Ginsenoside Rg1 prevents histaminergic modulation of rat adaptive behavior from elevation of ambient temperature

Effects of ginsenoside Rg1 (Rg1) on histaminergic modulation of both adaptive behavior and thermoregulation were investigated at high ambient temperature. Continuous infusion of Rg1 using an osmotic minipump into the rat third cerebroventricle attenuated anorexia induced by elevation of ambient temperature from 21 degrees C to 31 degrees C. Intraperitoneal injection of alpha-fluoromethylhistidine (FMH), a specific suicide inhibitor of a histamine synthesizing decarboxylase enzyme, also prevented the anorexia induced by elevated temperature. The ratio of water intake to food intake, which showed no change on the first day after elevation of room temperature, was not influenced by treatment of either FMH or Rg1. Rectal temperature, which was normally maintained at a constant level even after shifting ambient temperature from 21 degrees C to 31 degrees C, elevated after FMH treatment. The Rg1 infusion, however, maintained rectal temperature normally at 31 degrees C. Hypothalamic histamine content increased in response to elevation of ambient temperature. The Rg1 infusion maintained constant histamine level against elevation of environmental temperature. Under the heated condition FMH reduced hypothalamic histamine. These findings suggest that Rg1 may modulate rat adaptive behavior by blockade of temperature-related information into the hypothalamic histamine neurons.