Tu2016 Establishment of a Novel Automated Method to Assess the Food Intake Microstructure in Rats

Abstract

Background: Food intake is a parameter frequently assessed in rodent models. The classical approach is to measure food intake manually after defined time intervals. Although this technique is easy to learn and use, it holds several disadvantages: the animals are disturbed by the investigator, a real assessment of dark phase feeding is not possible, the measurement is rather rough as short-lasting effects may be missed and lastly, there is no information on the underlying feeding microstructure. Therefore, several approaches have been undertaken in order to assess this feeding microstructure including the use of liquid, powder or micropelleted food, which, however, does not represent the physiological solid food of rats. Aim: To evaluate an automated method to assess the physiological feeding microstructure in rats. Methods: Male Sprague Dawley rats were used and food intake was monitored manually and in an automated fashion using an automated episodic feeding monitoring system recently established for the use in mice (BioDAQ, Research Diets). In a separate experiment, intracerebroventricularly (ICV) cannulated rats were compared to naive rats (n=8/group). Results: Rats showed a linear daily body weight gain when housed in groups (3.1±1.5g) which did not significantly change directly after separation into single housing cages with feeding from the cage top (3.6±1.3g) or from the hopper of the automated monitoring device (2.7±0.1g, P=0.81). Also, the nighttime food intake, the period of the maximum food intake in rodents, was similar when assessed by the automated system on day 1 and 5 after starting the measurement (17.7±0.8 vs. 19.1±0.7g, P=0.24), indicating a rapid accommodation to this feeding device. In addition, daily food intake did not differ when assessed manually or in an automated fashion (21.9±0.4 vs. 21.1±0.2g, P=0.17), indicating a good concordance between both methods. The automated assessment allowed the measurement of parameters of the food intake microstructure, namely latency to first meal, inter-meal interval, meal size, duration and frequency, eating rate and the satiety ratio. The investigators observed the satiety sequence of rats in the automated feeding cages with a decrease in dark phase feeding behavior and an increase in grooming, exploration and resting indicating a physiological behavior. Lastly, in cages with an enlarged opening of the cage mount, ICV cannulated rats showed a similar dark phase food intake as naive rats (16.6±0.6 vs. 16.4±0.5g, P=0.86), indicating that the system can also be used in head device-bearing rats. Conclusions: The automated feeding monitoring device allows a detailed assessment of the food intake microstructure in undisturbed rats housed in regular cages and fed physiological rat chow. Therefore, this device will be a valuable tool in behavioral studies investigating food intake.