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ABSTRACT: The convergence between the anterior semicircular canal (AC) and utricular (UT) inputs, as well as the convergence between the AC and saccular (SAC) inputs in single vestibular neurons of decerebrated cats were investigated. Postsynaptic potentials were recorded intracellularly after selective stimulation of each pair of vestibular nerves AC/UT or AC/SAC. Neurons were recorded from the central parts of the vestibular nuclei, where the otolith afferents mainly terminate. Of a total of 105 neurons that were activated after stimulation of the AC and UT nerves, 42 received convergent inputs. Thirty-eight of these neurons received excitatory inputs from both afferents. Convergent neurons were further classified into vestibulospinal (n=28) and vestibulooculospinal (n=6) neurons by antidromic activation from the border between the C1 and C2 spinal cord and the oculomotor or trochlear nucleus. Eight neurons that were not antidromically activated from either site were classified as vestibular neurons. Forty three percent of the convergent vestibulospinal neurons and most of the convergent vestibulooculospinal neurons projected to the spinal cord through the medial vestibulospinal tract. The remaining vestibulospinal and vestibulooculospinal neurons descended through the ipsilateral lateral vestibulospinal tract. Of a total of 118 neurons that were activated after stimulation of the AC and/or SAC nerves, 51 received convergent inputs (27 vestibulospinal, 4 vestibulooculospinal, 5 vestibuloocular and 15 vestibular neurons). Forty-two of the convergent neurons received excitatory inputs from both afferents. Thirty seven percent of the convergent vestibulospinal neurons and all of the convergent vestibulooculospinal neurons projected to the spinal cord through the medial vestibulospinal tract. The remaining vestibulospinal and vestibulooculospinal neurons descended through the ipsilateral lateral vestibulospinal tract.
Experimental Brain Research 01/2003; 147(3):407-17. · 2.39 Impact Factor
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ABSTRACT: The properties of utricular (UT)-activated vestibular neurons that send axons to the contralateral vestibular nuclei (commissural neurons) were investigated intracellularly or extracellularly in decerebrate cats. A total of 27 vestibular neurons were orthodromically activated by stimulation of UT nerves and antidromically activated by stimulation of the contralateral vestibular nuclei. All neurons tested were classified as vestibulospinal (VS), vestibulooculospinal (VOS), vestibuloocular (VO), and unidentified vestibular neurons (V) after antidromic stimulation of the spinal cord and oculomotor/trochlear nuclei. Most UT-activated commissural neurons (20/27) received monosynaptic inputs. Twelve of 27 commissural neurons were located in the medial vestibular nucleus, 5 were in the lateral vestibular nucleus, 10 were in the descending vestibular nucleus, and no commissural neurons were recorded in the superior vestibular nucleus. Seven of 27 neurons were commissural VS neurons, 9 of 27 were commissural VOS neurons, and 11 of 27 were commissural V neurons. No commissural VO neurons were found. All VOS neurons and 3 VS neurons issued descending axons via the medial vestibulospinal tract. We also studied convergent inputs from the posterior semicircular canal (PC) nerve onto UT-activated commissural neurons. Five of 27 UT-activated commissural neurons received converging inputs from the PC nerves.
