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Biomedical subjects

V Honrubia

Publications and source records attributed to V Honrubia.

At least 19 recordsLinked to original sources
PubMed1992

Afferent innervation of the vestibular nuclei in the chinchilla. I. A method for labeling individual vestibular receptors with horseradish peroxidase.

A new method was developed for specific labeling of primary vestibular afferent fibers from selected end-organs with horseradish peroxidase (HRP) applied extracellularly in the inner ear space. In 48 chinchillas, labeling was performed successfully in all animals by scratching the surface of the sensory end-organ of interest with an electrolytically sharpened needle and replacing the fluid in the vestibule with 30% HRP solution. Merely replacing the vestibular fluid (endo- and perilymph) with HRP did not label the ganglion cells or the afferent fibers in the brain stem. The specificity of labeling was verified by histological inspection of the ganglion cells and nerve fibers innervating the damaged and intact receptors. When the posterior semicircular canal and saccular receptors were scratched, labeled fibers and ganglion cells were found in the nerve and ganglion rostrodorsally and caudoventrally, respectively. Labeled ganglion cells from different superior vestibular nerve (SVN) receptors did not show as clear a segregation pattern as did labeled receptors from the inferior vestibular nerve (IVN). Once inside the brain stem, labeled fibers from the SVN receptors were rostral to those from the IVN receptors. The fibers of the vestibular root divided into an ascending and a descending branch which formed the vestibular tract. Labeled fibers from the SVN receptors divided rostrolaterally to those from the IVN receptors. In the vestibular tract, fibers coursed in different locations according to the receptor of origin. Fibers from the utriculus were lateral to those from the horizontal semicircular canal, which were lateral to those from the anterior semicircular canal. Fibers from the sacculus were lateral to those from the posterior semicircular canal.

Afferent Pathways↗
PubMed1992

Afferent innervation of the vestibular nuclei in the chinchilla. II. Description of the vestibular nerve and nuclei.

The morphological characteristics of the vestibular nuclei of the chinchilla were studied in horizontally cut serial sections of the brain stem. Horseradish peroxidase labeling allowed unambiguous delineation of the vestibular nuclei and areas of innervation by the vestibular afferent fibers. The cytoarchitecture of the vestibular nuclei was documented with the aid of camera lucida drawings and quantitatively evaluated with computerized methodology. The cellular groups identified in other species were found in the chinchilla. The superior vestibular nucleus (SN) originated ventromedial to the mesencephalic tract and nuclei of the trigeminal nerve. This nucleus contained medium-sized cells with a central group of larger cells (20-34 microns in diameter). It received its maximum vestibular innervation caudally in the ventrolateral and dorsal aspects of the nucleus. Fibers projected to the SN in bundles with thick fibers surrounded by thin ones. The lateral vestibular nucleus (LN) originated 0.9-1.2 mm below the rostral aspect of the vestibular area. It was ventrocaudal to the SN and contained many large cells with diameters of 45-60 microns. The LN was innervated mainly in the ventrocaudal aspect by oblique and transverse fibers that formed a dense mesh. The medial vestibular nucleus (MN) originated 0.3-0.6 mm caudal to the beginning of the SN, adjacent to the floor of the IVth ventricle. It extended for 3-4 mm along the SN, LN and descending vestibular nucleus (DN). The MN contained the densest and most homogeneous cells, which had diameters of 10-20 microns. This nucleus received its greatest innervation at the level of the vestibular root. Thin fibers traveled to the MN through the SN and LN. The caudal pole of the nucleus did not receive fibers. The DN originated 1.8-2.5 mm caudal to the origination of the SN, between the caudal LN and the MN. Caudally it replaced the LN. Most of the cells of the DVN were medium-sized, with diameters of 10-20 microns. The main vestibular innervation of the DN was in the lateral aspect of the nucleus. Tertiary fibers projected in small, separate bundles of uniform-sized thick fibers. The interstitial nucleus originated 1.1-1.4 mm from the beginning of the SN. It occupied the center of the vestibular root, 0.8-0.9 mm medial to the root entry zone. It contained a few large cells (greater than 20 microns in diameter), many medium-sized cells, and some small cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1992

The exacerbation of symptoms in Menière's disease during the premenstrual period.

