| The life history of many animals includes periods of food shortage. Two behavioral strategies are involved in small mammals in response to food shortage: an increase in activity behavior, representing increased foraging or migratory behavior, and a decrease in activity level,serving as a mechanism for conserving energy. However, it is uncertain whether animals adopt both strategies in response to food shortage,whether the same species with different levels of basal metabolic rate use the same strategy in the response to food shortages, and whether hormone and neuroendocrine mechamisms are involved in both strategies. The striped hamsters (Cricetulus barabensis) were used as an animal model in the present study. Experiment 1: The animals were divided into two groups, the food deprivation group (FD, animals were deprived of food for 30 hours) and the feeding ad libitum group (ad, animals were fed ad libitum). Each group of animals was randomly divided into two subgroups, the exogenous leptin injection group (murine leptin were injected subcutaneously every 10h) and the phosphate buffered saline(PBS) control group (PBS was injected at the same time as leptin). In total, four groups of hamsters were included in the experiment:FD-Leptin, FD-PBS, ad-Leptin and ad-PBS. Experiment 2: The animals were assigned into high metabolic rate group (H-BMR) and low metabolic rate group (L-BMR), as well as high activity group (H-activity)and low activity group (L-activity), within which all animals fast for 36h.Experiment 3: Animals were randomly divided into H-activity and L-activity groups, and each group was stochastically deprived of food for 24h each week, and refed ad libitum for other 6 days during the 4-week experiment. We examined the changes of behavior, metabolic rate, body mass, food intake and body fat in stripe hamsters during the experiment.The hypothalamic neuropeptide gene expression was also examined. The results showed that: 1) The behavior of food-deprived hamsters significantly changed on basis of photoperiod phases: increasing activity during the dark phase compared to those fed ad libitum, whereas decreasing activity and simultaneously increasing resting behavior during the light phase; 2) Food deprivation resulted in a significant reduction in body weight, which decreased by about 13.1% in the fasting 30h group.Resting metabolic rate, body mass, and masses of fat depots and digestive tracts significantly decreased in food-deprived hamsters compared with ad libitum controls; 3) H-BMR, L-BMR, H-activity and L-activity groups responded to food deprivation by reducing their metabolic rate, especially in L-BMR and L-activity groups. The H-BMR and H-activity groups showed more food intake, but less body mass and body fat than L-BMR and L-activity groups during the ad libitum period, indicating that they spent more energy on maintaining their BMR and activities; 4) Leptin supplement tended to attenuate the increased activity in the dark phase,suggesting that leptin might act as a satiated signal to attenuate activity caused by food deprivation; 5) Gene expression of hypothalamic neuropeptide Y (NPY) and agouti related peptide (AGRP) was significantly up-regulated in food-deprived hamsters, while the gene expression of NPY was significantly attenuated by exogenous leptin.Gene expression of leptin was significantly reduced. These findings suggest that both behavior strategies are important behavioral adjustments in free living animals to cope with food shortage. Different behavioral strategies in day and night are employed by the stripe hamsters,respectively. There may be a close relationship between serum leptin levels, NPY and AGRP genes expression and activity behavior. Serum leptin levels, NPY and AGRP gene expression may be involved in the adjustments of physiology and behavior in animals in response to food shortage. |
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