Experimental Brain Research 01/2003; 147(4):419-25. · 2.39 Impact Factor
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ABSTRACT: Convergent inputs from the ipsilateral semicircular canal nerves onto single vestibular nucleus neurons were investigated in decerebrate cats using intracellular recording after selective stimulation of each ampullar nerve. One hundred and seventy-four neurons were activated by stimulating the anterior semicircular (AC) and/or posterior semicircular canal (PC) nerves. These neurons were also antidromically stimulated and classified according to the pattern of their collateral projections to the oculomotor complex and the spinal cord. Four types were found: vestibulo-ocular (VO), vestibulospinal (VS), vestibulo-oculospinal (VOS), and vestibular (V) neurons, the latter of which were not activated by stimulation of either the oculomotor complex or the spinal cord. Of 174 AC- and/or PC-activated vestibular nucleus neurons, 32 (18%) received convergent inputs from both nerves. These convergent neurons included 11 VS, 6 VOS, and 15 V neurons. We found no VO neurons with convergent input. The vast majority (82%) of AC/PC-activated VS and VOS convergent neurons received excitatory inputs from both nerves, 12% received reciprocal inputs (i.e., excitatory from one and inhibitory from the other), and the remaining neurons received inhibitory inputs from both nerves. By stimulating the horizontal semicircular (HC) and/or PC nerves, 183 neurons were activated. Of these, 44 (24%) received convergent inputs from both nerves. These convergent neurons included 19 VS, 5 VOS, 2 VO, and 18 V neurons. Approximately one-half (46%) of HC/PC-activated VS and VOS convergent neurons received excitatory inputs from both nerves and 42% received reciprocal inputs, and the remaining neurons received inhibitory inputs from both nerves. In both nerve pairs, the percentage of VS neurons was higher (AC/PC, 34%; HC/PC, 43%) than that of VOS or VO neurons. Approximately half of these convergent neurons were located in the lateral nucleus. These results suggest that, during mixed angular head accelerations, the vestibulocollic reflex may be partly accomplished by VS and VOS convergent neurons.
Experimental Brain Research 09/2002; 145(3):351-64. · 2.39 Impact Factor
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ABSTRACT: The components of the vestibular ascending pathway that transmit otolith information to the thalamus were studied electrophysiologically in anesthetized cats. Thalamic-projecting vestibular neurons (confirmed antidromically) were recorded extracellularly in the various vestibular nuclei. Otolith inputs to these neurons were examined with selective stimulation of the utricular (UT) or the saccular (SAC) nerves. Vestibular nerve branches other than the tested nerve were transected. Of 40 UT-activated vestibulothalamic neurons, 40% (16/40) were activated by UT nerve stimulation with latencies ranging between 0.9-1.4 ms, suggesting they were second-order neurons from the UT nerve. UT-activated vestibulothalamic neurons were recorded in the medial vestibular nucleus (MVN; 24/40), the lateral vestibular nucleus (LVN; 9/40), the descending vestibular nucleus (DVN; 6/40), and the superior vestibular nucleus (SVN; 1/40). Most of the neurons (38/40) were antidromically activated by focal stimulation of the ventral part of the ipsilateral thalamus. Antidromic stimulation of the pontine area revealed that trajectories of the ascending axons (14 of 38 neurons) to the ipsilateral thalamus passed through the pontine reticular formation, ventral to the ascending tract of Deiters (ATD) and the medial longitudinal fasciculus (MLF). Only three SAC-activated vestibulothalamic neurons were encountered in the LVN. All these neurons were second-order neurons from the SAC nerve and were antidromically activated by stimulation of the contralateral thalamus, in marked contrast to the UT-activated vestibulothalamic neurons. Only three UT-activated and two SAC-activated neurons sent descending collaterals to the spinal cord.
Experimental Brain Research 01/2002; 141(4):415-24. · 2.39 Impact Factor
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Y Uchino,
H Sato,
M Zakir,
K Kushiro, M Imagawa,
Y Ogawa,
S Ono,
H Meng,
X Zhang,
M Katsuta,
N Isu,
V J Wilson
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ABSTRACT: We examined whether otolith-activated second- and third-order vestibular nucleus neurons received commissural inhibition from the contralateral otolithic macula oriented in the same geometric plane. For this purpose we performed intracellular recording in vestibular nucleus neurons after stimulation of the ipsi- and contralateral utricular and saccular nerves. More than half (41/72) of the utricular-activated second-order vestibular nucleus neurons received commissural inhibition from the contralateral utricular nerve. The remaining neurons (31/72) showed no visible response to contralateral utricular nerve stimulation. About half (17/36) of utricular-activated third-order neurons also received commissural inhibition from the contralateral utricular nerve. Approximately 10% (7/67) of saccular-activated second-order vestibular neurons received polysynaptic commissural inhibition, whereas 16% (11/67) received commissural facilitation. The majority (49/67) of saccular second-order vestibular neurons, and almost all (22/23) third-order neurons, showed no visible response to stimulation of the contralateral saccular nerve. The present findings suggest that many utricular-activated vestibular nucleus neurons receive commissural inhibition, which may provide a mechanism for increasing the sensitivity of vestibular neurons to horizontal linear acceleration and lateral tilt of the head. Commissural inhibition in the saccular system was less prominent than in the utricular system.
