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Biomedical subjects

R Pujol

Publications and source records attributed to R Pujol.

At least 109 records · Page 6Linked to original sources
PubMed1993

Sulphhydryl-modifying reagents alter ototoxin block of muscarinic receptor-linked phosphoinositide turnover in the cochlea.

In the 12-day-old rat cochlea, the synthesis of inositol phosphates (IPs) can be activated via M3 cholinoceptors. This stimulation is blocked by ototoxins (mercury, ethacrynate, cisplatin, neomycin), drugs with side effects that lead to damage of hair cells and strial cells. As these toxic effects can be reversed in vivo by thiol molecules, we investigated whether modifications of thiol compounds could be involved in ototoxin-induced inhibition of the IP turnover in the cochlea. For this purpose, we assessed whether the sulphhydryl-modifying reagents N-ethylmaleimide and cadmium modify the carbachol-stimulated formation of IPs in the 12-day-old rat cochlea. Both molecules inhibit the carbachol effect on a dose-dependent way without altering the basal metabolism of IPs. As cadmium may block some calcium channels, the effect of verapamil, another calcium channel antagonist, was tested. Verapamil (1-50 microM) does not alter carbachol-evoked IP formation, suggesting that the inhibitory effect of cadmium is not due to a calcium influx block. Binding experiments with the muscarinic ligand quinuclidinyl benzylate (QNB) showed that the sulphhydryl-modifying reagents do not displace QNB from binding sites. Combining ototoxins and reagents shows that N-ethylmaleimide acts synergistically with all ototoxins but ethacrynate while cadmium does so only with mercury. Both N-ethylmaleimide and cadmium have additive effects with ethacrynate. As a supplement, disulphide bond-modifying agents do not alter the carbachol-enhanced metabolism of IPs. These results suggest that molecules having thiol-modifying properties inhibit the carbachol-induced turnover of IPs without acting at the muscarinic sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Characterization of muscarinic binding sites in the adult and developing rat cochlea.

The maturation of the cholinergic innervation of the rat cochlea is associated with a transient increase in the muscarinic-receptor activated inositol phosphate synthesis. In order to investigate the mechanisms involved in this transient enhancement of the inositol phosphate response, the binding properties of the cochlear muscarinic receptors were studied during rat cochlear development. Incubating the membranes from 4-day-old, 12-day-old and adult cochleas with [3H]quinuclidinyl benzylate indicates that their respective, mean concentrations of cholinoceptors are 454 +/- 51 (+/- SEM), 39 +/- 2 and 42 +/- 3 fmol/mg of protein. The dissociation constants at equilibrium are 207 +/- 80, 42 +/- 7 and 28 +/- 3 pM for the binding sites of the 4-day-old, 12-day-old and adult cochleas, respectively. Pharmacological characterization of the binding, using selective antagonists, shows that M3 cholinoceptors are expressed in developing and adult cochleas. The data demonstrate that changes in muscarinic receptor affinity and number do not correlate with the previously observed peak of the inositol phosphate metabolism. The transient enhanced inositol phosphate response is therefore not due to changes in cholinoceptors, but probably due to alterations involving the intrinsic activity of the phospholipase C and/or the efficacy of coupling of the transduction system.

Aging↗
PubMed1993

Inhibition of the carbachol-evoked synthesis of inositol phosphates by ototoxic drugs in the rat cochlea.

The ability of amikacin, neomycin, ethacrynate, mercuric chloride and cisplatin to alter the inositol phosphate (IP) signalling pathway was assessed in the 12-day-old rat cochlea, where the turnover of IPs is coupled to muscarinic receptors. This study was motivated by: (1) the demonstration of neomycin binding to phosphatidylinositol 4,5-biphosphate, the precursor of IPs, and (2) the fact that ototoxic drugs induce some common symptoms in outer hair cells. At concentrations below 1 mM, none of the compounds changed the control 3H-IP formation. Mercuric chloride, cisplatin and ethacrynate inhibited the carbachol-induced formation of IPs in a dose-dependent manner with IC50 values of 74,340 and 430 microM, respectively. The aminoglycosides were less efficient in reducing the carbachol-stimulated accumulation of IPs, since neither amikacin nor neomycin, both at 1 mM, had any significant effect. However, neomycin applied at 15 and 30 microM induced 29% and 43% of inhibition of the stimulated IP response. Finally, additive effects are obtained between some of the toxic drugs. The results suggest that a block of the IP transduction system, associated with the cholinergic efferent innervation of the organ of Corti, is a feature that may be involved in some types of ototoxicity. The inefficiency of aminoglycosides and the putative targets of the ototoxic agents are discussed.

