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PubMed1982

Effectiveness of some anions in sustaining the efferent inhibition in the frog labyrinth.

Efferent inhibition in the frog labyrinth is sustained by the release of acetylcholine (ACh) which opens a Cl(-)-channel in the hair cell membrane. To investigate more closely the nature of the permeability change underlying the ACh reaction, the external Cl(-) was replaced by anions of increasing hydrated size, and to test the possible role of a Cl(-)-pump in the sensory cells, drugs were applied which are known to block active cl(-) pumping in other systems. Experiments indicate that the ACh-operated inhibitory channel of the hair cell is larger than at other inhibitory synapses (or approximately 0.7 nm), while pharmacological treatments (DNP, NaN3, acetazolamide, ammonium acetate, DIDS) fail to demonstrate any active distribution of Cl(-) across the hair cell membrane.

Action Potentials↗
PubMed1986

Conditioning of crossed extensor reflex pathways by independent natural stimulation of labyrinth, neck and elbow joint afferents.

The present experiments demonstrated that labyrinth, neck and elbow joint afferents interact to influence the excitability of crossed extensor reflex pathways projecting to triceps brachii in decerebrate cats. Reflex excitability was dependent on head, neck and elbow position such that it was increased when the elbow was held at full flexion and either the head maintained side down or the neck rotated side up. Such interaction between these afferents is likely to be important in postural control.

Animals↗
PubMed1988

The effect of barium and some channel blockers on sensory discharge of the frog labyrinth posterior canal recorded at rest and during rotation.

The effect on the afferent synaptic transmission of Ba2+, Sr2+, tetraethylammonium (TEA) and 4-aminopyridine (4-AP) has been investigated in the isolated frog labyrinth by intracellularly recording the posterior canal resting and evoked receptor discharge. BaCl2 (0.3 mM) or SrCl2 (1.8 mM) substitution for normal external CaCl2 restored the afferent activity without affecting the membrane potential of the sensory fibres. On further increasing Ba2+ concentration (0.5-5 mM) a dose-dependent increase in the EPSP and spike discharges was observed in all the units examined. Ba2+ (1.8-4 mM) removed the depression of the sensory activity operated by CoCl2 (3 mM), while its facilitatory effect was completely antagonized by raising Ca2+ concentration (up to 10 mM). TEA (20 mM) elicited a clear-cut increase in the EPSP and spike discharges which, however, was less consistent than that produced by Ba2+ (1 mM). The increment in spike frequency produced by TEA and Ba2+ proved to be inversely related to the initial resting firing level of the different units. The 4-AP (4-20 mM) effect resulted in a decrease of the sensory activity, which was fully restored by TEA or Ba2+. In normal saline a linear relationship was found between the mean unit resting discharge and the respective excitatory peak response during sinusoidal rotation (0.1-0.3 Hz). This result suggest that the mechanical response is mainly determined by the unit resting level. Consistent evoked responses were obtained under TEA and Ba2+ treatment which proved to depend linearly on the new mean resting discharge of the different units. Conversely, a reduced evoked response was invariably observed in all the fibres tested in the presence of 4-AP. The present results suggest that Ba2+ and Sr2+ may substitute for Ca2+ in the transmitter release process at the cyto-neural junction, the ability of Ba2+ being even larger than that of Sr2+ and Ca2+ itself. The effects of TEA and 4-AP are discussed in the light of their possible interaction with the presynaptic K+-currents recently described in hair cells.

4-Aminopyridine↗
PubMed1991

Efferent control of posterior canal afferent receptor discharge in the frog labyrinth.

