Prefrontal cortex and hippocampus in posttraumatic functional recovery: Spatial delayed alternation by rats subjected to transection of the fimbria–fornix and/or ablation of the prefrontal cortex

Abstract

Lesions of the prefrontal cortex and the hippocampus often lead to impairment of the same behavioural tasks (e.g., allocentric as well as egocentric spatial orientation and spatial delayed alternation). In case of allocentric and egocentric spatial orientation we have previously found that the two structures mutually contribute to the posttraumatic functional recovery of such tasks. We therefore presently tested the hypothesis that this would even be true in case of spatial delayed alternation. The acquisition of a spatial delayed alternation task in a T-maze was studied in four groups of rats: animals in which the fimbria–fornix had been transected bilaterally, rats who had received bilateral ablations of the anteromedial prefrontal cortex, animals in which both of these structures had been lesioned, and a sham operated control group. All three lesion groups demonstrated an impaired task acquisition. The group given prefrontal cortical lesions in isolation underwent a complete functional recovery. Both of the fimbria–fornix transected groups were significantly impaired even when compared to the group given prefrontal cortical ablations in isolation. The two fimbria–fornix lesioned groups did, however, exhibit levels of functional recovery. The group in which both structures had been lesioned demonstrated a task acquisition, which was significantly inferior to that of the group given fimbria–fornix transections in isolation. After completion of the task acquisition period, all animals were subjected to two behavioural challenges including a session on which the duration of the inter-trial delay was doubled. This expansion of the inter-trial delay rather selectively impaired the task performance of the group given fimbria–fornix transections in isolation. Consequently, both during the acquisition period and in one of the challenges a differentiation of functional recovery was seen between the combined lesioned group and the group given fimbria–fornix lesions only. This indicates that even in case of a spatial delayed alternation task the prefrontal cortex normally contributes significantly to mediation of posttraumatic functional recovery after isolated lesions of the fimbria–fornix. The results are discussed in the context of models of posttraumatic functional recovery.