Neurogenesis occurs in the dentate gyrus of the hippocampus throughout the life of a rodent, but the function of these new neurons and the mechanisms that regulate their birth are unknown. Here we show that significantly more new neurons exist in the dentate gyrus of mice exposed to an enriched environment compared with littermates housed in standard cages. We also show, using unbiased stereology, that the enriched mice have a larger hippocampal granule cell layer and 15 per cent more granule cell neurons in the dentate gyrus.

G-CSF is a potent hematopoietic factor that enhances survival and drives differentiation of myeloid lineage cells, resulting in the generation of neutrophilic granulocytes. Here, we show that G-CSF passes the intact blood-brain barrier and reduces infarct volume in 2 different rat models of acute stroke. G-CSF displays strong anti-apoptotic activity in mature neurons and activates multiple cell survival pathways. Both G-CSF and its receptor are widely expressed by neurons in the CNS, and their expression is induced by ischemia, which suggests an autocrine protective signaling mechanism. Surprisingly, the G-CSF receptor was also expressed by adult neural stem cells, and G-CSF induced neuronal differentiation in vitro. G-CSF markedly improved long-term behavioral outcome after cortical ischemia, while stimulating neural progenitor response in vivo, providing a link to functional recovery. Thus, G-CSF is an endogenous ligand in the CNS that has a dual activity beneficial both in counteracting acute neuronal degeneration and contributing to long-term plasticity after cerebral ischemia. We therefore propose G-CSF as a potential new drug for stroke and neurodegenerative diseases.

Progress in the field of neurogenesis is currently limited by the lack of tools enabling fast and quantitative analysis of neurogenesis in the adult brain. Doublecortin (DCX) has recently been used as a marker for neurogenesis. However, it was not clear whether DCX could be used to assess modulations occurring in the rate of neurogenesis in the adult mammalian central nervous system following lesioning or stimulatory factors. Using two paradigms increasing neurogenesis levels (physical activity and epileptic seizures), we demonstrate that quantification of DCX-expressing cells allows for an accurate measurement of modulations in the rate of adult neurogenesis. Importantly, we excluded induction of DCX expression during physiological or reactive gliogenesis and excluded also DCX re-expression during regenerative axonal growth. Our data validate DCX as a reliable and specific marker that reflects levels of adult neurogenesis and its modulation. We demonstrate that DCX is a valuable alternative to techniques currently used to measure the levels of neurogenesis. Importantly, in contrast to conventional techniques, analysis of neurogenesis through the detection of DCX does not require in vivo labelling of proliferating cells, thereby opening new avenues for the study of human neurogenesis under normal and pathological conditions.

The dentate gyrus of the hippocampus is one of the few areas of the adult brain that undergoes neurogenesis. In the present study, cells capable of proliferation and neurogenesis were isolated and cultured from the adult rat hippocampus. In defined medium containing basic fibroblast growth factor (FGF-2), cells can survive, proliferate, and express neuronal and glial markers. Cells have been maintained in culture for 1 year through multiple passages. These cultured adult cells were labeled in vitro with bromodeoxyuridine and adenovirus expressing ,i-galactosidase and were transplanted to the adult rat hippocampus. Surviving cells were evident through 3 months postimplantation with no evidence of tumor formation. Within 2 months postgrafting, labeled cells were found in the dentate gyrus, where they differentiated into neurons only in the intact region of the granule cell layer. Our results indicate that FGF-2 responsive progenitors can be isolated from the adult hippocampus and that these cells retain the capacity to generate mature neurons when grafted into the adult rat brain.Most neurons in the adult central nervous system are terminally differentiated, exist through the life of the organism, and are not replaced when they die. However, evidence exists that small populations of neurons continue to be born in the adult ventricular zone (1-3), olfactory system (4-6), and hippocampus (7-10). In the adult hippocampus, newly born neurons originate from putative stem cells that exist in the subgranular zone of the dentate gyrus. Progeny of these putative stem cells differentiate into neurons in the granule cell layer within a month of the cells' birth, and this late neurogenesis continues throughout the adult life of the rodent (11-15). Paralleling these in vivo findings, in vitro studies have shown that the precursor cells isolated from adult mouse ventricular zone and forebrain have the capacity for in vitro neurogenesis when stimulated with epidermal growth factor (16) or basic fibroblast growth factor (FGF-2) (17), respectively. FGF-2 is a potent mitogen for fetal cells isolated from different areas of the brain (18)(19)(20)(21)(22). This proliferative property of FGF-2 has allowed the isolation and culturing of fetal hippocampal cells for over a year through multiple passages (21), some of which expressed neuronal phenotypes in vitro. These studies have raised the question whether the FGF-2 responsive cells can be isolated and cultured from the adult brain, particularly in the hippocampus, where neurogenesis occurs even in adulthood. In the present study we report that a population of FGF-2 responsive progenitor cells can be isolated and cultured from the adult rat hippocampus. Cells in culture express precursor, glial, and neuronal cell markers. Upon implantation into the adult rat hippocampus, cells migrate and differentiate into mature neurons or glia, depending on the terminal site of migration. Such a progenitor population will be valuable forThe publication costs of this article were defrayed in ...