SEARCH · PubMed Health

Results for “Cochlea”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1976

Choline acetyltransferase, glutamate decarboxylase and tyrosine hydroxylase in the cochlea and cochlear nucleus of the guinea pig.

Activities of choline acetyltransferase (ChAC), glutamate decarboxylase (GAD) and tyrosine hydroxylase (TH), enzymes catalyzing the synthesis of acetylcholine (ACh), gamma-aminobutyric acid (GABA) and catecholamines, respectively, were measured in the cochlea and cochlear nucleus of the guinea pig. ChAc activity in the organ of Corti, third turn, was 1270 pmole ACh formed/min/mg protein (ChAc, 1270) and was higher than in turn 4 (ChAc, 543). ChAc activity was higher when the preparation included the inner hair cell region than when not. GAD activity in samples of turn 3 and 4 combined was low, 0.17 nmole GABA formed/min/mg protein (GAD, 0.17). All 3 enzymes were low in auditory nerve: ChAc, 1.7, GAD, 0.10 and TH, 1.0 pmole DOPA formed/min/mg protein. In the cochlear nucleus, the values were: ChAc, 129, GAD, 1.70 and TH, 2.7. The findings on the distribution of ChAc activity in the organ of Corti fit the hypothesis that the olivocochlear nerve fibers are cholinergic. Because of low GAD in the cochlea, GABA is unlikely to be transmitter in the organ of Corti. Similarly, it is unlikely that ACh, GABA or a catecholamine is a transmitter between the auditory nerve and the cochlear nucleus.

Acetyltransferases↗

PubMed1978

Synapses involving auditory nerve fibers in primate cochlea.

The anatomical mechanisms for processing auditory signals are extremely complex and incompletely understood, despite major advances already made with the use of electron microscopy. A major enigma, for example, is the presence in the mammalian cochlea of a double hair cell receptor system. A renewed attempt to discover evidence of synaptic coupling between the two systems in the primate cochlea, postulated from physiological studies, has failed. However, in the outer spiral bundle the narrow and rigid clefts seen between pairs of presumptive afferent fibers suggest the possibility of dendro-dendritic interaction confined to the outer hair cell system. The clustering of afferent processes within folds of supporting cells subjacent to outer hair cells is in contrast to the lack of such close associations in the inner hair cell region. The difference reinforces the suggestion of functional interaction of some sort between the outer hair cell afferent nerve processes.

Afferent Pathways↗

PubMedDate not supplied

Nerve fiber synapses on spiral ganglion cells in the human cochlea.

Nerve fiber synapses were observed on the small myelinated and unmyelinated spiral ganglion cells of the human cochlea. The nerve fibers penetrated the junctions of the ensheathing satellite cells and myelin lamellae, and partly invaginated into the perikarya to establish axosomatic synapses. One small myelinated neuron with a nerve fiber synapse demonstrated multipolar cell processes. However, most small neurons with identical ultrastructural characteristics did not show these synapses. Axodendritic synapses were also seen on the dendritic processes of the small neurons and between varicose nerves and unmyelinated nerve fibers some distance from the small neurons. While these observations conform in some aspects with the concept of parasympathetic nerve fibers and neurons in the cochlea, they are also compatible with the idea that the small neurons may have an auditory function influenced by the synaptic contacts of efferent fibers from the olivocochlear bundle.

Adolescent↗

PubMed1978

[Vascularization of the ganglion spirale cochleae of the rat (author's transl)].

Investigation into the vascularization of the Ganglion spirale of the rat showed an irregular, loose network of capillaries, with a somewhat denser vacularization of the marginal areas of the ganglion; the horseradish peroxidase benzidine test according to Sugar was used to demonstrate the vessels. At least of the blood supply of the ganglion is effected via the vessels which run parallel to the nerve fibres through the osseous canals from the modiolus into the Rosenthal canal. The density of vascularization of the Ganglion spirale is surprisingly small, namely 1.89% by volume. The comparative figure for the Ganglion spirale, also measured by means of stereological methods, is approximately 6.8% by volume, whilst the vessels in the Nervus cochlearis occupy 2.1% by volume. The vascularization density of the ganglion corresponds roughly to that of the Cortex cerebri. Electro-microscopical tests have shown that there are unfenestrated capillaries with a small number of pinocytotic vesicles. Possible conclusions as to the permeability of the capillaries are discussed in the paper. The blood supply of the Ganglion spirale has so far received only little attention. In the case of internal ear diseases of vascular genesis, attention is mainly given to changes in the vessels of the lateral wall of the cochlea. Experimental findings, however, show the high sensitivity of the nervous apparatus of the cochlea in the case of disturbed blood supply.

Cochlear Nerve↗

PubMed1979

Vestibular effects of electrical stimulation of the cochlea. Monitored in the awake primate.

