Biomedical subjects

J M Aran

Publications and source records attributed to J M Aran.

At least 55 records · Page 3Linked to original sources

PubMed1993

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.

Animals↗

PubMed1993

Intracochlear electrical tinnitus reduction.

Several reports have indicated that some cochlear implant patients experience a reduction in their tinnitus while listening to noise or speech. In the present study, two patients reporting bilateral tinnitus were selected from a group of adults with the Nucleus cochlear implant. They rated their tinnitus loudness and severity and completed the Tinnitus Handicap Questionnaire. The stimuli for electrical stimulation were charge-balanced pulse trains of various repetition rates (frequencies) and inter-electrode distances. A range of electrodes was chosen in each subject, including basal, medial and apical electrodes. For each condition, the hearing threshold level and the uncomfortable loudness level were determined. A range of stimulus levels between these two values were presented randomly. After each presentation, the patients rated the stimulus loudness and the tinnitus loudness on a 0 to 100 scale. These judgements were used to carefully determine the psychometric function between stimulus level and stimulus loudness, and between stimulus level and tinnitus loudness. All the parameters explored were important for maximizing the relationship between tinnitus reduction and stimulus loudness. First, the effectiveness of electrical stimulation in tinnitus reduction depended on the place along the cochlear partition. Second, a pulse rate of 125 Hz showed the greatest efficiency in terms of the current level needed to suppress tinnitus. Third, these two subjects showed rather poor performances in speech perception when using their speech processor in the usual condition and the hypothesis of an influence from tinnitus annoyance is suggested in addition to some more classical predicting factors of speech recognition in cochlear implant users.

Acoustic Stimulation↗

PubMed1993

Gentamicin uptake by cochlear hair cells precedes hearing impairment during chronic treatment.

Immunodetection of gentamicin (GM) was carried out on surface preparations of the whole organ of Corti from cochleas of guinea pigs treated daily with GM at a dose of 60 mg/kg/day and sacrificed at the end of different treatment periods. Cochlear function was determined just before sacrifice, 24 h after the last injection. Threshold elevations, mainly at high frequencies, were noted only after 10-14 days of treatment. However, the presence of GM was observed much earlier, as early as after the second injection, and specifically in the sensory hair cells. GM labelling was essentially observed in the outer hair cells (OHC) and increased from the apex to the base of the cochlea and from the third to the first row of OHC. GM labelling of inner hair cells was less pronounced and was observed only after the 8th day of treatment. These observations demonstrate that GM specifically enters and accumulates in the sensory hair cells and that the uptake precedes the development of functional and cellular damage which may result from a long-term intracellular cytotoxic action of the molecule.

Animals↗

PubMed1993

Pharmacokinetics of gentamicin in the sensory hair cells of the organ of Corti: rapid uptake and long term persistence.

Confocal laser scanning microscopy and immunofluorescence were used to detect gentamicin at the single cell level in the sensory cells of the guinea-pig hearing organ after a chronic systemic treatment. Gentamicin uptake by the hair cells precedes largely the manifestation of hearing impairment. We demonstrate that for a non-ototoxic treatment the captured gentamicin is eliminated in two phases: one rapid and one slow with approximate half-life of 2 days and 5-6 months, respectively. These novel observations should be of primary importance for new rational approaches to both the mechanism of ototoxicity and therapeutic strategies for the treatment of infectious diseases requiring the aminoglycoside antibiotics.

Animals↗

PubMed1993

Degeneration and reorganization of vestibular epithelia after local aminoglycoside application in the mammalian inner ear.

The development of degeneration of vestibular end organs and their possible reorganization have been observed over a 2 year period after local application of sisomicin in the inner ear using scanning electron microscopy (SEM). Degeneration of stereocilia took place as early as 5 days after the treatment in the utricule, the saccule and the cristae. At 10 days, almost the entire surface of these sensory epithelia presented a smooth aspect without specific structure. However, after 15 days, an epithelial reorganization developed with clear limits between cells. At 25 days, systematic kinociliary structures were observed at the apical surface of the cells. Five months after the treatment, the new kinocilium was still present and sometimes stereociliary-like structures appeared in the three types of vestibular organs. Two years after treatment, the kinocilium persisted and the embryonic-like ciliary tufts had disappeared. These SEM observations suggest that in mammals some vestibular epithelial regeneration is possible but stops at a stage which could correspond to an early developmental level.

