Figure 2.

H₁ and H₂ receptors co-mediated the histamine-induced postsynaptic excitation on MVN neurons. (A) In the presence of TTX, the histamine-induced inward currents were partly blocked by mepyramine, a highly selective H₁ receptor antagonist, and abolished by combined application of mepyramine and ranitidine, a highly selective H₂ receptor antagonist. (B) In the presence of TTX, the histamine-induced inward currents were partly blocked by ranitidine, and abolished by the combination of mepyramine and ranitidine. (C) Group data of the tested MVN neurons. Data shown are means ± SEM; **P < 0.01, ***P < 0.001, significantly different from control. (D) Bar graphs showing the relative expression of H₁, H₂ and H₄ receptor mRNAs in the MVN. In this and the following figures, asterisks indicate samples showing no specific signal, and cycles necessary to get a signal are listed below each gene. (E1–G3) Double immunostaining results showed that histamine H₁ (E1–E3) and H₂ (F1–F3) receptors were not only present in the rat MVN but also co-localized in the same MVN neurons (G1–G3). Scale bars: (C1), (D1) and (E1), 550 μm; (C2), (D2) and (E2), 100 μm; (C3), (D3) and (E3), 20 μm. 4V, 4th ventricle; IVN, inferior vestibular nucleus; MVN, medial vestibular nucleus; Pr, prepositus nucleus.