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Biomedical subjects

E Carlier

Publications and source records attributed to E Carlier.

54 records · Page 3Linked to original sources
PubMed1980

Ontogenetic approach to inner and outer hair cell function.

Anatomo-functional relationships made during ontogenesis seem to offer possibilities of a better understanding of cochlear function. The asymmetrical kinetics of inner and outer hair cells (IHCs and OHCs) structural development can assist in determining their functional role. Light- and electron-microscopic observations of cochlear development in kittens, guinea pigs, hamsters and rats reveal that the maturation of IHC and their afferent and efferent innervation occurs first. The OHCs develop more slowly and the pattern of their innervation changes dramatically, the last stage involving the enlargement of efferent synapses. The timing of this maturation correlates well with the development of cochlear function. The findings suggest that IHCs are required for the onset of auditory function while mature OHCs are necessary for the more discriminative properties of the cochlea.

Animals↗
PubMed1979

Significance of presynaptic formations in early stages of cochlear synaptogenesis.

Very early stages of cochlear synaptogenesis are described in inner (IHCs) and outer hair cells (OHCs) of cat foetuses. Ten days before birth (DBB) well-formed synaptic contacts were found between afferent dendrites and both IHCs and OHCs. At the IHC level a preliminary stage before functioning has been proposed. But at the OHC level where the adult cell membrane becomes mainly postsynaptic, we could only formulate hypotheses based on phylogenetic considerations (afferents precede efferents), or on embryology (presynaptic specializations play a role in the arrival and growth of fibers around the hair cell).

Animals↗
PubMed1978

Different patterns of cochlear innervation during the development of the kitten.

The postnatal development of neuro-epithelial junctions inside the kitten cochlea has been investigated by electron microscopy, and correlated with previous electrophysiological results. Two main stages of development are described. During the first postnatal days, outer hair cells look very immature with only a few afferent endings adjoining them. The inner hair cells, on the other hand, are surrounded by numerous endings with mature afferent and efferent synapses. Thus, when the efferent olivo-cochlear system begins to function during the first postnatal day s, it is able to modify only inner hair cell responses. The second postnatal week is characterized by maturation of the large efferent endings below the outer hair cells. At the same time, direct efferent connections become sparce at the level of inner hair cells. The maturation of hearing, at the receptor level, seems to proceed in two steps, one related to inner hair cells and corresponding to a gross and primitive hearing, the other related to outer hair cells and corresponding to more precise and discriminative hearing abilities.

Age Factors↗
PubMed1975

[Mauration of unitary responses to tonal stimulation in the cochlear nerve of the kitten].

The maturation of single auditory nerve fiber responses to long-duration (500 ms) tone-bursts was studied in kittens at various stages after birth. Spike discharges were examined as a function of three criteria. 10 Latency. Mean value of the "on" peak latency was about 25 ms at 1 to 3 days after birth. It then regressed, reaching 8 to 12 ms at the end of the first week, and 2 to 4 ms at 20 days. 20 Peristimulus histograms (PSTH). Evolution of PSTH revealed the characteristic sequence of unit reactivity to long duration stimuli (i.e. on, rhythmic, and continuous responses). Rhythmic responses is assumed up to now to be related to the immaturity of synaptic junctions below the hair cells. 30 interval histograms. The interspike interval histograms of the discharges showed a similar evolution. A bimodal distribution corresponding to the rhythmic mode of reactivity, appeared at the end of the first week.

Acoustic Stimulation↗
PubMedDate not supplied

Similar effects of aging and corticosterone treatment on mouse hippocampal function.

Cumulative exposure to corticosterone (CORT) during the lifespan plays an important role in the hippocampal aging process, and similar disturbances have been observed in chronic stress. However, there is little information on the electrophysiological changes observed in these two situations at the hippocampal level. The present study investigates the electrophysiological changes observed in control conditions and after a 10 microM CORT bath application on hippocampal slices taken from control adult BALB/c mice, from adult animals subjected to chronic overexposure to corticosterone (20 mg/kg/day during 3 months) and from aged animals. No electrophysiological difference was observed in the CA1 area of chronically CORT treated and aged groups compared to the control group. Conversely, the input/output curves from the dentate area showed a similar, statistically significant right shift in these two groups compared to the control group. Furthermore, in control subjects, a 10 microM CORT bath application produced the classical population spike amplitude decrease. However, in slices taken from chronically CORT-treated and aged mice, this effect did not occur in the CA1 while it was replaced by a population spike amplitude increase in the dentate. This increase was blocked by spironolactone. These electrophysiological alterations may indicate that a part of the aged-induced functional disturbances is mediated by glucocorticoids, and may progressively lead to impairment of neuroendocrine functions and behavioral adaptation.

Aging↗
PubMedDate not supplied

Chronic RU486 treatment reduces age-related alterations of mouse hippocampal function.

The present study investigates the protective effect of a chronic blockade of the glucocorticoid receptor (type II) by a single weekly SC injection (20 mg/kg) of RU486 (a potent antiglucocorticoid) from mid-age (12 months old) until senescence (20 to 22 months old) on perturbations of some electrophysiological parameters classically observed in CA1 hippocampal slices of aged BALB/c mice. In this CA1 hippocampal area, no electrophysiological difference was observed at a stimulation frequency of 0.3 Hz. However, an important age-related effect was observed in not-treated animals concerning the three phases of the synaptic response during and after 4 Hz repetitive stimulation ith impairment of the frequency potentiation (FP). Interestingly, this electrophysiological disturbance disappeared completely in aged animals treated previously with RU486. Furthermore, a 10 microM CORT bath application had no effect in CA1 of aged animals, while it produced the classical type II-mediated population spike (PS) decrease in adult animals. This PS amplitude decrease was maintained in aged animals previously treated with RU486. These electrophysiological findings suggest an important type II-mediated glucocorticoid action on age-related alterations of hippocampal function.

Age Factors↗
PubMedDate not supplied

[Visual evoked responses on the primary auditory cortex in the cat after an early suppression of cochlear receptors (author's transl)].

In the adult cat, after an early degeneration (hereditary deaf white cats) or surgical removal of auditory receptors, it is possible to record visual evoked responses on the primary auditory cortex. The appearance of such potentials depends on two conditions: a complete (bilateral) and early (first postnatal month) deafferentation. This can be explained by an early multi-afferentation of the primary cortical areas. The early suppression of the primary modality may keep the other modalities still working in the adult.

Afferent Pathways↗
PubMedDate not supplied

Histo-physiological relationships in the deaf white cat auditory system.

An investigation is underway in deaf white cats in order to clear up some problems about the timing of cochlear degeneration, the relationships between physiological and histological findings, and the consequential state of central auditory pathways. The first results reported here show that degeneration of sensory structures was much more advanced than physiological results lead us to believe. The possibility of direct fibre stimulation is discussed. Although degeneration of nervous structures was delayed compared with sensory ones, some early abnormalities in myelination were found. In the adult, completely deaf for years, the electrical stimulation of cochlear nuclei evoked normal-looking field responses at the cortical level. Thus some degree of auditory pathway functional integrity appeared even long after they were disconnected from receptors.

Animals↗