Concurrent Serial Feature Negative and Simple Discrimination Training and Testing in the Mouse

Abstract

Prior research shows that rats can solve serial feature negative (serFN) and simple discrimination (SD) problems when both are trained concurrently. Furthermore, previous studies indicate that the solution to the serFN (but not the SD) problem depends on the functional integrity of the hippocampus. The present research aimed to determine if mice solve the serFN problem and if this is solved in a manner mediated by inhibitory modulation similar to that seen in rats. Establishing if mice, like rats, can solve the serFN problem using a potentially hippocampal-dependent strategy would provide researchers with greater flexibility when selecting research tools to investigate hippocampal-dependent memory functioning. In Experiment 1, male and female C57BL6J mice were concurrently trained on serFN (Light→Tone−, Tone+) and SD (Clicker+, White Noise−) problems, following which they were injected with cocaine. Animals acquired both discriminations, and subsequent performance was not affected by cocaine administration (unlike impairments reported with rats). Summation and retardation tests argued against a direct inhibitory association for serFN performance and indicated a modulatory form of inhibition. In Experiment 2, male and female C57BL6J mice were similarly trained on serFN and SD problems and then exposed to a Western-style diet for 12 days following training. Animals acquired both discriminations. Western diet consumption selectively impaired serFN performance while leaving SD performance intact (similar to effects reported in rats). Together, these findings demonstrate that mice can solve serFN discrimination. The basis for such learning appears to be modulatory inhibitory control, possibly mediated by the hippocampus.