Administration, Topical↗

PubMed1993

[Ototoxicity of aminosides: recent results on uptake and clearance of gentamycin by sensory cells of the cochlea].

Recent experiments using autoradiographic and immunohistochemical labelling of gentamicin have demonstrated that GM penetrates specifically into the sensory cells of the inner ear, with a good correlation between the intensity of the labelling and the respective degrees and localisations of ototoxic damages. In the sensory hair cells GM ils localised below the cuticular plate, in an area rich in lysosomes during the ototoxic treatment. This penetration precedes the development of ototoxicity and there seems to be a threshold of intracellular concentration of GM for development of intracellular ototoxic processes. Clearance is very slow since GM can still be observed 11 months after the end of a non toxic treatment (60 mg/kg/day for 6 consecutive days). This observation is of clinical interest, in view of the delayed development of ototoxicity often observed clinically, and with respect to other hazards, including new ototoxic treatments, to which the cells can be exposed while loaded with the aminoglycoside molecule.

Anti-Bacterial Agents↗

PubMed1993

[Implants for the middle ear, development of a human prototype].

Middle ear implants are a new type of hearing aid. Their principle is direct stimulation of the inner ear fluids, by a vibrator implanted in the middle ear. Two technologies are developed by different teams: electromagnetic vibrators, and piezoelectric vibrators. Middle ear implants should be partially implantable (P-MEI), or totally implantable (T-MEI). Authors develop, concurrently with animal experimentation an in vitro method to measure the performance date of the vibrators. The specifications of a future P-MEI have been defined, and vibrators tested with this method. First results encourage to develop this project.

Deafness↗

PubMed1992

Effects of chemical modification of nitrobenzylthioinosine on its binding to high-affinity membrane binding sites and inhibition of nucleoside transport.

Nitrobenzylthioinosine (NBTI) was systematically modified by attachment of substituents at the 2-, 5'-, 3'- and 2'-positions in order to assess the importance of these positions in the binding of NBTI to high-affinity membrane binding sites (Kd < or = 1 nM) and the inhibition of NBTI-sensitive, equilibrative nucleoside transport by mammalian cells. We determined the effect of the derivatives on the equilibrium binding of 1 nM [3H]NBTI to human erythrocytes and mouse P388 leukemia cells and on the inhibition of zero-trans influx of formycin B in P388 cells and equilibrium exchange of uridine in human erythrocytes. Placement of substituent groups at the 5'-position of NBTI had relatively little effect on its binding to high-affinity binding sites or its inhibition of nucleoside transport, regardless of the size of the substituent group (up to about 1000 kDa). All substituents at the 2-position considerably reduced the affinity of NBTI to membrane binding sites and its potency as an inhibitor of nucleoside transport, but some substituent groups reduced the affinity of binding more than the inhibition of nucleoside transport. The effect of the 2-substituents was not directly related to their size. Attachment of a succinate at the 3'- or 5'-position also reduced to a greater extent the binding of NBTI than its inhibition of nucleoside transport, which was relatively little affected. Attachment of succinates at both the 3' and 5'-positions almost completely abolished both binding to high-affinity sites and inhibition of nucleoside transport. Both functions of NBTI were abolished completely by the simultaneous blockage of the 2'- and 3'-positions. None of the NBTI derivatives significantly inhibited NBTI-resistant equilibrative formycin B transport in P388 and Novikoff rat hepatoma cells at concentrations of < or = 1 microM.

Animals↗

PubMed1992

Nucleoside transport-deficient mutants of PK-15 pig kidney cell line.

Previous studies indicated that PK-15 pig kidney cells express solely a nitrobenzylthioinosine-sensitive, equilibrative nucleoside transporter. In the present study, PK-15 cells were mutagenized by treatment with ICR-170 and nucleoside transport-deficient mutants selected in a single step in growth medium containing tubercidin and cytosine arabinoside at a frequency of about 2 x 10(6). The mutants were simultaneously at least 100-times more resistant to tubercidin, cytosine arabinoside and 5-fluorodeoxyuridine than the wild-type parent cells. The mutants failed to transport thymidine and uridine and had lost all high affinity nitrobenzylthioinosine binding sites. Residual low level uptake of thymidine by the mutants was shown to be due to nonmediated permeation (passive diffusion), which explains the sensitivity of the mutants to growth inhibition by high concentrations of the nucleoside drugs. Passive diffusion of thymidine at a concentration of 16 microM was not rapid enough to support the growth of nucleoside transport-deficient mutant cells that had been made thymidine-dependent by treatment with methotrexate, whereas wild-type cells grew normally under these conditions. The nucleoside transport-deficient mutants exhibited about the same growth rate and plating efficiency (60-80%) as wild-type cells, but formed larger colonies than wild-type cells because of a more extensive spread of the cells on the surface of culture dishes. PK-15 cells adhere very strongly to the surface of culture dishes and have been transformed with high efficiency with plasmid DNA either via lipofection or electroporation.