Amikacin↗
PubMed1993

Pathophysiology of the glutamatergic synapses in the cochlea.

The synapses between the inner hair cells (IHCs) and the radial auditory dendrites are thought to be glutamatergic. Besides its fast excitatory properties, glutamate is known to be neurotoxic when released in excess or incompletely recycled. In the cochlea, this may occur in two pathological conditions: ischemia and noise trauma. We have further investigated the acute excitotoxicity (i.e. the swelling of type I afferent dendrites) by electron microscopy processing on guinea pig cochleas after an ischemic exposure lasting 5 to 40 min. The radial auditory dendrites reacted to ischemia in a time-dependent manner, with the swelling extending when the duration of ischemia increased. The type and the specificity of swelling were comparable to what acutely occurs after an exposure to glutamate analogs such as kainic acid or AMPA. A protection against this swelling was obtained by perfusing the cochlea with glutamate antagonists prior to ischemia. DNQX, an antagonist at AMPA/kainate receptors, had a powerful protective effect, and almost complete protection was obtained by perfusing both DNQX and D-AP5 (a NMDA antagonist). The latter results indicate that the two classes of glutamate receptors (AMPA/kainate and NMDA), both found to be electrophysiologically active at the IHC-auditory nerve synapse, are also involved in the excitotoxic processes. In addition, we also report data involving dopamine (its D2 agonist piribedil) a putative neurotransmitter at the lateral efferent synapses, in a postsynaptic protection of primary auditory neurons during transient ischemia. Altogether, these findings constitute a promising pharmacological approach of cochlear pathologies such as neural presbycusis.

Animals↗
PubMed1993

Changes in 2f1-f2 distortion product otoacoustic emissions following alterations of cochlear metabolism.

This paper summarizes the results obtained from investigations in which distortion product otoacoustic emissions (DPOAEs) were studied together with other cochlear physiological parameters. The cochlear metabolism was subjected to three different experimental conditions: guinea pigs were either submitted to hypoxia, to an intra-cochlear perfusion of ouabain or to an intra-cochlear perfusion of naloxone. The data show that DPOAEs remain affected for a certain time after the metabolic perturbations were removed. The comparison of the behaviour of DPOAEs and of other cochlear parameters gives good indications on the way these different experimental procedures affect the functioning of the cochlea during and after their application.

Acoustic Stimulation↗
PubMed1992

Ultrastructure of the horseshoe bat's organ of Corti. II. Transmission electron microscopy.

The fine structure of the organ of Corti was investigated in the echolocating horseshoe bat (Rhinolophus rouxi) by transmission electron microscopy. Particular emphasis was placed on the receptor cells and their supporting cells. The receptor cells, inner hair cells (IHC) and outer hair cells (OHC), possess the typical mammalian shape, but OHCs are extremely short (length: 12-15 microns in the basal turn and up to 28-30 microns in the apical turn). The afferent innervation of both types of receptor cells and the efferent innervation of the IHC system conform to the general mammalian scheme; however, confirming earlier reports, an efferent innervation to the OHCs is absent. Throughout the cochlea, IHCs and OHCs possess a single layer of subsurface cisternae. Above the level of the nucleus of the OHCs, the arrangements of the subsurface cisternae and their connection to the lateral cell membrane via pillars are highly regular, whereas in IHCs, the cisternae are of irregular shape and the pillar system is much less distinct. In the basal turn of the cochlea, the attachment sites of the OHCs to the supporting cells possess specialized features: (a) in the reticular lamina, the contact sites of the cuticular plates of OHCs with the outer pillar cells and the Deiters cell phalanges are of exaggerated length, and (b) the cup formation of the Deiters cell body, which houses the bottom of the OHC, has a specialized shape and is packed with electron-dense material and microtubules. The results are discussed in relation to cochlear ultrastructure in other mammals and in the context of active processes in cochlear mechanics.

