The effect of early feeding experience on signal-directed response topography in the rat

Ten Hooded Lister rats were divided from weaning into two groups of five. One group was fed exclusively on a liquid diet in the home cage (Complan-fed subjects), the other group was given normal laboratory chow (Chow-fed subjects). At approximately 60 days of age both groups were reduced to 80% of their ad lib body-weight and given pairings of a retractable lever (conditioned stimulus, CS) and response-independent food (unconditioned stimulus, UCS). In the first experimental condition a liquid UCS was used (condensed milk solution) and in later conditions this was substituted with a solid UCS (45 mg food pellet). Analysis of CS-directed behavior in the two groups suggested that (1) only very early in autoshaping training did feeding experience in the home cage influence the topography of signal-directed behavior, and subsequently (2) both Complan-fed and chow-fed subjects bit rather than licked the CS paired with a solid UCS and licked rather than bit the CS when it was paired with a liquid UCS. These results suggest that, in the long-term, the topography of signal-centered behavior in rats is more likely to be influenced by the nature of the reinforcer signalled by the CS than by the subject's feeding experiences during early development.