Experimental Brain Research 03/2001; 136(4):421-30. · 2.39 Impact Factor
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ABSTRACT: Convergence between posterior canal (PC) and saccular (SAC) inputs in single vestibular nuclei neurons was investigated in decerebrated cats. Postsynaptic potentials were recorded intracellularly after selective stimulation of the SAC and PC nerves. Stimulation of either the SAC or PC nerve orthodromically activated 143 vestibular nuclei neurons. Of these, 61 (43%) were antidromically activated by stimulation of the C1-C2 junction, 14 (10%) were antidromically activated by stimulation of the oculomotor or trochlear nucleus, and 14 (10%) were antidromically activated by stimulation of both the oculomotor or trochlear nucleus and the spinal cord. Fifty-four (38%) neurons were not activated by stimulation of either or both. We named these neurons vestibulospinal (VS), vestibulo-ocular (VO), vestibulooculo-spinal (VOS) and vestibular (V) neurons, respectively. Both PC and SAC inputs converged in 47 vestibular nuclei neurons (26 VS, 2 VO, 6 VOS and 13 V neurons). Of these, 19 received monosynaptic excitatory inputs from both nerves. This input pattern was frequently seen in VS neurons. Approximately half of the convergent VS neurons descended to the spinal cord through the lateral vestibulospinal tract. The remaining half and all the convergent VOS neurons descended to the spinal cord through the medial vestibulospinal tract. Most of the convergent neurons were located in the lateral nucleus or descending nucleus.
Experimental Brain Research 05/2000; 131(3):253-61. · 2.39 Impact Factor
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ABSTRACT: The otolith system contributes to the vestibulo-ocular reflexes (VOR) when the head moves linearly in the horizontal plane or tilts relative to gravity. The saccules are thought to detect predominantly accelerations along the gravity vector. Otolith-induced vertical eye movements following vertical linear accelerations are attributed to the saccules. However, information on the neural circuits of the sacculo-ocular system is limited, and the effects of saccular inputs on extraocular motoneurons remain unclear. In the present study, synaptic responses to saccular-nerve stimulation were recorded intracellularly from identified motoneurons of all twelve extraocular muscles. Experiments were successfully performed in eleven cats. Individual motoneurons of the twelve extraocular muscles--the bilateral superior recti (SR), inferior recti (IR), superior obliques (SO), inferior obliques (IO), lateral recti (LR), and medial recti (MR) were identified antidromically following bipolar stimulation of their respective nerves. The saccular nerve was selectively stimulated by a pair of tungsten electrodes after removing the utricular nerve and the ampullary nerves of the semicircular canals. Stimulus intensities were determined from the stimulus-response curves of vestibular N1 field potentials in order to avoid current spread. Intracellular recordings were performed from 129 extraocular motoneurons. The majority of the neurons showed no response to saccular-nerve stimulation. In 17 (30%) of 56 extraocular motoneurons related to vertical eye movements (bilateral SR and IR), depolarizing and/or hyperpolarizing postsynaptic potentials (PSPs) were observed in response to saccular-nerve stimulation. The latencies of PSPs ranged from 2.3 to 8.9 ms, indicating that the extraocular motoneurons received neither monosynaptic nor disynaptic inputs from saccular afferents. The majority of the latencies of the depolarization, including depolarization-hyperpolarization, were in the range of 2.3-3.3 ms. Latencies of hyperpolarizations were typically longer than those of depolarizations. Only one contralateral SO motoneuron of 43 recorded oblique extraocular motoneurons (bilateral SO and IO) showed a depolarization-hyperpolarization in response to saccular-nerve stimulation at a latency of 2.5 ms. None of 30 recorded horizontal extraocular motoneurons (bilateral LR and MR) responded to stimulation of the saccular nerve. The neural linkage in the sacculo-ocular system is relatively weak in comparison to the utriculo-ocular and sacculo-collic systems, suggesting that the role of the sacculo-ocular system in stabilizing eye position may be reduced when compared with utriculo-ocular and semi-circular canal-ocular reflexes.