The effect of electrical stimulation of the cochlea on vestibular response was monitored in six rhesus monkeys. Eye movements and single-unit activity from the vestibular portion of the eighth nerve, vestibular nuclei, reticular formation, and abducens nucleus were observed while electrical stimulation was delivered through an implanted cochlear prosthesis. In one animal of this series, neural activity from the inferior colliculus and cochlear nuclear complex was also recorded. Electrical stimulation elicited eye-movement responses in only one animal. In the animals from which single-unit activity was recorded, no positive vestibular effects were noted. In one animal of this study, responses were elicited from auditory structures by relatively low intensities of electrical stimulation.

Acoustic Stimulation↗

PubMed1977

Evidence that catecholamines are not the afferent transmitter in the cochlea.

Beta-receptor blocking agents (practolol, propranolol) and alpha-receptor blocking agents (phenoxybenzamine, phentolamine), when applied intracochlearly do not eliminate the afferetn discharges or compound action potential of the cochlear nerve. Under the assumption that the drugs used reach the synaptic site, it is therefore concluded that these drugs do not interfere with afferent synaptic transmission. Phentolamine,, however, has a toxic effect upon the cochlea independent from the synaptic process. Local application of catecholamines does not increase spontaneous activity of single fibres of the cochlear nerve. These findings show that catecholamines are not likely to be the afferent transmitter.

Acoustic Stimulation↗

PubMed1976

Effects of incubator noise on the cochlea of the newborn.

The possible effects of incubator noise on the hearing of premature babies have long been debated. The type of hearing loss found in 12 low-birthweight children was examined; and the variable noise level in regularly used incubators was measured. This noise, applied to guinea pigs continuously during their second week after birth, was shown histologically to destroy a proportion of the sensory cells in the cochlea. Adult guinea pigs, however, were not vulnerable in this way. The conclusion is that there is definite circumstantial evidence of the damaging effect of many incubators on the hearing of premature infants.

Animals↗

PubMed1976

[Rupture of the round window membrane after slight head injury with flush of perilymph probably caused by large opening of aquaeductus cochleae (author's transl)].

A ringing deaf ear was noticed after slight head injury without loss of consciousness nor fracture of the skull. After performig tympanotomy a ruptured round window membrane with excessive flush of perilymph was found. We might rightly assume that this was induced by a large opening of aquaeductus cochleae combined with the force of inertia of the cerebral liquor and the direction of the push to the round window (blow behind the left ear).

Accidents, Home↗

PubMed1978

[Distribution pattern in the guinea pig cochlea of intravitally injected peroxidase].

Following perilymphatic perfusion and injection into the cisterna cerebello-medullaris, respectively, the distribution pattern of horseradish peroxidase in the cochlea of the guinea pig was studied light and electron microscopically. The findings prove effective tight junctions (zonulae occludentes) between the cells of the epithelial lining of the endolymphatic compartment. At the level of the reticular membrane the tight junctions are far more extended than elsewhere at the cochlear duct epithelium. From the findings a fairly rapid exchange is suggestive between the lymphatic space of the organ of Corti and the tympanic scale. Various types of cells of the cochlear duct actively take up considerable amounts of peroxidase. However, endocytosis of peroxidase by hair cells and particularly by the outer ones is rather scanty. Passive permeation of the tracer through the membran of undamaged hair cells was disproven.

Animals↗

PubMedDate not supplied

Fluorocitrate ototoxicity. A morphologic and cytochemical model for primary neural degeneration in the guinea pig cochlea.

Fluorocitrate, an inhibitor of the tricarboxylic acid cycle at the aconitase reaction, produces a time and dose related neural dystrophy in the guinea pig cochlea. There is direct inhibition of succinic dehydrogenase activity but not nicotinamide adenine dinucleotide dehydrogenase and cytochrome oxidase via cytochrome c activities. The dystrophic neural changes morphologically are similar to those noted in primary neural degeneration and neural presbycusis in man. Neural degeneration in aging appears to be the result of a dissociation of biochemical reactions preventing the proper utilization of organic fuel molecules for generation of energy and direct or indirect inhibition of respiration.

Animals↗

PubMed1979

Action of putative neurotransmitters in the guinea pig cochlea.

Scala tympani of the guinea pig was perfused with artificial perilymph containing putative transmitter substances. Single auditory nerve fibre activity was recorded during these perfusions and the responses of these fibres were studied using computer-controlled routine. Acetylcholine significantly inhibited tone-induced responses of a large proportion of the fibres tested. Glutamate appeared to be a potent depolarising agent when applied in concentrations between 2 and 10 mM. Noradrenaline did not affect tone-induced activity, but inhibited the spontaneous activity of some fibres. The results support the view that acetylcholine is the transmitter at synapses of the olivocochlear bundle, and that glutamate may be involved in the afferent synapse. The data do not support the hypothesis that noradrenaline is the afferent transmitter.

Acetylcholine↗

PubMed1978