Pharmacological alterations of the activity of afferent fibers innervating hair cells.
To determine whether some of the substances that may be present in hair-cell sensory organs could affect neural activity in afferent fibers, we examined 56 compounds for the ability to alter the discharge rate of afferent fibers innervating hair cells in the lateral line organ of Xenopus laevis, the African clawed frog. These compounds included amino acids, glutamyl dipeptides, standard neurotransmitter candidates, and other constituents of tissues and body fluids. Substances found to be excitatory included some neutral amino acids (alanine, serine, threonine, asparagine, glutamine, and proline), ATP, carnosine, histidine, and barium chloride. Compounds that suppressed discharge included the aromatic amino acids (phenylalanine, tryptophan, and tyrosine), serotonin, and gamma-glutamyl dipeptides. GABA and acidic amino acids (glutamate, aspartate, and cysteine sulfinate) produced a brief excitation followed by a suppression of discharge rate. Several of these substances were active at sufficiently low concentrations that their presence in body fluids may affect afferent fiber discharge rate under normal or pathological conditions.
Mroz
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Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston 02114.
Sewell
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D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001306:Auditory Pathways / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006198:Hair Cells, Auditory / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D009412:Nerve Fibers / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D012701:Serotonin / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects*; D000159:Vestibulocochlear Nerve / Q000187:drug effects; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D000596:Amino Acids; D018377:Neurotransmitter Agents; D012701:Serotonin; D005680:gamma-Aminobutyric Acid