Experimental Brain Research 05/2000; 131(3):262-8. · 2.39 Impact Factor
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ABSTRACT: Neural connections from the saccular and utricular nerves to the ipsilateral vestibular neurons and the commissural effects were studied by using intracellular recordings of excitatory (E) and inhibitory (I) postsynaptic potentials (PSPs) in vestibular neurons of cats after focal stimulation of the saccular and the utricular maculae. Neural circuits from the maculae to vestibular neurons, termed cross-striolar inhibition, may provide a mechanism for increasing the sensitivity to linear acceleration and tilt of the head. It was examined whether secondary vestibular neurons activated by an ipsilateral otolith organ received a commissural inhibition from a contralateral otolith organ that occupied the same geometric plane. Results suggest that utricular-activated vestibular neurons receiving commissural inhibition may provide a mechanism for increasing the sensitivity to horizontal linear acceleration and tilt of the head. The commissural inhibition of the saccular system was much weaker than that of the utricular system.
Annals of the New York Academy of Sciences 06/1999; 871:162-72. · 3.15 Impact Factor
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ABSTRACT: The morphology of single saccular afferents was studied by the intracellular horseradish peroxidase (HRP) method. Four neurons were sufficiently stained to allow reconstruction of their axonal arborizations. The main axon of these neurons bifurcated into an ascending and a descending branch at the level of the lateral nucleus. The ascending branches of two axons gave off collaterals with boutons in the caudal part of the superior nucleus, while the other two ascending branches lacked such terminations. By contrast, characteristics of the descending axonal arborization patterns of all the four neurons were substantially the same. The descending branches coursed caudally through the lateral part of the descending nucleus, and gave off up to 14 collaterals with boutons that extended throughout this nucleus. These collaterals also reached the ventral part of the lateral nucleus, the lateral border of the medial nucleus, and group f. A few axon collaterals ramified even outside the border of the vestibular nuclei into the spinal trigeminal nucleus and the reticular formation surrounding it. Axon collaterals from the stem axon also terminated in the interstitial nucleus of the vestibular nerve. There was a noticeable absence of any projection to the y group.
Neuroscience Letters 01/1998; 240(3):127-30. · 2.11 Impact Factor
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ABSTRACT: Axonal pathways, projection levels, conduction velocities, and locations of the cell bodies of saccular nerve-activated vestibulospinal neurons were studied in decerebrated cats and anesthetized cats, using a collision test of orthodromic and antidromic spikes. The saccular nerve was selectively stimulated by bipolar tungsten electrodes. Three monopolar electrodes were inserted into the left and right lateral vestibulospinal tract (LVST) and medial vestibulospinal tract (MVST) of the C1 segment, to determine the pathway of axons. Three pairs of similar electrodes were positioned bilaterally in the C3-4, T1, and L3 segments to examine projection levels. Another monopolar electrode was placed in the oculomotor nucleus to determine whether saccular nerve-activated vestibulospinal neurons have branches ascending to the oculomotor nucleus. Of 145 vestibular neurons orthodromically activated by stimulation of the saccular nerve, 46 were activated from the C1 segment antidromically. Forty-three were second-order vestibulospinal neurons and 3 were third-order vestibulospinal neurons. Four saccular nerve-activated vestibulospinal neurons were also antidromically activated from the oculomotor nucleus. Sixty-three percent of the saccular nerve-activated vestibulospinal neurons descended through the MVST; one-third of these terminated in the upper cervical segments, one-third reached the lower cervical segments and the remaining one-third reached the upper thoracic segments. Thirty percent of the saccular nerve-activated vestibulospinal neurons descended through the ipsilateral LVST; most of these reached the upper thoracic segments. Seven percent of the saccular nerve-activated vestibulospinal neurons descended through the contralateral vestibulospinal tracts terminating in the upper cervical segments. Most of the saccular nerve-activated vestibulospinal neurons originated in the caudal part of the lateral nucleus and rostral part of the descending nucleus.
