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.

Effect of unilateral vestibular stimulation on histamine release from the hypothalamus of rats in vivo

“…This report suggested that histamine might have acted as a hair cell transmitter in frog, and the action site of H, antagonists that were used to treat vertigo and motion sickness was in such a peripheral location as the semicircular canal. In contrast, Bledsoe et al ( 1989) reported that histamine (0.002-2.0 mM) had no effect on the spontaneous activity of frog's ampullar nerve, whereas pyrilamine (0.0 l-0.05 mM), an H 1 antagonist, suppressed the spontaneous activity. Because histamine (2.0 mM) failed to block the actions of pyrilamine (0.1 mM), they concluded that the action of pyrilamine was nonspecific, possibly because of blockade of voltage-dependent sodium channels.…”

Histamine and Its Receptors in the Mammalian Inner Ear: A Scoping Review

“…Only two studies have studied the electrophysiological function of histamine in the mammalian inner ear [54,59]. Previous results obtained using the vestibular organ of frogs and lateral line of Xenopus laevis have suggested that histamine may act as a hair cell transmitter [69][70][71]. These studies provided evidence that histamine increases the afferent firing rate in nerves and that this afferent firing could be blocked by H 1 R and H 2 R antagonists.…”