Sibutramine is a serotonin-noradrenaline reuptake inhibitor (SNRI) which has been shown to be a safe and effective weight-loss drug. The purpose of this study was to examine whether sibutramine has an effect on macronutrient selection in both female and male rats in addition to total food intake. Wistar rats of both sexes were divided into three groups and each group was offered a different set of three diets, each set included a carbohydrate-rich diet, a protein-rich diet and a fat-rich diet. Sibutramine (10mg/kg) was shown to consistently decrease carbohydrate and fat intake at all data points regardless of gender and diets. The effect of sibutramine on protein intake was diet and gender-specific. All doses of sibutramine decreased total food intake regardless of gender and diet group beginning at 6-h post-administration. In conclusion, sibutramine affected macronutrient selection and emphasis on dietary recommendations should be considered during therapy.

The effect of melatonin, a hormone that triggers biological rhythms, was examined in relation to food intake and macronutrient selection. Wistar rats (n = 48) of both sexes were divided into 3 groups and offered a simultaneous choice of 2 diets: a carbohydrate-rich diet and a protein-rich diet, with a different type of carbohydrate and protein in each of the groups. Increased short- (4h post-injection) and long-term (12h post-injection) nocturnal total food intake was found following intraperitoneal administration of melatonin (10 000 and 15 000 pg/ml blood) at dark onset. Melatonin increased short-term carbohydrate-rich diet intake similarly across sensory contrasting diets (dextrin/cornstarch, cornstarch, and sucrose/cornstarch) and genders. However, melatonin caused an inconsistent increase in protein-rich diet intake across the various diets (casein, soy isolate, and egg protein) and genders. In conclusion, melatonin favors carbohydrate intake at the beginning of the activity period, and may act as a time indicator that provides a night signal.

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Anticipatory satiety is the ability to reduce meal size when the diet at that meal is consistently followed by a short time interval to the next access to food. This prediction of intake is learnt, i.e. based on the association of a food's sensory characteristics with some consequence(s) of ingesting it. / Two pilot studies were conducted using male Sprague-Dawley rats in which (1) the ability of food texture to cue fasting duration was indicated by evidence of anticipatory satiety in the low-fat powder-long/paste-short group and in the high-fat paste-long/powder-short group and (2) the pattern of anticipatory satiety was seen only in the low-fat granules-long/powder-short group. / In the main experiment (n = 9), anticipatory satiety was reached twice in the highfat powder-long/pellet-short group on days 16--23 (p ≤ 0.1) and once in the low-fat pellet-long group/powder-short on days 20--23 (p ≤ 0.1). The acquisition of texture-cued fasting-anticipatory satiety seems to depend upon high-energy density of the diet and the utilisation of textures which make it easier for the rats to eat.

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When given a choice between two foods of equal caloric value but different flavors, rats show a robust preference for that food whose flavor was previously associated with a higher calorie food. This finding suggests that rodents may identify food quality by sensory signals such as taste. The first portion of this thesis explores this flavor-calorie conditioning effect in other rodents, namely hamsters and gerbils. When hamsters were tested in the same paradigm as rats, the conditioning effect was not observed. This discrepancy may have resulted from the hamsters' ability to store food mash in their cheekpouches. Accordingly, hamsters were next presented with liquid diets which could not be cheekpouched. The conditioning effect was observed when different flavors were associated with different quality liquid diets. However, the effect was less robust than that discovered for rats. A second species, gerbils, did show robust conditioning effects. Thus, unlike rats and gerbils who show a robust flavor-calorie conditioning effect, hamsters are less likely to identify food quality by using taste cues. Once conditioned to detect caloric density by using flavor cues, hamsters and gerbils were placed on an 8-arm radial maze that consisted of four arms baited with high-calorie liquid and four arms baited with low-calorie liquid. The purpose of this second, part of the thesis research was to investigate the rodents' preference for food locations that contained food of varying qualities. Both species were expected to visit and drink first from the arm locations containing the higher calorie liquid. Although hamsters did not visit more high-calorie arm locations, they did drink from these arms more often. When visiting arm locations, hamsters appeared to use a circling strategy that began in the same arm each trial and consisted of visits to consecutive arms. Gerbils neither visited nor drank more often from the high-calorie arm locations. Gerbils also did not appear to use a circling strategy. Thus, when foraging on an 8-arm radial maze for food of varying quality, hamsters' use of a circling strategy prohibited them from first visiting high-calorie arms but not from preferentially drinking from these locations. Unlike hamsters, gerbils did not adopt a strategy to collect food rewards and were not selective about the food reward that was consumed. The foraging strategies of hamsters was further explored in the third part of the thesis. Hamsters were allowed to forage on an equally-baited 17-arm radial maze. Each arm location was baited with a sunflower seed. Once again, hamsters visited arm locations by using a circling strategy which consisted of visits to consecutive arms. However, on the larger maze hamsters did not begin each trial in the same arm location. In addition, hamsters that were placed on the same maze with 4 of the 17 baited arms blocked, given 13 arm location choices, removed from the maze while the blocks were also removed, and placed back on the maze to select 4 additional arm locations, did not preferentially select the previously blocked arms. Thus, hamsters whose response algorithm was disrupted did not show a memory-based strategy for collecting seeds from the maze. The major conclusions from this research are that 1.) Hamsters can learn to associate caloric density and flavor cues, but the learned effect is easily extinguished. 2.) This dietary information may be used when deciding what to eat but not where to forage. 3.) Hamsters appear to be harvesters who visit all foraging locations by adopting a response strategy. 4.) Gerbils can also learn to associate caloric density and flavor, and the learned effect is robust. 5.) Gerbils do not appear to use this information when deciding which foods to eat or where to forage. It will be interesting for future studies to see if rats use flavor-calorie information in foraging settings. / Arts, Faculty of / Psychology, Department of / Graduate

Hoarding or hoarding behavior refers to the active storing and accumulation of food or other objects by an animal. Hoarding is often experimentally defined as the act of transporting food or objects, from some area outside the Ss home cage, back to the home cage. A typical hoarding experiment involves manipulation of an independent variable (e. g., amount of food deprivation, previous experience, early experience, strain of rat .• choice of hoarding material}, followed by measurement of the number of food pellets or objects hoarded during daily 30 min. hoarding trials. A hoarding trial involves allowing the subject access to the hoarding material by means of an alleyway attached to its home cage. Ss then have an allotted amount of time (e.g., 30 min., 24 hrs.) in which to transport the hoarding material to their home cages. To insure hoarding will take place, Ss are often food deprived prior to the first of a set of hoarding trials, or prior to each daily hoarding trial. Though laboratory rats will hoard food without being food deprived (Bindra, 1948) deprivation prior to trials facilitates the amount of hoarding (Morgan, Stellar & Johnson, 1943; Guerra, 1970).