Afferent Pathways↗
PubMed1992

Activation of muscarinic cholinergic receptors stimulates inositol phosphates synthesis in the developing avian cochlear duct.

We previously reported that the inositol phosphates (IPs) synthesis is induced by muscarinic agonists in the rat cochlea and that this stimulation is maximal at postnatal day 12. This peak response is concomitant with the onset of the efferent synaptogenesis at the outer hair cell level. Whether the correlation between this neuronal plasticity and the enhanced IPs formation is unique to the rat or a general feature of the developing vertebrate cochlea is not known. To examine this question, we measured, in the presence of LiCl, the accumulation of (3H)-IPs induced by carbachol, in the developing chick cochlear duct during a period ranging from embryonic day (E) 8 to post-hatching day (P) 20. Carbachol (1 mM) causes a significant increase of IPs formation relative to basal values at all ages. This IPs accumulation is maximal at E8 (1854% of the basal level), then, rapidly decreases until P13 when it reaches a steady-state level of 294% of the basal level. Strikingly, this gradual decline in IPs formation is interrupted between E15 and E19, by a transient increase in IPs synthesis. This rise peaks at E16 with a stimulation value of 757% of the control level. This maximal stimulation is inhibited by atropine in a dose-dependent manner, as is the case at E9, suggesting the involvement of muscarinic receptors. Interestingly, the occurrence of the peak response is concomitant with the plastic events associated with the maturation of the efferent innervation of the cochlear duct. Thus, these results suggest that there may be a correlation between cochlear plasticity and enhanced IPs synthesis, which is not species-specific.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Development of neurosensory structures in the human cochlea.

The present paper summarizes the main stages in the maturation of the cochlear neurosensory structures in humans. New trends in the field of the functional development of the cochlea, as well as some recent experimental data are also discussed.

Cell Differentiation↗
PubMed1992

Implication of non-NMDA and NMDA receptors in cochlear ischemia.

We have investigated the hypothesis that the acute ischemic swelling of the radial dendrites connected to the inner hair cells (IHCs) is mediated by glutamatergic receptors. In control cochleas, after 20 min ischemia all the dendrites were dramatically swollen. Conversely, after a perfusion of 50 microM 6-7-dinitroquinoxaline-2,3-dione (DNQX) before ischemia, most dendrites were protected although those contacting the IHCs on their modiolar side frequently swelled. After 50 microM of D-2-amino-5-phosphonopentanoate (D-AP5), no dendrite protection could be obtained. Finally, after DNQX and D-AP5, no dendrite swelling occurred. These results suggest that, in the cochlea, the acute ischemic swelling of dendrites primarily occurs via non-NMDA receptors. However, in radial dendrites contacting the IHCs on their modiolar side, NMDA receptors may contribute to excitotoxicity.

2-Amino-5-phosphonovalerate↗
PubMed1991

The sensory epithelium and its innervation in the mole rat cochlea.

The mole rat (Spalax ehrenbergi) burrows throughout its life in subterranean tunnels. Several structural and functional features which adapt the mole rat to its habitat have been discerned. The goal of this study was to elucidate the structural basis for adaptation of the auditory end-organ to an environment where low-frequency acoustical signals prevail. For this purpose, cochleae of adult mole rats were studied with light and electron microscopy. Inner hair cells throughout the cochlea, and outer hair cells in the basal (high-frequency) portion of the cochlea, were similar in structure to those seen in other mammals. In contrast, outer hair cells in the apical (low-frequency) portion displayed unique structural features. These features resembled the structure of inner hair cells or immature outer hair cells. The innervation of outer hair cells was most uncommon, in that classical medial efferent innervation was not found throughout the cochlear spiral.

Animals↗
PubMed1991

Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid electrophysiological and neurotoxic effects in the guinea-pig cochlea.

