Measuring meals: structure of prandial food and water intake of rats

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 288; no. 6; pp. R1450 - R1467
• Main Authors: Zorrilla, Eric P, Inoue, Koki, Fekete, Eva M, Tabarin, Antoine, Valdez, Glenn R, Koob, George F
• Format: Journal Article
• Language: English
• Published: United States 01.06.2005
• Subjects: Algorithms; Animals; Circadian Rhythm - physiology; Drinking - physiology; Eating - physiology; Factor Analysis, Statistical; Food Deprivation - physiology; Individuality; Male; Rats; Rats, Wistar; Satiety Response - physiology; Time Factors; Videotape Recording
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00175.2004

1 Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California; 2 Department of Neuropsychiatry, Osaka City University Medical School, Osaka, Japan; 3 Institute of Physiology, Pecs University Medical School, Pecs, Hungary; and 4 Laboratoire EA 3666 Homéostasie-Allostasie-Pathologie, Université de Bordeaux 2, Bordeaux, France Submitted 17 March 2004 ; accepted in final form 3 January 2005 Attempts to understand ingestion have sought to understand the control of meals. The present study evaluated a meal definition that included prandial drinking (drinking-explicit meals). The spontaneous nocturnal intake of male Wistar rats was studied. The meal breakpoint was defined as the interval between feeding or drinking events providing the most stable estimate of meal structure. Alternative breakpoints derived from prevailing methodology, log-survivorship, or frequency histogram analysis of interfeeding intervals without respect to drinking were compared (drinking-naive meals). Threshold interfeeding intervals that accounted for drinking indirectly were evaluated as surrogate breakpoints (drinking-implicit meals). Definitions were compared by determining which criterion better conformed to predictions of satiety. Microstructural differences resulting from the definitions were also studied. Under the drinking-explicit definition, rats averaged nine or ten 13-min meals/night, during which they consumed food and water equally in duration (5–6 min) and quantity (2.3 g). Individual differences were observed in microstructure measures. Meals defined by drinking-informed, but not drinking-naive, methods were followed by the behavioral satiety sequence and by an initially low likelihood of resuming feeding that monotonically increased with time. The drinking-explicit definition uniquely revealed preprandial and postprandial correlations of similar magnitude. Under drinking-informed definitions, food restriction increased meal size, whereas drinking-naive definitions increased meal frequency. Drinking-implicit definitions provided workable approximations of meal frequency and size but inferior estimates of feeding duration, eating rate, and the preprandial correlation. Thus log-survivorship analysis is not appropriate for identifying meal breakpoints, and the consideration of drinking in meal definitions can provide a better estimate of meal structure. feeding or drinking; food-associated drinking; meal size or duration; eating rate; intermeal interval; behavioral satiety sequence; bout microstructure analysis; meal pattern analysis; satiation Address for reprint requests and other correspondence: E. P. Zorrilla, Dept. of Neuropharmacology, CVN-7, The Scripps Research Institute, 10550 N. Torrey Pines Rd., La Jolla, CA 92037 (E-mail: ezorrilla{at}scripps.edu )