Direct or indirect action of histamine on dopamine metabolism in the rat striatum?

Intraventricular administration of 500 microgram of 2-pyridylethylamine, an agonist of the histamine (Hi) H1-receptor, produced a 20% increase of striatal HVA in the rat while the Hi H2-receptor agonist 4-methylhistamine had no influence on HVA and DOPAC levels. L-Histidine (1.5 g/kg) or amodiaquine (60 mg/kg) given i.p. increased HVA and DOPAC levels to the same extent as did pyridylethylamine. Histidine combined with tremorine had an additive effect with respect to the increase of DA acidic metabolites while mepyramine slightly attenuated the tremorine-induced rise of HVA.