We have recorded cochlear potentials after perilymphatic perfusion of cumulative doses of the excitatory amino acid alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) which selectively recognizes the non-N-methyl-D-aspartate ionotropic receptor formerly known as the quisqualate receptor. Our results show that AMPA (1-80 microM) caused a significant suppression of the amplitude of the compound action potential evoked by acoustic stimulation. A total elimination of this potential at the 100 microM concentration was observed in all animals. In no case was the cochlear microphonic potential, a hair cell receptor potential, affected by AMPA. Histological examinations were performed either at the end of the physiological studies or on cochleas perfused for 10 min with a single dose of AMPA (50 or 100 microM). In both experimental conditions, a selective dendritic swelling or radial afferent nerve endings under the sensory inner hair cells was observed. No damage was found in both types of hair cells supporting cells, lateral and medial efferent fibers and spiral afferent nerve ending on the outer hair cells. The occurrence of the radial dendrite swelling was prevented when 6,7-dinitroquinoxaline-2,3-dione (500 microM) was perfused in the cochlea 10 min prior, then concomitantly with AMPA. The present study strongly suggests that non-N-methyl-D-aspartate receptors, possibly of the AMPA subtype, are involved in the synaptic transmission between the inner hair cells and the primary auditory neurons. They provide further support for the hypothesis that L-glutamate, or another excitatory amino acid, acts as an inner hair cell neurotransmitter.

Acoustic Stimulation↗
PubMed1991

Electrophysiological evidence for the presence of NMDA receptors in the guinea pig cochlea.

An excitatory amino acid, possibly L-glutamate, which probably acts as a neurotransmitter at the inner hair cell-afferent fiber synapses in the cochlea. In the present study, we have used an electrophysiological approach to investigate at this level the presence of a major type of excitatory amino acid receptor, namely the glutamatergic receptor for which N-methyl-D-aspartate is a selective agonist. Our results show that, when N-methyl-D-aspartate and the antagonist 2-amino-5-phosphonovalerate are perfused through the perilymphatic scalae, they induced, by different mechanisms, a significant reduction of the amplitude of the compound action potential and an increase of the N1 latency, both predominant at high intensity tone burst stimulations. No significant difference was found in the presence or absence of Mg2+ in the artificial perilymph used as a vehicle. A further slight N-methyl-D-aspartate-induced decrease of the amplitude of the compound action potential, although non significant, was observed when the Mg2(+)-free perilymph contained 100 or 1000 microM glycine. In all the experimental conditions, no effect was observed on the cochlear microphonic potential. This observation is consistent with an action of N-methyl-D-aspartate and 2-amino-5-phosphonovalerate at receptors located on the auditory nerve dendrites contacting the inner hair cells. In conclusion, our results suggest the presence of N-methyl-D-aspartate receptors in the cochlea.

2-Amino-5-phosphonovalerate↗
PubMed1991

First appearance and development of motile properties in outer hair cells isolated from guinea-pig cochlea.

Cochleae from fetal guinea-pigs (37 to 64 gestation days, gd) were used to correlate the appearance of motile properties of isolated outer hair cells (OHCs) with the development of specific morphological features. Both the 'fast' electrically-driven and the 'slow' calcium-induced motilities appeared first in OHCs from basal turn of 52 gd fetuses. At 56 gd, most of basal and some apical OHCs responded positively to both types of stimulation. All tested cells were positive at 64 gd. It is noteworthy that this period closely corresponds to the onset and maturation of the gross cochlear potentials. Some structural changes in the organ of Corti may be correlated with the development of OHC motile properties: the acquisition of an adult-like cylindrical shape by the OHC, its lateral detachment from neighboring Deiters cells, and its surrounding by fluid spaces. At the ultrastructural level, the formation of a first layer of laminated cisternae regularly aligned along the OHC plasma membrane from the cuticular plate down to the nuclear level, temporally coincided with the onset of in vitro motility (52 gd). The following days, pillars and a sub-membrane lattice were clearly noticed between the outermost cisternal membrane and the plasma membrane. The results support the ideas that: motile properties observed in vitro reflect the in vivo active mechanisms, and that one single layer of laminated cisternae and its associated sub-plasma membrane material may be needed for OHC motility.

Animals↗
PubMed1991

Development of the human cochlea.

This paper summarizes the most recent findings dealing with the anatomical development of the human cochlea, and especially with ultrastructural data from both scanning and transmission electron microscopic studies. It also briefly reviews physiological findings and attempts to specify the timing of the main developmental events, i.e. the onset of function, the acquisition of adult properties, and the sensitive periods.