EPSP and spike discharges were intracellularly recorded from 90 afferent fibres of the posterior nerve in the isolated frog labyrinth and the effects of electrical activation of the efferent system were tested. Posterior canal efferent synapses were activated, via an axon reflex, by electrical shocks to the anterior-horizontal nerves. The afferent resting discharge of all fibres tested was affected by efferent stimulation: 39 units were inhibited (43%) and 51 (57%) were facilitated. The efferent system was activated with several stimulation frequencies in the 10-200 Hz range applied for different times (250 ms-10 s). By changing the stimulus parameters, inhibition did not reverse to facilitation or vice versa. Facilitation appeared within the train above a threshold frequency of about 10 Hz. The peak response was readily reached within the first second and then, with long lasting stimulation, a marked adaptation ensued. The increase in firing rate was independent of previous resting activity. The relationship between frequency and facilitatory response is described by a logarithmic function over the 30-200 Hz range tested. At the end of short trains a consistent post-stimulation after-discharge appeared, whose intensity is positively related to stimulation frequency and time. Inhibition was achieved at stimulation rates above 10 Hz, and a post-stimulation rebound discharge was evident, which was linearly dependent on previous stimulation rate. The latency values of both inhibitory and facilitatory effects were measured by taking into account either the EPSP release rate or the spike discharge modifications at all the frequencies tested. Latency proved to decrease exponentially with increasing stimulation time from a minimal value of 3 ms to a maximum of 200 ms, with minor differences between inhibition or facilitation. These long latency values, the presence of a threshold frequency and the stimulus- and frequency dependence indicate that the efferent synapses must be activated repetitively to produce detectable effects on the afferent discharge; this is in line with the discharge pattern of the efferent system fibres physiologically measured in some systems. The present results show that the dual central control of the crista ampullaris of frog posterior canal is potentially capable of setting the receptor population at a variable level of sensitivity to mechanical stimuli, with profound modifications in the canal transfer function and the spike encoding mechanism.

Animals↗
PubMed1996

Precise coexistence of regulatory peptides in the nerve fibers of the amphibian carotid labyrinth demonstrated by a combination of double immunofluorescence labelling and a multiple dye filter.

An application of double-immunolabelling in combination with a multiple dye filter system demonstrated new findings regarding the distribution pattern of peptidergic fibers in the carotid labyrinth to addition to our previous findings shown by the individual filter system. In high magnification images of about 10% of the yellowish fibers which represent the coexistence of two neuropeptides, there was a definite difference in localization between the fluorescence originating from rhodamine (substance P fibers) and from FITC (vasoactive intestinal polypeptide and neuropeptide Y fibers), but it was clear that they are intertwined within a single nerve bundle. This combination method was able to discriminate two different peptidergic fibers which run side by side. The coexistence suggested previously by the individual filter system may actually be due to the phenomenon described above. This means that it is necessary to apply the multiple dye filter system for reliable evidence of coexistence of different two substances in a single nerve fiber.

Animals↗
PubMed1986

Some hydrodynamic properties of the posterior canal in the frog labyrinth related to neuronal responses.

Measurements of the posterior-canal radius of curvature (R), the semicircular-duct radius (r) and the cupula radius (rC) were performed in the frog labyrinth. The Steinhausen-van Egmond equation led to an estimate of the canal endolymph flow, cupula deflection and sensory hair bending during constant angular accelerations (0.2-64 degrees/s2) of opposite directions and increasing duration (1.2-12 s). This analysis suggests that the non-linear canal afferent discharge behaviour exhibited by some units may not arise at the presynaptic level but rather postsynaptically, at the encoder site.

Acceleration↗
PubMed1988

High perilymphatic potassium and rubidium levels modulate the sensory resting discharge in the isolated frog labyrinth.

The effects of high perilymphatic K+ and Rb+ concentrations (20 mM) on the posterior canal resting discharge have been examined in the isolated frog labyrinth. Both K+ and Rb+ produced an increase in spike frequency which is sustained by a parallel increase in the excitatory postsynaptic potential (EPSP) emission rate. High K+ and Rb+ levels reduce the size of the afferent spike, broaden its time course but do not induce repetitive activity at the axon level. The K+ and Rb+ facilitation proved to be inversely related to the fibre's initial resting activity. The facilitation produced by increased K+ was usually larger than that in Rb+ solution. High sensitive and low sensitive units with similar low resting discharge were detected in relation to their response either to K+ or Rb+. The effects of both ions can be explained on the basis of their interactions with the presynaptic hair cell currents.

