated by whole-body tilt in the latter preparation. Most neurons were located outside the motoneuron nuclei and were arbitrarily classified as interneurons. Combinations of roll and pitch stimuli at frequencies of 0.1 or 0.05 Hz were used to determine the horizontal component of the polarization vector, i.e., the best direction of tilt, for each neuron. Two types of stimuli were used; rotation of a fixed angle of tilt around the head or body ("wobble," Ref. 22) or sinusoidal stimuli in several planes. Polarization vectors of the responses to neck stimulation were widely distributed; different neurons responded best to roll, pitch, and angles in between. For every neuron, the amplitude of the response decreased as the cosine of the angle between the direction of maximal sensitivity and the plane of the stimulus. The direction of the vector remained stable as the frequency of stimulation was varied. Neurons with different vectors had similar dynamics that resembled those of cervical interneurons (27). Many neurons responded to both neck and vestibular stimulation, although the vestibular response usually had a much lower gain. Neck and vestibular vectors were approximately opposite in direction. We suggest that neck responses originate in receptors, probably spindles, in perivertebral muscles. Each of these muscles presumably is best stretched by a particular direction of pull. It seems likely that convergence from receptors in selected muscles determines the direction of a spinal neuron's vector. Vestibular responses probably are due mainly to activity in otolith afferents.

Animals↗
PubMed1985

Tonic neck reflex of the decerebrate cat: a role for propriospinal neurons.

In decerebrate, acutely labyrinthectomized cats we used neck rotation to study the role of direct upper cervical afferents to the cervical enlargement and of cervical and lumbar propriospinal neurons in the tonic neck reflex. Interruption of the dorsal columns between C4 and C5 had no qualitative effect on the dynamics of the reflex although gain usually increased. Direct upper cervical afferents to the cervical enlargement therefore have no unique role in producing the reflex. Many medially located propriospinal neurons in C4 were modulated by neck rotation. About 40% had axons, mostly crossed, that terminated in the cervical enlargement. The others projected more caudally, some as far as L3-L4 or even the lumbar enlargement. For a population of C4 neurons, including propriospinal neurons, we measured the response vector with combinations of roll and pitch stimuli. These vectors ranged from pitch to roll. Many propriospinal neurons in L3-L4, projecting to the lumbosacral enlargement, were also modulated by neck rotation with a variety of response vectors. Some of these neurons had an ascending projection. As in previous experiments, C4 neurons were modulated by neck rotation after spinal transection rostral to the C1 dorsal root entry zone; a wide variety of response vectors was observed. In contrast, almost no modulated L3-L4 neurons were found in the same experiments. The results suggest a role for propriospinal neurons in the tonic neck reflex. They also demonstrate that responses of lumbar neurons to neck rotation are much more dependent on supraspinal pathways than are those of cervical neurons.

Animals↗
PubMed1984

Directional sensitivity of neurons in the lumbar spinal cord to neck rotation.

A combination of roll and pitch stimuli was applied to the head of decerebrate, labyrinthectomized cats to determine the direction of maximal sensitivity ('vector') of lumbar neurons to neck rotation. Some neurons were best modulated by pitch, others by roll or by intermediate stimulus planes. Among modulated neurons were propriospinal neurons activated antidromically from the lumbosacral enlargement.

Animals↗
PubMed1984

The effect of GABA on the terminations of vestibulospinal neurons in the cat spinal cord.

Although GABA and piperidine-4-sulphonate depolarize Ia afferent terminations in the lumbar spinal cord by activation of bicuculline-sensitive GABA receptors, no evidence was obtained for a bicuculline-sensitive alteration by either GABAmimetic of the excitability of vestibulospinal terminations. This suggests that the terminal arborizations of vestibulospinal fibers, unlike their cell bodies, are devoid of GABA receptors having properties similar to those on either central neuron cell bodies, primary afferent cell bodies or their central terminations.

