title: Analysis of histamine as a hair-cell transmitter in the lateral line of Xenopus laevis.
abstract: The actions of histamine and histamine antagonists on afferent nerve activity were investigated in the lateral line of Xenopus laevis. Histamine (0.002-2.0 mM) had no effect on spontaneous activity or excitatory responses to water motion. In contrast, pyrilamine, an H1 receptor antagonist, suppressed spontaneous activity beginning at 0.01-0.05 mM. Below 0.3 mM the suppression was often preceded by a small excitatory response and responses to high (24-30 dB re threshold), but not low (0-18 dB) levels of water motion were selectively suppressed. Higher concentrations (0.3-2.0 mM) abolished spontaneous activity and suppressed responses at all levels of water motion. Cimetidine, an H2 receptor antagonist, had similar actions but was one-tenth as potent as pyrilamine. Tetrodotoxin (0.001-0.1 microM), which blocks voltage-sensitive Na+ channels, mimicked the suppressive effects of the histamine antagonists. Histamine (2.0 mM) failed to block the actions of pyrilamine (0.1 mM) indicating its effects are mediated through a mechanism other than histamine receptors. In addition, pyrilamine (0.05-0.1 mM) non-selectively suppressed excitation to exogenously applied L-glutamate (1.0-2.0 mM), L-aspartate (1.0-2.0 mM), kainate (0.005-0.01 mM), and quisqualate (0.002-0.005 mM) and altered responses to N-methyl-D-aspartate (0.5-1.0 mM). The results are inconsistent with histamine being a transmitter in the Xenopus lateral line and reveal that the actions of histamine antagonists are nonspecific, possibly due, in part, to blockade of voltage-sensitive Na+ channels.
authors.affiliation: Kresge Hearing Research Institute, University of Michigan Medical School, Ann Arbor 48109-0506.
authors.forename: S C
authors.initials: SC
authors.lastname: Bledsoe
authors.forename: R J
authors.initials: RJ
authors.lastname: Sinard
authors.forename: S J
authors.initials: SJ
authors.lastname: Allen
mesh_terms: D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D005260:Female; D006198:Hair Cells, Auditory / Q000502:physiology*; D006632:Histamine / Q000502:physiology*; D008297:Male; D004856:Postural Balance; D011969:Receptors, Histamine H1 / Q000502:physiology; D011970:Receptors, Histamine H2 / Q000502:physiology; D012665:Semicircular Canals / Q000294:innervation*; D009435:Synaptic Transmission; D000159:Vestibulocochlear Nerve / Q000502:physiology*; D014982:Xenopus laevis / Q000502:physiology*
chemical_list: D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D006632:Histamine