Fos-Positive Neurons Are Increased in the Nucleus of the Solitary Tract and Decreased in the Ventromedial Hypothalamus and Amygdala by a High-Protein Diet in Rats

Abstract

Transition from a normal- (NP) to a high-protein (HP) diet induces a rapid depression in food intake and a progressive but incomplete return to the initial intake during the succeeding days. The aim of this study was to determine which CNS regions are involved in the HP diet-induced satiety in rats. Brains were collected from 3 groups of adult rats after habituation to an NP diet (21 d), during the transition phase to a HP diet (2 d), or after habituation to the HP diet (21 d). Fos expression was measured in several brain areas that are involved in the control of food intake (solitary tract nucleus, anterior piriform cortex, lateral hypothalamus, arcuate nucleus, posterior para ventricular nucleus, medio ventral hypothalamus, dorso medial hypothalamus, amygdala, and accumbens nucleus). Changes occurred in the majority of these regions during the transition period from the NP diet to the HP diet. After habituation to the HP diet, significant changes in Fos expression were restricted to an increase in the nucleus of the solitary tract and a decrease in the ventromedial hypothalamus and the cortex of the amygdala. Considering the functional characteristics of these areas, the present results suggest that the vagus nerve conveys the information relative to the quantity of protein ingested, that hypothalamic sites regulate food intake and may alter sympathetic nervous system activity, and that higher brain functions such as memory processing by the limbic system or food reward system are involved in the HP diet-induced satiety in rats.

Portal glucose influences the sensory, cortical and reward systems in rats

“…enough to overcome changes in food intake related to novelty and differences in palatability (Jean et al ., )]. In particular, rats rapidly decrease or increase their energy intake when switched to HP or HFHS diets, respectively, without a significant change in their body weight (Darcel et al ., ; la Fleur et al ., ). In this experiment, the group under HFHS diet was therefore introduced as a point of comparison with HP diet, under the hypothesis that contrasted c‐Fos activations would provide stronger clues to the regions implicated in the specific effects of HP diet.…”

Peripheral and central mechanisms involved in the control of food intake by dietary amino acids and proteins

“…The involvement of vagal afferent pathways in protein sensing and signalling to the brain is supported by results showing that intraduodenal protein activates vagal afferent fibres, and HP feeding induces c-Fos expression in neurons within the NTS (95,96) . Faipoux et al (97) showed that a reduction in food intake after a HP load (v. a NP load) resulted from activation of the noradrenergic neurons related to CCK-induced anorexia.…”

Homeostatic regulation of protein intake: in search of a mechanism

“…Thus, there is ample evidence that these neuronal populations classically associated with energy sensing are also responsive to amino acids. Beyond the hypothalamus, there is also evidence supporting a role for brain stem neurons in mediating the effect of protein, as both the nucleus of the solitary tract (NTS) appears to contribute to the effects of intracerebroventricular leucine, and also to respond to dietary protein (12,28,39,117).…”