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V J Wilson

Publications and source records attributed to V J Wilson.

At least 73 records · Page 4Linked to original sources
PubMed1982

Dynamic properties of vestibular reflexes in the decerebrate cat.

Vestibulocollic (VCR) and vestibulo-ocular (VOR) reflexes were studied during angular rotation in the horizontal plane in precollicular decerebrate cats. Angular position was modulated by sinusoids or sums of sinusoids with frequencies ranging from 0.05 to 5 Hz. Reflex motor output was measured by recording electromyographic (EMG) activity of the lateral rectus and dorsal neck muscles and discharge of abducens motoneurons. Measured with respect to input angular acceleration VCR motor output displayed a second order lag at low frequencies, bringing mean EMG phase (-136 degrees) and gain slope (-35 dB/decade) close to those of an angular position signal at 0.2 Hz. At higher frequencies the lag was counteracted by a second order lead bringing mean phase (-52 degrees) and gain slope (-5.6 dB/decade) back close to those of an angular acceleration signal at 3 Hz. By contrast, mean phase (-113 degrees to -105 degrees) and gain slope (-21 to -28 dB/decade) of the VOR motor output remained close to those of an angular velocity signal across the entire frequency range. The data suggest that neural pathways producing the VCR receive selective input from "irregular type" horizontal semicircular canal afferents which provide one lag and one lead in the overall transfer function while the other lag and lead are produced by central pathways. Transection of the medial longitudinal fasciculus (MLF), which eliminates all of the most direct (three neuron) arcs of the horizontal VCR, did not cause any detectable change in the horizontal VCR at either low or high frequencies. Reductions in overall gain occurred in some cases but these could be attributed to damage to axons outside the MLF. Less direct pathways, probably including vestibuloreticulospinal pathways, are thus able to produce both the low-frequency, phase-lagging and high-frequency, phase-leading components of the horizontal VCR.

Afferent Pathways↗
PubMed1981

Cervical input to vestibulocollic neurons.

Extracellular responses of vestibulospinal neurons projecting to neck segments (vestibulocollic neurons) to stimulation of cervical afferents were studied in decerebellate cats anesthetized with chloralose or decerebrated intercollicularly. These neurons were antidromically activated by microstimulation in the C2 ventral horn ipsilateral or contralateral to the vestibular nuclei. Contralateral neck afferents produce in vestibulocollic neurons the same responses they produce in other vestibulo-spinal neurons, although the response (early excitation, inhibition) which predominates varies with type of preparation. In intercollicular decerebrate cats, the main effect of stimulating the contralateral C2 ganglion was inhibition (latency greater than or equal to 6 msec), often followed by late excitation. Early excitation, at a latency less than 6 msec, was rarely seen, although it occurred in half the vestibulospinal neurons projecting to the cervical enlargement. In contrast to the results in decerebrate cats, stimulation of the contralateral C2 ganglion produced early excitation in over one-third of the vestibulocollic neurons studied in chloralose-anesthetized cats. Results on vestibulocollic neurons were similar whether the cells projected ipsilaterally or contralaterally, or whether or not the cells also projected to the cervical enlargement (branching neurons). The influence of cervical afferents on vestibulocollic neurons demonstrates supraspinal paths by which cervical afferents may act upon the neck and might modify vestibular reflexes of the neck.

Afferent Pathways↗
PubMed1979

Comparison of dynamic properties of canal-evoked vestibulospinal reflexes of the neck and forelimb in the decerebrate cat.

The responses of neck and forelimb muscles to sinusoidal polarization of the horizontal canal nerve were compared by recording from these muscles simultaneously. Contrary to results on the vestibulocollic reflex, the central phase lag in the vestibulo-forelimb reflex increases with increasing frequencies up to 3 Hz. This demonstrates a difference in the organization of vestibular-driven pathways to neck and forelimb muscles.

Animals↗
PubMed1979

Analysis of vestibulocollic reflexes by sinusoidal polarization of vestibular afferent fibers.

