Kinematic analysis of an appetitive food-handling behavior: the functional morphology of Syrian hamster cheek pouches.

Prodigious food hoarding in Syrian hamsters Mesocricetus auratus Waterhouse is strongly linked to appetite and is made possible by large internal cheek pouches. We provide a functional analysis of the cheek pouch and its associated retractor muscle. Frame-by-frame analysis of videotaped pouch-filling behavior revealed multiple jaw cycles for each food item pouched and the use of more jaw cycles to pouch large food items ( approximately 2.5 g chow pellets) than small (corn kernels or sunflower seed with husks). These results stand in contrast to previously reported pouching kinematics in the externally pouched Dipodomys deserti, which uses only one jaw cycle per pouching event. Comparison of pouching and mastication in the same individuals also suggests that in Syrian hamsters, feeding jaw cycles are modulated to accommodate pouch filling primarily by the addition of a pause between fast open and fast close phases, which we call ;gape phase'. Contrary to previous assertions, the retractor muscle does not merely provide structural support for the full pouch during locomotion. Video analysis of ten hamsters with unilaterally denervated retractor muscles and electrophysiological study of an anaesthetized subject confirmed that retractor muscle activity during pouch filling increases pouching efficiency for food items subsequent to the first.

Food hoarding is increased by food deprivation and decreased by leptin treatment in Syrian hamsters.

Compensatory increases in food intake are commonly observed after a period of food deprivation in many species, including laboratory rats and mice. Thus it is interesting that Syrian hamsters fail to increase food intake after a period of food deprivation, despite a fall in plasma leptin concentrations similar to those seen in food-deprived rats and mice. In previous laboratory studies, food-deprived Syrian hamsters increased the amount of food hoarded. We hypothesized that leptin treatment during food deprivation would attenuate food-deprivation-induced increases in hoarding. Baseline levels of hoarding were bimodally distributed, with no hamsters showing intermediate levels of hoarding. Both high (HH) and low hoarding (LH) hamsters were included in each experimental group. Fifty-six male hamsters were either food deprived or given ad libitum access to food for 48 h. One-half of each group received intraperitoneal injections of leptin (4 mg/kg) or vehicle every 12 h during the food-deprivation period. Within the HH group, the hoarding score increased significantly in food-deprived but not fed hamsters (P < 0.05). Leptin treatment significantly decreased hoarding in the food-deprived HH hamsters (P < 0.05). The LH hamsters did not increase hoarding regardless of whether they were food deprived or had ad libitum access to food. These results are consistent with the idea that HH hamsters respond to energetic challenges at least in part by changing their hoarding behavior and that leptin might be one factor that mediates this response.