Changes in cochlear function after double-membrane rupture in the guinea pig

We measured the transiently evoked otoacoustic emissions (TEOAEs), compound action potentials (CAPs) and cochlear microphonics (CMs) in guinea pigs after rupture of the round window membrane alone (n = 5) or of the round window membrane with localized cochlear damage (n = 10). The localized cochlear damage entailed rupture of Reissner's membrane with damage to the stria vascularis. We determined the time course of changes in the total echo power (TEP) in TEOAEs and the minimal detectable levels of CAPs and CMs. The endocochlear potential (EP) was measured in the cochlea with localized damage. There were no changes in TEOAEs, CAPs or CMs in the guinea pigs subjected to round window membrane rupture alone, but the minimal detectable levels of CAPs and CMs were increased in all the guinea pigs in which TEOAEs were absent after rupture of the round window membrane with localized cochlear damage. Our results suggest that double-membrane rupture (rupture of the round window membrane with localized cochlear damage) produces acute sensorineural hearing loss. The hearing loss appeared to be related to damage to the cochlea, which may be induced by influx of potassium-rich endolymph into the perilymph, and by morphological damage to the scala media.     

The tonic sympathetic input to the cochlear vasculature in guinea pig

Vascular tones is an essential component in maintaining steady regional blood flow and dynamic responsiveness of a vascular bed. Sympathetic innervation can contribute to vascular tone. Although certain studies have reported evoked changes in cochlear blood flow (CBF) with activation of the sympathetic fibers to the cochlear vasculature, other studies have failed to show evidence of sympathetic contribution to CBF regulation when the cervical sympathetic fibers were unilaterally sectioned. We hypothesized that the bilateral 'sympathectomy of the stellate ganglia' would remove sufficient sympathetic input to the cochlea to yield a change in CBF resting level. To test this hypothesis a new technique was used to expose the stellate ganglia (SG) bilaterally and induce a chemical sympathectomy. We observed that unilateral SG blockade with 2 microliters of 4 mM lidocaine hydrochloride on either side produced a 5-10% increase in CBF, which recovered to baseline during the following 2 min. A subsequent blockade of the contralateral SG produced a rapid 25-35% increase, which then recovered partially during the following 3-4 min, remaining 5-15% above the baseline over a 20 min measurement period. Superior cervical ganglion transection did not affect CBF. Our results provide evidence for the existence of a tonic sympathetic component in the control of vascular tone in guinea pig cochlea. This neural effect is derived bilaterally from SG. This result is consistent with previous anatomical studies showing the bilateral innervation of the cochlea by the SG sympathetic fibers and with previous physiological studies on the bilaterality of evoked changes in CBF due to electric stimulation of SG.     

Effects of K(+)-channel blockers on cochlear potentials in the guinea pig

The effects of different K+ channel blockers, 4-aminopyridine (4-AP), tetraethylammonium (TEA) and quinine, on the various cochlear potentials were observed by the means of perilymph infusion. Each of the three blockers depressed the compound action potential. However, they exerted quite different effects on other cochlear potentials, especially comparing 4-AP, a fast K(+)-channel blocker, with two other blockers. 4-AP induced a significant increase in the magnitude of summating potential, while TEA and quinine decreased it; 4-AP showed no effect on the general endocochlear potential (G-EP, the EP value recorded directly from the scala media, SM) and the negative EP component (N-EP), while TEA and Quinine increased G-EP and decreased the absolute value of N-EP. They also exerted different effects on the EP changes induced by exposure to intense noise. The results indicate the different roles of different K(+)-channels in the generation of cochlear potentials. The relationship of the two components of EP (positive and negative) and the G-EP was discussed.     

