Distal infrapyramidal granule cell axons possess typical mossy fiber morphology

Using both the Timm's sulfide silver and anterograde horseradish peroxidase (HRP) histochemical techniques, we have demonstrated that granule cell in the dentate gyrus of the rat have topographical projections to both suprapyramidal and distal infrapyramidal terminal fields in the rostral one-third of the hippocampus. An anterograde HRP technique modified for visualization of axonal morphology indicated that intrapyramidal mossy fiber axons possess classic periodic swellings characteristic of suprapyramidal mossy fibers. Most distal infrapyramidal mossy fiber axons appear to be in position to make synaptic contact with deeper-lying neurons in the pyramidal cell layer.