Animals↗

PubMed1992

High-affinity, equilibrative nucleoside transporter of pig kidney cell line (PK-15).

Nucleoside transport was determined in the cloned porcine kidney cell line PK-15 which exhibits properties of tubular cells. The cells did not express any Na(+)-dependent, concentrative nucleoside transport. They exhibited only nitrobenzylthioinosine-sensitive equilibrative nucleoside transport. Their transport activity, however, was only about 10% of that observed in many other mammalian cell lines. This low transport activity correlated with a relatively low number of high-affinity nitrobenzylthioinosine binding sites (5 x 10(3)/cell). Furthermore, although the equilibrative transporter of PK-15 cells exhibited a similar broad substrate specificity as the equilibrative nucleoside transporters of other mammalian cells, it exhibited a much higher affinity for certain nucleosides, especially cytidine and uridine, than the latter. The Michaelis-Menten constants for zero-trans transport and equilibrium exchange of uridine in ATP-depleted cells were about the same (about 40 microM), indicating equal mobility of the nucleoside-loaded and empty carrier. Concentrative nucleoside transport was detected in one set of PK-15 cultures, but was found to be due to mycoplasma contamination.

Adenosine Triphosphate↗

PubMed1992

Cellular and subcellular localization of tritiated gentamicin in the guinea pig cochlea following combined treatment with ethacrynic acid.

Guinea pigs (GPs) receiving one intra-muscular injection of gentamicin (GM) (150 mg/kg) in which 2 mg of tritiated GM (2 mCi) were incorporated, followed 1.5 h later by an intra-cardiac injection of ethacrynic acid (EA) (30 mg/kg) were sacrificed 25 min, 1, 4 and 24 h after the EA injection. Other GPs were treated with one injection of GM or EA alone and sacrificed 24 h later. Cochlear function was monitored by recording VIIIth nerve compound action potential (CAP) responses to clicks at 70 dB peak-equivalent Sound Pressure Level (pe SPL) and CAP audiograms. At 24 h thresholds were significantly elevated for high frequencies only in GPs treated with the GM/EA combination. GM was revealed in the cochlea and kidney by autoradiography using light and electron microscopy. In the kidney GM was already detected in the proximal tubule cells at 25 min and at 24 h. In the cochlea GM was systematically not observed at 25 min. At 1 h a weak labelling was detected in vessels of the stria vascularis and in sensory cells at the base of the cochlea. At 4 h the labelling disappeared in stria vascularis but increased in the hair cells. At 24 h GM labelling was found exclusively in hair cells, particularly outer hair cells, with a gradient from base to apex and from first to 3rd row, this distribution pattern correlating well with the pattern of threshold changes prominent at high frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1992

Kinetics of gentamicin in cochlear hair cells after chronic treatment.

Presence of gentamicin (GM) in cochlear hair cells was detected by immunohistochemistry in guinea pigs (GPs) cochlea 1, 9 and 41 days after a 6-day treatment with GM at 60 mg/kg/day (s.c.). The number of GPs in each group was respectively 7, 12 and 6. Twelve other non-treated GPs served as controls. Cochlear function was measured, just before sacrifice, by VIIIth nerve compound action potential (CAP) audiograms. Functional and immunohistological evaluations were performed by two independent naïve observers respectively. Functional changes were minimal: only one out of the 25 treated GPs, from the 41-day group, showed significant threshold elevations on high frequencies. Meanwhile GM labelling was observed in most outer hair cells (OHCs) from the three rows of all the treated GPs, with radial and longitudinal gradients, and found similar in the 3 groups. These results 1) confirm that GM is significantly present in OHCs before the development of ototoxicity and 2) indicate that GM accumulates and is maintained inside the OHCs for very long periods of time, i.e. that its clearance from the hair cells, if any, would be very slow.