Differences between guinea pig and rat in the dorsal cochlear nucleus: expression of calcium-binding proteins by cartwheel and Purkinje-like cells

This study describes differences between guinea pig and rat in the immunoreactivities for calbindin (CB-IR) and parvalbumin (PV-IR) in cartwheel (CWC) and Purkinje-like (PLC) cells of the dorsal cochlear nucleus (DCN). CWCs are the most important inhibitory interneurons of the DCN. Their soma and dendrites stain intensely for CB-IR in guinea pigs but only weakly and incompletely in rats. In both species, the CWCs do not show PV-IR. PLCs, a rare type of DCN cells often interpreted as displaced cerebellar Purkinje cells misrouted during migration, are known from rat and mouse and are here described for guinea pig DCN. PLCs are intensely and completely stained for CB-IR and PV-IR in guinea pigs. In rats, they stain with similar completeness only for CB-IR, PV-IR being weak and restricted to the cell's soma. Similar staining differences between the two species are seen with the cerebellar Purkinje cells, i.e., PLCs resemble the cerebellar Purkinje cells more than do the CWCs. Based on the present material (and preliminary findings in a primate (marmoset), we speculate that the PLCs have their place in the circuitry of the DCN receiving input via parallel fibers, like the CWCs, and possibly projecting their axon onto the cerebellum.     

Effects of electrical stimulation of the superior cervical ganglion on cochlear blood flow in guinea pig

A twenty-four-hour blood pressure (BP) monitoring was performed in 20 normotensive and 20 hypertensive subjects, matched by sex and age. Blood pressure and heart rate (HR) variability were evaluated both as absolute and percent standard deviation. In agreement with the literature no significant difference in HR and BP variability was observed between the two groups. The linear regression between HR and BP values was evaluated in both groups. The authors observed a significant difference in the relationship between these two cardiovascular variables between the two groups. In the hypertensive group the cardiovascular control of HR and BP showed a different relationship than in normotensive subjects, suggesting a different neurovegetative modulation.     

Effects of high intensity impulse noise on ionic concentrations in cochlear endolymph of the guinea pig

The time course of folding of a small beta-sheet protein reveals formation of a central ligand binding cavity before the consolidation of the native hydrogen bonding network. These results suggest that side chain interactions and not stable hydrogen bonding determine the beta-sheet architecture and play crucial roles in the overall chain topology.     

Neuronal degeneration of primary cochlear and vestibular innervations after local injection of sisomicin in the guinea pig

This paper reports on a dynamic study of the morphological changes within the cochlear and vestibular ganglia of the guinea pig after local application of Sisomicin in the inner ear. The treatment leads to a rapid, complete and irreversible destruction of the sensory cells in the cochlear and vestibular neuroepithelia. A progressive degeneration of the type I and type II afferent neurons, presenting a decreasing gradient from the base towards the apex of the cochlea, is rapidly observed and becomes almost complete as early as 15 days after the peripheral injury. Five months after the treatment the spiral ganglion cells have almost completely disappeared. At this time the vestibular ganglion cell density appears normal but the neurons exhibit important signs of alteration. Such damage to the cochlear and vestibular afferent neurons may result from either retrograde neuronal degeneration and/or direct neurotoxic effect of the drug. Thus the combination of the two mechanisms could lead to neuronal losses in spiral and Scarpa's ganglia after the local aminoglycoside intoxication of the inner ear. The difference in the time course of degeneration for these two afferent ganglia could be due to their specific susceptibilities or to their different anatomical locations.     

Photochemically induced focal cochlear lesions in the guinea pig: II. A transmission electron microscope study

We report the characterization of a de novo unbalanced chromosome rearrangement by comparative genomic hybridization (CGH) in a 15-day-old child with hypotonia and dysmorphia. We describe the combined use of CGH and fluorescence in situ hybridization (FISH) to identify the origin of the additional chromosomal material on the short arm of chromosome 6. Investigation with FISH revealed that the excess material was not derived from chromosome 6. Identification of unknown unbalanced aberrations that could not be identified by traditional cytogenetics procedures is possible by CGH analysis. Visual analysis of digital images from CGH-metaphase spreads revealed a predominantly green signal on the telomeric region of chromosome 10p. After quantitative digital ratio imaging of 10 CGH-metaphase spreads, a region of gain was found in the chromosome band 10p14-pter. The CGH finding was confirmed by FISH analysis, using a whole chromosome 10 paint probe. These results show the usefulness of CGH for a rapid characterization of de novo unbalanced translocation, unidentifiable by karyotype alone.     

