[Sulfasalazine-induced megaloblastic anemia in rheumatoid arthritis].
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Anemia, Macrocytic↗
Biomedical subjects
R Pujol
Publications and source records attributed to R Pujol.
Selective attention modifies the active micromechanical properties of the cochlea.
The micromechanical properties of the cochlea accounting for the exquisite properties of sensitivity and frequency selectivity depend on the integrity of an active biomechanism probably based upon a motile activity of outer hair cells (OHCs). Evoked oto-acoustic emissions (EOAEs), i.e. sounds emitted by the cochlea in response to a click, reflect this active biomechanism. We demonstrate here that a selective attention task in human subjects alters EOAEs. This means that the central nervous system can modify active cochlear micromechanics prior to the transduction process, probably by using the medial efferent system which, coming from the brainstem, innervates the OHCs.
Adolescent↗
Screening for auditory dysfunction in infants by evoked oto-acoustic emissions.
Auditory threshold using auditory brain-stem responses (ABR) was determined in 30 ears from normally-hearing infants and 16 ears from infants with sensorineural deafness. In the same population, evoked oto-acoustic emissions (EOAEs) in response to a click of 20-dB hearing level were recorded. The presence of EOAEs was correlated with ABR thresholds. Evoked oto-acoustic emissions were always present when ABR wave V threshold was equal to or below 30-dB hearing level. On the contrary, infants with ABR thresholds higher than 40-dB hearing level never had EOAEs. As the recordings of EOAEs could be obtained more rapidly than ABR thresholds (average duration: five minutes vs 40 minutes), EOAEs could hold some promise as an objective, easy, and noninvasive test for screening auditory dysfunction in infants.
Brain Stem↗
A correlative study of evoked otoacoustic emission properties and audiometric thresholds.
Correlations were made between the detection thresholds of evoked otoacoustic emissions (EOAEs), subjective click thresholds, and mean audiometric thresholds in 240 normal and hearing-impaired ears. EOAEs have never been observed when subjective click thresholds or mean audiometric thresholds were equal to or greater than 35 dB HL. EOAEs were always found when click thresholds were equal to or lower than 15 dB HL and when mean audiometric thresholds were equal to or lower than 22 dB HL. The incidence of EOAEs decreased and EOAE thresholds increased with increasing click or mean audiometric thresholds.
Adolescent↗
Immunoelectron microscopy identifies several types of GABA-containing efferent synapses in the guinea-pig organ of Corti.
Using an immunoperoxidase technique, we have localized by light and electron microscopy GABA-immunostained fibers within a component of the efferent innervation of the organ of Corti. At the light microscopic level, GABA-immunostained fibers were observed within the inner spiral bundle (below the inner hair cells) and the tunnel spiral bundle. The immunostaining was clearly more intense in the upper turns than in the basal turns. Mostly in the upper turns, GABA-immunostained fibers were seen crossing the tunnel of Corti to reach the outer hair cells where they formed large immunostained patches at the base of the cells. Unevenly distributed throughout these upper turns, immunostained fibers were seen climbing along the outer hair cells and traveling near the non-sensorineural Hensen's cells. The electron microscopic observations of GABA-immunostained fibers in the upper turns allowed us to identify within the inner spiral bundle vesiculated varicosities synapsing with radial dendrites connected to the inner hair cells. In the outer hair cell area, the GABA-immunostained fibers made several kinds of synaptic contacts. They included a minor population of the large axosomatic synapses with the basal pole of the outer hair cells and many axodendritic synapses with the spiral dendrites connected to these cells. Occasionally, the GABA-immunostained climbing fibers also synapsed with the outer hair cells at a supranuclear level. These result confirm previous light microscopic data dealing with the projection of the GABA-immunostained fibers along the cochlear partition. Moreover, they extend them in characterizing several kinds of GABA-immunostained synapses. These latter findings agree with previous neurochemical electrophysiological data which suggests an efferent neurotransmitter role for GABA. Nevertheless, such an existence of an efferent innervation predominantly projecting to the upper turns of the cochlea adds another criterion distinguishing the "apical" from the "basal" cochlea.
Animals↗
Synaptophysin in the developing cochlea.
The immunoreactivity to SY38 (anti-synaptophysin antibody) was investigated in rat and guinea-pig cochleas during development. In rat pups SY38 reactivity first appeared in the inner spiral bundle (below inner hair cells) at postnatal day 3. Later on (days 10 and 15) the basal pole of outer hair cells (OHCs) was also reactive. In fetal guinea-pigs, the inner spiral bundle was reactive on day 45 of gestation, while the reactivity occurred below OHCs on day 62 of gestation. A preliminary electron microscopic finding (from a guinea-pig 62 days of gestation) indicated that SY38 immunoreactivity is localized within varicosities of efferent (olivo-cochlear) endings. Synaptophysin is thus present in the cochlea at the level where the two efferent systems terminate. Moreover, the occurrence of SY38 immunoreactivity, first at the ISB then at the OHC levels, is in accordance with the observation that the maturation of lateral efferents precedes that of medial efferents.
