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Studies of the effects of nicotine (NIC) on meal patterns in rats often employ chow pellet diets that contain little fat, whereas humans using NIC commonly consume diets relatively rich in fat. The aim of the present study was therefore to compare the impact of NIC administration and NIC cessation on meal pattern in adult male rats offered a standard powdered chow (CHOW: 10.9% fat by calories) diet or a palatable high-fat (HIFAT: 58.3% fat by calories) diet. Computerized meal pattern analyses were conducted for male rats treated for 14 days with injections of either saline or 1.4 mg/kg/day of NIC (as the free base given in 5 equal amounts) during the dark phase and continued for 10 days after NIC cessation. The suppression of daily caloric intake by NIC was larger in HIFAT-NIC rats than in CHOW-NIC rats (p < .01), such that NIC induced a greater suppression of body weight in HIFAT-NIC rats, relative to CHOW-NIC rats (p < 0.02). NIC administration reduced MS in both CHOW and HIFAT rats. CHOW fed rats showed a gradual increase in meal number in response to NIC, whereas HIFAT fed rats showed a significant initial suppression of meal number, which returned to control levels by day 4 of the 14 day NIC treatment period. In addition, NIC increased water intake more in HIFAT fed rats than in CHOW rats. Cessation of NIC resulted in transient increases in daily caloric intake in CHOW and in HIFAT rats. The present study demonstrates that NIC actions on food intake suppression, meal patterns, and weight reduction differ depending on whether the rats are fed low- or high-fat diets.

Continuous administration of nicotine (NIC) reduces food intake (FI) and body weight (BW), whereas rebound eating and BW gain occur after NIC cessation. However, generalizations derived from prior studies on meal patterns in rats using continuous 24-h NIC administration are limited, because human smokers use NIC intermittently during their active period. In the present study, computerized meal pattern analyses (MPA) were conducted for adult male rats treated for 14 days with either saline or 2 or 4 mg/kg/day of NIC spread over five equal amounts during the dark phase. MPA analyses continued for 14 days after cessation of NIC. Only the 4 mg/kg/day NIC dose caused consistent changes in meal patterns and only that dose is reported herein. Dark period FI was reduced, whereas light period FI was unchanged in the NIC-treated group; thus, there was no rebound eating during the 12-h nontreatment phase. MPA analyses revealed the FI reduction on Day 1 of NIC administration was caused by a persistent decrease in dark phase meal size. On Day 5 of NIC, the rats compensated by significantly increasing the number of meals they took, which tended to normalize dark phase FI. Congruently, dark phase intermeal interval was decreased. Importantly, these changes in meal patterns persisted for 2 weeks after termination of NIC. Upon NIC cessation, the NIC group had a transient elevated FI. The NIC-treated group's BW was significantly suppressed by Day 6 of NIC and after stoppage these rats slowly, but incompletely, regained lost BW over the next 14 days. These results document that administration of NIC during the dark phase resulted in a reorganization of the microstructure of FI in male rats and that long-lasting alterations in the microstructure of FI (e.g., meal size and meal number) were noted for up to 2 weeks after cessation of NIC. These results differ from studies in which NIC was given continuously 24-h/day and indicate that dark phase NIC administration in rats may represent an appropriate model to study the impact of NIC on meal patterns.