Experimental Brain Research 11/1997; 116(3):381-8. · 2.39 Impact Factor
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ABSTRACT: Neuronal connections and pathways underlying sacculocollic reflexes were studied by intracellular recordings from neck extensor and flexor motoneurons in decerebrate cat. Bipolar electrodes were placed within the left saccular nerve, whereas other branches of the vestibular nerve were removed in the inner ear. To prevent spread of stimulus current to other branches of the vestibular nerve, the saccular nerve and the electrodes were covered with warm semisolid paraffin-Vaseline mixture. Saccular nerve stimulation evoked disynaptic (1.8-3.0 ms) excitatory postsynaptic potentials (EPSPs) in ipsilateral neck extensor motoneurons and di- or trisynaptic (1.8-4.0 ms) EPSPs in contralateral neck extensor motoneurons, and di- and trisynaptic (1.7-3.6 ms) inhibitory postsynaptic potentials (IPSPs) in ipsilateral neck flexor motoneurons and trisynaptic (2.7-4.0 ms) IPSPs in contralateral neck flexor motoneurons. Ipsilateral inputs were about twice as strong as contralateral ones to both extensor and flexor motoneurons. To determine the pathways mediating this connectivity, the lateral part of the spinal cord containing the ipsilateral lateral vestibulospinal tract (i-LVST) or the central part of the spinal cord containing the medial vestibulospinal tracts (MVSTs) and possibly reticulospinal fibers (RSTs) were transected at the caudal end of the C1 segment. Subsequent renewed intracellular recordings following sacculus nerve stimulation indicated that the pathway from the saccular nerve to the ipsilateral neck extensor motoneurons projects though the i-LVST, whereas the pathways to the contralateral neck extensors and to the bilateral neck flexor motoneurons descend in the MVSTs/RSTs. Our data show that sacculo-neck reflex connections display a qualitatively bilaterally symmetrical innervation pattern with excitatory connections to both neck extensor motoneuron pools, and inhibitory connections to both neck flexor motoneuron pools. This bilateral organization contrasts with the unilateral innervation scheme of the utriculus system. These results suggest a different symmetry plane along which sacculus postural reflexes are organized, thus supplementing the reference planes of the utriculus system and allowing the gravistatic system to represent all three translational spatial degrees of freedom. We furthermore suggest that the sacculocollic reflex plays an important role in maintaining the relative position of the head and the body against the vertical linear acceleration of gravity.
Journal of Neurophysiology 07/1997; 77(6):3003-12. · 3.32 Impact Factor
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ABSTRACT: Intracellular recordings from 200 identified extraocular motoneurons in the bilateral III, IV and VI cranial nuclei were studied to determine the connectivities between the utricular nerve and the extraocular motoneurons in cats. Stimulating electrodes were placed within the left utricular nerve, while other branches of the vestibular nerve were removed. Monosynaptic and disynaptic connections between the utricular nerve and the ipsilateral abducens motoneurons and interneurons were recorded as described previously. Stimulation of the utricular nerve evoked longer latency depolarizing and hyperpolarizing potentials in contra- and ipsilateral medial rectus motoneurons, respectively. Depolarizing and hyperpolarizing potentials with longer latencies were also recorded in the ipsilateral inferior oblique and contralateral trochlear motoneurons. The short and longer latency circuits between the utricular nerve and extraocular motoneurons may play a role in stabilizing the retinal image during head tilt and horizontal linear acceleration.
Acta oto-laryngologica. Supplementum 02/1997; 528:44-8.
