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Biomedical subjects

V Honrubia

Publications and source records attributed to V Honrubia.

At least 73 records · Page 4Linked to original sources
PubMed1989

Regeneration of the eighth cranial nerve. III. Central projections of the primary afferent fibers from individual vestibular receptors in the bullfrog.

The projection site in the central nervous system of individual end-organ branches of regenerated vestibular nerves was documented in bullfrogs. The eighth cranial nerve was surgically sectioned in 12 bullfrogs (Rana catesbeiana) and allowed to regenerate. Horseradish peroxidase was used to label the primary vestibular afferent fibers from the whole nerve (one frog) and the whole anterior branch (two frogs), and the individual receptor end-organ branches to the anterior semicircular canal (three frogs), the horizontal semicircular canal (three frogs), and the sacculus (three frogs). A sufficient number of fibers from the individual receptors were labeled in nine specimens to allow a description of their central projection pattern. The overall pattern of central projections of the regenerated nerves was similar to the pattern of normal nerves. In the eighth nerve root proper and in the area proximal to the vestibular nuclei, fibers from the anterior semicircular canal were ventral, fibers from the sacculus and posterior branch were dorsal, and fibers from the horizontal semicircular canal were in an intermediate position. In ventral, superior, and descending vestibular nuclei, a projection pattern was also identifiable in some specimens. The fibers of the anterior semicircular canal projected ventral to the fibers of the horizontal semicircular canal, with fibers from the posterior branch more dorsal. The saccular fibers projected to the dorsal aspect of the ventral nucleus and the ventral aspect of the dorsal nucleus. For the most part, projections in the regenerated specimens, as verified histologically, were comparable to individual end-organ projections previously identified in normal frogs. The only major discrepancy between the findings from the regenerated specimens and those from normal frogs was in the position of the vestibular tract and the innervation to the medial nucleus. The regenerated vestibular tract was shifted laterally in the brain stem. Regenerated thick and thin fibers were intermixed in the tract and projected to the medial nucleus. Normally, the thin fibers are lateral to the thick fibers in the tract. Therefore, the regenerated afferent fibers of the vestibular nerve selectively reinnervated the vestibular nuclei, and the fibers to the individual end-organs selectively reinnervated particular parts of the nuclei. In addition, the thick and thin regenerated fibers preserved the type of bouton endings normally found. The regenerated thick fibers had rare boutons en passant and a great number of collaterals, while the thin fibers had numerous boutons en passant and only a few collaterals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Horizontal vestibulo-ocular reflex after acute peripheral lesions.

We studied the dynamics of the horizontal vestibulo-ocular reflex using a broad range of sinusoidal rotational stimuli in 14 patients with acute unilateral peripheral vestibular lesions. From plots of slow phase velocity (SPV) versus stimulus velocity (phase shifts removed) we calculated the DC offset and gain to ampullopetal (AP) and ampullofugal (AF) stimulation of the remaining intact labyrinth. DC offset values were highly correlated with spontaneous nystagmus SPV values for all frequencies (0.0125-0.8 Hz) and amplitudes (30-120-deg/sec) of stimulation. Mean AP gain values were consistently higher than mean AF values with the greatest difference occurring at low frequencies of stimulation. Saturation nonlinearities were present with AF stimulation at high amplitudes. These findings can be explained by dynamic asymmetries at the level of the primary and secondary vestibular neurons.

Acute Disease↗
PubMed1989

Quantitative vestibular function testing in elderly patients with dizziness.

Electronystagmography was used to examine 103 elderly patients complaining of dizziness. This series of tests included tests for pathologic nystagmus, saccades, smooth pursuit, and optokinetic nystagmus, as well as bithermal caloric testing and rotational testing. One or more specific diagnoses were identified in 100 patients (86.2%), with the two most common diagnoses being benign positional vertigo (30 patients, or 25.9%) and cerebrovascular disorders (25 patients, or 21.6%). An abnormality was found on ENG in 75 (65%) of the patients tested, the most common of these being a unilateral hypoexcitability to caloric stimulation. In most cases, the ENG data was used to support a presumptive diagnosis that was based on the patient's history and examination, although in 4 cases ENG provided the critical diagnostic information by identifying decreased caloric and rotational responses in patients with nonspecific dizziness and dysequilibrium.

Aged↗
PubMed1988

Ultralow vestibuloocular reflex time constants.