Glycine receptors in adult guinea pig brain stem auditory nuclei: regulation after unilateral cochlear ablation

Behavioral, endocrinological, and pharmacological data suggest that the emotional response of rodents to the elevated plus-maze alters as a function of prior test experience. In the present study, 74 intact male Swiss-Webster mice were exposed to the plus-maze for 5 min on each of 3 consecutive days, with all test sessions recorded on videotape. Behavior patterns for each trial were scored using ethological analysis software and the resultant database subjected to a number of statistical treatments. Analysis of full session profiles (i.e., 5 min total scores) showed that a single prior undrugged experience of the maze increases behavioral indices of anxiety and that these alterations are either maintained or further enhanced on subsequent trials. Furthermore, the behavioral profile evident by trial 3 was largely unchanged when animals were reexposed to the maze 10 days later. More detailed (i.e., min by min) examination of behavior patterns within and between trials demonstrated that unambiguous open arm avoidance is acquired by the third minute of trial 1, and that the behavioral profile evident by the end of trial 1 is (a) markedly different to that seen at the beginning of that trial, and (b) generally maintained or even accentuated on trials 2 and 3. The implied impact of prior test experience on future behavioral strategy in the maze was strongly supported by a series of factor analyses. Thus, while the factor associations of vertical activity and directed exploration remained constant across trials, trial 2 and 3 anxiety measures loaded on a separate factor to that loading trial 1 anxiety measures. A similar trial 1 vs. trials 2 and 3 dissociation was observed for measures of locomotor activity. Although the present findings are consistent with the proposal that prior test experience produces a qualitative shift in emotional response to the elevated plus-maze, the precise basis for this change as well as its full significance for our understanding of anxiety-related processes remain to be determined.     

Lipopolysaccharide-induced expression of reactive oxygen species and peroxynitrite in the guinea pig vestibular organ

The purpose of this study was to investigate the occurrence of reactive oxygen species and peroxynitrite in the vestibular organ of the guinea pig following inoculation with bacterial lipopolysaccharide (LPS). The animals were injected transtympanically with 1 mg of LPS 24 h after the intraperitoneal injection of 0.1 mg LPS. Forty-eight hours after the inoculation, varying degrees of degeneration of the vestibular end organs were observed. Immunohistochemical study revealed immunoreactivity to xanthine oxidase (which generates O-2) in the vestibular organ after inoculation with LPS. Immunohistochemical investigation with a specific antinitrotyrosine antibody also showed intense staining of sensory epithelium, fluid transporting cells and the endolymphatic sac, suggesting formation of peroxynitrite in the vestibular organ through the reaction of NO with O-2. On the basis of these data, it can be concluded that NO together with O-2, which form more reactive peroxynitrite, may be the most important pathogenic agents in LPS-induced labyrinthitis in the guinea pig.     

Skin surface lipids of the guinea pig

Skin surface lipids of the guinea pig were found to contain sterol esters (33%), wax diesters (diacyl alkanediols) (24%), glycerol ether diesters (28%), free fatty alcohols (6%) and free sterols (9%). The sterol esters and diacyl alkanediols contained saturated fatty acids (40 and 67%, respectively) having straight and singly-branched chains and mono-unsaturated acids (60 and 33%,respectively) derived predominantly by delta 9-desaturation of C15 and C16 straight-chain saturated fatty-acid precursors. The 1-O-alkylglycerols and fatty acids from the glycerol ether diesters were both entirely saturated series containing straight, branched and multi-branched chains. Both the free and the esterified sterols consisted principally of cholesterol with a small proportion of lathosterol.     

