Histamine excites rat lateral vestibular nuclear neurons through activation of post-synaptic H2 receptors.

Through whole-cell patch recordings in brainstem slices, the effects of histamine on neuronal activity of the lateral vestibular nucleus (LVN) were investigated. Bath application of histamine elicited a concentration-dependent excitation of both spontaneous firing (n=19) and silent (n=7) LVN neurons. Moreover, histamine induced a stable inward current in the LVN neurons (n=5) and the histamine-induced depolarization of membrane potential persisted in the presence of tetrodotoxin (n=4), indicating a direct post-synaptic effect of the histamine on the LVN neurons. Selective histamine H2 receptor antagonist ranitidine effectively blocked the histamine-evoked excitatory responses on the LVN neurons (n=4), but selective histamine H1 receptor antagonist triprolidine did not (n=4). In addition, selective histamine H2 receptor agonist dimaprit (n=3) rather than 2-pyridylethylamine (n=4), a selective histamine H1 receptor agonist, mimicked the excitatory action of histamine on LVN neurons. The results demonstrate that histamine excites the LVN neurons via post-synaptic histamine H2 receptors and suggest that the central histaminergic projection arising from the hypothalamus may modulate LVN neurons activity and actively influence the vestibular reflexes and functions.