Biomedical subjects

N Isu

Publications and source records attributed to N Isu.

33 records · Page 2Linked to original sources

PubMed1994

Coriolis effects are principally caused by gyroscopic angular acceleration.

A cause of nausea evoked by cross-coupled rotation (termed Coriolis stimulus) was determined. Subjects were provided with two types of cross-coupled rotations: neck-forward flexion (Neck Flx) and upper body-forward flexion (Body Flx) during horizontal whole body rotation at a constant angular velocity. These Coriolis stimuli were given alternatively in an experimental sequence, and the severity of the nausea they evoked was compared by the subjects. The results indicated that the same quality of nausea was evoked by a slightly higher angular velocity during Body Flx (100.5 degrees/s) than during Neck Flx (90 degrees/s). While Body Flx generated Coriolis linear acceleration several times larger than Neck Flx, both the stimuli generated a similar magnitude of gyroscopic angular acceleration in this condition. Therefore, it was inferred that the nausea evoked by a Coriolis stimulus is principally caused by gyroscopic angular acceleration.

Acceleration↗

PubMed1991

Is there a three neuron arc in the cat utriculo-trochlear pathway?

The utriculo-ocular pathway was examined in decerebrated and anesthetized cats, in which all the vestibular afferents in the labyrinth, except for those innervating the utricular (UT) macula, had been transected. The UT nerve was stimulated with tungsten electrodes which were insulated except for 200 microns at the tips. Stimulation of the UT nerve evoked a small negative (N1) potential in the vestibular nuclei, with a threshold (N1T) less than 25 microA. The stimulus evoked disynaptic EPSPs in ipsilateral abducens (AB) motoneurons. The threshold and latency of the excitatory postsynaptic potentials (EPSPs) was 1.3 x N1T and 1.2 ms, respectively, in accordance with the data of Schwindt et al. (1973). On the other hand, EPSPs with a clear rising phase and short latency, suggesting the existence of a disynaptic pathway, were never observed in any contralateral trochlear (TR) motoneurons, even when triple shocks at intensities of up to 4 x N1T were applied. This stimulus strength was strong enough to activate the UT nerve. Thus it seems very likely that a disynaptic pathway from the UT nerve to contralateral TR motoneurons, is absent or very poorly organized.

Animals↗

PubMed1991

The neuronal organization of horizontal semicircular canalactivated inhibitory vestibulocollic neurons in the cat.

1. The somatic location and axonal projections of inhibitory vestibular nucleus neurons activated by the horizontal semicircular canal nerve (HCN) were studied in anesthetized cats. Cats were anesthetized with ketamine hydrochloride and pentobarbital sodium. 2. Intracellular recordings were obtained from 11 neck extensor motoneurons which were identified by antidromic activation from the dosal rami (DR) in the C1 segment. Stimulation of the ipsilateral (i-) HCN and the ipsilateral abducens (AB) nucleus evoked IPSPs in the motoneurons. These IPSPs were fully or partially occluded when they were evoked simultaneously. 3. Intracellular recordings were obtained from 8 AB motoneurons. Stimulation of the i-HCN and the i-C1DR motoneuron pool evoked IPSPs in the AB motoneurons. These IPSPs were also partially occluded when they were evoked simultaneously, which implied that some HCN-activated neurons inhibit both i-AB motoneurons and ipsilateral neck motoneurons. 4. Unit activity was extracellularly recorded from 30 vestibular neurons that were activated monosynaptically by i-HCN stimulation. Their axonal projections were determined by stimulating the i-AB nucleus and the i-C1DR motoneuron pool. Eight neurons were activated by both stimuli, and were termed vestibulooculo-collic (VOC) neurons. Their axonal branching was examined by means of local stimulation in and around the i-AB nucleus and the i-C1DR motoneuron pool. Eighteen neurons were antidromically activated from the i-C1DR motoneuron pool but not from the i-AB nucleus. These were termed vestibulo-collic (VC) neurons. Four neurons were activated from the i-AB nucleus but not from the ventral funiculus in the C1 segment, and were termed vestibulo-ocular (VO) neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Abducens Nerve↗

PubMed1991

Vestibulo-thalamic neurons give off descending axons to the spinal cord.

