RELATIONSHIP BETWEEN HISTAMINE-RECEPTORS IN THE BRAIN AND DIAZEPAM-INDUCED HYPERPHAGIA IN RATS

We investigated whether histaminergic neurons in the brain are involve d in diazepam-induced hyperphagia in rats. Pretreatment with intracere broventricular (ICV) injection of either histamine H-1-receptor antago nist, pyrilamine (10 and 30 mu g) or histamine H-2-receptor antagonist , famotidine (3 and 10 mu g) did not affect only diazepam (1 mg/kg, su bcutaneous, SC)-induced hyperphagia in nondeprived rats, but also spon taneous feeding in food-deprived rats. In addition, pretreatment with ICV injection of histamine H-3-receptor antagonist, thioperamide, and histamine H-3-receptor agonist, (R) alpha methylhistamine, enhanced an d inhibited diazepam-induced hyperphagia (1 mg/kg, SC) in nondeprived rats, respectively. However, thioperamide and (R) alpha methylhistamin e did not affect spontaneous feeding in food-deprived rats. These find ings suggest that histaminergic neurons are not directly involved in d iazepam-induced hyperphagia in rats. Furthermore, enhancement or inhib ition of diazepam-induced hyperphagia by histamine H-3-receptor antago nist or agonist may occur via histamine H-3-receptors localized in the other neurons in the rat brain.