Neurokinin receptors in the guinea pig ileum

The gating kinetics of apical membrane Na channels in the rat cortical collecting tubule were assessed in cell-attached and inside-out excised patches from split-open tubules using the patch-clamp technique. In patches containing a single channel the open probability (Po) was variable, ranging from 0.05 to 0.9. The average Po was 0.5. However, the individual values were not distributed normally, but were mainly < or = 0.25 or > or = 0.75. Mean open times and mean closed times were correlated directly and inversely, respectively, with Po. In patches where a sufficient number of events could be recorded, two time constants were required to describe the open-time and closed-time distributions. In most patches in which basal Po was < 0.3 the channels could be activated by hyperpolarization of the apical membrane. In five such patches containing a single channel hyperpolarization by 40 mV increased Po by 10-fold, from 0.055 +/- 0.023 to 0.58 +/- 0.07. This change reflected an increase in the mean open time of the channels from 52 +/- 17 to 494 +/- 175 ms and a decrease in the mean closed time from 1,940 +/- 350 to 336 +/- 100 ms. These responses, however, could not be described by a simple voltage dependence of the opening and closing rates. In many cases significant delays in both the activation by hyperpolarization and deactivation by depolarization were observed. These delays ranged from several seconds to several tens of seconds. Similar effects of voltage were seen in cell-attached and excised patches, arguing against a voltage-dependent chemical modification of the channel, such as a phosphorylation. Rather, the channels appeared to switch between gating modes. These switches could be spontaneous but were strongly influenced by changes in membrane voltage. Voltage dependence of channel gating was also observed under whole-cell clamp conditions. To see if mechanical perturbations could also influence channel kinetics or gating mode, negative pressures of 10-60 mm Hg were applied to the patch pipette. In most cases (15 out of 22), this maneuver had no significant effect on channel behavior. In 6 out of 22 patches, however, there was a rapid and reversible increase in Po when the pressure was applied. In one patch, there was a reversible decrease. While no consistent effects of pressure could be documented, membrane deformation could contribute to the variation in Po under some conditions.     

Taurine entry into perilymph of the guinea pig

Taurine is a beta-aminosulfonic acid and is a ubiquitous amino acid whose role in the cochlea is not well established. In this study, its entry from blood into perilymph was investigated in the guinea pig as animal model. The penetration rate of [3H]taurine (molecular weight 125) into the perilymph of the scala vestibuli was measured 1 and 2 h after the intravenous infusion of [3H]taurine in nephrectomized animals. Results showed a rate of penetration in perilymph related to plasma at 36 +/- 4.7% (n = 5) after 1 h and 43 +/- 5.6% (n = 5) after 2 h. Compared to the penetration rate of urea (molecular weight 60) and mannitol (molecular weight 186) reported previously in rats, a passive entry of taurine into perilymph through the blood-perilymph barrier is suggested.     

Regulatory mechanism of pepsinogen gene expression in monolayer cultured guinea pig gastric chief cells

We have investigated the effects of dibutyryl cAMP, forskolin, carbamylcholine chloride (carbachol), ionomycin, and 12-O-tetradecanoylphorbol-13-acetate (TPA) on the expression of guinea pig pepsinogen mRNA in monolayer cultured gastric chief cells. After exposure of the cells to each of these compounds for 4 to 24 hr, and at 48 hr after primary culture, total cellular RNA was isolated using acid guanidium-phenol-chloroform and then was reverse transcribed to cDNA. Obtained cDNA was amplified by polymerase chain reaction (PCR) using primers detecting guinea pig pepsinogen mRNA and human beta-actin mRNA as an internal standard. The PCR products were separated and quantified using capillary electrophoresis. Dibutyryl cAMP and forskolin significantly increased pepsinogen mRNA, but carbachol, ionomycin, and TPA failed to increase that. These findings suggested that pepsinogen gene expression was up-regulated by intracellular cAMP, but not by intracellular calcium or protein kinase C in guinea pig chief cells.     

Uptake of tetracycline in otoconia of the guinea pig

Calcium ion turnover in the otoconia of adult guinea pigs was investigated by observing the uptake of tetracycline. Oral administration of tetracycline resulted in the deposition of tetracycline (fluorescence) on the outer surface of otoconia, indicating the occurrence of dynamic exchange and/or uptake of calcium ions in the otoconia. Prolonged administration of tetracycline induced with fluorescence deposition in the central portion as well as on the surface of the otoconia. These findings suggest the occurrence of neogenesis, regeneration and/or growth of otoconia even in adult animals.