Spatial cues are relevant for learned preference/aversion shifts due to amino-acid deficiencies

Rats are able to choose appropriately between two versions of a novel diet, when one is amino-acid devoid and the other corrected. Recognition of the deficiency has been reported to occur within hours and to initiate a strong conditioned aversion. For that purpose the rat can use either oro-sensory cues or another alternative as the conditioned stimulus (CS) with which to associate the unconditioned stimuli (US) of either the adequate diet or the devoid diet. The present investigation was designed to determine whether rats have the ability to use place as a cue in amino-acid preference/aversion. In order to avoid interfering with any other than spatial sensory discrimination between the devoid diet and its corrected version, rats were offered two food cups containing an identical threonine-devoid diet. This was supplemented with an intra-gastric delivery of either threonine or its vehicle, that varied according to the position of the feeder from which the rats had chosen to eat. After three choice sessions, rats chose the food container on the side corresponding to the threonine load. Our results showed that rats use place as a cue for an amino-acid replete nutritional state by learning a conditioned place preference/aversion and that they achieve this type of learning in spite of the long delay elapsing between CS and US.