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At least 253 records · Page 14Linked to original sources
PubMed1985

Cochlear nerve of the alligator lizard.

The innervation of the auditory organ of the alligator lizard is described. Patterns of distribution of the nerve fibers were studied at the light microscopic level with the horseradish peroxidase technique, and the types of synaptic contacts with hair cells were studied at the transmission electron microscopic level with standard techniques. The innervation of the two regions of the basilar papilla differs in the following ways. In the apical region, some fibers send branches along the length of the basilar papilla, and both afferent (non-vesiculated) and efferent (vesiculated) nerve endings are present. In the basal region, all fibers terminate in the immediate area where they enter the papilla without sending branches along the length of the papilla; efferent endings are lacking, and nerve fibers are of a smaller average diameter. The punctate nature of the innervation of hair cells in the basal region is consistent with the hypothesis that the systematic organization according to frequency sensitivity observed in electrophysiological recordings from basal nerve fibers may be related to the length of the stereocilia on the hair cells with which the nerve synapses.

Animals↗
PubMed2003

Loss of alpha CGRP reduces sound-evoked activity in the cochlear nerve.

alpha-Calcitonin gene-related peptide (alphaCGRP) is one of several neurotransmitters immunolocalized in the unmyelinated component of the cochlear efferent innervation, the lateral olivocochlear (OC) system, which makes axo-dendritic synapses with cochlear sensory neurons. In rodents, CGRP is also immunocolocalized in the myelinated medial OC system, which contacts cochlear outer hair cells (OHCs). To understand the role(s) of this neuropeptide in the OC system, we characterized the auditory phenotype of alphaCGRP-null mice. Cochlear threshold sensitivity was normal in mutant mice, both via a neural metric, the auditory brain stem response (ABR), and an OHC-based metric, distortion product otoacoustic emissions (DPOAEs). Medial OC function and resistance to acoustic injury were also unaffected by alphaCGRP deletion: the former was assessed by measuring cochlear response suppression with electrical stimulation of the OC bundle, the latter by measuring temporary threshold shifts after exposure to high level sound. However, significant abnormality in alphaCGRP-null mice was seen in the growth of cochlear neural responses with increasing stimulus level. This observation, contrasted with normal amplitude-versus-level functions for DPOAEs, is consistent with a selective, postsynaptic effect on cochlear neurons via alphaCGRP release from lateral OC terminals. This constitutes the most direct evidence to date for a functional role of the lateral OC system in the auditory periphery.

Acoustic Stimulation↗
PubMed1991

The influence of DC-polarization of the endocochlear potential on single fibre activity in the pigeon cochlear nerve.

The endocochlear potential (EP) in the pigeon ear was altered by injecting current into the scala media. Simultaneous recordings from afferent fibres in the cochlear ganglion were performed. The mean rate of spontaneous activity was little affected by current injection and the consequent shifts in EP. In contrast to this lack of effect, the preferred intervals seen in some fibres in birds were accentuated by positive current injection and reduced or in some cases suppressed by negative current injection. The threshold of the tuning curve was raised by injection of negative current but the characteristic frequency showed little change. Sharpness of tuning decreased. Analysis of the results shows that current injection in the scala media produces significant changes in the filter characteristics of the cochlea, as well as altering the driving force for the transduction process (difference between EP and hair cell membrane potential).

Acoustic Stimulation↗