Vestibular sympathetic nervous system in guinea pig

Analysis of Factors Affecting the Outcomes of In-hospitalized Vestibular Rehabilitation in Patients With Intractable Dizziness

OBJECTIVE

To analyze somatic and psychological factors affecting the outcomes of in-hospital vestibular rehabilitation in patients with intractable dizziness.

MATERIALS AND METHODS

The study involved 138 patients with persistent dizziness caused by peripheral vestibular dysfunction. They were hospitalized and taught to conduct a vestibular rehabilitation program for 30 minutes by themselves three times a day over 5 days. They were then instructed to continue performing the program every day after discharge. Several questionnaires were conducted immediately before, and 1 month after, the treatment. For example, the dizziness handicap inventory (DHI), the somatosensory catastrophizing scale (SSCS), and indexes of depression and anxiety. Posturography was also performed. The main outcome was the difference between the DHI scores before and after rehabilitation. Body sway was objectively evaluated using static posturography.

RESULTS

The vestibular rehabilitation significantly improved the DHI score, the SSCS score, depression, and anxiety. Multivariate analysis indicated that the improvement in the DHI score was poorer in patients who showed high SSCS score before intervention. A higher prevalue of the DHI was associated with greater improvements in this perceived handicap after the rehabilitation. Small body sway pre-rehabilitation was related to positive effects on the DHI score in patients with a high prevalue of the DHI.

CONCLUSION

The vestibular rehabilitation contributed to the improvement of perceived handicap due to dizziness, catastrophization of bodily sensation, and emotional distress. Patients who catastrophized their bodily sensations before vestibular rehabilitation saw smaller improvements in perceived handicap due to dizziness.

Alpha-9 nicotinic acetylcholine receptor immunoreactivity in the rodent vestibular labyrinth

Vestibular tissues (cristae ampullares, macular otolithic organs, and Scarpa's ganglia) in chinchilla, rat, and guinea pig were examined for immunoreactivity to the alpha9 nicotinic acetylcholine receptor (nAChR) subunit. The alpha9 antibody was generated against a conserved peptide present in the intracellular loop of the predicted protein sequence of the guinea pig alpha9 nAChR subunit. In the vestibular periphery, staining was observed in calyces around type I hair cells, at the synaptic pole of type II hair cells, and in varying levels in Scarpa's ganglion cells. Ganglion cells were also triply labeled to detect alpha9, calretinin, and peripherin. Calretinin labels calyx-only afferents. Peripherin labels bouton-only afferents. Dimorphic afferents, which have both calyx and bouton endings, are not labeled by calretinin or peripherin. In these experiments, alpha9 was expressed in both calyx and dimorphic afferents. A subpopulation of small ganglion cells did not contain the alpha9 nAChR but did stain for peripherin. We surmise that these are bouton-only afferents. Bouton (regularly discharging) afferents also show efferent responses, although they are qualitatively different from those in irregularly discharging (calyx and dimorphic) afferents, much slower and longer lasting. Thus, regular afferents are probably more affected via a muscarinic cholinergic or a peptidergic mechanism, with a much smaller superimposed fast nicotinic-type response. This latter response could be due to one of the other nicotinic receptors that have been described in studies from other laboratories.

Comparison of the vascular innervation of the rat cochlea and vestibular system

In order to gain a better understanding of the neuronal and local control of inner ear blood flow, the vascular innervation to the rat cochlea and vestibular system was examined. Specimens were removed in toto beginning at the basilar artery extending to the anterior inferior cerebellar artery, labyrinthine artery, common cochlear artery, modiolar artery and anterior vestibular artery. When possible the vessels were dissected in continuity through the cribrose area. The vestibular endorgans were also removed. Specimens were examined using immunohistochemical techniques for the presence of vasoactive intestinal peptide, neuronal nitric oxide synthase, neuropeptide-Y, substance P and calcitonin gene related peptide. Results show that the vasculature to the cochlea and vestibular portion of the inner ear receive similar types of nonadrenergic innervation, that within the vestibular endorgans, only CGRP and SP were found in the neuroepithelium or in association with vessels, and that within the vestibular system, the majority of the vascular innervation appears to stop at or near the cribrose area. In the cochlea however, it extends to include the radiating arterioles. These findings suggest that cochlear blood flow is under finer control and that neuronally induced changes in blood flow may have a more global effect in the vestibular periphery.

