BDNF expressed in granule cells rescued the aberrant mossy fiber extension induced by a submaximal dose of K252a (100 nM). (A-C) Compared with control slices (A), K252a-treated slices infected with mock viruses showed an abnormal distribution of mossy fibers (B). Meanwhile, the BDNF-expressing mossy fibers extended into the SL (C) in a manner similar to that observed in the control slices. The dotted line indicates the incision line made 4 days after transfection to adjust the axonal extension to the expression of proteins. (D and E) Mossy fiber distribution analyzed by a ratio distribution of the co-expressed Venus in the CA3c (D) and CA3a (E) areas. *P < 0.05 and **P < 0.01; Tukey's test after analysis of variance (n = 7–9 slices obtained from 4 independent experiments). SR: stratum radiatum, SP: stratum pyramidale, and SO: stratum oriens.