Histamine excites rat cerebellar granule cells in vitro through H-1 and H-2 receptors

The effects of histamine on the firing of cerebellar granule cells were inv estigated in vitro. Histamine predominantly produced excitatory (117/123, 9 5.1%) and in a few cases inhibitory (6/123, 4.9%) responses in granule cell s. The histamine-induced excitation was not blocked by perfusing the slice with low Ca2+/high Mg2+ medium, supporting a direct postsynaptic action of histamine. The H-1 receptor antagonists triprolidine and chlorpheniramine s ignificantly diminished the histamine-induced excitation, but the H-2 recep tor antagonist ranitidine did not significantly reduce the excitation. On t he other hand, the H-2 receptor agonist dimaprit could elicit a weak excita tion of granule cells. This dimaprit-induced excitation was blocked by rani tidine but not triprolidine. These results reveal that the excitatory effec t of histamine on cerebellar granule cells is mediated by both H-1 and H-2 receptors with a predominant contribution of H-1 receptors. The relevance o f these findings to the possible function of the hypothalamocerebellar hist aminergic fibers in cerebellum is discussed. (C) Elsevier, Paris.