Animals↗
Evoked otoacoustic emissions: a fundamental and clinical survey.
Evoked otoacoustic emissions (EOAEs) hold some promise as a fast, objective and noninvasive procedure to study the cochlea at the outer hair cell level. This paper summarizes the fundamental aspects of EOAEs, in particular their relationship with the active biomechanical properties of the cochlea. The properties of EOAEs are analyzed in normally hearing ears, in ears with sensorineural hearing loss, especially in Ménière's disease, in acoustic neuromas and in central deafness; the properties of EOAEs were also evaluated as to their suitability for screening auditory dysfunction in infants.
Adult↗
[Nail dystrophy of the big toe. Description of a clinical case].
We report on four cases of great toenail dystrophy. This malformation presented itself in the first months of life. Involvement of other toenails and also of fingernails has been observed. In some of the cases spontaneous involution was referred. Pathogenesis, differential diagnosis and therapy are discussed.
Child↗
Opioid receptors inhibit the adenylate cyclase in guinea pig cochleas.
The effects of mu- and delta-preferring agonists on adenylate cyclase activity have been investigated in vitro in homogenates of guinea pig cochleas. Morphine, Leu-enkephalin, D-Ala2, N-methyl-Phe4, Gly-ol5-enkephalin (DAGO) and D-Ser2-Leu-enkephalin-Thr (DSLET) each inhibited the synthesis of cyclic AMP. This effect was reversed by naloxone which had a greater affinity in blocking the effect of the mu-preferring agonists (morphine, DAGO) than in blocking the effect of the delta-preferring agonists (Leu-enkephalin, DSLET). Finally, no additive effects were observed when various combinations of two agonists were used. These results indicate that opioid receptors exist in the guinea pig cochlea and that they are negatively linked to adenylate cyclase. The different affinities shown by naloxone to reverse the inhibition induced by the mu- and delta-preferring agonists suggest that morphine and DAGO act through mu-receptors, whereas Leu-enkephalin and DSLET act through delta-receptors. Since no additive effects have been found when combining two different agonists, it can be hypothesized that the mu- and delta-receptors are coupled to the same pool of adenylate cyclase. It may be proposed from these findings that in vivo enkephalins inhibit the synthesis of cyclic AMP via mu- and delta-receptors. However, whether this effect occurs at a presynaptic level (within opioid-containing olivocochlear varicosities) or at the postsynaptic level (within dendrites of the primary auditory neurons) remains to be determined.
Adenylyl Cyclases↗
Choline acetyltransferase (ChAT) immunoelectron microscopy distinguishes at least three types of efferent synapses in the organ of Corti.
Using anatomical criteria, the olivo-cochlear fibers ending in the organ of Corti (efferent fibers) have recently been separated into two systems: a lateral system innervating principally the inner hair cell (IHC) area and a medial system innervating mainly the outer hair cells (OHCs). Electrophysiological and biochemical experiments suggest that acetylcholine may be a neurotransmitter of these efferent fibers. However, efferent synapses that use acetylcholine as neurotransmitter have not yet been identified at the electron microscopic level. Using a pre-embedding immunoelectron microscopic technique with a monoclonal antibody against choline acetyltransferase (ChAT), we localized ChAT-immunostained fibers below both the IHCs and OHCs. In the inner spiral bundle, one type of ChAT-immunostained fibers was vesiculated and formed axo-dendritic synapses with the afferent auditory dendrites contacting the inner hair cells. A second type of ChAT-immunostained fibers seen in the inner spiral bundle was unvesiculated. Unstained vesiculated varicosities synapsing with the auditory dendrites were also seen in the inner spiral bundle. At the OHC level, ChAT immunostaining was found in nearly all the terminals synapsing with the OHCs. The finding of two types of ChAT-immunostained efferent synapses in the organ of Corti, i.e. axo-dendritic synapses in the inner spiral bundle and axo-somatic synapses with the OHCs, supports the hypothesis that both the lateral and the medial olivo-cochlear systems use acetylcholine as a neurotransmitter. The finding of numerous unstained synapses in the inner spiral bundle, and some below OHCs, together with previous data about putative cochlear neurotransmitters, suggests the possibility of additional non-cholinergic olivo-cochlear systems. It might soon appear useful to reclassify efferents according to the nature of the different neurotransmitters/co-transmitters found in the various efferent synapses of the organ of Corti.
