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We employed a behavior-analytic analog of the sunk cost effect in which all trials started out with a short expected ratio to an imaginary monetary reward, but some trials assumed a longer expected ratio part way through the trial. Subjects had the (preferable) option of “escaping” the trial if the longer expected ratio had come into effect in order to bring on a new trial that again had a short expected ratio. With a between-subjects design we tested whether the presence of discriminative stimuli correlated with the expected ratios would affect escaping behavior. In one condition, such stimuli were present; in the other condition, they were absent. Subjects persisted significantly more in the condition where discriminative stimuli were absent.

From the earliest days of behavioral psychology (e.g., Thorndike, 1911), aversive control — what we now call punishment and negative reinforcement — was recognized as a partner to what we now call positive reinforcement. Although much is controversial about aversive control (Dinsmoor, 2001; Johnston, 1991), one thing is not in doubt: Aversive control is a prominent component of the natural world (e.g., Skinner, 1953) and therefore deserves serious scientific scrutiny.

The present study evaluated the effects of 5-HT1A receptor agonist 8-OH-DPAT on the Behavioral Satiety Sequence (BSS) in rats. The 8-OH-DPAT was administered via central in the hypothalamic ventromedial nucleus (VMN) in rats. The experimental subjects were kept under a dietary self-selection paradigm consisting of proteins, carbohydrates and fats. Food and water were available all the time. Intra-VMN administration of 5-HT1A agonist was associated with the selective increase in carbohydrate intake. The BSS analysis revealed that the administration of 8-OH-DPAT delayed the natural development of the BSS. The results lead to the conclusion that 5-HT1A receptors in the NVH involved in the modulation of food intake, is discussed the possible involvement of interactions with other neurotransmitters systems.

The endocannabinoid system plays an important role in feeding behavior regulation, mainly via CB1 receptors (CB1R). The CB1R are expressed in the paraventricular hypothalamus (PVN) and it has been proposed that these receptors are mediators of the cannabinoid-induced hyperphagia; however, the behavioral mechanism has not been fully characterized. The aim of the present study was to assess the role of PVN CB1R on the expression of satiety using the behavioral satiety sequence analysis (BSS). Male Wistar rats were cannulated unilaterally in the right PVN, they were injected with the CB1R agonist, ACEA (0.25 micro g), and the BSS was evaluated during 2 hours. The BSS analysis showed that ACEA administration prevented the satiety expression and the CB1R antagonist, AM 251 (0.25 micro g), blocked the effect. The present results showed that the CB1R play a inhibitory role on satiety, which strongly suggest that the behavioral mechanism related to the cannabinoid-induced effects involves the inhibition of satiety expression.

Dopamine is a neurotransmitter strongly involved in the feeding behavior regulation. It has been reported that different dopamine receptor agonists inhibited voluntary food intake, nevertheless, dopamine depletion induced intense hypophagia. Current knowledge of D2 receptors and D3 mRNA expression in the paraventricular nucleus of the hypothalamus (PVN) suggests that D2-like receptors may be playing a main role in the dopaminergic feeding behavior regulation. The aim of the present study was to evaluate the effects of paraventricular D2/D3 receptor activation on food intake and behavioral satiety sequence (BSS) in rats. Male Wistar rats (220-240 g) were intra-PVN injected with D2/D3/D4 receptor agonists and/or antagonists, and food intake and BSS were evaluated during 2 hours (dark phase of light cycle). The obtained results showed that intra-PVN D2/D3 activation significantly decreased food intake without disrupting the BSS. The above results strongly suggest that hypothalamic dopamine induces inhibitory effects on food intake via D2/D3 receptors in the PVN.

The objective of this study was to evaluate the effects of two types of stress, chronic or acute, in either controlled or uncontrolled situations, on body weight, food, and water consumption in rats. Acute stress consisted of two sessions of 60 electric shocks and chronic in 12 sessions of 10 shocks. Subjects exposed to the controllable situation could finished the shock with a specific response, and the group uncontrollable was yoked to the uncontrollable group. Control group was kept in its box-room. The results were: reduction of the body weight during exposure to acute stress and a slowdown in the rate of body weight increase during chronic stress, as well as a reduction in the consumption of both food and water during exposure to both acute and chronic stress. The effects observed with chronic stress were more evident robust in males than in females. There were no differences between groups exposed to controllable and uncontrollable stress. These results are discussed in relation to the hypothesis of regulatory change and behavioral ecology.

The progressive ratio (PR) schedule of reinforcement is widely used to assess reinforcement strength. Rats typically complete higher ratio requirements for more palatable food. This effect is well characterized by the Mathematical Principles of Reinforcement (MPR). In this experiment, either standard food pellets or amaranth grain were delivered according to PR schedules, with requirements increasing in steps of 1 (PR 1) or 3 (PR 3). Rats completed higher ratio requirements and displayed shorter pre-ratio pauses for pellets than for amaranth. Nevertheless, run-rates were similar across reinforcers. In terms of the theoretical parameters of MPR, similar values in a parameter (which indices incentive value) were obtained for amaranth and pellet reinforcers. This finding suggests that, although amaranth engenders less responding than pellets, amaranth grain is a reliable reinforcer for operant procedures. The MPR model accounted for the differences in quality of food.

This study evaluated searching and intake strategies in groups of rats; group size and arrangement of sources with food were varied. Group of rats were exposed to a wood table with food containers. Group Matrix n=4 integrated by four rats was exposed to 4 containers which were arranged in a matrix figure and were near; Group Matrix n=8 was exposed to same arrangement of containers y was integrated by eight rats; Zig-Zag n=4 was exposed to 4 containers which were away and arranged in irregular figure, four rats were in the group; Zig-Zag n=8 was exposed to same arrangement and was composed with eight rats. Data show that arrangement of sources with food had effects in the number of containers exploted by all rats in the group and in the tendency of producing-scrounging strategies; the number of rats by group produced changes on the proportion in that producing and scrounging responses were performed in each group and on pattern of arrive to sources of food. These results were analyzed according to maximization rate model.

The overcrowding and isolation conditions are often experienced by people living in big cities around the world, the literature suggest that under certain conditions it could promote stress-induced anxiety and obesity. The goal of this study was to investigate the effects of post-weaning overcrowding or isolation over the food intake, growth and anxiety in rats. 30 male rats were housed from weaning (21 days old) till 60 days old on three different conditions: 1) optimal recommended for lab rodents with at least 168 cm2 per rat (control group), 2) with no more than 50.4 cm2 per rat (overcrowding group) and 3) individual housed (isolation group). Were recorded daily food intake, weight gain and increased size. On days 58, 59 and 60 was assessed the anxiety level in elevated plus-maze followed by recorded of food intake. Our results shown anxiety in adulthood and food intake was altered in the beginning of dark cycle.

Previous research reported that rats demonstrated large consumptions of solutions made up with glucose and that they did not seem to show preference for solutions made up with sucralose. Those findings suggested that the animals showed large consumptions of the sweet solution, as long as it contains calories. Although, the sequence to which the animals are exposed could contribute on the observation of these responses: history of flavor consumption may alter the consumption of new foods. In the present study, a group of rats was exposed to two sweeteners: glucose and sucralose at different times, with the purpose of determining whether the history of consumption of a sweetener with calories may modify the consumption of another sweetener without calories, and vice versa. The results demonstrated that the subjects showed great consumptions of glucose, regardless of the previous exposure to sucralose, and that the consumption of sucralose was not affected by the previous consumption of the glucose. These findings suggest that the previous consumption of sugars seems not to have an effect on subsequent sweet solution consumption.