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

Abstract

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

Delayed Satiety-Like Actions and Altered Feeding Microstructure by a Selective Type 2 Corticotropin-Releasing Factor Agonist in Rats: Intra-Hypothalamic Urocortin 3 Administration Reduces Food Intake by Prolonging the Post-Meal Interval

“…Responses were recorded automatically by an IBM PCcompatible microcomputer with 10 ms resolution. Spillage is low in this system (1.270.2% of food responses; n ¼ 105 sessions) (Zorrilla et al, 2005a). Rats were removed from the apparatus daily for 60 min 1 h before the onset of the dark cycle to permit cage maintenance and experimental treatment.…”

“…Therefore, using arbitrary or log-survivorship analysis of inter-feeding intervals to define meals, as has been done previously, can lead to invalid conclusions regarding the microstructure of ingestion. In contrast, microstructure definitions that account for prandial drinking and acknowledge the log-normal distribution of inter-ingestion intervals within and between meals allow the microstructure of prandial food and water intake to be studied (Zorrilla et al, 2005a;Geary, 2005). Meals were defined as consecutive responses for food or water that contained at least five fooddirected responses (0.225 g of food), greater than estimated lower bounds for meal size (Zorrilla et al, 2005a).…”

“…In contrast, microstructure definitions that account for prandial drinking and acknowledge the log-normal distribution of inter-ingestion intervals within and between meals allow the microstructure of prandial food and water intake to be studied (Zorrilla et al, 2005a;Geary, 2005). Meals were defined as consecutive responses for food or water that contained at least five fooddirected responses (0.225 g of food), greater than estimated lower bounds for meal size (Zorrilla et al, 2005a). The meal threshold breakpoint was calculated as the inter-event interval(s) between feeding-and drinking-directed behavior that provided the most stable joint estimates of meal size and meal duration, as described and validated previously (Zorrilla et al, 2005a).…”

“…Meals were defined as consecutive responses for food or water that contained at least five fooddirected responses (0.225 g of food), greater than estimated lower bounds for meal size (Zorrilla et al, 2005a). The meal threshold breakpoint was calculated as the inter-event interval(s) between feeding-and drinking-directed behavior that provided the most stable joint estimates of meal size and meal duration, as described and validated previously (Zorrilla et al, 2005a). Based on this analysis, ingestive responses were considered to continue a meal if they occurred within 5 min of the previous response.…”

“…To evaluate candidate sites of Ucn 3-CRF 2 anorectic signaling, the present studies infused Ucn 3 into the LV (forebrain) and fourth (hindbrain) ventricle and into feeding-regulatory regions in which Ucn 3 mRNA expression or Ucn 3 terminals occur in proximity to CRF 2 expression. The behavioral mechanism of Ucn 3 anorexia was explored through microstructure analyses (Zorrilla et al, 2005a) and conditioned taste aversion (CTA) procedures.…”