We report detailed oculomotor studies in 3 patients with central nervous system lesions and markedly decreased time constants (less than 2 seconds) of the vestibuloocular reflex (VOR). In 1 patient with Chiari type I malformation, serial measurements over 3 years documented a progressive decrease in the duration of postrotatory nystagmus (100 deg/sec steps, acceleration 140 deg/sec2) until finally there was no sustained nystagmus. At this time, the patient had no response to caloric stimulation or to sinusoidal rotation below 0.2 Hz but normal gain (peak slow-phase eye velocity/peak chair velocity) above 0.4 Hz (phase lead increased). Gaze holding, saccades, smooth pursuit, and optokinetic nystagmus were normal, but optokinetic-after-nystagmus disappeared. The other 2 patients (combined brainstem-cerebellar atrophy) had impaired gaze holding, abnormal smooth pursuit and optokinetic nystagmus, and absent optokinetic-after-nystagmus. VOR gain to step and high-frequency sinusoidal stimuli was increased. The neural mechanism that normally prolongs the VOR time constant may have reduced it in our patients.

Adult↗
PubMed1988

Eye movements induced by linear acceleration on a parallel swing.

1. Horizontal and vertical eye movements were induced in normal human subjects by sinusoidal linear acceleration on a parallel swing. The swing frequency was 0.3 Hz and the peak horizontal and vertical acceleration ranged from 0.17 to 0.48 and 0.03 to 0.34 g, respectively. Eye movements were recorded with the scleral search coil technique. 2. With the subjects seated in the dark to stimulate the otolith-ocular reflex, swing displacement along the interaural axis induced horizontal eye movements with a mean sensitivity to translation (ST) (peak eye velocity/peak swing velocity) of 3.8 to 4.7 degrees/m and a mean phase shift (eye velocity re swing velocity) of -152 to -160 degrees. Vertical eye movements had ST and phase values comparable to those of the horizontal eye movements. When the subjects sat facing forward so that the horizontal linear accelerations occurred in the occipitonasal axis, almost identical vertical but no consistent horizontal eye movements were induced. In each case the horizontal and vertical eye movements were proportional to the horizontal and vertical displacement of the swing. 3. With the subject seated in the light looking to an earth-fixed target (synergistic visual-vestibular interaction), the gain (peak eye velocity/peak target velocity) of induced eye movements was near 1, and the phase was compensatory (i.e., approximately -180 degrees) for all stimuli (even at target velocities at which the pursuit gain was less than 1). Subjects were able to suppress the otolith-ocular responses by fixating on a target attached to the swing. The ST decreased by an order of magnitude compared with measurements in the dark without a fixation target. 4. Subjects were able to augment the ST (horizontal and vertical) by imagining an earth-fixed target. Halving the distance of the imagined target approximately doubled the ST. 5. In two of three subjects tested, the ST measured with mental alerting in the dark adaptively increased (approximately doubled) after 20 min of continuous synergistic visual-vestibular interaction. The subject who did not show an adaptive increase in ST began with the highest value of the 10 normal subjects. 6. We conclude that during linear accelerations of the head the otolith signal is correctly interpreted as head movement and not rotation of the gravity vector. The otolith-ocular reflex interacts with the visual pursuit system to improve ocular stability during translational head movements.

Adult↗
PubMed1988

Vertigo in the hyperviscosity syndrome.

Diseases that cause hyperviscosity of the blood can result in otologic symptoms--especially vertigo. These symptoms are predominantly produced by peripheral vestibular involvement. The pathophysiology probably involves vascular obstruction in the venules. Specific changes in the microvasculature are presumed to be comparable to those that occur with hyperviscosity disorders in the retina. Maintenance of a normal blood viscosity will prevent damage to the ear, as well as other organs. Additionally, reduction of the blood viscosity can greatly improve otologic symptoms. Case studies and a review of the pertinent literature are included.

Adult↗
PubMed1988

Vestibular function in experimental endolymphatic hydrops.

Endolymphatic sac ablation in the guinea pig can result in a dilated membranous labyrinth and low-frequency hearing loss similar to patients with Meniere's disease. However, this animal model fails to develop analogous symptoms of a Meniere's crisis such as sudden hearing loss and marked vestibular imbalance. Possibly, factors in addition to endolymphatic hydrops must be present to result in a crisis episode. By placing animals in an inverted posture, their intralabyrinthine pressure was elevated, causing additional stress on the inner ears. Standard electronystagmographic techniques were used to monitor vestibular imbalance, which appeared as spontaneous nystagmus in the dark. Nineteen of 23 animals with unilateral endolymphatic hydrops showed spontaneous nystagmus in an inverted posture. Physiologic mechanisms explaining these results are described.

Animals↗
PubMed1988

A comparison of the dynamics of horizontal and vertical smooth pursuit in normal human subjects.

