Biomedical subjects

K Ackroff

Publications and source records attributed to K Ackroff.

8 recordsLinked to original sources

PubMed1992

Foraging for macronutrients: effects of protein availability and abundance.

A laboratory simulation of foraging required rats to search for opportunities to obtain meals of pure-macronutrient foods (separate sources of carbohydrate, fat, and protein). Reductions in protein availability (increases in the cost of procuring protein meals) and reductions in protein abundance (decreases in the likelihood of encountering protein meal opportunities) were examined in separate phases. Rats foraged selectively, composing high-fat, adequate-protein diets; they tended to alternate between protein and nonprotein meals when protein was accessible. When protein became less available or relatively less abundant, meal patterns changed, and the proportional intake of protein fell. The tactic of shifting relative nutrient intake was used to a greater extent than the tactic of increasing foraging behavior. The foraging constraints revealed a flexible nutritional strategy that balanced responses to internal and external demands.

Animals↗

PubMed1991

Flavor preferences conditioned by sugars: rats learn to prefer glucose over fructose.

The reinforcing effects of glucose and fructose were compared using flavor preference conditioning paradigms. Female rats given access to flavored glucose and flavored fructose solutions developed preferences for the glucose- over the fructose-paired flavor, as well as for unflavored glucose over unflavored fructose. This effect was obtained with 8% and 32% solutions, and with nondeprived and deprived rats. In most cases, the glucose preference was not immediate but appeared only after the rats had one-bottle experience with the two sugars. Female rats also preferred a glucose-paired flavor over a flavor that was paired with a noncaloric saccharin solution. A similar but somewhat weaker preference was displayed for a fructose-paired flavor over a saccharin-paired flavor. Both male and female rats acquired preferences for flavored chow that was paired with the intake of a 32% glucose solution over flavored chow paired with 32% fructose intake. Together, these results indicate that glucose has more potent postingestive reinforcing effects than does fructose. This may explain why rats consume more glucose than fructose in one-bottle acceptance as well as two-bottle preference tests.

Animals↗

PubMed1991

Sucrose to polycose preference shifts in rats: the role of taste, osmolality and the fructose moiety.

Rats given continuous access to 32% sucrose and Polycose solutions initially preferred sucrose but over days reversed their preference and drank more Polycose than sucrose. The role of taste and postingestive factors in this preference shift were investigated in several experiments. A strong and persistent preference for saccharin-sweetened Polycose over unsweetened Polycose was eliminated by intervening experience with a sucrose vs. Polycose choice test, suggesting that the postingestive effects modify the attractiveness of sweet taste. Osmolality differences between sucrose and Polycose were ruled out as an important factor; increasing the osmolality of Polycose by addition of glucose did not prevent the sucrose to Polycose preference shift. Rather, the shift in preference appears to result from some postingestive consequence of the fructose moiety contained in sucrose. This is indicated by the findings that rats did not reliably prefer a fructose-Polycose mixture to a sucrose solution in long-term tests, but developed preferences for maltose over sucrose solutions, and for glucose + Polycose over fructose + Polycose mixtures. Also, a 32% glucose solution was strongly preferred to a 32% fructose solution. Other studies examined the parameters of the sucrose to Polycose preference shift. The Polycose preference was accomplished by increases in both Polycose meal size and frequency. It occurred only with relatively concentrated solutions (16 and 32%) and was incomplete when the carbohydrates were presented in powdered form. Preexposure to Polycose enhanced the preference shift, whereas preexposure to sucrose retarded the development of the preference, suggesting that the shift occurs because Polycose is more rewarding, rather than because sucrose is more aversive. Polycose preference was lost after several days without the solutions but redeveloped in subsequent sucrose vs. Polycose choice tests. Thus the preference shift appears to be due to taste-postingestive consequence conditioning but its expression is dependent upon the nutritional state of the animal.

Animals↗

PubMed1990

Fat appetite in rats: the response of infant and adult rats to nutritive and non-nutritive oil emulsions.

Fat appetite was studied in rats using corn oil and mineral oil emulsions. In Experiment 1 ingestive responses to intraoral infusions were measured in rat pups 6-15 days of age. By 12-15 days of age pups responded more to oil emulsions (10% and 30%) than they did to water or emulsifier solution. The corn and mineral oil emulsions were almost as effective as milk but less effective than sucrose (0.3M) in stimulating ingestion. Experiments 2 and 3 examined the acceptance and preference for oil emulsions in adult rats. The corn oil and mineral oil emulsions were equally acceptable to non-deprived rats, as measured by 3-min and 30-min one-bottle tests. Food deprivation increased the one-bottle intake of both emulsions. In two-bottle tests, rats displayed a slight corn oil preference when non-deprived, but developed a strong preference when food deprived. Taken together, the results suggest that rats have an unlearned attraction to the orosensory qualities of emulsified oils and they learn to prefer corn oil based on its postingestive nutritive effects.

