Effects of grafting on abnormal mossy fiber sprouting in the host hippocampus. Figures illustrate neuropeptide Y (NPY) immunostaining in the hippocampus of a naive adult rat (A1–A2), a rat that exhibited SE-induced chronic epilepsy (B1–B2), and a rat that underwent SE and received grafts of striatal precursor cells (C1–C2). A2, B2 and C2 are magnified views of a dentate gyrus region from A1, B1, and C1. In naive rat (A1–A2), NPY immunostaining visualizes mainly the interneurons in the dentate hilus, whereas in the rat that underwent SE-induced chronic epilepsy (B1–B2), NPY expression is found in mossy fibers including those mossy fibers that sprout aberrantly into the dentate supragranular layer (DSGL). Note that the extent of aberrant sprouting in the DSGL is comparable between the rat that underwent SE alone (B1–B2) and the rat that underwent SE and received striatal precursor cell grafts (C1–C2). Scale bar, A1, B1, C1 = 500μm; A2, B2, C2 = 100μm. DH, dentate hilus; GCL, granule cell layer; ML, molecular layer.