1. Canal vestibular-neck (vestibulocollic) reflexes have been studied in decerebrate cats by applying modulated polarizing current to individual ampullary nerves, usually the horizontal nerve. 2. Computer-generated stimuli sometimes consisted of sine or square waves at frequencies of 0.01--5 Hz. More often we used a compound wave form of nine superimposed sinusoids within an available frequency range of 0.009--6.11 Hz. The frequencies used were odd, relatively prime multiples of a base frequency selected to minimize distortion or interaction of responses. The response to each of the nine stimulating frequencies could be obtained in subsequent data analysis. 3. Responses to these stimuli were studied by recording the EMG of contralateral neck muscles and extracellular activity of second-order neurons. These neurons were identified by their monosynaptic responses to single-shock stimulation of ampullary nerves. 4. EMG was modulated sinusoidally. Below 0.1 Hz the response was variable, most likely due to differences in the preparations. In the frequency range of 0.1--0.4 Hz there was usually a phase lag, which decreased with incresing frequency and often reversed to a lead at 3 and 6 Hz. Gain decreased from the lowest frequencies, occasionally with an upturn at 3 or 6 Hz. 5. Second-order neuron firing was approximately in phase with the stimulus at the lowest frequencies. Phase advanced with increasing frequency to a lead of 30--50 degrees at 6 Hz. Gain generally increased with frequency. 6. By recording simultaneously from muscle and from second-order neurons, or by comparing the mean behavior of the two, it was possible to determine the central phase lag and gain of the vestibulocollic reflex. The lag was variable at low frequencies, had an average of 50 degrees at 0.18 Hz, and decreased to 20 degrees at 6 Hz. These results are comparable to those obtained by others using natural stimulation at frequencies of 1.0 Hz and below, and provide new information about the behavior of the central processer at higher frequencies. 7. The medial vestibulospinal tract (MVST), which contains the axons of crossed second-order vestibular neurons, was transected in six experiments. In agreement with previous workers there was no effect on phase at frequencies up to 0.4 Hz. There was also no selective effect of phase or gain at the higher frequencies. This shows that the disynaptic pathways in the MVST do not play any role that cannot be taken over by parallel pathways.

Animals↗
PubMed1978

Properties and connections of cat fastigiospinal neurons.

1. Neurons in the cat fastigial nucleus that project to the upper cervical spinal segments (fastigiospinal neurons) were fired by antidromic stimulation of the contralateral spinal cord. Dye ejection from the recording electrode was used to show that most neurons were in the rostral half of the fastigial nucleus. 2. Fastigiospinal neurons can be excited and/or inhibited by stimulation of forelimb and hindlimb nerves and by stimulation of the vestibular nerve. These inputs converge on many neurons. 3. Antidromic microstimulation was used to trace fastigiospinal axons to the vicinity of motor nuclei in in C2-C3. 4. The rostral fastigial nucleus was stimulated in preparations with the medial longitudinal fasciculus transected by a wide lesion that impinged on the medial reticular formation in the caudal medulla, to eliminate some potential axon reflexes. Short-latency EPSPs were recorded in some trapezius and biventer-cervicis motoneurons. In many cases there was little or no occlusion between these EPSPs and others evoked by stimulation of the vestibular nerve ipsilateral to the motoneurons. 5. Movement of the stimulating electrode and placement of this electrode lateral to the fastigial nucleus show that the zone from which low threshold EPSPs can be evoked is localized. 6. Latency measurements and lack of temporal facilitation with double shocks suggest that the EPSPs are monosynaptic. The evidence suggests that they are caused by fastigiospinal fibers terminating on motoneurons.

Animals↗
PubMed1978

Properties of central vestibular neurons fired by stimulation of the saccular nerve.

In 4 cats all vestibular afferents in one labyrinth except those innervating the saccular macula were transected and allowed to degenerate. 23--53 days after the initial surgery the central connections of the remaining saccular nerve were studied under chloralose anesthesia. Stimulation of the saccular nerve evoked N1 field potentials in the ipsilateral lateral and descending vestibular nuclei; little or no field potential activity was seen in the superior nucleus. The distribution of field potentials overlapped with that of neurons of origin of the vestibulospinal tracts. Forty-two neurons in the ipsilateral vestibular nuclei, many in the lateral nucleus, responded, often monosynaptically, to stimulation of the saccular nerve with single or double shocks; some of the neurons projected to the spinal cord. All saccular-fired neurons were tested for commissural actions by stimulation of the contralateral vestibular nerve. Many were facilitated, almost none were inhibited. In agreement with earlier work, we conclude that commissural inhibition may be a property of the canal system only.

Afferent Pathways↗
PubMed1978

Frequency-response analysis of vestibular-induced neck reflex in cat. II. Functional significance of cervical afferents and polysynaptic descending pathways.