Age Factors↗

PubMed1989

Dietary fat-induced hyperphagia in rats as a function of fat type and physical form.

The influence of dietary fat on food intake and weight gain was assessed by feeding adult female rats diets that differed in the type and form of fat, as well as in the availability of other macro- and micronutrients. Compared to chow-fed controls, the various fat diets increased total food intake by 4% to 27%. Specifically, rats fed chow and a separate source of fat (fat option diet) consumed more fat and total calories, and gained more weight when the fat source was emulsified corn oil rather than pure corn oil or was vegetable shortening rather than corn oil. However, corn oil and shortening had similar effects on caloric intake and weight gain when presented as emulsified gels. Also, pure and emulsified-gel forms of shortening did not differ in their effects on caloric intake and weight gain. Supplementing the vegetable shortening with micronutrients, however, enhanced its hyperphagia-promoting effect. The results of two-choice tests revealed that the rats' preferences for the orosensory properties of the various fat sources did not account for the differential hyperphagias obtained. Rather, it appears that long-term fat selection and caloric intake are influenced primarily by postingestive factors. Fat selection and total intake were determined not only by the fat source itself, but also by the other diet options. That is, rats selected more fat and consumed more calories when chow was the alternative food than when separate sources of carbohydrate and protein were available.

Animals↗

PubMed1988

Sucrose-induced hyperphagia and obesity in rats fed a macronutrient self-selection diet.

Adult female rats were allowed to self-select their diet from separate sources of fat, protein, and carbohydrate (starch). Other rats were fed a composite diet that matched the nutrient composition chosen by the self-selecting rats (50% fat, 28% protein, 22% carbohydrate) or a low-fat, high-carbohydrate chow diet. Half of the rats in each diet condition were given access to a 32% sucrose solution for 30 days. Sucrose availability increased total caloric intake (approximately 20%) and body weight gain in all three groups compared to control groups not fed the sucrose solution. The selection animals compensated for their sucrose intake by reducing their fat intake, and to a lesser degree, their starch intake; protein intake was the least affected by sucrose availability. The selection rats consumed less sucrose than the chow-fed rats and displayed a smaller increase in weight, relative to controls, than the chow-fed rats. These differences were attributed to the high-fat intake of the selection animals since similar results were obtained with the rats fed the composite diet. In particular, both the selection and composite diets produced mild obesity in the absence of sucrose. The results demonstrate that sucrose-induced overeating and overweight is not an artifact of restraining the diet choices of rats to a pure sugar and a nutritionally complete diet.

Animal Nutritional Physiological Phenomena↗

PubMed1986

Macronutrient selection by foraging rats.

Rats were studied in a laboratory simulation of foraging for separate sources of carbohydrate, fat, and protein. Fixed ratios of bar-presses were required to search for a cue signalling the availability of a meal and to procure each meal. In the first phase, the costs of procuring all three foods were raised equally for three rats. Meal frequency declined and meal size increased for all three foods. Protein opportunities were accepted more frequently than those for other foods, and the proportion of calories taken from protein remained low and constant. Two rats were studied in the remaining three phases. When protein meal cost was raised while the costs of energy foods were low, protein intake was gradually reduced and at the highest cost was dropped from the diet. There were individual differences in the preferred source of energy calories; when each animal's preferred energy source was made more costly, these preferences persisted over the range of costs studied in one rat, but shifted abruptly in the other rat. Finally, when search costs were raised, the animals became less selective in accepting meal opportunities and composing their diets. These results suggest that diet selection in the rat is flexible and responsive to changes in the costs of acquiring food. This ability is consistent with the foraging behaviors required by omnivorous generalized feeders.

Animals↗

PubMed1986

Changes in rats' meal patterns as a function of the caloric density of the diet.

Rats in a laboratory foraging paradigm were offered each of four diets which differed in caloric density, and intakes, meal frequencies, meal sizes, and eating rates were monitored. The rats maintained a constant daily caloric intake by eating more frequent, larger meals of the lower density foods. However, caloric meal size was not regulated, and significant correlations between meal size and the length of the post-meal interval were rarely found. The 24-hour pattern of calorie intake was the same regardless of diet. Higher-calorie foods were consumed at a faster rate within meals than were lower-calorie foods. The feeding patterns observed suggest that caloric intake may be regulated over a time frame of several meals rather than on a meal-to-meal basis.

Adaptation, Physiological↗