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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.

Sophisticated voluntary movements of the tongue are essential to speech articulation and swallowing in humans. Voluntary tongue movements are finely controlled by communications between the cortex and tongue muscles. A large number of previous studies have reported that functional connections between the cortex and muscles are reflected by cortico-muscular coherence (CMC), which is measured between electroencephalography (EEG) or magnetoencephalography (MEG) and surface electromyography (EMG), during isometric finger movements in humans. Recent studies indicate that CMC reflects a bi-directional flow of information between the cortex and fingers, along the descending corticospinal pathway and with ascending sensory feedback. However, CMC for the tongue has not been well-studied, despite the fact that increased knowledge would be helpful in understanding cortical entrainment of voluntary tongue movements.