A role of glucocorticoid receptors in the guinea pig vestibular system

To investigate glucocorticoid receptor (GR) function in the vestibular periphery, GR antagonist RU38486 was administered to the guinea pig inner ear by osmotic pump, and we observed post-rotatory nystagmus (PRN) changes as a marker of vestibular function. Ten days after treatment, RU38486 (1 mM) resulted in ipsilateral vestibule hyperexcitability in response to rotation stimulation. This effect was dose-dependent. These data indicate that steroid hormones may play an important role in maintaining vestibular function.

Presence of catecholamines and serotonin in the rat vestibule

The concentrations of norepinephrine (NE), dopamine (DA) and its metabolites DOPAC and HVA, and serotonin (5-HT) and its metabolite 5-HIAA, were quantified in the rat vestibule. For this purpose, homogenates of vestibules, of albino and pigmented rats, were analyzed using HPLC with electrochemical detection. Vestibules of pigmented rats showed higher DOPAC and HVA concentrations than those of albino rats, and male pigmented rats also showed significantly more DA than male albino rats. These results could indicate that the rate of DA metabolism in vestibules was higher in pigmented than in albino rats. The vestibular concentrations of NE and 5-HT did not differ significantly between the two strains. In contrast, 5-HIAA concentration was higher in vestibules of pigmented rats than in those of albino rats, suggesting an increased 5-HT metabolism for the former strain. Differences in monoamine concentrations between the two sexes o the same strain were scarce. Only, a higher HVA concentration in vestibules of females could indicate a higher DA metabolism.

Nerve fibres of the endolymphatic sac: electronmicroscopic findings in the Mongolian gerbil

The presence of separate bundles of nerve fibres in the gerbilline endolymphatic sac (ES) is described, paying particular attention to their ultrastructure and localization. One bundle, localized in the area of the subepithelium which separates the sigmoid sinus from the ES, is composed only of myelinated fascicles which, moreover, seem to have an isolated contact with the ES area. Other two single nerve fibres, much smaller in caliber, are localized in the ES subepithelium and laterally to the ES area, still close to the sigmoid sinus. These fibres, composed of myelinated and unmyelinated fascicles, seem to have a rather longitudinal orientation and, moreover, contract close relationships with the rich vascular network of the ES subepithelial tissue. As far as the course is concerned, the serial sectioning technique would suggest that the nerve fibres get very close to the ES epithelial cell layer, going proximal to distal. Speculations on the origin of this nerve contingent in the ES are proposed and discussed in view of possible new theories for pathogenesis and therapy of some inner ear diseases.

Functional architecture of vestibular primary afferents from the posterior semicircular canal of a turtle, Pseudemys (Trachemys) scripta elegans

Physiological studies in many vertebrates indicate that vestibular primary afferents are not a homogeneous population. Such data raise the question of what structural mechanisms underlie these physiological differences and what functional role is played by afferents of each type. We have begun to answer these questions by characterizing the architecture of 110 afferents innervating the posterior canal of Pseudemys scripta. We emphasize their spatial organization because experimental evidence suggests that afferent physiological properties exhibit significant spatial heterogeneity. The sensory surface of the posterior canal comprises paired, triangular hemicristae, which are innervated by two afferent types. Bouton afferents (66% of total afferents) are found over the entire sensory surface. They differ significantly in the shape and size of their collecting areas, number of boutons, soma size, and axon diameter; this morphological variation is systematically related to the afferent's spatial position. In addition, multivariate analyses suggest that bouton afferents may comprise two subtypes: alpha afferents have delicate processes and are found throughout the crista; beta afferents are more robust and are concentrated preferentially toward the canal center. Calyx-bearing afferents comprise two morphological subtypes: dimorphs (13% of total afferents) bear calyceal and bouton endings; calyceal afferents (21%) bear calyceal endings only. Both types occur exclusively in an elliptical region near the center of each hemicrista; their morphology varies with radial distance from the center of this elliptical region. Our data provide evidence that in Pseudemys: (1) the classical vestibular afferent types (bouton, calyx, dimorph) are structurally heterogeneous, and (2) their spatial sampling characteristics are highly structured and distinctive for each type. These spatial patterns may shed light on regional differences in physiological profiles of vestibular afferents, and they raise questions about the role of this spatial heterogeneity in signaling head movement.

