Diet/taste and feeding behavior of genetically obese mice (C57BL/6J-ob/ob)

Trigeminal Pain Responses in Obese ob/ob Mice Are Modality-Specific

How obesity exacerbates migraine and other pain disorders remains unknown. Trigeminal nociceptive processing, crucial in migraine pathophysiology, is abnormal in mice with diet induced obesity. However, it is not known if this is also true in genetic models of obesity. We hypothesized that obese mice, regardless of the model, have trigeminal hyperalgesia. To test this, we first evaluated trigeminal thermal nociception in leptin deficient (ob/ob) and control mice using an operant thermal assay. Unexpectedly, we found significant hypoalgesia in ob/ob mice. Because thermal hypoalgesia also occurs in mice lacking the transient receptor potential vanilloid 1 channel (TRPV1), we tested capsaicin-evoked trigeminal nociception. Ob/ob and control mice had similar capsaicin-evoked nocifensive behaviors, but ob/ob mice were significantly less active after a facial injection of capsaicin than were diet-induced obese mice or lean controls. Conditioned place aversion in response to trigeminal stimulation with capsaicin was similar in both genotypes, indicating normal negative affect and pain avoidance. Supporting this, we found no difference in TRPV1 expression in the trigeminal ganglia of ob/ob and control mice. Finally, we assessed the possible contribution of hyperphagia, a hallmark of leptin deficiency, to the behavior observed in the operant assay. Ob/ob and lean control mice had similar reduction of intake when quinine or capsaicin was added to the sweetened milk, excluding a significant contribution of hyperphagia. In summary, ob/ob mice, unlike mice with diet-induced obesity, have trigeminal thermal hypoalgesia but normal responses to capsaicin, suggesting specificity in the mechanisms by which leptin acts in pain processing.

Hyperresponsiveness to palatable and aversive taste stimuli in genetically obese (bombesin receptor subtype-3-deficient) mice

Taste preference in obese mice was examined using genetically obese (bombesin receptor subtype-3: BRS-3 deficient) animals. Preference for either sodium saccharin (0.2%). sodium chloride (0.9%), citric acid (0.1%), or quinine sulfate (0.002%) solution was examined using a two-bottle test situation, and BRS-3 deficient mice not only showed a stronger preference for saccharin solution, but also a stronger aversive response to quinine solution, relative to wild-type littermates. Furthermore, a conditioned taste-aversion test measured the consumption of sodium saccharin (0.2%) and sodium chloride (0.9%) solutions after intraperitoneal injection of LiCl (0.3 M, 1 mg/kg), and BRS-3-deficient mice exhibited stronger aversion to both solutions than did control animals. In situ hybridization demonstrated that the BRS-3 gene is expressed in the parabrachial nucleus, the medial and central nuclei of the amygdala, and the hypothalamic nuclei such as paraventricular nucleus, all of which are known to be involved in taste perception. These results suggest that expression of the BRS-3 gene in these nuclei is important for the modulation of taste preference, as well as the development of obesity.

Heritable variation in food preferences and their contribution to obesity

What an animal chooses to eat can either induce or retard the development of obesity; this review summarizes what is known about the genetic determinants of nutrient selection and its impact on obesity in humans and rodents. The selection of macronutrients in the diet appears to be, in part, heritable. Genes that mediate the consumption of sweet-tasting carbohydrate sources have been mapped and are being isolated and characterized. Excessive dietary fat intake is strongly tied to obesity, and several studies suggest that a preference for fat and the resulting obesity are partially genetically determined. Identifying genes involved in the excess consumption of dietary fat will be an important key to our understanding of the genetic disposition toward common dietary obesity.

Circadian feeding and drinking patterns of genetically obese mice fed solid chow diet

Feeding and drinking were recorded in male ob/ob mice and lean mice fed pelleted Purina Lab Chow No. 5001 with water to drink. The circadian patterns of eating and drinking of obese mice differed from those of lean mice, in both the proportional temporal distributions of feeding and of drinking behavior across the 24-hour day and in the absolute amounts consumed hourly. The pattern of increased food consumption by the obese mice was different than that underlying increased water consumption. When meal parameters were analyzed in terms of 'complete meals' of both feeding and drinking (the end of a meal defined as at least 12 consecutive minutes with no ingestion), obese and lean mice had the same number of meals and their periodicity was similar, but meal size was much greater in the obese mice. In the dark, both obese and lean mice showed strong postprandial correlations of meal size with time from the start of a meal to start of the next meal.

The meal pattern of genetically obese (ob/ob) mice

The purpose of this investigation was to determine the meal pattern that characterizes the increased food intake of the ob/ob mouse. The major result was that obese mice ate larger and less frequent meals than lean mice during the dark phase of the light-dark cycle. There was a sex difference in that obese females ate the largest meals. To investigate the possibility that the different meal patterns observed in obese and lean mice was an artifact of the temporal criterion used to define a minimal intermeal interval, the meal patterns of obese and lean male mice were analyzed using two temporal criteria, 1 min and 5 min, and a behavioral criterion, the behavioral sequence of satiety. This analysis demonstrated that obese mice ate larger meals than lean mice whenever the criterion for an intermeal interval included the behavioral sequence of satiety. The mechanisms responsible for the increased meal size in obese mice are not known, but we suggest that preabsorptive satiety mechanisms may be less potent in obese mice.

Practical liquid diets for rats: effects on growth

Liquid diets based on the AIN-76 formula are described. The diets employ xanthan gum as a stabilizer. Information is provided on how these diets may be modified to meet the requirements of a particular experiment (e.g., variations in water content, type of protein or carbohydrate or fat, etc.). These diets are superior to widely used diets with regard to nutritional adequacy, cost, ease of preparation, versatility, stability, osmolality, and use of natural ingredients. An experiment is described which compares the effects of feeding rats a solid diet or a liquid diet prepared three different ways. The results confirm that a properly prepared liquid diet can produce overweight and obesity.