Food consistency modulates eating volume and speed through brain histamine in rat.

Changes in meal parameters of rats fed with different consistency of food were examined using hard and soft pellets. Meal size and eating speed of the first meal after 1800 h increased significantly in rats fed with soft pellets compared to those fed with hard pellets. Effects of histamine depletion on meals treated with hard or soft pellets were investigated after an intraperitoneal injection of 0.11 mmol/kg alpha-fluoromethylhistidine (FMH), a specific suicide inhibitor of the histamine synthesizing decarboxylase enzyme. When rats were fed with hard pellets, FMH significantly decreased eating speed and prolonged meal duration without affecting meal size. When rats were fed with soft pellets, FMH increased meal size and duration, but not eating speed. The meal parameter of eating speed was significantly decreased and meal size and duration were increased in obese Zuckers, a hereditary histamine-depleted animal model, when compared to their lean littermates. These results indicate that proprioceptive sensation from the oral cavity may regulate meal parameters through histaminergic neurons in the brain.