Vestibulo-thalamic (VT) neurons were physiologically studied in the anesthetized cat. Forty-seven VT neurons were recorded extracellularly. More than half of the VT neurons responded monosynaptically to vestibular nerve stimulation while the others responded polysynaptically. They were activated antidromically from one or two sites in the VPL. VPM, VL, VM, SG, and PO of the contralateral thalamus. Four fifths of the VT neurons were activated from the C1 segment of the spinal cord. Half of them were also activated from the C4 segment, but none were activated from the L5 segment. It is suggested that most VT neurons project descending axons to the cervical spinal cord. Axonal branching was shown by means of systematic microstimulation in the thalamus and the ventral horn in the C1 segment. The VT neurons were mainly located in the descending vestibular nucleus.

Animals↗

PubMed1990

Localization and synaptic effects of inhibitory vestibulocollic neurons activated by the posterior semicircular canal nerve in the cat.

Cellular locations, axonal projections, and synaptic effects of inhibitory vestibulocollic (VC) neurons activated by the ampullary nerve of the posterior semicircular canal (PCN) were studied in anesthetized cats. The inhibitory VC neurons were identified by their monosynaptic responses to PCN stimulation and by their antidromic responses to stimulation of the ipsilateral (i-) and contralateral (c-) neck extensor motoneuron pools, which are inhibitory targets of the PCN. They were classified as VCi (vestibulocollic neuron sending an axon to the i-neck extensor motoneuron pool) and VCc (vestibulocollic neuron sending an axon to the c-neck extensor motoneuron pool) neurons. Neither VCi nor VCc neurons were activated antidromically by localized stimulation of the ascending medial longitudinal fasciculus (asc. MLF) or the 3rd nuclei. Their cell somata were localized in the rostral part of the descending vestibular nucleus and the ventral part of the lateral vestibular nucleus. VCi and VCc neurons produced unitary IPSPs in neck extensor motoneurons in the C1 segment.

Action Potentials↗

PubMed1990

Axonal trajectories of inhibitory vestibulocollic neurons activated by the anterior semicircular canal nerve and their synaptic effects on neck motoneurons in the cat.

Somatic location, axonal trajectories and synaptic effects of inhibitory vestibulocollic neurons which were activated by selective stimulation of the anterior semicircular canal nerve (ACN) were studied in the anesthetized cat. ACN stimulation evoked disynaptic inhibitory postsynaptic potentials (IPSPs) in neck flexor motoneurons. This was seen in all the (64/64) tested motoneurons innervating the ipsilateral (i-) longus capitis (LC) and the i-sternocleidomastoideus (SCM) muscles and in 86% (38/44) of the motoneurons innervating the contralateral (c-) LC muscle. The inhibitory relay neurons, identified by orthodromic and antidromic responses to stimulation of the ACN and the i- and c-LC motoneuron pools, were classified as VCi (vestibulocollic neurons sending an axon to the i-LC motoneuron pool) and VCc (vestibulocollic neurons sending an axon to the c-LC motoneuron pool) neurons. Neither VCi nor VCc neurons were activated antidromically by localized stimulation of the ascending medial longitudinal fasciculus (asc. MLF) or the 3rd nuclei. They were located in the medial, descending and ventral lateral vestibular nuclei. It was also observed that VCi neurons produced unitary IPSPs in i-LC and i-SCM motoneurons in the C1 segment. Inhibitory synapses were estimated to be on the cell somata and/or the proximal dendrites of the motoneurons.

Animals↗

PubMed1989

Extracellular recording of vestibulo-thalamic neurons projecting to the spinal cord in the cat.

Forty vestibulo-thalamic (VT) neurons were recorded extracellularly in the vestibular nuclei of the anesthetized cat. More than half of the VT neurons responded monosynaptically to vestibular nerve stimulation; the others responded polysynaptically. The VT neurons were activated antidromically from one or two sites in the contralateral VPL, VPM, VL, VM, SG, and PO in the thalamus. Their axonal arborizations in the thalamus were likely restricted in narrow areas. About three quarters of the VT neurons were also activated antidromically from the ventral funiculus in the C1 segment. Axonal branchings were found in the contralateral C1 gray matter. The VT neurons were mainly localized in the descending vestibular nucleus.

Animals↗

PubMed1988

Properties and localization of the anterior semicircular canal-activated vestibulocollic neurons in the cat.