Action Potentials↗
PubMed1990

Responses of locus coeruleus and subcoeruleus neurons to sinusoidal stimulation of labyrinth receptors.

In precollicular decerebrate cats the electrical activity of 141 individual neurons located in the locus coeruleus-complex, i.e. in the dorsal (n = 41) and ventral parts (n = 67) as well as in the locus subcoeruleus (n = 33), was recorded during sinusoidal tilt about the longitudinal axis of the whole animal, leading to stimulation of labyrinth receptors. Some of these neurons showed physiological characteristics attributed to the norepinephrine-containing locus coeruleus neurons, namely, (i) a slow and regular resting discharge, and (ii) a typical biphasic response to fore- and hindpaw compression consisting of short impulse bursts followed by a silent period, which has been attributed to recurrent and/or lateral inhibition of the norepinephrine-containing neurons. Furthermore, 16 out of the 141 neurons were activated antidromically by stimulation of the spinal cord at T12 and L1, thus being considered coeruleospinal or subcoeruleospinal neurons. A large number of tested neurons (80 out of 141, i.e. 56.7%) responded to animal rotation at the standard frequency of 0.15 Hz and at the peak amplitude of 10 degrees. However, the proportion of responsive neurons was higher in the locus subcoeruleus (72.7%) and the dorsal locus coeruleus (61.0%) than in the ventral locus coeruleus (46.3%). A periodic modulation of firing rate of the units was observed during the sinusoidal stimulus. In particular, 45 out of the 80 units (i.e. 56.2%) were excited during side-up and depressed during side-down tilt (beta-responses), whereas 20 of 80 units (i.e. 25.0%) showed the opposite behavior (alpha-responses). In both instances, the response peak occurred with an average phase lead of about + 18 degrees, with respect to the extreme side-up or side-down position of the animal; however, the response gain (imp./s per deg) was, on average, more than two-fold higher in the former than in the latter group. The remaining 15 units (i.e. 18.7%) showed a prominent phase shift of this response peak with respect to animal position. Similar results were obtained from the subpopulation of locus coeruleus-complex neurons which fired at a low rate (less than 5.0 imp./s), as well as for the antidromically identified coeruleospinal neurons. The response gain of locus coeruleus-complex neurons, including the coeruleospinal neurons, did not change when the peak amplitude of tilt was increased from 5 degrees to 20 degrees at the fixed frequency of 0.15 Hz. This indicates that the system was relatively linear with respect to the amplitude of displacement.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Bilateral communication between vestibular labyrinths in pigeons.

Extracellular action potentials from single horizontal semicircular canal primary afferent fibers were recorded in paralysed decerebrate pigeons during pulse mechanical stimulation of the contralateral horizontal semicircular canal. Clear responses to the contralateral membranous duct displacement stimuli were observed in 51% of the tested 158 horizontal semicircular canal afferents. Generally, three different types of responses were obtained in the primary afferent fibers including excitation, inhibition, and a few complex type neural activity profiles. Inhibitory responses were of larger amplitude and had longer time constants than did excitatory responses. The few complex type responses observed were characterized by an initial excitatory discharge followed by a longer duration decrease in the fiber's firing rate. The sensitivity to stimulation and type of response obtained for each afferent was significantly correlated with the fiber's coefficient of variation value. Regular firing afferents were less sensitive and exhibited primarily excitatory responses (71%) to contralateral canal stimulation. Irregular firing afferents were more sensitive and exhibited mostly inhibitory responses (84%). The present results demonstrate that a communication network for information exchange between the bilateral labyrinths exists in pigeons. The observed responses in primary afferent fibers to contralateral horizontal semicircular canal stimulation are proposed to be mediated by the vestibular efferent system, which could provide an anatomical pathway for information exchange from vestibular receptors on opposite sides of the head.

