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Set-point of body weight was assessed by the behavioral method of the weight threshold to hoard food. Intra-peritoneal injection of nicotine (0.02-0.05 mg/kg) significantly lowered the rats' body weight set-point by 8.5+/-2.7 and 19.2+/-2.6 g (p< or =0.05). These results suggest that the administration of low-dose nicotine lowers the body-weight set-point and may be important in predicting the anticipated gain in weight frequently reported upon withdrawal.

Hoarding behavior of rats can be described by the equation y = ax + b, where y is the amount of food hoarded, x the rat's body weight, a the negative slope of the regression line, and b, the ordinate at zero abscissa. We repeatedly evaluated the parameters of this equation in six obese Zucker rats and six controls, from 8 to 32 weeks of age. The mean slope of the regression lines remained close to -11 in both groups of rats, until 24 weeks of age. From then on, the slopes of the obese rats decreased dramatically to c. -3, and remained as such for the rest of the experiment, while that of controls remained constant. At this age (24 weeks), controls weighed 453 +/- 14 g and obese rats 729 +/- 18 g. We suggest that the decreased slope of hoarding in obese rats was due to an increased cost of the hoarding behavior., (Copyright 1998 Academic Press.)

The mass of food hoarded by rats given access to food only two hours per day is proportional to the rats' body weight deficit. The present work investigated whether this behavior might reflect the amount of body fat rather than body weight. The hoarding behavior of three rats was measured every other day at various body weights. After each hoarding session the animals were anesthetized and their percentage of fat was measured in vivo with a total body electrical conductivity method (TOBEC). The results showed that the amount of food hoarded in the two-hour sessions was inversely proportional to the fat content of the body. This result shows that, in the rat, the fat stored is correlated with the behavioral response leading to the defence of body weight, and therefore satisfies a condition necessary for a lipostat.

The pleasure of eating palatable food was pitted against the displeasure of giving money away in a situation where subjects had to spend money to buy their food. Ten healthy subjects taken individually had lunch in the laboratory on four different days. During the first session, they rated the palatability of small sandwiches, of ten different varieties. In the three following sessions, they were asked to eat the same number of sandwiches as in the first session and they had to buy each sandwich at a price that increased with palatability. The rate of the price increase was varied in the three sessions. As this rate increased, the subjects moved their preference to the less palatable sandwiches. The subjects' actual behavior was predictable from the quantitative relationship of pleasure ratings and price. This result supports the hypothesis according to which behavior tends to maximize multidimensional pleasure experience.