Effects of intragastric injection of glutamate on efferent sympathetic nerve activity in rats.

Niijima previously reported that intragastric infusion of glutamate has increased the activity of the efferent parasympathetic nerves that innervate the stomach and pancreas in urethane-anesthetized rats. In the present study, the effects of intragastric injection of glutamate on the efferent sympathetic nerve outflow to the kidney and the white adipose tissue in rats were analyzed. Although the sympathetic nerve activities of the renal and white adipose tissues were not affected after intragastric glutamate injection in rats that were fasted for 3h, these activities were significantly accelerated after intragastric glutamate injection in rats that were fasted for 48h. Moreover, to test the role of the afferent neural pathway on sympathoexcitation caused by glutamate injection, the effects of vagotomy, or sympathetic denervation, were also examined. In vagotomized rats, the sympathetic nerve activities of the renal and white adipose tissues were eliminated after glutamate injection, but these activities remained unaffected in rats that underwent sympathetic denervation. Thus, the stimulating effects of glutamate administration on the sympathetic nerve activities of the renal and white adipose tissues could depend on the length of the fast and the vagal afferent pathway.