The effects of histamine and its antagonists on the cochlear microphonic and the compound action potential of the guinea pig.
OBJECTIVE
we studied the effects of histamine, the H1 receptor antagonist pyrilamine, and the H2 receptor antagonist cimetidine on the cochlear potential of guinea pigs (cochlear microphonic, CM; compound action potential, CAP).


METHODS
histamine was applied into the cochlear perilymph at three different dosages (10 microM, 50 microM or 10 mM). Pyrilamine and cimetidine were applied at 50 microM each.


RESULTS
histamine increased the CAP at 10 and 50 microM without any significant effects on the CM. The effects of histamine at 50 microM were suppressed by the 50-microM of pyrilamine and cimetidine. At 10 mM of histamine, CAP and CM amplitudes were significantly decreased.


CONCLUSIONS
in low concentrations, histamine may act as an extracellular signal on inner hair cells (IHCs) or it may stimulate the afferent nerve by binding to their H1 and H2 receptors. A possible explanation for the inhibitory effects of histamine at 10-mM dosage was apparently found in that the effects of the high concentration may be supraphysiological; and furthermore, there is a difference in the mechanism by which histamine exerts its effects mediated by the histamine receptors on the cochlea.
Minoda
R
R
Department of Otolaryngology, Head and Neck Surgery, Kumamoto University School of Medicine, 1-1-1 A. Honjo, Kumamoto 860-8556, Japan. minoda@gpo.kumamoto-u.ac.jp
Toriya
T
T
Masuyama
K
K
Yumoto
E
E
D000287:Administration, Topical; D000818:Animals; D002927:Cimetidine / Q000494:pharmacology*; D003051:Cochlea / Q000187:drug effects* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005071:Evoked Potentials / Q000187:drug effects*; D006168:Guinea Pigs; D006632:Histamine / Q000378:metabolism*; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D006635:Histamine H2 Antagonists / Q000494:pharmacology*; D011738:Pyrilamine / Q000494:pharmacology*; D014432:Tympanic Membrane / Q000601:surgery
D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D002927:Cimetidine; D006632:Histamine; D011738:Pyrilamine