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Biomedical subjects

M E Warchol

Publications and source records attributed to M E Warchol.

4 recordsLinked to original sources
PubMed1991

Hair cell regeneration: the identities of progenitor cells, potential triggers and instructive cues.

Hair cells are produced and accumulate in the ears of fish and amphibians as they grow during postembryonic life; hair cell regeneration occurs in lateral line organs in those groups and in the cochlea in birds. Continuous time-lapse microscopy has directly demonstrated that supporting cells divide to give rise to hair cells during regeneration in lateral line neuromasts. Supporting cells also appear to give rise to hair cells during regeneration in the avian ear, but additional cell types have been proposed as hair cell progenitors. Alternative interpretations of current evidence are discussed in relation to the possibility that supporting cells may be the common progenitor in all cases of hair cell regeneration. The regenerative proliferation of hair cells in birds occurs in populations of cells that are mitotically quiescent in undamaged ears. Evidence suggests that the extrusion of damaged hair cells and the breaking of intercellular junctional adhesions may be a trigger for regenerative proliferation. The potential triggering influence of phagocytes is also discussed. The differentiation of replacement cells during regeneration in the cochlea may be regulated by surface interactions between cells. A model that could account for the reconstitution of the mosaic pattern of hair cells and supporting cells is proposed.

Animals↗
PubMed1990

Neural coding in the chick cochlear nucleus.

Physiological recordings were made from single units in the two divisions of the chick cochlear nucleus-nucleus angularis (NA) and nucleus magnocellularis (NM). Sound evoked responses were obtained in an effort to quantify functional differences between the two nuclei. In particular, it was of interest to determine if nucleus angularis and magnocellularis code for separate features of sound stimuli, such as temporal and intensity information. The principal findings are: 1. Spontaneous activity patterns in the two nuclei are very different. Neurons in nucleus angularis tend to have low spontaneous discharge rates while magnocellular units have high levels of spontaneous firing. 2. Frequency tuning curves recorded in both nuclei are similar in form, although the best thresholds of NA units are about 10 dB more sensitive than their NM counterparts across the entire frequency range. A wide spread of neural thresholds is evident in both NA and NM. 3. Large driven increases in discharge rate are seen in both NA and NM. Rate intensity functions from NM units are all monotonic, while a substantial percentage (22%) of NA units respond to increased sound level in a nonmonotonic fashion. 4. Most NA units with characteristic frequencies (CF) above 1000 Hz respond to sound stimuli at CF as 'choppers', while units with CF's below 1000 Hz are 'primary-like'. Several 'onset' units are also seen in NA. In contrast, all NM units show 'primary-like' response. 5. Units in both nuclei with CF's below 1000 Hz show strong neural phase-locking to stimuli at their CF. Above 1000 Hz, few NA units are phase-locked, while phase-locking in NM extends to 2000 Hz. 6. These results are discussed with reference to the hypothesis that NM initiates a neural pathway which codes temporal information while NA is involved primarily with intensity coding, similar in principle to the segregation of function seen in the cochlear nucleus of the barn owl (Sullivan and Konishi 1984).

Acoustic Stimulation↗
PubMed1989

Neural response to very low-frequency sound in the avian cochlear nucleus.

Recordings were made in the chick cochlear nucleus from neurons that are sensitive to very low frequency sound. The tuning, discharge rate response and phase-locking properties of these units are described in detail. The principal conclusions are: 1. Low frequency (LF) units respond to sound frequencies between 10-800 Hz. Best thresholds average 60 dB SPL, and are occasionally as low as 40 dB SPL. While behavioral thresholds in this frequency range are not available for the domestic chick, these values are in good agreement with the pigeon behavioral audiogram (Kreithen and Quine 1979). 2. About 60% of the unit population displays tuning curves resembling low-pass filter functions with corner frequencies between 50-250 Hz. The remaining units have broad band-pass tuning curves. Best frequencies range from 50-300 Hz. 3. Spontaneous discharge rate was analyzed quantitatively for LF units recorded from nucleus angularis. The distribution of spontaneous rates for LF units is similar to that seen from higher CF units (300-5000 Hz) found in the same nucleus. However, the spontaneous firing of LF units is considerably more regular than that of their higher CF counterparts. 4. Low frequency units with low spontaneous rates (SR's less than 40 spikes/s) show large driven rate increases and usually saturate by discharging once or twice per stimulus cycle. Higher SR units often show no driven rate increases. 5. All LF units show strong phase-locking at all excitatory stimulus frequencies. Vector strengths as high as 0.98 have been observed at moderate sound levels. 6. The preferred phase of discharge (relative to the sound stimulus) increases with stimulus frequency in a nearly linear manner. This is consistent with the LF units being stimulated by a traveling wave. The slope of these phase-frequency relationships provides an estimate of traveling wave delay. These delays average 7.2 ms, longer than those seen for higher CF auditory brainstem units. These observations suggest that the peripheral site of low frequency sensitivity is the very distal region of the basilar papilla, an area whose morphology differs significantly from the rest of the chick basilar papilla. 7. LF units are described whose response to sound is inhibitory at frequencies above 50 Hz.

Acoustic Stimulation↗