The pathophysiology of the characteristic episodic symptoms of vertigo, low-frequency hearing loss, and tinnitus in Menière's disease remains poorly understood. It is likely that the manifestation of this condition may be multifactorial and related to elements affecting the inner ear beyond the underlying pathology of endolymphatic hydrops. We have identified a subgroup of female patients with Menière's disease in which the symptoms of this disorder are correlated with the late luteal phase of the menstrual cycle (premenstrual period). Through audiometric and vestibular testing, we have documented these inner ear effects in six women. Although many hormonal effects occur during the premenstrual period, compartmental fluid redistribution within the body may be the most pertinent. Endolymphatic hydrops represents a fluid imbalance within the inner ear and, when combined with an additional fluid shift, may produce symptomatic dysfunction. Case histories demonstrating the correlation of the symptoms of Menière's disease and the premenstrual period will be presented along with theoretical mechanisms of pathophysiology.

Adolescent↗
PubMed1992

Regeneration of the eighth cranial nerve in the bullfrog, Rana catesbeiana.

The present study was done in order to document the ability of the eighth cranial nerve of the bullfrog (Rana catesbeiana) to regenerate, the anatomic characteristics of the regenerated fibers, and the specificity of projections from individual endorgan branches of the nerve. The eighth cranial nerve was sharply transected between the ganglion cells and the brain stem in 40 healthy bullfrogs and allowed to regenerate. Anatomic studies were performed in these animals a minimum of 3 months postoperatively. Horseradish peroxidase was used to label the whole vestibular nerve or its individual endorgan branches. Labeled regenerated fibers could be identified crossing the site of the nerve section and projecting centrally to the vestibular nuclei in a pattern similar to that of normal frogs. Labeling of individual branches showed that regenerated fibers innervated the same specific areas found in normal frogs. Unlike normal animals, both thick and thin fibers projected to the medial nucleus.

Animals↗
PubMed1992

Optokinetic and vestibular interactions with smooth pursuit: psychophysical responses.

The effect was evaluated in normal subjects of the subjective perception of motion of a small visual target (VT) when combined with the effect of vestibular stimulation produced by different magnitudes of constant angular accelerations in the dark or the effect of optokinetic stimulation produced by different constant velocities of rotation. The visual target appeared to the subject to travel more slowly and for a shorter duration when it moved in the direction of the body's angular acceleration or against that of the optokinetic drum. The perceived error in motion was: (i) in the same direction as the subject's motion sensation produced by either of the two stimuli, and (ii) quantitatively related, although differently, to the magnitude of each of the two stimulus modalities; an heuristic model is proposed to account for these observations.

Acceleration↗
PubMed1992

Is human galvanically induced triceps surae electromyogram a vestibulospinal reflex response?

Interest in understanding the human vestibulospinal reflex has increased enormously over the past three decades, because this reflex is the primary effector of maintenance of posture and balance. On a posture platform, forces exerted by the triceps surae (TS) and tibialis anterior muscles are measured to calculate center of mass sway. We wished to determine whether the TS response is a direct component of the vestibulospinal reflex. Ten healthy human beings were stimulated with sinusoidal galvanic currents delivered over their mastoid processes. Sway response on a posture platform and TS electromyogram (EMG) were recorded for the following conditions: (1) standing unrestrained; (2) standing completely restrained above the leg; and (3) sitting unrestrained. Results were similar for all subjects. Computer-aided analysis for case 1 reveals that TS EMG and horizontal body sway responses are generated at the same frequency as the stimulating current, with a phase lag of 90 degrees. For case 2, body sway response and any component of the TS EMG over the unstimulated condition were absent in all subjects. For case 3, body sway persisted, but no TS EMG above the unstimulated condition was recorded. As the TS EMG disappears when the standing subject is restrained from swaying or in the unrestrained seated subject, we conclude that the TS EMG response is compensatory to motion of more superior portions of the musculoskeletal system; it is not part of the vestibulospinal reflex.

Adult↗
PubMed1991

Experimental evidence in the in vivo canine for the collapsible tube model of phonation.