Cochlea↗
PubMed1990

[T lymphoblastic leukemia with leukemoid reaction or the extramedullary blast crisis of Philadelphia chromosome-negative chronic myeloid leukemia? Comments apropos 2 cases].

Reactive leukocytosis has been reported in patients with non-Hodgkin's lymphoma of different histologic types. On the other hand, the blastic crisis of chronic myelocytic leukemia (CML) can sometimes be localized outside the bone marrow and simulate lymphoma, particularly when the blasts are of lymphoid lineage and the blastic crisis is the presenting feature of the disease. We report two patients in whom the differential diagnosis between lymphoblastic lymphoma with reactive leukocytosis and blastic crisis of CML outside the bone marrow was raised. They were two males aged 32 and 22 years, respectively, with lymphadenopathy (and one with splenomegaly), who were initially diagnosed of T lymphoblastic lymphoma. In both cases, leukocytosis was detected with myelemia and dysgranulopoiesis in the onset in one of them and when lymphadenopathy reappeared after remission in the other one. In addition, one patient had marked eosinophilia. In the bone marrow there was marked granulopoietic hyperplasia, with a reduction of fatty cells, and the granulocyte alkaline phosphatase index was reduced. However, the cytogenetic study did not disclose the existence of Philadelphia (Ph) chromosome, and bcr/abl molecular rearrangement was also not observed in the molecular study of both cases. We discuss the basic aspects of differential diagnosis between T lymphoblastic lymphoma with leukemoid reaction and T lymphoid lymphadenopathic blastic crisis of Ph-negative, bcr/abl-negative CML.

Adult↗
PubMed1990

Carbachol-induced inositol phosphate formation during rat cochlea development.

The age related-intensity developmental pattern of the phosphoinositide breakdown, which leads to the formation of intracellular second messengers, was investigated in rat cochleas by measuring the accumulation of inositol phosphates induced by carbachol in the presence of LiCl. The accumulation of the phosphoinositide metabolites elicited by this muscarinic agonist is very low at post-natal day 1 and particularly large during the period between post-natal days 8 and 14 with a peak around day 12. In the 25-day-old rat cochlea, carbachol induced a 2-fold increase in inositol phosphates (IPs) accumulation, with respect to the basal control level. The apparent affinities of the carbachol-induced IPs responses are 49.6, 31.6 and 36.7 microM in cochleas of 12-, 16- and 25-day-old rats, respectively, thus suggesting that the specific developmental changes are rather due to a modification in the number of muscarinic cholinergic receptors than to alterations of the apparent affinity of carbachol for its receptors. This developmental pattern of carbachol-elicited IPs accumulation reveals a striking time coincidence with both the efferent synaptogenesis at the outer hair cells (OHCs) level and the period of increased sensitivity of OHCs to aminoglycoside toxicity. Phosphoinositide breakdown may, consequently, play a role in the maturation of OHCs and their efferent supply. In addition, the remaining IPs response measured at 25 post-natal days indicates that muscarinic agonist-mediated IPs metabolism also occurs in mature cochlea, and might be involved in the regulation of OHCs motility.

Aging↗
PubMed1990

A M3 muscarinic receptor coupled to inositol phosphate formation in the rat cochlea?

Various neuroactive substances, including excitatory and inhibitory amino acids, biogenic amines and neuropeptides, were tested for their ability to stimulate the inositol phosphate (IPs) cascade in the presence of lithium in the rat cochlea. Among them, only the muscarinic agonists (carbachol and oxotremorine M) were able to stimulate the IPs formation in 12-day-old rat cochleas. The carbachol-elicited IPs formation was inhibited by muscarinic antagonists with the following relative order of potency: atropine greater than 4-DAMP much greater than pirenzepine greater than methoctramine = AF-DX 116. This pharmacological profile suggests that the activation of the M3 muscarinic receptor subtype is responsible for the increase in IPs synthesis in the rat cochlea. However, an interaction with a m5 receptor subtype could not be completely excluded. The unusual link of only one receptor subtype with the phosphoinositide breakdown in the cochlea, as opposed to the usual existence of several receptors coupled to this transduction system in other organs such as the brain, suggest a unique role for muscarinic agonists in the cochlea.

Animals↗