Unit activities of secondary vestibular neurons that selectively responded to stimulation of the anterior semicircular canal nerve (ACN) were recorded extracellularly in the anesthetized cat. Axonal pathways and projections in the spinal cord of the ACN-activated neurons were examined by recording their antidromic responses to stimulation of the lateral and medial vestibulospinal tracts (LVST and MVST), and the bilateral neck extensor motoneuron pools in the C1 segment (C1 dorsal rami [DR] motoneuron pools). In order to determine whether the neurons had ascending axon collaterals to the extraocular motoneurons, the contralateral (c-) inferior oblique (IO) motoneuron pool was also stimulated. Twenty-seven neurons sent their axons to the ipsilateral (i-) C1DR motoneuron pool via the LVST without any projection to the extraocular motoneuron pool. All the cells except one were located in the ventral part of the lateral vestibular nucleus. This pathway produced monosynaptic EPSPs with short time-to-peak and short half-width in C1DR motoneurons (16/16 motoneurons). Eight neurons sent axons to the i-C1DR motoneuron pool via the MVST without any to the extraocular motoneuron pool. Cell somata were located in the descending nucleus or in the ventral part of the lateral nucleus. These neurons did not produce postsynaptic potentials (PSPs) in any C1DR motoneurons. All thirty-five neurons sending axons to the c-C1DR motoneuron pool have ascending axon collaterals to the c-IO motoneuron pool.

Action Potentials↗

PubMed1988

Axonal trajectories of posterior canal-activated secondary vestibular neurons and their coactivation of extraocular and neck flexor motoneurons in the cat.

Unit activities of 148 secondary vestibular neurons related to the posterior semicircular canal were recorded extracellularly in anesthetized cats. Axonal projections of these neurons were examined by their antidromic responses to stimulation of the excitatory target motoneurons of the contralateral (c-) inferior rectus muscle (IR) and bilateral (bi-) motoneuron pools of longus capitis muscles, neck flexors, in the C1 segment (C1LC). The neurons were classified into 4 groups according to their axonal projections. The first group of neurons, termed vestibulo-oculo-collic (VOC) neurons, sent axon collaterals both to the c-IR motoneuron pool and to the c-C1LC motoneuron pool. The majority of them (72%) were located in the descending nucleus. The second group of neurons were termed vestibuloocular (VO) neurons and sent their axons to the c-IR motoneuron pool but not to the cervical cord. Most of them (86%) were located in the medial nucleus. The third group of neurons, termed vestibulo-collic (contralateral) (VCc) neurons, sent axons to the c-C1LC motoneuron pool via the contralateral ventral funiculus but not to the oculomotor nuclei. They were mostly (75%) found in the descending nucleus. The last group of neurons were vestibulo-collic (ipsilateral) (VCi) neurons, which gave off axons to the ipsilateral (i-) C1LC motoneuron pool via the ipsilateral ventral funiculus but not to the oculomotor nuclei. One of them also sent an axon collateral to the c-C1LC motoneuron pool. The majority of them (74%) were located in the ventral part of the lateral nucleus. It was also observed in some of the VOC and VCi neurons that they produced unitary EPSPs in the c-C1LC and i-C1LC motoneurons, respectively. Their synaptic sites were estimated to be on the cell somata and/or proximal dendrites of the motoneurons.

Animals↗

PubMed1987

Skin potential reflex corresponding to transient motion discomfort.

The qualitative and quantitative correspondence between the degree of motion discomfort and the skin potential reflex (SPR) was examined in four subjects. Head movement was provided three times during body rotation at three different angular velocities (Coriolis stimulus) to induce motion discomfort, and at rest as a control. SPRs were caused in the arousal sweat area by head movement. The wave form, latency, time-to-peak, and amplitude of SPR were analyzed. The amplitude of the depolarizing response (P response) of SPR increased proportionally to the angular velocity of body rotation and decreased in the course of repetitive Coriolis stimulation. It was revealed that the amplitude of P response of SPR in the arousal sweat area corresponds to the degree of transient motion discomfort.

Adult↗

PubMed1987

Changes of skin potential level and of skin resistance level corresponding to lasting motion discomfort.

The qualitative correspondence between degree of motion discomfort and electrodermal activity was investigated. Skin potential level (SPL) and skin resistance level (SRL) in the arousal sweat area and the thermal sweat area were recorded. In order to induce motion discomfort, Coriolis stimulation and/or horizontal body rotation were provided by using a rotatory chair. The degree of discomfort was evaluated according to reports by the subjects. It was observed that SPL depolarized in the arousal sweat area as well as in the thermal sweat area and SRL lowered in the thermal sweat area coincidentally with lasting motion discomfort. SPL showed better correspondence the recovery period from the motion discomfort.