The in vivo canine model of the larynx was used to measure transglottic pressures and airflow during phonation. Conditions of supraglottal resistance were also simulated. Pressure drop-flow curves were compared with data on collapsible tubes. The in vivo in canine model of the larynx demonstrates a number of features similar to oscillation in collapsible tubes.

Air Movements↗
PubMed1991

The electrically evoked vestibulo-ocular reflex: I. Normal subjects.

Recent animal studies indicate that electric currents applied through perilymphatic-space electrodes stimulate vestibular primary afferent neurons directly. These findings suggest that electrical stimulation may provide a testing method by which the vestibular nerve and central pathways could be evaluated separately from the vestibular end-organ. The goal of this study was to obtain normative data on human beings for an electrically evoked vestibulo-ocular reflex (EVOR). Sinusoidal electrical stimuli (0.0125 to 0.8 Hz, 4 mA peak intensity) were applied along the interaural axis through mastoid electrodes in 10 subjects. Horizontal eye movements were recorded by an infrared limbus-tracking device. The subjects also underwent rotational stimulation at the same frequencies so that their horizontal vestibulo-ocular reflex (VOR) could be evaluated. Nystagmus was observed in the EVOR at lower stimulus frequencies, whereas purely sinusoidal eye deviations occurred at higher frequencies. The phase of the EVOR slow-component eye velocity consistently lagged the stimulus. This contrasts with the phase measurements of the VOR in the same subjects, which exhibited a lead relative to head velocity. These findings suggest that currents applied to human beings may activate vestibular primary afferents independent of peripheral receptor mechanisms and thereby provide a "site-of-lesion" testing method by which the vestibular nerve and central pathways can be evaluated separately from the vestibular end-organ.

Adolescent↗
PubMed1991

Comparative study of the effect of gentamicin on the vestibulo-ocular and visual vestibulo-ocular reflexes in the cat.

The ototoxic effect of an aminoglycoside, gentamicin, on the vestibular system was investigated in cats given daily doses of 40 mg/kg i.m. for 14 days. Periodically, measurements were made of the vestibulo-ocular reflex (VOR) and visual vestibulo-ocular reflex (ViVOR) responses induced by rotatory stimuli at various frequencies from 0.0125 Hz to 0.8 Hz. After the cessation of drug administration, a progressively declining response to VOR stimuli continued, manifested by gain (ratio of peak response to peak stimulus amplitude) and phase relationships. The ViVOR was affected only in the gain measurements. The changes in the response amplitude (gain) were greater for the VOR than for the ViVOR responses and also for the lower (0.0125 Hz) than for the higher frequencies (0.8 Hz). There was some indication that the responses improved about one month after treatment was terminated. All of these specific response changes in cats are comparable to the known effects of aminoglycides in humans, and the same theoretical interpretation of the data in the context of a model of vestibular function can be applied in both cases.

Animals↗
PubMed1979

Modification of constant optokinetic nystagmus by vestibular stimuation.

Experiments were conducted to quantify the effect of a vestibular stimulation of known magnitude on a constant optokinetic nystagmus (OKN). Ten normal human subjects were tested with varying magnitudes of vestibular stimuli that were superimposed on a constant 30 degrees optokinetic stimulus. The gain of the vestibular system in the dark was 0.42 +/- 0.11, and the gain in the light during superimposition testing was 0.12 +/- 0.02. From these results, predictions were made that the degree of vestibular imbalance necessary to produce an asymmetric OKN would generate a spontaneous nystagmus in the dark, which would be equivalent to 20 to 30 degrees. Data from a large group of patients were used for corroboration of the results.

Adult↗
PubMed1979

Uniocular nystagmus in monocular visual loss.

Uniocular nystagmus was studied by electro-oculography in ten patients with monocular visual loss caused by ocular and optic nerve lesions. In these patients, visual loss was congenital or acquired in childhood or adult life. In all patients the oscillations were present in the primary position of gaze and were vertical, pendular, and of variable and low frequency (less than, or equal to, 1.0 HZ) and amplitude (usually less than 5 degrees). Refixation saccades, smooth pursuit, optokinetic nystagmus, and vestibuloocular responses to rotation in the horizontal and vertical planes were within normal limits. The irregularity, low frequency, and low amplitude of this form of nystagmus cause it to often be missed during casual clinical examination, but easily differentiate it from other causes of uniocular nystagmus.

