Increased neurogenesis and the ectopic granule cells after intrahippocampal BDNF infusion in adult rats Helen Scharfman a,b,c, * , Jeffrey Goodman a , Adam Macleod a , Sudar Phani a , Cara Antonelli a , Susan Croll d a Center for Neural Recovery and Rehabilitation Research (CNRRR), Helen Hayes Hospital, NY State Department of Health, Rte 9W, West Haverstraw, NY 10993-1195, USA b Department of Pharmacology, Columbia University, New York, NY 10032, USA c Department of Neurology, Columbia University, New York, NY 10032, USA d Psychology Department, City University of New York, Queens College, 65-30 Kissena Boulevard, Flushing, NY 11367, USA Received 6 October 2003; revised 22 July 2004; accepted 9 November 2004 Abstract There is evidence that BDNF influences the birth of granule cells in the dentate gyrus, which is one of the few areas of the brain that demonstrates neurogenesis throughout life. However, studies to date have not examined this issue directly. To do so, we compared the effects of BDNF, phosphate-buffered saline (PBS), or bovine serum albumin (BSA) on neurogenesis after infusion into the hippocampus of the normal adult rat, using osmotic pumps that were implanted unilaterally in the dorsal hilus. BDNF, PBS, and BSA were infused for 2 weeks. The mitotic marker bromodeoxyuridine (BrdU) was administered twice daily during the 2-week infusion period. At least 1 month after infusion ended, brains were processed immunocytochemically using antibodies to BrdU, a neuronal nuclear protein (NeuN), or calbindin D28K (CaBP), which labels mature granule cells. Stereology was used to quantify BrdU- labeled cells in the dorsal hippocampus that were double-labeled with NeuN or CaBP. There was a statistically significant increase in BrdU + / NeuN + double-labeled cells in the granule cell layer after BDNF infusion relative to controls. The values for BrdU + /NeuN + cells were similar to BrdU + /CaBP + cells, indicating that most new neurons were likely to be granule cells. In addition, BrdU + /NeuN + -labeled cells developed in the hilar region after BDNF infusion, which have previously only been identified after severe continuous seizures (status epilepticus) and associated pathological changes. Remarkably, neurogenesis was also increased contralaterally, but BDNF did not appear to spread to the opposite hemisphere. Thus, infusion of BDNF to a local area can have widespread effects on hippocampal neurogenesis. The results demonstrate that BDNF administration to the dentate gyrus leads to increased neurogenesis of granule cells. They also show that ectopic granule cells develop after BDNF infusion, which suggests that ectopic migration is not necessarily confined to pathological conditions. These results are discussed in light of the evidence that BDNF increases neuronal activity in hippocampus. Thus, the mechanisms underlying neurogenesis following BDNF infusion could be due to altered activity as well as direct effects of BDNF itself, and this is relevant to studies of other growth factors because many of them have effects on neuronal excitability that are often not considered. D 2004 Elsevier Inc. All rights reserved. Keywords: Hippocampus; Dentate gyrus; Hilus; Neurotrophin; TrkB; Osmotic pump; Regeneration; Seizure; Plasticity Introduction BDNF is a member of the neurotrophin family, and is highly expressed in hippocampus. In the dentate gyrus, BDNF protein is strongly expressed in granule cells, where it appears to be anterogradely transported to the axons of the granule cells, called the mossy fibers (Conner et al., 1997; Yan et al., 1997). Functionally, BDNF appears to have several 0014-4886/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.expneurol.2004.11.016 * Corresponding author. Center for Neural Recovery and Rehabilita- tion Research (CNRRR), Helen Hayes Hospital, NY State Department of Health, Rte 9W, West Haverstraw, NY 10993-1195, USA.Fax: +1 845 786 4875. E-mail address: scharfmanh@helenhayeshosp.org (H. Scharfman). Experimental Neurology 192 (2005) 348 – 356 www.elsevier.com/locate/yexnr