Animals↗
PubMed1984

Interaction of tonic neck and vestibular reflexes in the forelimb of the decerebrate cat.

Tonic neck reflexes, studied with EMG recording, have similar dynamics in forelimb extensor muscles of acutely labyrinthectomized cats, and in cats with intact labyrinths. The reflex occurs more frequently in the latter and its gain is higher. In intact preparations we evoked vestibular and tonic neck reflexes separately or in combination, at frequencies of 0.05-0.5 Hz. As expected from earlier work, the two reflexes oppose each other and frequently cancel; the two reflexes add linearly.

Animals↗
PubMed1984

Tonic neck reflex of the decerebrate cat: response of spinal interneurons to natural stimulation of neck and vestibular receptors.

In order to investigate the neural basis of the tonic neck reflex, we studied the response of neurons in the cervical spinal cord of decerebrate, paralyzed cats to neck rotation about the longitudinal axis (roll), to vestibular stimulation produced by roll tilt, and to a combination of these stimuli. Most neurons were outside the motoneuron nuclei and were arbitrarily classified as interneurons. Three types of preparation were used--one with intact labyrinths, one acutely labyrinthectomized, and one with acute spinal transection. The activity of 115 neurons recorded extracellularly was modulated by sinusoidal neck rotation in the range 0.02-4 Hz; their behavior was sufficiently linear for sinusoidal analysis. The phase and gain of the responses of neurons in all three preparations were similar except that the absolute gain in cats with intact labyrinths was higher than that of the others. The location of neurons in segments C4-C8 was mainly in laminae 7-8. Some neurons were excited by rotation of the chin to the ipsilateral side (type I) and others by contralateral chin rotation (type II). The dynamic behavior of type I and type II neurons was the same; phase was flat over most of the frequency range and close to the phase of peak neck rotation, while gain enhancement occurred at higher frequencies. This behavior was similar to that of the neckforelimb reflex evoked in unparalyzed intact-labyrinth and labyrinthectomized cats. In cats with intact labyrinths, vestibular input to neurons whose activity was modulated by the neck stimulus was studied using whole-body roll tilt. Many neurons received otolith input; some received canal input. Neck and vestibular inputs to spinal neurons always had opposite polarities (complementary inputs). Thus, type I neurons were always excited by tilt to the ipsilateral side (ipsilateral ear down) while type II neurons were excited by tilt to the contralateral side. Combined neck and vestibular stimulation indicated that the dynamic behavior of neurons was determined by a linear summation of the responses to these stimuli. Interaction of neck and vestibular input at the neuron level was similar to that observed previously at the reflex level in forelimb extensor muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

'Vomiting center' reanalyzed: an electrical stimulation study.

Electrical stimulation of the brainstem of 15 decerebrate cats produced stimulus-bound vomiting in only 4 animals. Vomiting was reproducible in only one cat. Effective stimulating sites were located in the solitary tract and reticular formation. Restricted localization of a 'vomiting center', stimulation of which evoked readily reproducible results, could not be obtained.

Animals↗
PubMed1983

Responses of different compartments of cat's splenius muscle to optokinetic stimulation.

The EMG in different compartments of the splenius muscle was recorded simultaneously with the horizontal electrooculogram in the alert, head restrained and head freed cat during optokinetic and vestibular stimulation. All compartments of the splenius muscle behaved qualitatively similarly. Tonic and phasic muscle activity was closely related to eye position.

Animals↗
PubMed1983

Response of cat semicircular canal afferents to sinusoidal polarizing currents: implications for input-output properties of second-order neurons.

