title: Effects of histamine, H1- and H2-receptor antagonists on the activity of serotonergic neurons in the dorsal raphe nucleus.
abstract: We investigated the effects of histamine applied by microiontophoresis onto serotonin-containing (serotonergic) cells recorded extracellularly in the dorsal raphe nucleus of the rat. Application of histamine at low iontophoretic currents (1-5 nA) produced a rapid depression of the firing of all serotonergic neurons tested. The H1-receptor antagonists mepyramine and diphenhydramine were unable to attenuate the histamine-induced response. Antagonism of the effect of histamine by the iontophoretic application of the H2-receptor antagonists cimetidine and metiamide was not possible to evaluate since both were found to exert potent inhibitory effects by themselves. In contrast, the nonimidazole-derived H2-receptor antagonist ranitidine, which had no effect by itself, selectively antagonized the histamine-induced depression of neuronal activity. Histidine, 3-methylhistamine and a variety of histamine agonists selective for H1- or H2-receptors were unable to mimic the effect of histamine in dorsal raphe. Histamine's effects may, in part, be mediated at a gamma-aminobutyric acid receptor complex as the gamma-aminobutyric acid antagonists bicuculline and picrotoxin rapidly and reversibly antagonized both the histamine- and the cimetidine-induced depression of serotonin cell firing; the glycine antagonist strychnine selectively blocked the inhibitory effect of glycine without altering the histamine-induced response. These data show an inhibitory effect of histamine on serotonin-containing neurons in the dorsal raphe; this effect may be partially mediated at a subtype of H2-receptor. These data further indicate that the inhibitory effects of histamine and cimetidine observed in the dorsal raphe nucleus may result, in part, from an action directly or indirectly at a gamma-aminobutyric acid receptor complex.
mesh_terms: D000818:Animals; D001933:Brain Stem / Q000187:drug effects*; D002927:Cimetidine / Q000494:pharmacology; D004155:Diphenhydramine / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology*; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D006635:Histamine H2 Antagonists / Q000494:pharmacology*; D008297:Male; D008785:Metiamide / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D011738:Pyrilamine / Q000494:pharmacology; D011899:Ranitidine / Q000494:pharmacology; D011903:Raphe Nuclei / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects; D011963:Receptors, GABA-A; D012701:Serotonin / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects; D005680:gamma-Aminobutyric Acid
chemical_list: D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D012701:Serotonin; D008785:Metiamide; D005680:gamma-Aminobutyric Acid; D002927:Cimetidine; D006632:Histamine; D011899:Ranitidine; D004155:Diphenhydramine; D011738:Pyrilamine