Information acquired by the hippocampus interferes with acquisition of the amygdala-based conditioned-cue preference in the rat.

White and McDonald (1993, Behav Brain Res 55:269-281) previously reported that animals with amygdala lesions failed to acquire a conditioned-cue preference (CCP) based on spatial cues, but that animals with fornix lesions exhibited larger CCPs of this type than normal animals. The present experiments focused on the hippocampal interference with amygdala-based CCP learning inferred from this finding. In experiment 1 we tested the hypothesis that this interference was due to the acquisition of information about the maze and its environment during a 10 min period of free exploration of the maze before the start of CCP training, hitherto given to all animals in these experiments. Normal animals that were not preexposed to the maze and animals that were preexposed to a similar maze in a different room both exhibited larger CCPs than animals that were preexposed to the same maze in the same room as CCP training and testing. This suggests that normal animals acquire context-specific information during the preexposure period and that this may be the cause of the hippocampus-based interference with the amygdala-mediated CCP. In experiment 2 we attempted to determine if the information thought to be acquired by the hippocampal memory system interferes with acquisition or expression of the CCP. As previously demonstrated, animals that received fornix lesions before preexposure (i.e., before the start of the experiment) exhibited larger than normal CCPs. Animals that received fornix lesions after preexposure but before CCP training and animals that received fornix lesions after CCP training but before testing both exhibited normal CCPs.(ABSTRACT TRUNCATED AT 250 WORDS)