Effects of intraperitoneally administered l-histidine on food intake, taste, and visceral sensation in rats

To evaluate relative factors for anorectic effects of l-histidine, we performed behavioral experiments for measuring food and fluid intake, conditioned taste aversion (CTA), taste disturbance, and c-Fos immunoreactive (Fos-ir) cells before and after i.p. injection with l-histidine in rats. Animals were injected with saline (9 ml/kg, i.p.) for a control group, and saline (9 ml/kg, i.p.) containing l-histidine (0.75, 1.5, 2.0 g/kg) for a l-histidine group. Injection of l-histidine decreased the average value of food intake, and statistically significant anorectic effects were found in animals injected with 1.5 or 2.0 g/kg l-histidine but not with 0.75 g/kg l-histidine. Taste abnormalities were not detected in any of the groups. Animals injected with 2.0 g/kg l-histidine were revealed to present with nausea by the measurement of CTA. In this group, a significant increase in the number of Fos-ir cells was detected both in the area postrema and the nucleus tractus solitarius (NTS). In the 0.75 g/kg l-histidine group, a significant increase in the number of Fos-ir cells was detected only in the NTS. When the ventral gastric branch vagotomy was performed, recovery from anorexia became faster than the sham-operated group, however, vagotomized rats injected with 2.0 g/kg l-histidine still acquired CTA. These data indicate that acute anorectic effects induced by highly concentrated l-histidine are partly caused by induction of nausea and/or visceral discomfort accompanied by neuronal activities in the NTS and the area postrema. We suggest that acute and potent effects of l-histidine on food intake require substantial amount of l-histidine in the diet. Keywords: l-histidine, Anorexia, Visceral sensation, Area postrema, NTS, CTA, Rats
Author(s): Yuka Okusha[sup.1,2,3], Yoshiyuki Hirai[sup.3], Hitoshi Maezawa[sup.3], Kazunari Hisadome[sup.3], Nobuo Inoue[sup.1], Yutaka Yamazaki[sup.1] and Makoto Funahashi[sup.3] Introduction Several studies have demonstrated an anorectic effect of dietary histidine [1-4], and intraperitoneal [...]