LiCl-induced flavor avoidance compared between rats and mice using a nondeprivation protocol

The present studies examine some parameters involved in flavor avoidance learning, using LiCl to induce malaise, in a novel nondeprivation protocol that allows direct comparison between rats and mice. The procedure involves daily presentation of a gelatin dessert that contains carbohydrate (Polycose) and a distinctive food flavor. Regular chow is additionally available at all times. Both rats and mice showed robust intakes of these gels with little change of gram intake as concentration of Polycose was varied in the range 2-30%; at the highest concentration, the caloric yield was ∼7% of normal daily intake in both species. Rats that were injected on three occasions with LiCl (0.75 meq/kg) 1 h after consumption of a flavored gel formed a complete and sustained conditioned flavor avoidance (CFA). In a two-flavor discrimination protocol, in which a second flavor was followed by injections of saline, rats showed complete avoidance of the LiCl-paired flavor and partial avoidance of the saline-paired flavor. Mice injected on three occasions with LiCl (6 meq/kg) 1 h after intake of a flavored gel formed a partial CFA; a more complete CFA was formed when there was no delay between removal of the flavor and the injection. Using this no-delay protocol, mice, like rats, showed avoidance of a saline-paired flavor in a two-flavor discrimination protocol, and the CFA was strong when the dose of LiCl was reduced to that used in rats (0.75 meq/kg). In comparable protocols, mice thus are able to form complete CFAs using low doses of LiCl that are comparable to CFAs observed in rats, but the interval between flavor and sickness over which associative learning can occur may be shorter in mice.

Nutritional status and intake regulation in sheep. VII.* Control of voluntary intake of three diets and the responses to intraruminal feeding

In six experiments, sheep were fed ad libitum on either chopped lucerne hay, chopped wheaten straw, or a ground, pelleted lucerne hay/barley diet. On each diet either the dietary material itself, a more highly digestible material, or sawdust was introduced per fistulam into the reticulorumen in amounts equal to c. 25% of the normal daily intake by weight. For each diet, with intraruminal additions on a single occasion only, the most accurate adjustments of oral intake on a weight or a digestible energy basis were observed when the diet itself was added. On the pellet diet, reduction of oral intake was most rapid and of greater magnitude when materials of high digestibility were introduced, though intake was also reduced when sawdust was introduced. On the chopped lucerne hay diet and on the chopped wheaten straw diet, oral intake was depressed more after the introduction of materials of lower digestibility. When pellets were introduced into animals fed on chopped wheaten straw, oral intake was at first reduced but subsequently increased, which indicated an interaction between the basal diet and the supplement. In longer-term experiments, daily introduction per fistularn of the dietary material at c. 25% of the mean daily intake resulted in a rapid decrease in oral intake of each diet. The decreases in intake, expressed as a percentage of the weight of diet added per fistulam (response index), were 95–115% (pellets), 60–80% (lucerne hay), and 76–104% (wheaten straw), and generally became greater with time. With the pellet diet, trends in intake with time showed an increasingly greater adjustment to materials of high digestibility, and an apparent accommodation or compensation for imposition of a load of indigestible material. Such compensation for indigestible material was not apparent on the two all-roughage diets. Introduction of lucerne/barley pellets into the rumen of sheep fed on chopped wheaten straw resulted in no change, or a slight increase, in straw consumption, and an overall increase in intake of digestible dry matter. In two further experiments a bladder, expanded with water to volumes of 1,2, or 3 litres, caused significant decreases in intake of both the pellet diet and the chopped wheaten straw diet, effects being more rapid and more drastic in the case of the wheaten straw diet. Although there was subsequently a partial recovery of oral intake with the pellet diet, no such apparent compensation occurred with the wheaten straw diet. The results indicate that sensitivity to indigestible material can limit the intake of roughage even though the digesta content of the reticulorumen is not at a maximum, and confirm that important relationships exist between the nutritive value of the diet or nutritional status of the animal and the ability to accommodate indigestible material. ____________________ *Part VI, Aust. J. Agric. Res., 21: 735 (1970).

Obesity from eating elicited by daily stimulation of hypothalamus

Rats who were forced to overeat wet mash by electrical stimulation of the lateral hypothalamus 2 hr/day for 31 days became obese by maintaining an intake and rate of weight gain far greater than nonstimulated animals or animals similarly stimulated without food present. The rats stimulated without food present gained less weight over the 31-day period, ate less in the hour after each stimulation, but were not significantly different from the nonstimulated rats in total daily intake. In a second experiment, using a high-fat diet instead of wet mash, rats stimulated to eat varying fractions (0, 33, 66, 100%) of their normal daily intake in a short time each day were found abruptly to reduce their intake the rest of the day so that total daily intake remained normal.

Effect of Acute Simultaneous Food and Water Deprivation upon Bar-Pressing Behavior

Twelve rats were allowed to press two levers, one for food, the other for water, while simultaneously deprived of these substances from 0 to 120 hr. The two levers were equated physically and delivered comparable percentages of the normal daily intake of food or water. Thirst and hunger drives appear to be of equal strength near 72 hr. simultaneous deprivation.