We compared horizontal and vertical smooth pursuit recorded with a scleral contact lens technique at multiple sinusoidal frequencies (0.2-1.6 Hz) and peak velocities (12.5-100 degrees.s-1) in 10 normal subjects. The gain was significantly higher (p less than 0.05) and the harmonic distortion significantly lower (p less than 0.05) for horizontal pursuit compared to vertical pursuit for all stimuli except the lowest frequency and peak velocity. Both horizontal and vertical pursuit exhibited a phase lag that was minimal at lower frequencies but reached a mean of about 37 degrees at 1.6 Hz. This difference between horizontal and vertical pursuit could be explained by current models of the smooth pursuit system if one postulates a lower saturation level of retinal error velocity for vertical pursuit compared to horizontal pursuit.

Adult↗
PubMed1987

The neural generators of the vestibular evoked response.

A new method for the induction and recording of a short-latency vestibular evoked response (VsER) to intense acceleration impulses with skin electrodes was studied in cats. The first two waves, P1 and P2, had latencies of 2.5 and 3.5 ms, respectively, and coincided with the recorded gross neural activity in the vestibular nerve and nuclei, respectively. Single second-order vestibular neurons with low and irregular activity responded to the same acceleration impulses with a latency as short as 3.5 ms.

Animals↗
PubMed1987

Fast component threshold for vestibular nystagmus in the rabbit.

The existence of a threshold for the production of fast components of vestibular nystagmus was investigated in the rabbit. The characteristics (position and velocity) of reflexive eye movements were precisely monitored with the use of the search-coil method and a laboratory computer. The threshold largely depended on the eye position in the orbit during nystagmus and, to a much lesser extent, on the eye velocity. The basic characteristics of the threshold remained unchanged under vestibular stimulation in the dark and in the light, and for different frequencies and peak velocities of rotation. A pattern of vestibular nystagmus was demonstrated whereby it is possible to predict the occurrence of fast components.

Animals↗
PubMed1987

Recording of short-latency vestibular evoked potentials induced by acceleration impulses in experimental animals: current status of the method and its applications.

The short-latency vestibular evoked potential (VsEP) induced by angular acceleration impulses (maximal amplitude 30,000 deg/sec2, rise time 2-3 msec) was recorded by skin electrodes in intact cats after various surgical and pharmacological procedures. The normal VsEP consists of 5-8 waves, several microvolts in amplitude, during the first 10 msec. The latency of the first wave (P1) is about 2 msec with respect to the start of head acceleration. The first and the second waves (P1 and P2) were shown to originate from the vestibular nerve and nucleus, respectively. The VsEP disappears permanently after bilateral labyrinthectomy, excision of the 8th nerves, or administration of large doses of gentamicin. Temporary disappearance is caused by anoxia induced for a brief period of time or injection of lidocaine (4%) into the vestibular nerve or into the inner ear after contralateral labyrinthectomy. The VsEPs in the intact cat are similar whether clockwise or counterclockwise stimuli are used and are not affected by changing the position of the head. Unilaterally labyrinthectomized animals, however, show asymmetric response whereby excitatory stimulation of any of the intact semicircular canals evokes prominent P1 and P2 waves which are absent with inhibitory stimulation. The rate and input-output intensity functions of the VsEP are described. The threshold of the VsEP was found to be 1000-1500 deg/sec2. In addition to the neurogenic waves, 2 other potentials appear occasionally in the response: large-amplitude and longer-duration waves with latencies of 8-20 msec, which are of myogenic origin, and smaller waves with shorter latency which probably represent vestibular microphonics and generator potentials. Extracellular recordings of the responses of single second-order neurons in the vestibular nuclei to the same acceleration impulses confirmed that the kinetic vestibular neurons can respond to these stimuli with a latency as short as 3.5 msec. This method for inducing and recording VsEPs has proved to be a powerful tool for the evaluation of vestibular function in experimental animal models.

Acceleration↗
PubMed1987

Saccadic eye movements in myasthenia gravis.

The peak velocities of horizontal saccades were measured in patients with myasthenia gravis (MG) to determine whether they can differentiate MG from other causes of ophthalmoplegia. Eye movements were recorded with electrooculography (EOG) or infrared scleral reflection (IR) in 42 patients with MG, 26 patients with sixth cranial nerve palsy (CNP), 19 patients with chronic progressive external ophthalmoplegia (PEO) and 28 normal subjects. Despite limitation of ductions in MG, the group means of velocities of 10 deg saccades recorded with IR were similar in MG and normal subjects. With EOG, small but statistically significant decreases in mean velocities of 10, 20 and 30 deg saccades were found in MG, compared to those in normal subjects. Twenty-one to 28% of MG patients had velocities outside of the normal range (outliers). In contrast, the group means in CNP and PEO were markedly lower than those in MG and normal subjects. The frequencies of outliers were 89 to 100% in CNP and 88 to 100% in PEO. Measurement of saccadic velocities can be helpful in differentiating MG from other causes of ophthalmoplegia.