Adult↗

PubMed1986

The commissural inhibition on secondary vestibulo-ocular neurons in the vertical semicircular canal systems in the cat.

The commissural inhibition on secondary vestibulo-ocular neurons (VOns) from the contralateral (c-) vertical canal system in the same geometric plane was studied in the anesthetized cat. The secondary VOns were identified by their orthodromic responses to stimulation of the ampullary nerves of the anterior (ACN) or posterior (PCN) semicircular canals and also by their antidromic responses to stimulation of the IIIrd and IVth nuclei. The majority of ACN-activated excitatory VOns in the descending and medial nuclei (32/36, 89%) and in the superior nucleus (20/23, 87%), received commissural inhibition from the c-PCN, while only few ACN-activated inhibitory VOns (3/35, 9%) in the superior nucleus received commissural inhibition from the c-PCN. On the other hand, all of the PCN-activated excitatory (50/50) and inhibitory (30/30) VOns in the vestibular nuclei received commissural inhibition following c-ACN stimulation.

Action Potentials↗

PubMed1986

Dynamics of adaptive change in vestibulo-ocular reflex direction. I. Rotations in the horizontal plane.

Horizontal and vertical vestibulo-ocular reflex (VOR) eye movements were recorded in alert cats before and after adaptation to vertical optokinetic motion coupled with horizontal rotation at 0.05, 0.25 or 1.0 Hz. Within 15-30 min, the VOR measured in darkness acquired a vertical component; the maximal directional change in the VOR occurred at the frequency of the adapting stimulus. At other frequencies the gain was less and there were phase leads or lags for higher or lower frequencies, respectively. Adaptive VOR was stable for at least 14 h in unrestrained animals with no visual input and decayed within 30 min during rotation in a stationary visual world.

Adaptation, Physiological↗

PubMed1986

Dynamics of adaptive change in vestibulo-ocular reflex direction. II. Sagittal plane rotations.

Alert cats were rotated sinusoidally (0.25 Hz) in their sagittal plane while viewing optokinetic motion in their horizontal plane. Vertical and horizontal vestibulo-ocular reflex (VOR) was measured in the dark before and after 2 h of these adaptation stimuli in upright or onside orientation of the cat. Onside exposure produced maximal adaptive horizontal VOR at the training frequency. Upright exposure produced highest gain at lower frequencies. A cat with inoperative vertical canals adapted only to upright exposure. We conclude that in the presence of horizontal image rotation either vertical canal or otolith stimulation can produce adaptation in VOR direction and stimulation of both produces complex adaptation dynamics.

Adaptation, Physiological↗

PubMed1983

Morphophysiological study on the divergent projection of axon collaterals of medial vestibular nucleus neurons in the cat.

(1) Spikes of single neurons were extracellularly recorded in the medial vestibular nucleus (MVN) in decerebrate cats and were functionally identified as secondary type I neurons by observing their responses to horizontal rotation and monosynaptic activation after stimulation of the ipsilateral vestibular nerve. Axonal projection of these neurons was examined by their antidromic responses to stimulation of the contralateral abducens nucleus, the spinal cord, and the ascending and descending MLF. (2) Almost all secondary type I vestibular neurons which sent their axon to the contralateral abducens nucleus were antidromically activated from the descending MLF at the level of the obex as well. Nearly half of these neurons sent their collateral axon to the level of C1 segment in the spinal cord and approximately one third to the ascending MLF close to the oculomotor complex. (3) The mean conduction velocity was 29 m/s for descending collateral axons and 30 m/s for ascending collateral axons. (4) Systematic tracking for antidromic microstimulation in the contralateral abducens nucleus and spinal gray matter at C2-C3 suggested that collateral axons of single type I vestibular neurons gave off local branches in the abducens nucleus and the motoneuron pool in the upper cervical gray matter. Existence of terminal branches in the neck motoneuron pool was confirmed by intraaxonal staining with horseradish peroxidase (HRP). (5) Neurons which projected to both the contralateral abducens nucleus and the spinal cord were located in a fairly localized region in the ventrolateral part of the rostral MVN. Neurons which projected to the contralateral abducens nucleus and not to the spinal cord were located in a rostrocaudally wider area in the ventrolateral MVN. Neurons projecting to the spinal cord and not to the contralateral abducens nucleus were located in the widest area in the rostrocaudal direction, covering almost the whole extent of the rostral half of the MVN.

Animals↗