Some behavioral effects of histamine H1-, and H2-receptor agonists in rats.

2-Pyridylethylamine (2-PEA) and 4-methylhistamine (4-MeHI) when given intraventricularly at doses of 30 and 100 microgram had no discernible effect on spontaneous locomotor activity and did not visibly change gross behavior of rats. 4-MeHI(100 micrograms) injected to tranylcypromine-pretreated rats increased locomotor activity and induced head twitches. Locomotor activation was not antagonized by either cimetidine or metergoline but was prevented by alpha-methyl-p-tyrosine and haloperidol and reduced by phentolamine. 4-MeHI-, and histamine (HI)-induced head twitches were not antagonized by either cimetidine or metiamide but were completely abolished by metergoline and p-chlorophenylalanine. It is concluded that 4-MeHI--induced locomotor activation and both HI-, and 4-MeHI-induced head twitches are respectively catecholamine-, and serotonin-dependent phenomena. The behavioral effects of HI and HI H1-and H2-receptor agonists are discussed with regard to possible HI interactions with both catecholamine and serotonin systems in brain.