Sensory ganglia as a target of autonomic and sensory nerve fibres in the guinea-pig

The distribution of neuropeptide- (neuropeptide Y, substance P, vasoactive intestinal peptide) and catecholamine-synthesizing enzyme-immunoreactive axons in guinea-pig trigeminal, nodose, and cervical dorsal root ganglia was studied by double-labelling immunofluorescence in controls and after extirpation of either the cervical sympathetic trunk or the stellate ganglion; tyrosine hydroxylase- and dopamine-beta-hydroxylase-immunoreactive terminals in dorsal root ganglia were ultrastructurally investigated. Six neurochemically identifiable axons innervated the trigeminal ganglion, five kinds were found in the nodose and dorsal root ganglia. Two of them (catecholaminergic with and without neuropeptide Y) were of sympathetic origin and, besides their termination at arteries, provided a direct innervation of capsule cells of the trigeminal and cervical dorsal root ganglia facing the subarachnoid space. Varicosities which were interpreted as being of sensory origin were equally numerous in all ganglia, whereas those being likely of parasympathetic origin decreased in numbers from the trigeminal to the dorsal root and nodose ganglia. It is concluded that the sensory ganglia are the target of postganglionic sympathetic, parasympathetic and primary afferent neurons, each of which are specifically organized with respect to the neurochemical phenotype and inter- and intraganglionic distribution. Among other targets, these "nervi gangliorum" appear to be intimately linked to the ganglionic capsular cells and meningeal sheaths facing the liquor spaces.

Rat utricular macula: blood flow and stereological assessment of capillary morphology

Vascular compromise has long been proposed as a cause of inner ear disorders. However, the examination of blood flow and its control mechanisms in the vestibular system has been very limited. Combining stereological techniques with the microsphere injection technique, capillary morphology and regional blood flow were determined for the rat utricular macula. Results are as follows: total utricular blood flow 0.158 +/- 0.078 microL/min; blood flow to the neuroepithelium (excluding nerve) 0.0995 +/- 0.046 microL/min; blood flow per unit volume 7.71 +/- 4.31 microL/min per cubic millimeter, neuroepithelial volume 0.01344 +/- 0.0018 mm3; absolute capillary surface area 0.159 +/- 0.039 mm2; mean capillary diameter 5.84 +/- 0.56 microns; absolute capillary length 8.45 +/- 1.6 mm; and capillary lumen volume fraction 0.0175 +/- 0.004. Comparisons to previous data for the posterior canal ampulla indicate that the capillary diameter in the rat utricular macula is smaller; the capillary length is greater; and the end organs are similar with respect to neuroepithelial volume, capillary surface area, and blood flow. The size of the microsphere used in the present study (9.21 microns), in comparison to the mean capillary diameter (5.84 microns) of the utricular neuroepithelium, would indicate that the blood flow data likely represent a minimum value. These findings indirectly indicate that the utricular macula metabolic rate is greater than that of the posterior canal crista, and that there is variation from end organ to end organ in mean capillary diameter.

Blood flow and assessment of capillaries in the aging rat posterior canal crista

Vascular change has been proposed as an etiological factor in inner ear aging and in several inner ear disorders. Moreover, some successful medical management of the episodic vertigo and tinnitus associated with Ménière's disease has been directed toward pharmacologically increasing blood flow, changing vascular permeability or ion homeostasis. While there are many studies of cochlear capillary morphology and blood flow, there are very few examining these variables in the vestibular system and none with respect to aging. The purpose of this study was to examine the rat posterior canal ampullary crista for age-related changes in blood flow and capillary morphology. By combining stereological techniques with microsphere injection, we have determined that in the rat posterior canal crista there is a statistically significant age-related decrease in blood flow (75%), mean capillary diameter (31%), and volume fraction of capillary lumen (31%). There is also an overall 18% decrease in the volume of the ampullary crista, a 72% decrease in blood flow/unit volume and a 36% increase in capillary length/unit volume. There were no significant changes in the capillary surface area/unit volume, the absolute capillary length, or the absolute capillary surface area. These data suggest impaired blood flow and degenerative loss of the ampullary crista may be relate to impaired end organ function.

