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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↗
PubMed1990

Morphological aspects of the human vestibular nerve.

A quantitative study was made of the number of fibers, their diameters, and distribution in the nerves innervating individual vestibular receptor organs of three human temporal bones. The specimens were obtained from autopsies conducted within 4 hours postmortem. The temporal bones containing the nerves were fixed in 3% glutaraldehyde and decalcified with EDTA until they were soft enough to allow dissection of the nerve branches to the individual receptors. The nerve branches were processed for osmium staining, embedded in plastic, and cut serially in 1-micron-thick sections for light-microscopic histologic evaluation of their fiber composition. Quantitative evaluation of nerve-fiber characteristics was made with the aid of a laboratory computer and programs for graphic representation and statistical analysis. In the nerves to the individual cristae the number of fibers ranged between 1416 and 2335. Fibers with diameters between 2.5 microns and 3 microns were the most numerous. The number of fibers decreased exponentially with increased size. The thickest fibers had diameters up to 11.5 microns. The distribution of fibers in the nerve of each crista was different for the central and intermediate areas of the crista than it was for the ends. Thin fibers with diameters less than 2.5 microns, which represented 36% of the population, projected to the ends of the receptor area. Thick fibers with diameters greater than 4.5 microns, which represented 8% of the fibers, were distributed relatively uniformly except for the extreme ends of the crista, where they were nearly absent. Fibers with intermediate diameters were distributed throughout the crista, although they were more concentrated at the ends. In the nerves to three maculae, the number of fibers ranged from 3744 to 5538. The percentage of fibers of each size, however, was similar to that in the cristae. The greater portion of fibers had diameters between 3.0 microns and 3.5 microns. Because of the anatomical configuration of the maculae, it was not possible to compare fiber diameters from one area to another. The composition and differential projection of fibers to the crista in the human labyrinth were similar to those found earlier in squirrel monkeys and bullfrogs. On the basis of these similarities in the pattern of innervation, it is suggested that the physiological properties in humans must be similar to those in animals.

Aged↗
PubMed1989

Primary vestibular projections in the chinchilla.

The central projections of fibers from the vestibular nerve were studied in 19 chinchillas after horseradish peroxidase labelling. In addition, the limits of the vestibular nuclei and the anatomical characteristics of their neurons were also studied. All five vestibular nuclei received primary afferents, but there were extensive areas of them that received very little or no projections at all, such as the rostral part of the superior vestibular nucleus, the dorsocaudal part of the lateral vestibular nucleus, the caudal half of the medial vestibular nucleus and the caudalmost aspect of the dorsal vestibular nucleus.

Afferent Pathways↗
PubMed1989

Anatomic and physiological correlates in bullfrog vestibular nerve.

1. The correlations between anatomic and physiological characteristics of primary afferent neurons innervating the anterior semicircular canal in the bullfrog were investigated. These characteristics were examined separately in large groups of neurons, and the direct correlations between them were established in a subset of neurons by means of intraaxonal recording and labeling. 2. Anatomic features of the anterior canalicular nerve that were related with fiber diameter were studied. This nerve was composed of an average of 1,142 fibers (standard deviation of 171 in 5 samples), of which 42% were less than 2 microns in diameter and 8% were greater than 7 microns. The nerve branched into 6 clearly defined bundles, whose fiber diameter-dependent composition could be determined in 5 samples. In the 2 center bundles, 32% of the fibers had diameters greater than 7 microns. In contrast, these thick fibers comprised only 4% of the fiber population in the 2 lateralmost bundles, in which 44% of the fibers had diameters less than 2 microns. The projections of labeled afferent fibers were traced into the neuroepithelium, and it was demonstrated that all thick fibers, even those of the lateral bundles, turned toward more central regions of the crista. Consequently, in the bullfrog, there is a clear predominance of thick afferent fibers innervating the anterior crista's central region and thin fibers in the peripheral region. 3. The dendritic morphology of the broad classes of afferent fibers (i.e., thick and thin) was elucidated. Individually labeled thick afferents possessed dendrites forming short, thick, clawlike extensions to contact a few hair cells. The thinnest afferents were labeled through extracellular horseradish peroxidase (HRP) injections. In contrast to the thick fibers, thin afferents were characterized by an unbranched trajectory with serially located bouton-like structures that were apposed to successive hair cells. 4. The characteristics of spontaneous firing and the responses to rotational stimuli were determined for 138 anterior canalicular neurons. Spontaneous firing rates ranged from 0 to 95 spikes.s-1. The coefficient of variation (CV) of spontaneous firing ranged from 0.12 to 2.5. Response gains to high- (0.5 and 0.4 Hz) and medium- (0.05 Hz) frequency sinusoidal acceleration stimuli were positively correlated with CV (P less than 0.001) for neurons with a CV value less than or equal to 0.5. The gain of neurons characterized by more irregular spontaneous firing (CV values greater than 0.5) was uncorrelated with CV.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Idiopathic bilateral vestibulopathy.

We report the clinical features of 22 patients with acquired bilateral vestibulopathy of unknown cause. All had either absent or markedly decreased responses to both caloric and rotational testing. They presented with dysequilibrium and imbalance, worse at night; most reported oscillopsia but none had associated hearing loss or other neurologic symptoms. Nine reported prior prolonged episodes of vertigo consistent with the diagnosis of bilateral sequential vestibular neuritis. Of the remaining 13, none had exposure to known ototoxins or a positive family history. Idiopathic bilateral vestibulopathy is an important cause of progressive imbalance in adults and should be considered even though hearing is normal.

Adult↗
PubMed1989

The firing properties of second-order vestibular neurons in correlation with the far-field recorded vestibular-evoked response.

Action potentials of the second-order vestibular neurons of ten cats were recorded, both in rest and responding to sinusoidal and intense impulse acceleration stimuli. The data were compared with the far-field recorded vestibular-evoked response induced by the same impulse stimuli. It was found that the irregular (kinetic) neurons, which had a phase lead relative to head velocity, were capable of responding to these impulses with a latency as short as 3.5 msec after the start of head acceleration. It is assumed, therefore, that these neurons are the generators of the second wave of the vestibular-evoked response, having a similar latency. A high correlation was found between the latency of the first peak in the poststimulus time histogram in response to acceleration impulses and the phase of the response to sinusoidal rotations. The regular (tonic) vestibular neurons did not respond to acceleration impulses and probably did not contribute to the vestibular-evoked response.

Animals↗