1. We studied the response of cat vestibular afferents, most likely innervating the semicircular canals, to sinusoidal polarizing currents applied to an electrode implanted near the horizontal ampulla. 2. Electrode implantation abolished responses to natural stimulation and reduced the level of resting activity compared to a population of afferents from unimplanted animals. The distribution of coefficients of variation of resting activity was, however, similar to that seen when the labyrinth is intact. 3. Many fibers were modulated sinusoidally by polarizing currents in the frequency range 0.175-4 Hz. Phase was mainly constant and typically led stimulus negativity by approximately 14 degrees, although about half the regular fibers had a phase lead that increased with frequency. Mean sensitivity (spikes X s-1 X microA-1) of regular and irregular fibers increased by a factor of about 1.5 over the frequency studied. Absolute sensitivity was about 7 times higher for irregular than for regular fibers. The overall behavior of the afferents could be well described by a transfer function in the form, sk, with 0 less than k less than 1. 4. We compared the response of afferent fibers to sinusoidal current with the response of second-order neurons studied under similar conditions in earlier experiments (15, 23). While the slopes of the sensitivities were similar, second-order neurons developed a phase advance over afferents at frequencies around 1 Hz. This difference in dynamics can be described by a transfer function in the form tau S + 1, with tau = 12 ms. This predicts that second-order neurons can develop a phase lead of about 25 degrees with respect to afferents at 6 Hz, a frequency still in the physiological range. It remains to be determined whether this applies to a particular subset of second-order neurons contributing to vestibulocollic reflexes.

Afferent Pathways↗
PubMed1983

Dynamics of neck-to-forelimb reflexes in the decerebrate cat.

We have studied the neck-to-forelimb reflex evoked by head rotation around the longitudinal axis (roll) in the long and medial heads of triceps brachii of decerebrate, acutely labyrinthectomized cats. Reflexes were measured by recording mass electromyogram (EMG). As expected from the work of others, they were reciprocal in the two limbs, with excitation in the limb toward which the chin rotates. The reflex was sufficiently linear for a sinusoidal analysis. Although there was sometimes adaptation at stimulus frequencies of 0.1 Hz and below, response phase at these frequencies was usually in phase with position, and gain was flat. At higher frequencies there was some sensitivity to the velocity of the stimulus: gain increased with a slope of 10 dB/decade and phase advanced in some cats but not in others. Gain at low frequencies of head rotation, expressed as percent modulation of EMG, was typically 1%/deg or less. Reflexes evoked by head rotation in triceps and in the neck extensor splenius capitis have different dynamics. It remains to be determined whether this difference is due to activation of different receptors. We compared the dynamics of roll reflexes evoked by stimulation of neck receptors with those of vestibular reflexes evoked by tilt of the whole animal (23). Taking into account dynamics and gain, the two reflexes should cancel at low frequencies, as predicted by others. Above 0.2 Hz, cancellation becomes less effective.

Animals↗
PubMed1983

Vestibular-induced vomiting after vestibulocerebellar lesions.

Vestibular stimulation, by means of sinusoidal electrical polarization of the labyrinths of decerebrate cats, can produce vomiting and related activity resembling that seen in motion sickness. The symptoms include panting, salivation, swallowing, and retching as well as vomiting. These symptoms can be produced in cats with lesions of the posterior cerebellar vermis. In contrast to a previous proposal by Wang and Chinn in 1956, we suggest that a transcerebellar pathway from the vestibular apparatus through the nodulus and uvula to the 'vomiting center' is not essential for vestibular-induced vomiting and, by analogy, for the occurrence of many symptoms of motion sickness.

Animals↗
PubMed1982

Localization of proprioceptive reflexes in the splenius muscle of the cat.

Activity of the cat splenius muscle was modulated by sinusoidal rotation of the head around the C1-C2 joint in decerebrate cats with labyrinth intact or with all semicircular canals plugged, or, in one intact and alert cat, by rotation of the body with the head fixed in space. EMG modulation, recorded from the areas of splenius innervated by the C1-C4 nerves, was due to the cervicocollic reflex. Modulation was not uniform, but decreased with progressively more caudal recording locations; with stimuli of small amplitude it was often possible to obtain modulation of the rostral part of the muscle only. The results demonstrate localization of proprioceptive reflexes, including the stretch reflex, within the splenius muscle.

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