Afferent Pathways↗
PubMed2005

The murine placenta contains hematopoietic stem cells within the vascular labyrinth region.

In the midgestation murine embryo, several major vascular tissues contain hematopoietic stem cell (HSC) activity. These include the aorta-gonad-mesonephros region (AGM), yolk sac, and fetal liver. Recently, the placenta was demonstrated to harbor hematopoietic progenitors, but it was not examined for HSC activity. We demonstrate here that the placenta also harbors adult-repopulating HSCs. Placental HSCs begin to be detected at embryonic day (E) 11, and HSC numbers increase dramatically between E11 and E12, exceeding the numbers in the circulating embryonic blood. Furthermore, all placental HSC activity is restricted to the GFP+ fraction of cells in Ly-6A (Sca-1) GFP transgenic embryos. Cells coexpressing GFP and endothelial markers CD34 and CD31 are found in the embryonic vasculature of the placental labyrinth. Moreover, placental cell expression of other HSC markers and transcription factors suggests that HSC emergence may occur in the placenta, as has been proposed for other embryonic hematopoietic sites.

Animals↗
PubMedDate not supplied

Morphogenesis and fine structure of the near-term placenta of Talpa europaea: I. Endotheliochorial labyrinth.

Morphological studies of placentation of Talpa europaea confirm an antimesometrially orientated discoidal and chorioallantoidic placentome. This placentome, near term, shows a villous labyrinthine zone with interspersed haematomal areolae on its fetal side, a centrally located fetomaternal junctional zone, and a uterine gland zone towards the myometrium. As shown by light and electron microscopy the interhaemal membrane in the labyrinthine zone develops to an endotheliochorial placentation type. It consists of a prominent maternal endothelium, a distinct interstitial layer, which contains some endometrial debris and is interrupted by some endotheliochorial contact points, a bilayered trophoblast with a thin syncytial and a larger cytotrophoblastic component, and a small fetal endothelium. Disintegration of endometrial epithelium takes place at the areolar glandular mouths and in the junctional zone where a decidual cell reaction can also be observed, but no decidual cells become integrated into the labyrinth. In the spectrum from epitheliochorial to haemochorial placentation, Talpa europaea exhibits a less endotheliochorial type of placentation than is the case with carnivores.

Allantois↗
PubMed1997

Breakdown of stria vascularis blood-labyrinth barrier in C3H/lpr autoimmune disease mice.

Sensorineural hearing loss related to autoimmune disease is a well-recognized condition, although the exact pathophysiologic mechanisms remain unclear. One current theory postulates immune complex-induced interference with blood-labyrinth barrier integrity in the stria vascularis. The C3H/lpr autoimmune mouse was chosen to study the permeability of capillaries in the stria vascularis because this mouse model has demonstrated abnormalities of the stria vascularis and shifts in the auditory brain stem response threshold during active disease. C3H/lpr mice with active disease were compared with younger mice without disease, as well as age-matched C3H/HeJ control mice. The mice were injected with the tracer ferritin and examined by transmission electron microscopy to evaluate the integrity of the capillary tight junctions in the stria vascularis. Four of five mice with active disease were noted to have extensive leakage of ferritin into the perivascular tissues. Neither the young, disease-free autoimmune mice nor the nonautoimmune control mice demonstrated vessel leakage. Thickening of the basement membrane was also noted in the diseased animals. The results imply that active disease leads to a breakdown in the blood-endolymph barrier, which could underlie the hearing loss accompanying autoimmune and other immune diseases.

Age Factors↗
PubMed2002

Effect of noise exposure on blood-labyrinth barrier in guinea pigs.