1. Three major inputs to cervical motoneurons were analyzed with frequency-response methods in decerebrate and unanesthetized cats: the afferent system including the gamma-loop, the vestibulospinal tract, and some polysynaptic tract that transmits vestibular influences in the vestibulocollic reflex. 2. The dorsal roots C1-C4 were cut in order to open the feedback loop through the gamma-fiber spindle-afferent system. No effects were observed on the gain and the phase lag of motor-unit response. However, the DC components of the response were consistently decreased by deafferentation both in motor-unit and compound EMG responses. Firing of muscle spindle afferents was modulated during oscillation of the turntable. The majority of responses of spindle afferents was in phase with the simultaneously recorded extrafusal motor activity. These results indicate the existence of alpha-gamma coactivation in the vestibulocollic reflex. 3. Intracellular recording from cervical motoneurons showed that monosynaptic EPSP's were induced by dorsal root stimulation. By far the larger EPSP's, however, were observed with latencies of 10-15 ms, showing the existence of more powerful polysynaptic routes. It is postulated that the cervical afferent system controls the gain of the reflex by changing the number of motor units participating in the vestibulocollic reflex through some polysynaptic pathways, and that the afferent system scarcely changes, the gain or phase lag of individual motor units through a short stretch reflex loop. 4. The medial vestibulospinal tract in the MLF was interrupted, but no effects were detected on the dynamic characteristics of the frequency response. This shows the existence of other effective descending pathways which function as an integrator. 5. Remarkable phase advances were induced by intravenous infusion of Nembutal. This suggests that the Nembutal decreased the activity of the polysynaptic pathways and that the neural integrator, composed of polysynaptic networks, was prevented from fulfilling its ordinary function.

Animals↗
PubMed1977

Properties of vestibular neurones projecting to neck segments of the cat spinal cord.

1. Vestibular neurones projecting to the upper cervical grey matter (vestibulocollic neurones) were identified by localized microstimulation in the C3 segment of the cat spinal cord.2. The neurones were found in the lateral (Deiters'), medial and descending nuclei bilaterally and projected to the spinal cord in the lateral and medial vestibulospinal tracts (LVST and MVST). Ipsilateral axons of Deiters' neurones were mostly in the LVST, axons of medial and descending neurones in the MVST; a few Deiters' neurones had axons in the MVST; some descending neurones had axons in the LVST. Most axons of contralateral neurones were in the MVST.3. The axons of 62% of ipsilateral vestibulocollic Deiters' neurones not only gave off a collateral to C3, but also extended as far as the cervical enlargement (;branching'); some of these neurones projected as far as the upper thoracic cord, almost none to the lumbar cord. Ipsilateral descending nucleus neurones branch in the same fashion, but there is no branching in the relatively small medial nucleus population.4. A large majority of vestibulocollic neurones receive monosynaptic excitation from the ipsilateral labyrinth and a number are inhibited by stimulation of the contralateral labyrinth (commissural inhibition). It is possible that commissural inhibition acts on a broad population of vestibular neurones involved in the control of eye, head and trunk movement.5. Vestibulocollic neurones do not make up a homogeneous population acting only on the neck. Instead it is likely that subpopulations, for example branching and non-branching neurones, have different functions.

Animals↗
PubMed1977

Synaptic actions of individual vestibular neurones on cat neck motoneurones.

1. Unitary synaptic potentials evoked by the activity of single vestibulocollic neurones were recorded by means of spike-triggered signal averaging in neck extensor motoneurones of decerebrate cats. Properties of the vestibulocollic neurones which produced the potentials were examined.2. Vestibulocollic neurones were first identified as projecting to the C3 grey matter by antidromic microstimulation within the C3 extensor motoneurone pool. The spontaneous or glutamate-driven activity of the vestibulocollic neurones was then used to trigger the averaging computer. In this way ten inhibitory and two excitatory neurones were identified (20% of neurones tested).3. Action potentials in local branches of vestibulocollic neurones were usually recorded in the vicinity of motoneurones. Mean orthodromic conduction time from the foot of the extracellular spike, recorded in the vestibular nuclei, that triggered the averager was 0.72 msec. Mean synaptic delay was 0.4 msec.4. I.p.s.p.s had a mean time to peak of 0.81 msec and were readily reversed by injection of hyperpolarizing current. These data, together with the shape indices of i.p.s.p.s indicate that they are generated proximally on motoneurones.5. All vestibulocollic neurones making synapses with motoneurones were monosynaptically driven by stimulation of the ipsilateral vestibular nerve. Four out of seven tested were inhibited by stimulation of the contralateral vestibular nerve (commissural inhibition).6. Two excitatory neurones were located in Deiters' nucleus or on the Deiters'-descending border. Inhibitory neurones were found relatively medially in the vestibular complex in the medial, descending and Deiters' nuclei.7. Vestibulocollic neurones acting on motoneurones were tested for axon branching to more caudal levels of the spinal cord with electrodes placed at C5-7. Both of the excitatory and two out of nine inhibitory neurones branched.

Action Potentials↗