Histamine elicits neuronal excitatory response of red nucleus in the rat via H2 receptors in vitro

Perfusing slices with histamine (1-100 muM) produced an excitatory response in rat rubral neurons (118/132, 89.4%). The histamine-induced excitation was not blocked by the low-Ca2+/high-Mg2+ medium (n = 10), supporting a direct postsynaptic action of the amine. Histamine H-2 receptor antagonist ranitidine effectively blocked the excitatory response of rubral neurons to histamine (n = 26), but H-2 receptor antagonist triprolidine did not (n = 24). The excitatory effect of histamine could be mimicked by dimaprit, a highly selective H-2 receptor agonist (n = 24), and the dimaprit-elicited excitation of the rubral neurons could be blocked by ranitidine (n = 16), but not by triprolidine (n = 9). In addition, H, receptor agonist 2-pyridylethylamine could not elicit any response in rubral neurons (n = 12). These results indicate that histamine excites red nucleus neurons through H2 receptors and suggest that the histaminergic afferent fibers may play an important functional role in the sensorimotor integration through the red nucleus. (C) 2003 Elsevier Ireland Ltd. All rights reserved.