The influence of noise exposure on the endothelial transport system in the cochlea was investigated using cationic polyethyleneimine (PEI), since systemically administered PEI passes through the capillary endothelial cell and attaches to basal lamina (BL) anionic sites in the cochlea. Under general anesthesia, all guinea pigs were administered an intravenous injection of 0.5% PEI. Thirty minutes later, five animals were exposed to noise (10 kHz, broad band noise, 105 dB SPL) for 30 min, via speakers inserted into the external auditory canal. The remaining five animals (controls) were left without noise exposure for 1 h following PEI injection. All guinea pigs were then immediately sacrificed, and the bony labyrinths were removed. PEI distribution on the BL was assessed in the stria vascularis, spiral ligament, basilar membrane, spiral limbus and Reissner's membrane throughout the cochlea with transmission electron microscopy. Compared to control animals, PEI distribution in the noise-exposed animals was significantly increased in the strial vessels of the basal and second turns and in Reissner's membrane of all turns. In the spiral ligament, basilar membrane and spiral limbus, no significant difference in PEI distribution was observed between the control and noise-exposed animals. These findings indicate that noise exposure increases macromolecular transport in the stria vascularis but not in the spiral ligament, spiral limbus and basilar membrane and that systemically administered macromolecules are more readily transported to Reissner's membrane by noise exposure.

Animals↗
PubMed2003

Automatic measurement of the labyrinth using image registration and a deformable inner ear atlas.

RATIONALE AND OBJECTIVES: This article presents a new method for measuring the shape of the cochlea, vestibule, semi-circular canals, and internal auditory canal using image registration and a deformable inner ear atlas. MATERIALS AND METHODS: Computed tomography images of the inner ear are analyzed by placing them into a common orientation and then registering a digital atlas of the inner ear to the data set. The atlas is deformed from its original shape to match the shape of the inner ear in the computed tomography data set using inverse consistent elastic image registration. This process produces an individualized inner ear atlas containing subject-specific measurements and segmentations of the inner ear anatomy in the target computed tomography data set. The shape measurements include the volume and length of the cochlea, vestibule, semi-circular canals, and internal auditory canal; and the angles between the semi-circular canals. RESULTS: A simulated population of inner ear shapes were generated based on the shape of a real population of inner ear shapes and were used to characterize the measurement error of this method. The deformable atlas was used to measure the shape of the left and right inner ear of six individuals. CONCLUSION: Measurement error for 15 of the 24 measurements of our simulated population had an average error of less than 1% and only one measurement had an average error greater than 2.54%. The deformable human inner ear atlas shows promise as a new method for automatically measuring the shape of the labyrinth.

Adult↗
PubMed1999

Streptomycin perfusion of the labyrinth in the treatment of Menière's disease: a modified technique.

The ideal surgical procedure for Menière's disease would combine the high rate of vertigo control and the good hearing preservation of vestibular nerve section with the low morbidity of labyrinthectomy. Shea's technique of streptomycin perfusion of the labyrinth has been modified by making an additional opening into the posterior semicircular canal in an effort to limit the amount of streptomycin going into the cochlea. Seventeen patients with definite Menière's with poor hearing have had this procedure. Vertigo was controlled in 94% and the hearing preserved in 55%. Vestibular rehabilitation was not a problem. It is speculated that hearing preservation would be better if the procedure were not restricted to those with poor hearing. This method of destruction of the vestibular system carries the possibility of hearing preservation and maintains the possibility of cochlear implantation should this ever be required.

Adult↗
PubMed2004

Subclassification of vestibular disorders by means of statistical analysis in caloric labyrinth testing.

