Biomedical subjects

D F Dolan

Publications and source records attributed to D F Dolan.

40 records · Page 3Linked to original sources

PubMed1985

Postnatal development of physiological responses in auditory nerve fibers.

The discharges of auditory nerve fibers in kittens 4-37 days of age were recorded from micropipette electrodes. Tuning curves, thresholds, and the degree of tuning (Q 10) are compared over this age range. The tuning curves for fibers during the first postnatal week are relatively flat, with thresholds above 100 dB SPL. The response areas of VIII-nerve fibers during this period are restricted to low-to-middle frequencies. With increasing age there is a reduction in threshold and an increase in the sharpness of tuning which is dependent on fiber CF. Response characteristics similar to adult VIII-nerve fibers were observed first for fibers with CFs near 5 kHz. For the response measures used here, VIII-nerve fibers in kittens are adultlike by the third to fourth postnatal week. The results are discussed in relation to the morphological development of the cochlea reported by other investigators.

Aging↗

PubMed1985

Transient inhibitory effect of isoflurane upon oxidative halothane metabolism.

The duration of inhibition of halothane oxidative metabolism by isoflurane was studied in rats exposed for 2 hr to an anesthetic concentration of isoflurane (0.6% inspired), followed by a 2-hr exposure to a subanesthetic concentration of halothane (0.06% inspired), starting either 0.5, 4, or 24 hr after the end of the isoflurane exposure. Other rats were exposed to halothane, isoflurane, or a mixture of both. Tissue levels of total nonvolatile fluorine were used as a measure of oxidative metabolism of halothane and hepatic levels of 1,1,1-trifluoro-2-chloroethane and 1,1-difluoro-2-chloroethylene as a measure of reductive metabolism of halothane. Isoflurane administered simultaneously with or 30 min prior to halothane significantly inhibited oxidative metabolism of halothane, but this inhibition was transient and was no longer apparent when halothane was administered 4 or 24 hr after the end of isoflurane anesthesia. The reductive metabolism of halothane was unaffected. This study suggests that isoflurane may transiently modify the action of some drugs administered during the perianesthesia period by inhibiting their oxidative metabolism. Differences in elimination kinetics of nonvolatile fluorine-containing metabolites after isoflurane and halothane exposure suggest the presence of an unidentified isoflurane metabolite.

Animals↗

PubMed1983

Relation between discharges in auditory nerve fibers and the whole-nerve response shown by forward masking: an empirical model for the AP.

Whole-nerve action potentials evoked by a standard click were recorded from a gross electrode on the RW and the discharges of auditory nerve fibers to the same standard click were recorded from micropipette electrodes in the auditory nerve. The effect of a preceding tone burst (2, 4, or 8 kHz) upon the responses was measured for forward-masker intensities from 20 to 80 dB SPL. All forward maskers reduced the discharges of auditory nerve fibers to the standard click with the greatest reduction occurring for fibers with characteristic frequencies (CFs) near the masker frequency. The 4- and 8-kHz forward maskers produced similar effects on N1, P1, and N2 of the RW response. However, the 2-kHz forward masker produced enhancement at P1 and N2 in the RW response to the standard click. An empirical summation model of estimated elemental waveforms at latencies dependent on CF produces synthesized AP response waveforms which are similar to the observed RW response. The model permits the exclusion of discharges from segments along the cochlear partition in a manner similar to the effect of a forward masker. Alterations in the synthesized waveforms due to the exclusion of segments are similar in direction to the alterations observed in the RW responses for forward masking.

Acoustics↗

PubMedDate not supplied

Pathways for protection from noise induced hearing loss.

There is increasing evidence that at least one function of both the medial and the lateral olivocochlear efferent systems is to provide adjustment of the set point of activity in their postsynaptic target, the outer hair cells and afferent processes, respectively. New results, summarized in this review, suggest that both efferent systems can provide protection from noise through this mechanism. There are also intracellular pathways that can provide protection from noise-induced cellular damage in the cochlea. This review also summarizes new results on the pathways that regulate and react to levels of reactive oxygen species in the cochlea as well as the role of stress pathways for the heat shock proteins and for neurotrophic factors in protection, recovery and repair.

Acoustic Stimulation↗