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Biomedical subjects

R Pujol

Publications and source records attributed to R Pujol.

At least 199 records · Page 11Linked to original sources
PubMed1980

Supra-normal sensitivity to ototoxic antibiotic of the developing rat cochlea.

A period of increased sensitivity to the ototoxic antibiotic amikacin was found in the cochlea of the developing rat. Starting either at birth, 10 or 30 days of age, rat were injected i.p. daily with 200 mg/kg of amikacine for 10 days. Only in the group injected with drug from 10 to 20 days of age was there evidence of a substantial (40-100 dB) permanent threshold shift (PTS). To characterize the period of supra-normal sensitivity more precisely, independent groups of pups were injected with 50 mg/kg of amikacin from 10 to 20, 15 to 25, 20 to 30, and 30 to 40 days of age. Only those pups injeced from 10 to 20 or 15 to 25 days of age showed PTS (30-60 dB). These data, taken together with those on rat cochlear maturation indicate that the sensitive period to ototoxicity starts at the age of onset of cochlear function (around day 10) and ends few days after the cochlea shows adult-like characteristics (3rd postnatal week).

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

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↗
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↗
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↗
PubMed1977

Receptor maturation and synaptogenesis in the golden hamster cochlea.

Maturation of hamster cochlea was studied using light and electron microscopy. Critical stages of receptor and neural structure development have been determined. At birth the hamster cochlea shows a pronounced immaturity, but innervation can already be found. 2 or 3 days later, characteristic afferent synapses can be recognized beginning at the inner hair cell level. Similarly, efferent endings first appear on the inner side at the end of the first week. The onset of auditory function must be related to structures depicted at around 10 days, and cochlear maturation is achieved at about 25 days. The sequence of synaptic development in the cochlea is discussed regarding the general morphogenesis of synapses within the nervous system. Some determinations of the timing of peripheral myelination are given. This process begins almost a week before the presumable date of the onset of function.

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↗