OBJECTIVE: In the past, various attempts were made to perform a quantitative analysis of nystagmographic findings but their diagnostic value was limited. Therefore, the authors present a multivariate analysis of nystagmus findings with the aim of increasing the precision of diagnostic differentiation in cases of vestibular dysfunction. MATERIAL AND METHODS: A group of 387 patients and 40 healthy volunteers were examined over a 14-month period using electronystagmography after stimulation by bithermal, bilateral irrigation of the labyrinth. Amplitude, slow-phase velocity, frequency and directional preponderance were evaluated. RESULTS: No defined normal values for caloric nystagmus parameters could be obtained. However, by using the Mann Whitney U-test and logistic regression analysis a differentiation between pathological and healthy findings as well as between central and peripheral vestibular disorders and even between distinct vestibular disease entities is possible. Using these methods, the nystagmus amplitude was found to be the strongest discriminating parameter. Therefore, sole assessment of nystagmographic findings by selective calculation of the nystagmus slow-phase velocity falls short of the potential offered by electronystagmographic registration. CONCLUSION: For daily clinical routine, counting nystagmus beats leads to the same diagnostic precision as the analysis of slow-phase velocities. In contrast, multivariate analysis of several nystagmus parameters can distinguish between distinct diseases with fairly high precision. This stepwise analysis of nystagmographic data could create the basis for an expert-system tool in the near future.

Caloric Tests↗
PubMed2005

Comparison of the life-time of P25 and A11 TiO2 in a labyrinth flow photoreactor.

A series of experiments for the comparison of activity and life-time of anatase titanium dioxide, Tytanpol All (Chemical Factory "Police", Poland) with Degussa P25 (Germany) was conducted in a labyrinth flow reactor with an immobilized catalyst bed. Phenol, with relatively high concentration up to 100 mg dm(-3), was chosen as a model organic compound. Photocatalytic materials were characterized by determination of: phenol decomposition degree, reaction rate constant, band gap energy, FTIR spectra and phase composition. The pureanatase Tytanpol All shows comparable activity as Degussa P25. However, the life-time of P25 Degussa at high phenol concentration was lower compared to that of anatase A11 because of the carbon deposit formation on P25 surface. The catalytic activity of rutile phase in P25 in the reaction of carbon deposits formation is postulated.

Catalysis↗
PubMed2006

Molecular phylogenetics and evolutionary diversification of labyrinth fishes (Perciformes: Anabantoidei).

Labyrinth fishes (Perciformes: Anabantoidei) are primary freshwater fishes with a disjunct African-Asian distribution that exhibit a wide variety of morphological and behavioral traits. These intrinsic features make them particularly well suited for studying patterns and processes of evolutionary diversification. We reconstructed the first molecular-based phylogenetic hypothesis of anabantoid intrarelationships using both mitochondrial and nuclear nucleotide sequence data to address anabantoid evolution. The mitochondrial data set included the complete cytochrome b, partial 12S rRNA, complete tRNA Val, and partial 16S rRNA genes (3332 bp) of 57 species representing all 19 anabantoid genera. The nuclear data set included the partial RAG1 gene (1494 bp) of 21 representative species. The phylogenetic analyses of a combined (mitochondrial+nuclear) data set recovered almost fully resolved trees at the intrafamily level with different methods of phylogenetic inference. Phylogenetic relationships at this taxonomic level were compared with previous morphology-based hypotheses. In particular, the enigmatic pike-head (Luciocephalus) was confidently placed within the "spiral egg" clade, thus resolving the long-standing controversy on its relative phylogenetic position. The molecular phylogeny was used to study the evolution of the different forms of parental care within the suborder. Our results suggest that the evolution of breeding behavior in anabantoids is highly correlated with phylogeny, and that brood care evolved three times independently from an ancestral free spawning condition without parental care. Ancestral character state reconstructions under maximum parsimony and maximum likelihood further indicated that both bubble nesting and mouthbrooding have evolved recurrently during anabantoid evolution. The new phylogenetic framework was also used to test alternative biogeographic hypotheses that account for the disjunct African-Asian distribution. Molecular divergence time estimates support either a drift vicariance linked to the breakup of Gondwana or Late Mesozoic Early Tertiary dispersal from Africa to Asia or vice versa.

Animals↗