Biomedical subjects

W F Sewell

Publications and source records attributed to W F Sewell.

25 records · Page 2Linked to original sources

PubMed1987

Isolation and culture of auditory cells from the goldfish (Carassius auratus).

Large numbers of hair cells and VIIIth nerve ganglion cells are obtained from the inner ears of adult goldfish by a combination of enzymatic and mechanical dissociation. Centrifugation of the dissociated tissue through a discontinuous density gradient produces one fraction enriched in hair cells and another enriched in nerve cells. The fraction of cells enriched in neurons can be put into cell culture and kept for a period of weeks. During that period, the neurons send out processes that can extend for millimeters. The morphology of these cultured neurons is similar to that of the goldfish auditory neurons in histological material.

Animals↗

PubMed1987

Neuroactive substances in inner ear extracts.

To identify the neurotransmitter released by sensory hair cells, as well as to find other substances that might influence neural function of the inner ear, we have prepared extracts from inner ears of fishes (which have large numbers of hair cells), fractionated the extracts, and studied the effects of the fractionated extracts on the discharge rate of afferent fibers innervating hair cells in the lateral line organ of the African clawed frog Xenopus laevis. The extracts contain active substances that do not bind to a cation-exchange resin at neutral pH. Gel-permeation chromatography suggests that at least 2 unidentified excitatory substances are present in the extracts: one of low molecular weight (Mr about 200) and one of high molecular weight (Mr less than or equal to 5000). Some extracts also contain a high-molecular-weight inhibitory substance (Mr greater than 5000). The low-molecular-weight active substance is detected in extracts of inner ear, but not in brain or muscle. The high-molecular-weight excitatory substance is present both in brain and in inner ear.

Action Potentials↗

PubMed1986

Single unit clues to cochlear mechanisms.

In recent years studies on isolated hair cells have suggested that there is an inherent tuning of hair cells determined by their mechanical and electrical properties. However, tuning for mammalian cochleas appears to be much more complicated since there are typically two types of receptor cells (inner and outer hair cells) imbedded in a highly organized framework of supporting cells, membranes and fluids. The major neural output of the cochlea can be monitored by recording the activity of myelinated axons of spiral ganglion cells, not only under normal conditions, but also when the discharge patterns are altered by ototoxic drugs, acoustic trauma or olivocochlear bundle stimulation. A model system with two excitatory influences, one sharply tuned and highly sensitive, and a second, broadly tuned and relatively insensitive, can account for much of the existing data. Results from single-neuron marking studies support the notion that these two influences probably involve interactions between inner and outer hair cells. More global influences such as the endocochlear potential also can act on auditory-nerve fibers through the hair-cell systems. Thus, the inherent frequency selectivity of the receptor cell is only one of many factors that determine the tuning of mammalian auditory-nerve fibers.

Adaptation, Physiological↗

PubMed1984

The effects of furosemide on the endocochlear potential and auditory-nerve fiber tuning curves in cats.

Furosemide was injected intravenously in anesthetized cats while the endocochlear potential (EP) and tuning curves from fibers of the auditory nerve were simultaneously monitored in the same ear. The characteristic frequencies (CF's) of the fibers studied ranged from 0.25 to 28 kHz. Furosemide administration produced reversible, dose-related decreases in the EP which were accompanied by threshold elevations and alterations in the tuning curves of auditory nerve fibers. There was approximately 1 dB of threshold elevation for every millivolt decrease in the EP. For fibers with CF's above 3 kHz, threshold elevation at CF (in the tip of the tuning curve) was three times that in the tail of the tuning curve. Threshold elevation in the tip was always accompanied by threshold elevation in the tuning curve tail. Threshold elevation was dependent upon the CF of the fiber, with higher CF fibers showing larger threshold shifts than lower CF fibers. Threshold elevation was accompanied by a systematic shift in the CF of the fiber. Fibers with CF above 1 kHz exhibited downward shifts in CF, while those with CF less than 1 kHz generally exhibited upward shifts in CF.

Action Potentials↗

PubMed1984

Furosemide selectively reduces one component in rate-level functions from auditory-nerve fibers.

Furosemide, an ototoxic diuretic, was administered intravenously while rate- and phase-level functions of auditory nerve fibers were measured in the cat. Normal level functions can demonstrate two components distinguished by an abrupt shift in the phase of the response as the sound level is increased. Furosemide, administered at doses that decrease the endocochlear potential, selectively reduces the discharge rate in response to tones at sound levels below that of the abrupt phase shift.

Animals↗

PubMed1984

The relation between the endocochlear potential and spontaneous activity in auditory nerve fibres of the cat.

The relation between the endocochlear potential and spontaneous discharge rate in auditory nerve fibres was determined following intravenous injections of furosemide in anaesthetized cats. Following furosemide administration, both the endocochlear potential and the spontaneous discharge rates of auditory nerve fibres decreased synchronously. The logarithm of the spontaneous discharge rate was proportional to the endocochlear potential. The slope of the logarithmic relation increased as a function of the characteristic frequency of the fibre. The slope of the logarithmic relation is steeper for fibres with 'medium' spontaneous discharge rates (0.5-12 spikes/s) than for fibres with 'high' spontaneous discharge rates (greater than 18 spikes/s). Among high spontaneous rate fibres, the slope does not appear to vary systematically with the spontaneous rate of the fibre. The decrease in spontaneous discharge rate in auditory nerve fibres is interpreted as follows: (1) the injection of furosemide causes a decrease in the endocochlear potential, (2) a decrease in the endocochlear potential produces a linearly related hyperpolarization of the membrane potential of the hair cell by altering the standing current which flows through the transducer membrane, and (3) the logarithm of the rate of release of transmitter quanta decreases with the hyperpolarization of the membrane potential of the hair cell, which decreases the rate of occurrence of action potentials at the hair cell afferent junction.

Action Potentials↗

PubMed1978

Detection of an auditory nerve--activating substance.

A substance or substances capable of increasing the firing rate of primary auditory fibers is detectable in the perilymph of frogs and guinea pigs subjected to sound stimulation. The increase in firing rate occurs in single units of the frog auditory nerve after perilymph obtained from frogs or guinea pigs during sound stimulation is infused into the frog perilymphatic sac. Perilymph collected from animals maintained in silence failed to cause an increase in firing rate of primary auditory fibers of the frog.

Animals↗