Evidence for the elaboration of multiple axons by developing dentate granule cells

A sample of 185 Neurobiotin-filled dentate granule cells has been collected from rats aged P14 to P120 in a study of the effects of serotonin (5-hydroxytryptamine, 5-HT) depletion on granule cell development. A small number (5.9%) of these neurons exhibit more than one axon. These neurons have morphologies consistent with that described for dentate granule cells. One axon typically arises from the soma while additional axons take origin from either dendrites or the soma. Both axons may be mossy fibers or one axon may be a mossy fiber and the second assume a morphology and distribution similar to that described for interneurons. These latter neurons therefore exhibit a mixed phenotype by having a granule cell morphology and an interneuronal axon type. These data suggest that some granule cells give rise to multiple mossy fibers or express a mixed axonal phenotype during maturation.