Adolescent↗
PubMed1987

Benign positional vertigo: clinical and oculographic features in 240 cases.

We report the clinical and oculographic features in 240 patients with benign positional vertigo (BPV). In each case, after a rapid position change from the sitting to head-hanging position, a stereotyped torsional paroxysmal positional nystagmus was visually observed and recorded with electronystagmography (ENG). The mean age of onset was 54 years, with a range of 11 to 84 years. In slightly more than one-half of the cases (122/240) a likely diagnosis was determined. The most common identifiable causes were head trauma (17%) and viral neurolabyrinthitis (15%). Females outnumbered males approximately two to one in the idiopathic group. Abnormalities on bithermal caloric testing were found in 47% of patients. Only two patients, both with well-documented neurologic disorders, had central signs on ENG. Our data are consistent with a peripheral, posterior semicircular canal origin of BPV.

Adolescent↗
PubMed1987

Morphological aspects of the vestibular nerve of the squirrel monkey.

A morphological study of the vestibular nerve of a primate, the squirrel monkey, revealed a systematic organization of neurons according to fiber diameter. At the center of the cristae, thick fibers align in two parallel rows along the long axis; in the periphery of the cristae, thin fibers predominate. Within the superior vestibular nerve the thick fibers of the anterior and horizontal semicircular canals and utricle are situated in the anterosuperior area, the thin fibers in the posterior part. A similar segregation occurs with fibers of the posterior ampullary nerve and the saccule within the inferior vestibular nerve. The fibers continue to segregate at the root entry zone where they lose their Schwann's cell ensheathing and begin to divide into secondary central branches. There is a correspondence between the volume of the ganglion cell and the fiber diameter; hence, a segregation of ganglion cells according to their size also takes place in the vestibular nerve. The organization of the primate's vestibular nerve is similar to that found earlier in an anuran. The relevance of the phylogenetic preservation of the vestibular nerve's anatomical organization is discussed in terms of current physiological findings, which support the differential role of fibers of different diameters in vestibular function.

Animals↗
PubMed1987

Regeneration of the eighth cranial nerve. II. Physiologic verification in the bullfrog.

Two experiments were performed to document the functional capacity of the regenerated eighth cranial nerve. In experiment 1, the eighth cranial nerve was sectioned preganglionically and allowed to regenerate in a group of bullfrogs with normal contralateral eighth nerve and labyrinth. Posture and reflex to lateral tilt were measured preoperatively and postoperatively for a minimum of 3 months. Similar measures were performed in a second group of bullfrogs in which the eighth nerve had been destroyed by ganglionectomy and in a third with peripheral labyrinthectomies. In experiment 2, the eighth nerve was sectioned and allowed to regenerate in bullfrogs in which the contralateral nerve had previously been destroyed. Posture and reflex to lateral tilt were measured as in experiment 1. Similar measures were performed in a group of bullfrogs that had undergone bilateral nerve destruction. Regeneration of the eighth cranial nerve in bullfrogs in both experiments was documented histologically by labeling the regenerated fibers with horseradish peroxidase (HRP). In both experiments, posture recovered completely only in the bullfrogs in which the eighth cranial nerve was allowed to regenerate. Reflex to lateral tilt recovered more rapidly in the bullfrogs with regenerated nerves than in any of the other bullfrogs.

Animals↗
PubMed1987

Vestibular ototoxicity of gentamicin assessed by the recording of a short-latency vestibular-evoked response in cats.

The short-latency vestibular-evoked response (VsER) and the auditory brain stem response (ABR) were recorded with scalp electrodes in four cats before, during, and after systemic administration of gentamicin. The VsER was altered and later disappeared in three cats, and in one cat it became asymmetric, typical of a unilateral vestibular lesion. In all cats the ABR was unaffected and remained normal through the end of the experiment 4 months later. Histopathological examination of the temporal bones of three cats showed severe damage to the vestibular end-organ, particularly in the summit of the cristae, but in lesser amounts in the hair cells on the slopes of the cristae and in the maculae. In one cat, the pathological condition was greater in one ear, corresponding to the asymmetry in the VsER records. This new method of inducing and recording the VsER has been demonstrated by the present study to be an effective tool for experimentally assessing vestibular end-organ and nerve function in animal models. Furthermore, these results indicate that the VsER is generated in the vestibular labyrinth, most probably by the cristae of the semicircular canals.

Animals↗