Spatial, contextual and working memory are not affected by the absence of mossy fiber long-term potentiation and depression

The mossy fibers of the hippocampus display NMDA-receptor independent long-term plasticity. A number of studies addressed the role of mossy fiber long-term plasticity in memory, but have provided contrasting results. Here, we have exploited a genetic model, the rab3A null-mutant, which is characterized by the absence of both mossy fiber long-term potentiation and long-term depression. This mutant was backcrossed to 129S3/SvImJ and C57Bl/6J to obtain standardized genetic backgrounds. Spatial working memory, assessed in the eight-arm radial maze, was unchanged in rab3A null-mutants. Moreover, one-trial cued and contextual fear conditioning was normal. Long-term spatial memory was tested in the Morris water maze. Two different versions of this task were used, an 'easy' version and a 'difficult' one. On both versions, no differences in search time and quadrant preferences were observed. Thus, despite the elimination of mossy fiber long-term plasticity, these tests revealed no impairments in mnemonic capabilities. We conclude that spatial, contextual and working memory do not depend on mossy fiber plasticity. (C) 2002 Published by Elsevier Science B.V.