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ABSTRACT: The axonal pathway, conduction velocities, and locations of the cell bodies of utricular nerve-activated vestibulospinal neurons were studied in decerebrated or anesthetized cats using the collision test of orthodromic and antidromic spikes. For orthodromic stimulation, bipolar tungsten electrodes were placed on the utricular nerve and the other vestibular nerve branches were transected. Monopolar tungsten electrodes were positioned on both sides of the upper cervical segments (C2-4), caudal end of the cervical enlargement (C7-T1), and from the lower thoracic to the upper lumbar segments (T12-L3) and were used for antidromic stimulation of the spinal cord. Another monopolar electrode was also placed in the oculomotor nucleus to study whether utricular nerve-activated vestibulospinal neurons have ascending branches to the oculomotor nucleus. Of the 173 vestibular neurons orthodromically activated by the stimulation of the utricular nerve, 46 were second-order vestibulospinal neurons and 5 were third-order neurons. The majority of the utricular nerve-activated vestibulospinal neurons were located in the rostral part of the descending vestibular nucleus and the caudal part of the ventral lateral nucleus. Seventy-three percent of the utricular nerve-activated vestibulospinal neurons descended through the ipsilateral lateral vestibulospinal tract. Approximately 80% of these neurons reached the cervico-thoracic junction, but a few reached the upper lumbar spinal cord. Twenty-seven percent of the utricular nerve-activated vestibulospinal neurons descended through the medial vestibulospinal tract or the contralateral vestibulospinal tracts. Those axons terminated mainly in the upper cervical segments. Almost none of the utricular nerve-activated vestibular neurons had ascending branches to the oculomotor nucleus.
Experimental Brain Research 12/1996; 112(2):197-202. · 2.39 Impact Factor
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ABSTRACT: 1. Intracellular recordings of synaptic potentials in extraocular motoneurons were studied to determine the connectivities between the utricular nerve and the extraocular motoneurons in cats. 2. Stimulating electrodes were placed within the left utricular nerve, while other branches of the vestibular nerve were removed. Subsequently, the N1 field potentials evoked by utricular nerve stimulation were recorded in the vestibular nuclei. The potential typically grew until reaching a plateau (submaximal stimulation). Stimulus spread to the other nerve branches appeared as an additional increase in N1 amplitude after the plateau discontinued (supramaximal stimulation). 3. Intracellular recordings were made from 200 identified motoneurons in the bilateral III, IV, and VI cranial nuclei. 4. Stimulation of the utricular nerve at submaximal intensity evoked a longer latency depolarizing and hyperpolarizing potentials in contra- and ipsilateral medial rectus motoneurons, respectively. Complex potentials with longer latencies also were recorded in ipsilateral inferior oblique and contralateral trochlear motoneurons after stimulation of the utricular nerve at a submaximal intensity. Monosynaptic and disynaptic connections between the utricular nerve and ipsilateral abducens motoneurons and interneurons were recorded as described previously. 5. The results of the present study confirm our initial findings that a disynaptic pathway from the utricular nerve to contralateral trochlear motoneurons is absent or very poorly developed, whereas polysynaptic circuits from the utricular nerve to inferior oblique and trochlear motoneurons may play a role in eye rotation during head tilt.
Journal of Neurophysiology 10/1996; 76(3):1896-903. · 3.32 Impact Factor
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ABSTRACT: Axonal projections of utricular (UT) afferents in cats were examined by three approaches: recordings of field potentials, labelling of UT nerve fibres by localized infusion of horseradish peroxidase (HRP) and intraaxonal infusion of HRP into a single UT afferent. UT afferents project principally into the rostral part of the descending nucleus and the ventral part of the lateral nucleus. Projection into the superior and the medial nuclei and the ipsilateral abducens nucleus were also observed.