Animals↗
Stereocilia and tectorial membrane development in the rat cochlea. A SEM study.
Maturation of the rat cochlea, from postnatal days 2 to 60, was studied using scanning electron microscopy (SEM), with emphasis on stereocilia and tectorial membrane (TM). Two days after birth, the organ of Corti was very immature. An adult appearance of its surface was observed by day 16 in the basal turn, and by the end of the 3rd postnatal week in the apex. Stereocilia started their development first on inner hair cells. By contrast, the apical pole of outer hair cells ended its maturation before that of inner hair cells. Top-links were detected very early in inner hair cell stereociliary development (postnatal day 2). Marginal pillars temporarily attached the TM to the organ of Corti; they disappeared first in the apical region. This transient attachment seems to play a role in the coupling of outer hair cells to the TM, as prints of their longest stereocilia appeared at the undersurface of the TM by the same time. Moreover, these prints were more clear and regular at the base than at the apex of the cochlea. Results are discussed in relation to ultrastructural and functional data on rat cochlea maturation.
Animals↗
Modulation of the masking phenomenon by the crossed part of the medial olivocochlear bundle.
The masking phenomenon is used in clinical investigation of the inner ear to determine the frequency selectivity properties of the auditory system. Sectioning of the crossed part of the medial efferent bundle in a guinea pig model decreases the simultaneous masking phenomenon. The efferent effect seen in the forward masking varied with the masking paradigm used. When the masker onset precedes the maskee onset by more than 40 ms, masking diminishes after sectioning the crossed part of the medial efferent bundle. When this duration was shortest (30 ms), no effect was observed. This phenomenon could be explained by the time necessary to stimulate the medial efferent loop. Our results could explain some differences observed in the compound action potential masking curves with different masking paradigms.
Acoustic Stimulation↗
Variations of cochlear microphonic potential after sectioning efferent fibers to the cochlea.
Cochlear microphonic (CM) potentials were recorded, in guinea pig, with differential electrodes before and after sectioning the medial efferent innervation at the level of the brainstem. Sectioning the crossed part of the medial efferent innervation did not change the CM whatever the frequency or level of stimulation used. Sectioning the medial--crossed and uncrossed--efferent fibers diminished CM amplitude at frequencies above 2 kHz. Thus, the ipsilateral medial efferent tract seems to be involved, through a tonic action, in controlling outer hair cell micromechanics.
Acoustic Stimulation↗
Surface aspects of the developing human organ of Corti.
Thirteen cochleas from human fetuses ranging in age from week 9 to week 22 were observed by scanning electron microscopy. The classical 'base-to-apex' and 'internal-to-external' gradients of maturation were confirmed by surface observations of the developing organ of Corti. The tectorial membrane begins to be secreted around week 9, i.e. 2 weeks before the onset of the ciliogenesis. Its structure appears to be first amorphous and then fibrillar. The surface of the organ of Corti looks mature around week 22, but, in fact, its complete maturation, especially at outer hair cell level, probably occurs during the last trimester of pregnancy.
Cell Differentiation↗
[Transfacial anastomosis: continuation or the end? Apropos of the ultrastructural study of nerve grafts in 3 cases of failure].
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Facial Nerve↗
[New data on the physiology of the olivo-cochlear efferent systems].
The medial part of the olivocochlear efferent tract seems to be involved in two distinct phenomena. The crossed part is involved in the masking function and the uncrossed one in the control, through a tonic action, of the cochlear micromechanics.
Action Potentials↗
[Latency, threshold and frequency selectivity of the crossed medial cochlear efferent pathways].
The efferent innervation of guinea pig cochleas was sectioned medially, at the level of the floor of the fourth ventricle, to study the effects of the crossed part of the medial efferent pathway on the compound action potential (CAP) masking phenomenon. Sectioning reduced CAP masking for a masker level varying with the frequency of the masker and the time elapsed between the masker onset and the probe onset. Functional properties of the crossed part of the medial efferent tracts: latency, thresholds and frequency selectivity, could be deduced from these data. This intensification of the masking phenomenon permitting the improvement of the signal to noise ratio, may thus be attributed to the crossed part of the medial efferent bundle which innervates the outer hair cells.
Animals↗
[Oto-acoustic emissions. I. Evoked oto-emissions: a new technic of functional study of the cochlea].
Otoacoustic emissions (OAE) are sounds emitted by the cochlea and recordable in the external ear canal by a miniature microphone. These OAE reflect the existence of an active mechanism within the cochlea, probably based upon outer hair cells (OHC). Recordings of OAE are easy, noninvasive, objective and permit the exploration of an essential property of the cochlea which was impossible to study by the usual electrophysiological techniques. Clinical applications are discussed in this paper.
Adolescent↗