Catecholaminergic innervation in the vestibular labyrinth and vestibular nucleus of guinea pigs

The vestibular sympathetic fibers of 20 guinea pigs were examined by immunohistochemical demonstration using tyrosine hydroxylase and dopamine B-hydroxylase. The vestibular sympathetics originated in the ipsilateral superior cervical ganglion and entered the internal auditory meatus along the labyrinthine artery. At the Schwann-glial border, some of the sympathetic fibers left the artery and went into the superior and inferior divisions of the vestibular nerve and made a loose meshwork among the Scarpa's ganglion cells, while other fibers kept following the labyrinthine artery. Both groups of fibers entered the cristae ampullaris and saccular and utricular maculas after several bifurcations in the cribrose areas and terminated either near the capillaries beneath the sensory epithelia, or among the vestibular nerve fibers. These fibers travelled freely in the vestibular labyrinth without being restricted to following blood vessels or vestibular nerve fibers. Some sympathetic fibers made direct contacts with the vestibular efferent fibers or the vestibular afferent fibers at the node of Ranvier. Sympathetic fibers were not observed in the sensory epithelia or semicircular canals, and were rarely found in the vicinity of the dark cells. The vestibular nucleus was also innervated by other catecholaminergic nerve fibers originating from the locus ceruleus, and the synaptic contacts were observed between the catecholaminergic nerve terminals and other neurons. These two peripheral and central catecholaminergic nervous systems were quite independent at the level of Schwann-glial border.

Sympathetic and CGRP-positive nerve supply to the endolymphatic sac of guinea pig

The distribution of sympathetic fibers and calcitonin gene related peptide (CGRP)-positive fibers was examined in the endolymphatic sac of 10 guinea pigs by using immunohistochemical techniques to demonstrate tyrosine hydroxylase (TH) and CGRP. A meshwork of TH-positive fibers, found around the sigmoid sinus, sent branches to the distal and the intermediate parts of the endolymphatic sac. In these areas. TH-positive fibers traveled freely from blood vessels and formed a loose plexus beneath the lining epithelium. Such fibers were rare in proximal portion of the endolymphatic sac and in the endolymphatic duct. Seven days after elimination of the ipsilateral superior cervical ganglion, some of the TH-positive fibers were gone, however, there were still a few fibers in the endolymphatic sac as well as around the sigmoid sinus, thus their origin remains obscure. CGRP-positive fibers also branched from the fibers around the sigmoid sinus, and were distributed throughout the endolymphatic sac, some occasionally extending to the endolymphatic duct. They not only formed a dense plexus in the sublining space, but also spread through the lining cell layer. Elimination of the ipsilateral superior cervical ganglion did not affect the distribution of CGRP-positive fibers, indicating that they are probably not sympathetic fibers.

Distribution of Tyrosine Hydroxylase-Like Immunofluorescence in Guinea Pig Vestibular Ganglia and Sensory Areas

The distribution of tyrosine hydroxylase (TH)-like immunofluorescence was analyzed in the guinea pig vestibular ganglia and end organs using a monoclonal antibody to TH. TH was chosen as a marker for the sympathetic fibers because TH regulates the first step of catecholamine synthesis by converting tyrosine to dopa. In the vestibular ganglia, there were TH-positive nerve fibers having distinct varicosities surrounding the vestibular ganglion cells. In the sensory areas, there was a sympathetic plexus in the subepithelial tissue of the saccule, the utricle, and the crista ampullaris. We speculated that the sympathetic innervation has a direct influence on the vestibular ganglion cells and diffuse influence on the capillary permeability.

Vestibular sympathetic nervous system in guinea pig

The vestibular sympathetic fibers were examined in 20 guinea pigs by immunohistochemical demonstration of tyrosine hydroxylase and dopamine beta-hydroxylase. The vestibular sympathetics originated in the ipsilateral superior cervical ganglion and entered the internal auditory meatus along the labyrinthine artery. At the Schwann-glial border, some of the sympathetic fibers left the artery and went into both the superior and inferior divisions of the vestibular nerves and made a loose mesh-work among the Scarpa's ganglion cells while other fibers followed the labyrinthine artery. Both types of fibers entered the crista ampularis and otoconial macula after several bifurcations in the cribrosa and terminated either near the capillaries beneath the sensory epithelial or among the vestibular nerve fibers. These fibers traveled freely in the vestibular labyrinth and were not restricted to following blood vessels or vestibular nerve fibers. Some sympathetic fibers made direct contact with the vestibular efferent fibers or the vestibular afferent fibers at the node of Ranvier. Sympathetic fibers were not observed in the sensory epithelia and semicircular canals and were rarely found in the vicinity of the dark cells: however, they were found to be distributed in the endolymphatic sac.