Neuroscience Letters 03/1995; 186(2-3):87-90. · 2.11 Impact Factor
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ABSTRACT: 1. Connections from the utricular (UT) nerve to motoneurons and interneurons in the ipsilateral abducens (AB) nucleus were studied in anesthetized and decerebrated cats. Bipolar electrodes were fixed on the left UT nerve under visual observation. The other branches of the vestibular nerve and the facial nerve were transected in the left inner ear. 2. Stimulation of the UT nerve evoked a small positive-negative (P/N) deflection and a negative (N1) potential in the vestibular nuclei, with mean latencies of 0.56 and 0.84 ms, respectively. In the AB nucleus a small P/N deflection with a mean latency of 0.72 ms was recorded, which was considered as a incoming volley of the UT nerve. 3. Excitatory postsynaptic potentials (EPSPs) were recorded from AB motoneurons with short latencies after UT nerve stimulation. They were classified into two types, M and D. M-type EPSPs, which followed repetitive high-frequency stimuli and were recorded from the majority of AB motoneurons, had latencies ranging from 0.9 to 1.2 ms. Double shocks to the UT nerve evoked EPSPs that had the same latency. It was suggested that the AB motoneurons had monosynaptic connections with the UT nerve. D-type EPSPs, which were recorded from most of the AB motoneurons, had slightly longer latencies ranging from 1.2 to 1.8 ms. They showed temporal facilitation when double shocks were provided to the UT nerve. They did not follow repetitive high-frequency stimuli (< or = 2.5-ms interval). It was suggested that D-type EPSPs were di-synaptically evoked via secondary vestibular neurons. Interneurons in the AB nucleus had the same characteristics as AB motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal of Neurophysiology 04/1994; 71(3):950-8. · 3.32 Impact Factor
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ABSTRACT: Second-order vestibular neurons form the central links of the vestibulo-oculomotor three-neuron arcs that mediate compensatory eye movements. Most of the axons that provide for vertical vestibulo-ocular reflexes ascend in the medial longitudinal fasciculus (MLF) toward target neurons in the oculomotor and trochlear nuclei. We have now determined the morphology of individual excitatory second-order neurons of the anterior semicircular canal system that course outside the MLF to the oculomotor nucleus. The data were obtained by the intracellular horseradish peroxidase method. Cell somata of the extra-MLF anterior canal neurons were located in the superior vestibular nucleus. The main axon ascended through the deep reticular formation beneath the brachium conjunctivum to the rostral extent of the nucleus reticularis tegmenti pontis, where it crossed the midline. The main axon continued its trajectory to the caudal edge of the red nucleus from where it coursed back toward the oculomotor nucleus. Within the oculomotor nucleus, collaterals reached superior rectus and inferior oblique motoneurons. Some axon branches recrossed the midline within the oculomotor nucleus and reached the superior rectus motoneuron subdivision on that side. Since these neurons did not give off a collateral toward the spinal cord, they were classified as being of the vestibulo-oculomotor type and are thought to be involved exclusively in eye movement control. The signal content and spatial tuning characteristics of this anterior canal vestibulo-oculomotor neuron class remain to be determined.
Experimental Brain Research 02/1994; 97(3):387-96. · 2.39 Impact Factor
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ABSTRACT: 1. We studied connections between the utricular (UT) nerve and dorsal neck motoneurons in decerebrate cats. Electrodes were fixed in place on the UT nerve under visual observation; the other branches of the vestibular nerve were transected. 2. The N1 field potential evoked by UT nerve stimulation was recorded in the vestibular nuclei at the start of each experiment. The potential typically grew until it reached a plateau. Stimulus spread (if any) to the central ends of other nerve branches was revealed by an additional increase in N1 amplitude after the plateau was reached. 3. We recorded intracellularly from 55 motoneurons in C1-C3. Some were identified as having axons in the dorsal rami, which innervate dorsal neck muscles. Others projected in nerves that were not available for stimulation. 4. UT nerve stimulation evoked synaptic potentials in essentially all motoneurons studied. The predominant pattern consisted of disynaptic excitatory postsynaptic potentials in ipsilateral motoneurons and inhibitory postsynaptic potentials that were at least trisynaptic in contralateral motoneurons. 5. The results demonstrate the presence of short-latency connections between the utricular nerve and dorsal neck motoneurons. The functional role of this pathway remains to be investigated.
Journal of Neurophysiology 07/1992; 67(6):1695-7. · 3.32 Impact Factor
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ABSTRACT: Extracellular spike activities of medullary expiratory (E) neurons in the caudal ventral respiratory group were recorded in cats anesthetized with sodium pentobarbital. The majority of E neurons extended their axons in the lower lumbar or the sacral segments and distributed collaterals in L5-L7. These results suggest that E neurons are involved not only in respiratory activities but also in the respiratory modulated motor activities of the lower lumbar segments.
Brain Research 08/1991; 553(1):159-62. · 2.73 Impact Factor
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ABSTRACT: 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)
Experimental Brain Research 02/1991; 86(1):9-17. · 2.39 Impact Factor