Animals↗

PubMed1992

Axo-somatic contacts in the postnatal developing white rat spiral ganglion.

Development of the spiral ganglion in white rats was followed during the first 2 weeks after birth and morphological characteristics of the two neuronal types (I and II) were examined. In some neurons different stages of partial degeneration leading to formation of residual bodies were found without observation of degenerated cell, supporting the idea that differentiation at this time is not associated with cell death. Contacts between cell body of type II neurons and neuronal endings is reported for the first time. Such axo-somatic contacts previously observed only in monkey and man, also exists in lower mammals.

Animals↗

PubMed1992

[Tinnitus: peripheral and central aspects].

Tinnitus is often related to a peripheral impairment which seems to trigger an abnormal autonomous functioning of the central auditory system. Moreover peripheral stimulations may diminish, and even suppress their perception, either through masking or through inhibition of an aberrant neuronal activity. Here we present an experimental model of peripheral deafferentation in which a decrease of neurochemical activity is observed in the brainstem auditory nuclei, followed by a progressive recovery after the peripheral destruction. This activity could represent a central morphofunctional correlate of tinnitus. Development of experimental models of tinnitus must be continued. Such models should allow the study of the basic physiological mechanisms behind tinnitus and suggest some therapeutic approaches which could be objectively evaluated.

Animals↗

PubMed1991

Fitting integrated enzyme rate equations to progress curves with the use of a weighting matrix.

A method is presented for fitting the pairs of values product formed-time taken from progress curves to the integrated rate equation. The procedure is applied to the estimation of the kinetic parameters of the adenosine deaminase system. Simulation studies demonstrate the capabilities of this strategy. A copy of the FORTRAN77 program used can be obtained from the authors by request.

Adenosine Deaminase↗

PubMed1991

In vivo noise exposure alters the in vitro motility and viability of outer hair cells.

The in vitro motility and viability of outer hair cells isolated from cochleae of normal control guinea pigs have been compared to that of guinea pigs exposed, just before sacrifice, to low-frequency high-intensity noise inducing acute 30 dB thresholds shifts at all frequencies below 10 kHz. The results indicate that the cells' viability is shortened, their contractile response to Ca2+/ATP reduced, while their electrically-induced motility is not modified. These experiments demonstrate that in vivo cochlear dysfunction can correlate with changes in in vitro outer hair cell's properties. Thus the morphological and "functional" investigation of hair cells in vitro can be a valuable approach to the study of cochlear physiopathology. Here the acoustic overstimulation seems to have modified the outer hair cells' Ca2+/ATP dependent slow contractile apparatus in a way which could modify in turn their mechanical excitation by the noise.

Adenosine Triphosphate↗

PubMed1991

Extracellular ATP elevates cytosolic Ca2+ in cochlear inner hair cells.

The local extracellular application of ATP to isolated sensory inner hair cells (IHC) generated a rapid and transient increase in the concentration of cytosolic free Ca2+, peaking within 1 to 5 s. The dose-response curve indicated a half-max stimulation to be 5 microM ATP. The application of the structural derivatives ADP and alpha-beta-methyleneATP did not generate significant Ca2+ response. By contrast, ATP-alpha-S, an agonist for P2z receptor, was fully active in generating Ca2+ responses. In the absence of extracellular free calcium, the ATP-induced Ca2+ increase was still observed, indicating that ATP generated the liberation of Ca2+ from internal stores. These results suggest that extracellular ATP, through an activation of P2-purinergic receptors, may have a neuromodulatory role in the cochlear physiology at the level of the IHC.

Adenosine Triphosphate↗

PubMed1991

Presence of adenosine deaminase on the surface of mononuclear blood cells: immunochemical localization using light and electron microscopy.

Adenosine deaminase, which is essential for lymphoid differentiation and function, has previously been considered to be a cytosolic enzyme. In this report we demonstrate that it can be found associated with the plasma membrane of lymphocytes. By means of immunological techniques using both light and electron microscopy, adenosine deaminase was localized on the external side of the plasma membrane of normal lymphocytes and monocytes. Since the enzyme expression differed depending on the type of cell examined, new hypotheses about the mechanisms involving purine metabolism in immune dysfunctions or immunodeficiency syndromes may be considered.

Adenosine Deaminase↗