Perinatal choline treatment modifies the effects of a visuo-spatial attractive cue upon spatial memory in naive adult rats

Abstract

The improvement in memory functions by choline supplementation is hypothesized to be due to increased synthesis and release of acetylcholine in the brain. We have found previously that combined pre- and postnatal choline supplementation results in long-lasting facilitation of spatial memory in juvenile rats when training was conducted in presence of a local salient cue. The present work aims to analyze the effects of peri- and postnatal choline supplementation on spatial abilities of naive adult rats. Treated rats were trained in various cued procedures of the Morris navigation task of 5 months of age. The treatment had a specific effect of reducing the escape latency of the rats when the platform was at a fixed location in space and indicated by a suspended cue. This effect was associated with an improved spatial memory when the cue and the platform were removed. In this condition, the control rats showed impaired spatial discrimination following the removal of the target cue, most likely due to an overshadowing of the distant environmental cues. This impairment was not observed in the treated rats. Further training with the suspended cue at unpredictable places in the pool revealed longer escape latencies in the control than in the treated rats suggesting that this procedure induced a selective perturbation of the normal but not of the treated rats. A special probe trial with the cue at an irrelevant location and no escape platform revealed a significant bias of the control rats towards the cue, but in treated rats towards the uncued spatial escape position. This behavioral dissociation suggests that a salient cue associated with the target induces an alternative "non spatial" guidance strategy in normal rats, with the risk of overshadowing attention towards more distant spatial cues. As a consequence, the improved escape in the presence of the cue in the treated rats is associated with a stronger memory of the spatial position following disappearance of the cue. This and previous observations suggest that a specific spatial attentional process relies on the buffering of highly salient visual cues to facilitate integration of their relative position in the environment.