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Biomedical subjects

M Lenoir

Publications and source records attributed to M Lenoir.

63 records · Page 4Linked to original sources
PubMed1980

Cochlear receptor development in the rat with emphasis on synaptogenesis.

Maturation of the albino rat cochlea was studied using light and electron microscopy. Critical stages of receptor morphology were examined. At birth, cochlear structures are very immature, but even at this early stage synapses are recognizable. Under inner hair cells (IHCs) both afferent and efferent synapses are present. Under outer hair cells (OHCs) only afferent endings are seen. During the first postnatal week, synaptic development proceeds slowly. Between 6 to 12 days of age, substantial changes occur in the pattern of hair cell innervation. There are fewer efferent synapses at the IHC level and the first efferent junctions form on OHCs. In addition, a pattern of temporary innervation is seen under the OHC, with axo-dendritic synapses between efferent endings and afferent fibres. Between 12 and 16 days of age the main changes in hair cell innervation are at OHC level where afferent junctions regress and large efferent synapses form. By 16 days of age sensory-neural relationships seem adult-like. The results are discussed in relation to rat cochlear electrophysiological development and the period of supra-normal sensitivity to acoustic trauma.

Age Factors↗
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

Brain stem evoked potential findings in children with otitis media.

Sixty-three children from 2 to 12 years of age were studied by means of brain stem evoked potentials (BEP) and otoscopic evaluation in a preliminary assessment of the sensitivity of BEP latency measures to middle ear abnormality. Wave I proved to be the most sensitive component; 81.25% of subjects with acute suppurative otitis media and 62.50% of subjects with secretory otitis media demonstrated latencies prolonged by more than 1 SD beyond the values observed in normal control subjects. Of the same subject groups, 86.21% and 93.31% demonstrated wave I latencies within normal limits upon retesting after the otitis had resolved. The BEP technique permitted identification of several subjects with abnormal audiometric findings despite normal otoscopy. There are implications for use of the BEP as a clinical adjunct to traditional methods of auditory assessment.

Acute Disease↗
PubMed1979

Supra-normal susceptibility to acoustic trauma of the rat pup cochlea.

1 Young and adult rats were exposed to a continuous 120 dB SPL white noise for 30 min. 2 Animals exposed before the 40th postnatal day showed drastic and permanent threshold shifts (PTS) at high frequencies (between 6 and 20 kHz). 3 After 60 days of age, only temporary threshold shifts (TTS) were noticed, which lasted 7 days. 4 Thus the sensory structures of the rat cochlea showed a supra-normal susceptibility to acoustic trauma, during and just after their anatomical differentiation. 5 These results support previous data obtained on hamsters and guinea-pigs and are discussed in terms of anatomo-functional relationships.

Aging↗
PubMed1975

Development of IgE and allergy in infancy.

Serum IgE levels were followed throughout the first year of life in a sample of 34 infants from atopic and nonatopic families. Their parents' serum IgE levels were also measured. Neonatal levels ranged from 0 to 10 U/ml. Half of the study group, which included a high proportion of infants from atopic families, maintained serum IgE levels below 10 U/ml until 1 yr of age. In the remainder, the serum IgE exceeded 10 U/ml before 1 yr of age, but the time of increase and the rate of increase varied from infant to infant; the sooner the IgE started to increase, the higher was the serum IgE level at 1 yr of age. The relationship of serum IgE level to the development of atopic disease and to other parameters was analyzed. Elevation of serum IgE level at or before 1 yr of age was highly correlated with atopic disease in the first 2 yr of life. The elevation preceded the manifestation of atopy.

Aging↗
PubMedDate not supplied

Morphological and molecular changes in the inner hair cell region of the rat cochlea after amikacin treatment.

This study investigates the morphological and molecular changes that occur in the inner hair cell area of the rat cochlea following aminoglycoside treatment. Rats were injected daily with 500 mg/kg of amikacin between postnatal day 9 (PND9) and PND16. Cochleae were examined at PND16 to PND120 using both scanning and transmission electron microscopy and molecular fluorescent labeling. The inner hair cells showed obvious signs of apoptosis in response to amikacin treatment and most of them were missing by one week after the end of the aminoglycoside exposure period. Concomitantly, the epithelium became scarred as the surrounding supporting cells expanded and filled the space vacated by the missing IHCs. The mid-basolateral region of these modified supporting cells was surrounded by many afferent and efferent terminals. However, these cells expressed neither calbindin nor SNAP25, proteins that are both expressed by IHCs in the normal, untreated organ of Corti in the rat. In addition, these supporting cells remained attached to the basal lamina by a thin cytoplasmic process. The supporting cells surrounding the inner hair cells therefore appear unable to convert directly into inner hair cells following aminoglycoside induced hair-cell loss but may be able to provide trophic support for the remaining afferent and efferent neurites.

Actins↗
PubMedDate not supplied

Sensitive period to acoustic trauma in the rat pup cochlea. Histological findings.

In a previous paper we demonstrated physiologically a sensitive period for acoustic trauma in the rat pup cochlea, with a maximum at 22 days of age. Seven or 60 days after noise exposure these 22-day exposed rats were used for light and electron microscopy. At 7 days, surface preparation revealed restricted damage to the basal cochlear coil, while with electron microscopy signs of cytoplasmic degeneration appeared in the great majority of basal coil structures. Two months after noise exposure these structures have completely degenerated. These results were discussed in terms of mechanical versus metabolic explanations of the critical period for acoustic trauma.

Animals↗