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Eating is a central feature of the lives of opportunistic omnivores such as humans and Norway rats. Yet in most laboratory research with Rattus norvegicus, the food landscape is monotonous, and the studies utilizing a variety of foods shed little light on intake of individual foods or choice behavior. The present study provides the most comprehensive description to date of female and male laboratory rats’ intake of foods that they and humans encounter outside of the laboratory. In eleven experiments, test foods included varieties of peanut butter, cheese, cookies, meat, chocolate, fruits, and vegetables. Rats were given commercial products or custom versions that controlled for proportion of calories from fat and caloric density, one or two foods at a time. A final experiment examined pure macronutrient self-selection. Intraspecies diversity was modeled with rat lines selectively bred on a taste phenotype. All groups voluntarily ate every food, with intake (in grams) highest for vegetables and lowest for pure macronutrients. When Low- (LoS) and High-Saccharin-Consuming (HiS) rats differed, LoS rats ate more meat and fat and were choosier whereas HiS rats ate high-carbohydrate foods more avidly; exceptions and sex-dependent differences occurred. Using these results to enrich the food landscape for laboratory rats can enhance the comparative study of food intake and its relation to other behavioral systems.

When, where, and how much animals eat are influenced by food scarcity and risk of predation. The present study concerned the mediation of risk-related feeding patterns by emotion. Occidental Lowsaccharin- consuming (LoS) and High-saccharin-consuming (HiS) rats, which differ in both ingestion and emotionality, were studied in three steady-state paradigms: an “open economy” procedure (discrete session cyclic-ratio operant schedule) and two “closed economy” procedures (meal patterning, free feeding with running wheel access). Cyclic-ratio performance showed better defense of stable food intake against variable cost among LoS rats. In closed economies, LoS rats consumed a larger number of smaller meals and showed a more pronounced circadian rhythm in meal initiation and running than HiS rats. Taste finickiness appears to serve as a marker for heightened cross-modal risk reactivity, the expressions of which include tighter behavioral regulation of eating in conditions of scarcity and exaggerated nocturnality.

In many mammals, including humans and rats, acute starvation increases locomotor activity. This seemingly paradoxical and potentially lethal behavior pattern may reflect an evolved, multisystem response to sudden threats to metabolic homeostasis. The present study provides a novel test of this idea. Occidental High- (HiS) and Low- (LoS) Saccharin-Consuming rats differ on the taste phenotype and also on some affective measures, on which LoS rats score higher. Wheel running was measured in HiS and LoS rats with food available freely versus for 1 hr daily. As predicted, restricted feeding stimulated significantly more running among LoS rats. Two independent tests of emotionality (acoustic startle, stress-induced analgesia) also distinguished the lines. The confluence of taste, emotion, and reactivity to starvation conditions in species as distantly related as rats and humans points to integrated biobehavioral systems that warrant further exploration.

Exposure to inescapable shock typically reduces eating and body weight in rats. The present study examined the modulation of stress effects by prestress diet and poststress sugar availability. Maintenance on a high-fat, high-energy food attenuated stress-induced weight loss and anorexia and increased high-energy food selection when a low-energy wet mash was the only alternative. Access to sugar after stress also reduced short-term weight loss; among rats maintained on high-energy food, body weight was spared absolutely. The dependence of stress effects on pre- and poststress diet alternatives may speak to individual differences in the stress-eating relationship in humans. More generally, these results support a conceptualization of stress in terms of metabolic challenge and the integrated reorganization of energy regulatory processes.

The regulatory shift hypothesis was supported by two experiments showing the effect of stress on food-rewarded operant behavior of rats. According to the regulatory shift hypothesis, the decreases in food consumption and body weight caused by stress are not signs of failed regulatory processes, but indicate adoption of a conservative strategy of ingestion as an orderly response to dangerous situations. The effects of stress depend on the severity of the stressor and the reinforcement schedule which sets the 'cost' of food.

The present study determined whether individual differences in neophobia during an open-field pretest predict vulnerability to inescapable electric shock, as measured by 2 tests of learned helplessness in rats. Shuttle-escape latencies and saccharin finickiness increased across groups that had received increasing numbers of inescapable shocks 24 hr earlier. Dispersion in the test measure as well as the percentage of variance explained by pretest neophobia were greater when no or few shocks were delivered in the interpolated stress phase. Pretest neophobia was positively related to stress vulnerability in both tests under these conditions. Further increments in stressor severity overwhelmed even the most stress-resistant rats, thereby decreasing dispersion in the test measure and eliminating the predictive value of pretest neophobia. This pattern of outcomes was more robust for the shuttle-escape measure of helplessness.

Six experiments examined the effects of signaling the termination of inescapable shock (cessation conditioning) or shock-free periods (backward conditioning) on later escape deficits in the learned helplessness paradigm, using rats (Sprague-Dawley and Bantin-Kingman). A cessation signal prevented later performance deficits when highly variable inescapable shock durations were used during pretreatment. The inclusion of short minimum intertrial intervals during pretreatment did not alter the benefits of cessation conditioning but eliminated the protection afforded by a safety signal. The beneficial effects of both cessation and backward signals were eliminated when a signle stimulus signaled shock termination and a shock-free period. Finally, a combination of cessation and backward signals was found to be most effective in immunizing against the effects of subsequent unsignaled, inescapable shock on later escape performace. These data suggest that cessation conditioning may be crucial to the prophylactic action of an escape response.

Taste signals food quality and reflects energy status and associated processes. Occidental high- and low-saccharin consuming rats (HiS, LoS) have been selectively bred for nearly 60 generations on intake of 0.1% saccharin in a 23-h two-bottle test, as a tool for studying individual differences in taste and its correlates in the domains of feeding, defensive, and social behavior. The saccharin phenotype itself has not been well characterized until now. The present series of parametric studies examined suprathreshold saccharin concentration-intake functions (Experiment 1), saccharin preference threshold (Experiments 2A and 2B), and intra- and inter-sweetener carryforward effects (Experiments 2B, 3A–3D). Results indicate high stability in line differences in behavior toward saccharin and also line-specific mutability of intake of saccharin and certain other sweeteners. Methodological and conceptual implications are discussed. [ABSTRACT FROM AUTHOR]

This article examines whether women who are highly arousable, currently dieting, and are sensitive to the bitterness of saccharin exercise excessively. The authors, assessing responses to a questionnaire, conclude sensitivity to the bitterness of saccharin predicted hyperactivity in highly aroused female dieters which reveals another factor in anorexia nervosa.