Histamine regulates food intake through modulating noradrenaline release in the para-ventricular nucleus

Histamine is one of the neurotransmitters suppressing appetite, but the interactions of histaminergic neurons with other neurons in satiety centers have not been clarified. Noradrenaline in the para-ventricular nucleus (PVN) has been shown to stimulate feeding. This study was designed to determine whether histamine modulates noradrenaline release via histamine H1-receptors in the PVN. Freely-fed rats were i.c.v. injected with an histamine H1-receptor antagonist, triprolidine (82 microg), and/or an alpha 2-adrenoceptor antagonist, rauwolscine (0, 20 and 40 microg), and food intake (n=8 each) over 2 h was measured. Food intake was significantly (p<0.01) increased in rats injected with triprolidine alone. The triprolidine-elicited increase in food intake was suppressed by rauwolscine at a dose of 40 microg. The noradrenaline content in perfusates collected by a microdialysis probe aimed at the PVN was significantly (p<0.05) increased by the presence of triprolidine in the perfusates. The noradrenaline concentrations in perfusates collected from the PVN were elevated after tyramine (a noradrenaline uptake inhibitor) administration, but not when both tyramine and histamine were given. In conclusion, these results suggest that histamine inhibits noradrenaline release from hypothalamic nerve terminals in the PVN, and thus suppresses feeding behavior.