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J Fex

Publications and source records attributed to J Fex.

44 records · Page 3Linked to original sources
PubMed1979

Uptake of putative neurotransmitters in the organ of Corti.

In vitro uptake of putative neurotransmitters into the organ of Corti of the guinea pig was studied by autoradiography. After incubation in 3H-glycine the label was heaviest over the inner hair cell, but was not confined to the synaptic region of the cell. After incubation in 3H-GABA, 3H-glutamate and 3H-aspartate, heavy labeling was seen over the fibers and terminals of the efferent olivocochlear bundle. Leucine, an amino acid not thought to be a neurotransmitter, was uniformly taken up by all cochlear structures. The fact that GABA, glutamate and aspartate are taken up into efferents, which are almost certainly cholinergic, suggests that high affinity uptake of these substances is not restricted to terminals in which these substances are released as neurotransmitters.

Animals↗
PubMed1978

Kainic acid injections result in degeneration of cochlear nucleus cells innervated by the auditory nerve.

When kainic acid, a putative neurotoxin for neurons with glutamatergic input, is injected into the brainstem, it produces a selective pattern of degeneration in the cochlear nucleus. The rate and extent of degeneration is correlated with the distribution of the primary auditory fibers. This evidence supports the hypothesis that glutamate is the neurotransmitter for primary auditory fibers.

Animals↗
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↗
PubMedDate not supplied

Electrokinetic shape changes of cochlear outer hair cells.

Rapid mechanical changes have been associated with electrical activity in a variety of non-muscle excitable cells. Recently, mechanical changes have been reported in cochlear hair cells. Here we describe electrically evoked mechanical changes in isolated cochlear outer hair cells (OHCs) with characteristics which suggest that direct electrokinetic phenomena are implicated in the response. OHCs make up one of two mechanosensitive hair cell populations in the mammalian cochlea; their role may be to modulate the micromechanical properties of the hearing organ through mechanical feedback mechanisms. In the experiments described here, we applied sinusoidally modulated electrical potentials across isolated OHCs; this produced oscillatory elongation and shortening of the cells and oscillatory displacements of intracellular organelles. The movements were a function of the direction and strength of the electrical field, were inversely related to the ionic concentration of the medium, and occurred in the presence of metabolic uncouplers. The cylindrical shape of the OHCs and the presence of a system of membranes within the cytoplasm--laminated cisternae--may provide the anatomical substrate for electrokinetic phenomena such as electro-osmosis.

Animals↗