Several feeding-related factors can affect taste sensitivity or preferences and therefore may be part of a homeostatic regulatory mechanism. Cholecystokinin (CCK), a hormone which reduces food intake in several species, has also been postulated to interact with the orosensory characteristics of food. To test this hypothesis, the effects of CCK-8 and food deprivation on the short-term intakes of water, sucrose solutions (0.05 to 1.0 M), and saline solutions (0.05 and 0.15 M) were determined. In most cases, CCK (2 μg/kg) reduced sucrose intake when measured either as the amount consumed or the number of licks in a short period (nine minutes). Additionally, CCK reduced the intake of 0.15 M NaCl in satiated rats and water intake in both hungry and satiated rats. Rats usually consumed more sucrose when hungry than when satiated or fed ad libitum; CCK-induced suppression of intake, however, was generally greater in the satiated or ad libitum conditions than in the hungry condition. There was no systematic effect of sucrose concentration on the amount of CCK-induced suppression of intake, which suggests that CCK regulates rather than interferes with ingestion. To determine whether the CCK-induced suppression is due to a change in the peripheral taste signal, the integrated chorda tympani responses to sucrose and NaCl tastes were recorded in rats anesthetized with either urethane, Innovar-Vet, or a combination of urethane and alpha-chloralose. The only significant effect of CCK was the slight increase in the initial response to 0.3 M sucrose after the infusion of a total of 10 μg of CCK-8 into rats anesthetized with Innovar-Vet. In general, therefore, the effect of CCK on sucrose intake does not appear to be due to a peripheral taste change; an analysis of single taste fibers, however, would be more conclusive. An examination of the effects of CCK on central gustatory and reward areas might yet provide a mechanism for the CCK effect on taste-motivated ingestion.

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Rats are nocturnal animals, their ingestive behaviours show circadian rhythms and the suprachiasmatic nuclei (SCN) of the hypothalamus are the primary pacemaker of these rhythms. Serotonin (5-HT) is one of the most abundant neurotransmitter in the SCN and it is involved in the regulation of ingestive behaviour. In this study, we compared food and water intakes of male adult Wistar rats infused during 7 days with serotonin (2.5 nmol/24h) or artificial cerebrospinal fluid (CSF) in the SCN in a three-way selection of macronutrients. Within 5-HT infusion, nocturnal and diurnal water intakes, and the nocturnal caloric intake from the protein diet were significantly lower than those of the CSF infused group. Decrease in water consumption was most significant in the early and middle dark phases. Besides, increased diurnal energy intake and decreased nocturnal energy intake were observed during 5-HT and CSF infusion. In conclusion, this first chronic and continuous infusion work on 5-HT in the SCN specifically disrupted the circadian rhythmicities in water and protein consumptions.

Dietary selection involves the process of relating the postingestional consequences of eating a food to its sensory characteristics. Diet texture, the most plausible sensory characteristic affecting ingestion, may play an important role in the control of food selection. In this study, we compared the circadian rhythmicity of protein- and carbohydrate-rich diet ingestion of adult male Wistar rats presented with diets in different textural forms (high-protein powder and high-carbohydrate granular (HPP-HCG) diets vs. high-protein granular and high-carbohydrate powder (HPG-HCP) diets) during 15 days. Rats fed HPP-HCG diets selected significantly less protein (kcal) vs. rats fed HPG-HCP diets, during the 24 h, 12 h dark phase and the 4 h early and late dark phases. Carbohydrate intakes of the two dietary groups were not significantly different. Total caloric intake for HPG-HCP group was significantly higher than that of HPP-HCG group during the 24 h and 12 h dark phase. In conclusion, macronutrient-rich diets presented in different textural forms alter the circadian rhythmicity of protein-rich diet ingestion and total energy intake.

No description available.

No description available.

Serotonin has been implicated as a modulator of feeding behavior. This experiment was designed to alter brain serotonin levels through dietary means in hypothalamic ventromedial-lesioned and unlesioned rats. Daily food, water, and animal weights were measured. The purpose was to determine if VMH lesions altered the feeding pattern found in unlesioned rats. Although food intake for tryptophanenriched diets and tryptophan-deficient diets did not differ from their respective control groups, in some cases gross animal weights did differ significantly between experimental and control groups and between lesioned and unlesioned groups. A proposed model explains how a "low" energy signal and a "high" protein signal cycles amino acids through gluconeogenesis to comPensate for an energy deficit.

Learning processes play a major role in controlling intake of food. Through repeated experiences an animal acquires the ability to predict the postingestive effects of a particular food (i.e., of its nutrients and energy) from its sensory characteristics. What is unclear from the literature, however, is whether an animal can anticipate the duration of subsequent food deprivation from predictive sensory qualities of a food, and hence increase the amount eaten of that cueing food. Therefore, the aim of this work was to investigate the characteristics of this under-researched type of learning, i.e., anticipatory eating, using laboratory rats trained on two lengths of fasting (short: 2-3 h, long: 8-10 h). The main findings were as follows. 1) Anticipatory eating is learnt when a choice is given between protein- and carbohydrate-rich foods as well as on a single balanced test food. 2) The learnt extra intake of food is instrumental to preventing the return of hunger, removal of which negative reinforcement extinguishes the response. 3) The resulting return of hunger induces re-learning of anticipatory eating. 4) During the training sessions, learning of anticipatory eating competes with classical conditioning of sensory preference. Conditioning of preference is likely to be stronger with the shorter than with the longer length of fasting. Therefore, the difference between intakes before the long and the short fast at each trial is the summed result of these two mechanisms of acquired increase in intake. While preference conditioning usually reaches a maximum rapidly, depletion-avoidance increases for as long as has been tested, with interruptions of rapid self-extinction and re-learning, This self-extinction contributes to the homeostatic character of this learning. 5) High-fat maintenance diet attenuates the learning of anticipatory eating. Overall, the findings provided robust evidence that eating in rats can be controlled by instrumental learning reinforced by hunger. Accordingly, the design of an experiment on such instrumental control of eating in human subjects is proposed to conclude this thesis.

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No description available.