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 ...

The nervous system of adult mammals, unlike the rest of the organs in the body, has been considered unique in its apparent inability to replace neurons following injury. However, in certain regions of the brain, neurogenesis occurs postnatally and continues through adulthood. The nature, fate, and longevity of cells undergoing proliferation within the CNS are unknown. These cells are increasingly becoming the focus of intense scrutiny; this is a recent development that has led to considerable controversy over the appropriate terminology to describe neural cells as they pass through different stages of proliferation, migration, and differentiation. Continuing studies detailing the properties of mitotic populations in the adult CNS will provide a better understanding of the nature of these cells during their development and should lead to a more consistent nomenclature. Studies of neural precursors isolated from the embryonic brain have indicated that many subgroups of cells undergo mitosis and subsequent differentiation into neurons and glia in vitro. A number of substances, such as growth factors and substrate molecules, are essential for these processes and also for lineage restriction and fate determination of these cells. Recent studies have shown that cells with proliferative capabilities can also be isolated from the adult brain. The nature of these cells is unknown, but there is evidence that both multipotent cells (stem cells) and lineage-restricted cells (neuroblasts or glioblasts) are resident within the mature CNS and that they can be maintained and induced to divide and differentiate in response to many of the same factors that influence their embryonic counterparts. Presently, it is unclear how many potentially quiescent precursor cells exist in the adult brain or what combination of growth factors and substrate molecules is involved in the proliferation and differentiation of these cells. Some of these questions are currently being addressed by using immortalized neural precursors or growth factor-expanded populations of primary precursors to model precursor responsiveness to environmental manipulations. Because in vitro culture conditions are unlikely to provide all of the factors necessary for inducing the proliferation and differentiation of neural precursors, recent studies have explored the properties of well-characterized precursor populations after implantation back into specific regions of the developing or adult CNS. These studies have highlighted the importance of the microenvironment in precursor differentiation and further suggested that precursor plasticity is a characteristic that is probably common to neural precursors throughout the CNS.(ABSTRACT TRUNCATED AT 400 WORDS)

The cholinergic system plays a crucial role in learning and memory. Lesions of cholinergic nuclei, pharmacological manipulations of cholinergic systems, intracerebral transplantation of fetal tissue and anatomical changes in cholinergic pathways during ageing have all been correlated with altered cognitive behaviour. However, it has not been proved that regional acetylcholine is causally required for learning and memory. Here we describe how we achieved a permanent and selective impairment of learning and memory by damaging the nucleus basalis magnocellularis, a nucleus that provides the major cholinergic innervation of the neocortex, in adult rats. To test the hypothesis that acetylcholine is essential for restoration of cognitive function, we implanted genetically modified cells that produce acetylcholine into denervated neocortical target regions. After grafting, rats with increased neocortical acetylcholine levels showed a significant improvement in a spatial navigation task. Acetylcholine is thus not only necessary for learning and memory, as previously argued, but its presence within the neocortex is also sufficient to ameliorate learning deficits and restore memory following damage to the nucleus basalis.

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Alzheimer's disease is a devastating degenerative disorder of the central nervous system that results in gradual deterioration of cognitive function and severe alteration of personality. Degeneration of neurons in the nucleus basalis Meynert, the origin of the major cholinergic projections to the neocortex, occurs early in the course of the disease, and is correlated with the cognitive decline. This link between cholinergic dysfunction in the basal-cortical system and cognitive deficits has focused scientific efforts on developing tools to elucidate the neurobiological role of the cholinergic system in cognition and to develop therapeutic interventions in the disorder. An important step in understanding the mechanisms underlying cognitive dysfunction has been the development of in vivo rodent models that mimic some of the features of Alzheimer's disease. Acute excitotoxic or immunotoxic lesions of the nucleus basalis in rodents have revealed a role of the basal-cortical system in attention, learning and memory. More recent advances in developing mouse gene technology offer newer models to systematically examine the underlying neuropathological cascade leading to dysfunctions in mnemonic processing. Using in vivo rodent models, several cholinergic enhancement strategies have been tested and proven to be effective in alleviating lesion-induced cognitive deficits, including neuropharmacological approaches (acetylcholinesterase inhibitors), neurotrophic factor administration (nerve growth factor), and transplantation of cholinergic-enriched fetal grafts. Successful results have also been obtained using ex vivo gene transfer to deliver nerve growth factor or acetylcholine to compromised regions of the basal-cortical system. Gene therapy may be of particular interest for clinical applications, because this approach provides a method for topographically restricted and selective delivery of therapeutic genes and their products to afflicted areas of the brain. Advanced techniques in molecular biology (e.g., exogenous regulatable gene transfer) and newly developed tools of modern neuroscience (e.g., neural precursor cells) will be important contributions for deciphering the biological bases of neuronal degeneration and for refining therapeutic strategies for Alzheimer's disease.