Individual hippocampal mossy fiber distribution in mice correlates with two-way avoidance performance.

Mice systematically bred for randomization of their genotype show large individual differences when performing a two-way avoidance task (shuttle-box learning). Their behavioral scores correlate strongly (r = -0.80, P less than .01) with the number of mossy fibers synapsing on basal dendrites of hippocampal pyramidal neurons, poor avoiders having relatively more such terminals. This confirms previous findings showing that rat and mouse strains known for genetically dependent poor avoidance learning have extended intra- and infrapyramidal mossy fiber projections.