Formalin pain does not modify food-hoarding behaviour in male rats

Many animal species hoard food by carrying it to their home area. In this experiment we evaluated the interaction between persistent (formalin) pain and food-hoarding behaviour. A food-hoarding apparatus, consisting of a home cage connected with an alley at the end of which were placed food pellets, was used to test (60 min each day) food-restricted rats which had been familiarized with the apparatus for three days. Three groups of animals were used, one of which was tested in the apparatus in the absence of pellets. On the day of testing, the two groups of rats allowed to perform food-hoarding were either sham- or formalin-injected (50 μl, 10%) in the dorsal surface of the hind paw immediately before testing; the third group, not allowed to hoard pellets, was also injected with formalin. In animals treated with formalin, the availability of food resulted in shorter durations of Licking, Self-Grooming and Inactivity. In animals allowed to hoard food, formalin injection affected neither hoarding parameters nor exploratory activities. Our results show that, in food-restricted rats, food-hoarding behaviour is not modified by persistent nociceptive stimuli while Licking, a complex response to formalin pain, is decreased by the drive to relieve hunger.