Adolescent↗
PubMed1979

Benign paroxysmal positional nystagmus.

A characteristic nystagmus profile of benign paroxysmal positional nystagmus was determined from analyses of horizontal and vertical electro-oculographic recordings in 32 patients. The vertical component was upbeat in both eyes (fast phase toward the ground in the head-hanging position), whereas the horizontal component was dissociated with the ipsilateral eye beating away from the down ear and the contralateral eye beating toward the down ear. The amplitude of the vertical component was larger in the ipsilateral eye. This dissociated nystagmus profile is consistent with a burst of excitatory activity originating in the posterior canal of the ear that is undermost at the end of the positioning maneuver.

Adult↗
PubMed1979

Neural correlates of nystagmus in abducens nerve.

1. The firing rates of action potentials of abducens nerve single fibers were recorded in the cat's orbit during a variety of vestibular and optokinetic stimulations. 2. Comparison was made of the neural firing rates associated with agonist and antagonist responses during slow and fast components of vestibular and optokinetic nystagmus. It was found that the relationship between the motoneuron firing rates and the eye motion was independent of the reflex with which they were associated--vestibular or optokinetic, or the type of response--agonist or antagonist. No neurons were observed that responded only during the fast or only during the slow nystagmus phase. Motoneuron firing rates were proportional to both velocity and position of the eye in a ratio of 1 (spikes/s)/(deg/s) to 7.2 (spikes/s)/deg. The behavior of the motoneurons was compatible with the hypothesis that thier firing rates are sufficient to overcome both elastic and viscous forces by which the muscles and ligaments hold the eye in the orbit. 3. For low-frequency head rotations, eye displacement and neural responses showed a small phase angle difference. At higher frequencies, however, while the eyes maintained a fixed relationship to the head rotation, the neural responses showed an increasing phase lead. One component of this phase lead compensated for the phase lag introduced by the orbital mechanics. The other was modeled as a constant delay of approximately 70 ms, which may be accounted for by neuromuscular transmission and transduction.

Abducens Nerve↗
PubMed1979

The mechanism of benign paroxysmal positional nystagmus.

A characteristic nystagmus profile of benign paroxysmal positional nystagmus (BPPN) was determined from analyses of horizontal and vertical electro-oculographic recordings in 8 patients. The vertical component was upbeat in both eyes (fast phase toward the ground in the head-hanging position) while the horizontal component was dissociated with the ipsilateral eye beating away from the down ear and the contralateral eye beating toward the down ear. The amplitude of the vertical component was larger in the contralateral eye while that of the horizontal component was larger in the ipsilateral eye. This dissociated nystagmus profile is consistent with a burst of excitatory activity originating in the posterior canal of the ear that is undermost at the end of the positioning maneuver.

Electrooculography↗
PubMed1979

Visual-vestibular interaction and cerebellar atrophy.

The vestibular and optokinetic ocular control systems were studied in 10 patients with cerebellar atrophy and in 10 normal subjects using (1) constant velocity optokinetic stimulation, (2) sinusoidal rotation in the dark, and (3) sinusoidal rotation in the light with a surrounding fixed optokinetic drum. The gain (maximum slow component velocity/maximum head or drum velocity) of induced nystagmus was calculated from electro-oculographic recordings. Optokinetic nystagmus was abnormal in seven patients and the average optokinetic gain in the patients was significantly (p less than 0.01) less than that of the normal group. Three patients with "clinically pure" cerebellar atrophy had increased vestibular responses, and one patient with clinical signs of peripheral neuropathy had decreased responses, probably due to associated vestibular nerve disease. The average vestibulo-ocular reflex gain in patients did not differ significantly from controls (p greater than 0.05). Three patients had normal vestibular and optokinetic responses when tested independently, but had abnormal visual-vestibular interaction. These patients probably had selective disorders of the midline cerebellar pathways that mediate visual-vestibular interaction. By studying each system, both independently and during interaction, all patients were identified as abnormal, and a more precise anatomic localization of the atrophy was obtained.

Adolescent↗