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Biomedical subjects

F H Gage

Publications and source records attributed to F H Gage.

At least 127 records · Page 7Linked to original sources
PubMed1995

Axonal regeneration and limited functional recovery following hippocampal deafferentation.

Although central neurons do not naturally recover following injury, damaged adult septal neurons can regenerate when nerve growth factor (NGF) is provided along with a suitable cellular substrate. This study investigates the outgrowth of axotomized septal neurons grafted with primary fibroblasts genetically modified to produce NGF. Confocal microscope images of double staining for neuritic markers (neurofilament or low-affinity NGF receptor) and the astrocytic marker glial fibrillary acidic protein (GFAP) demonstrated that regenerating neurites crossed dense buildups of astrocytic processes at the edges of NGF-producing grafts and were in apposition with astrocytic processes within NGF-producing grafts. Immunoreactivity for acetylcholinesterase and low-(p75) and high-affinity (TrkA) NGF receptors was dense in NGF-producing grafts but absent in control grafts. NGF-grafted rats exhibited significantly increased hippocampal density of p75-immunoreactive fibers and significantly decreased ectopic hippocampal sympathetic ingrowth as compared to control-grafted rats. Rats with unilateral fimbria-fornix lesions and NGF-producing grafts exhibited ameliorated performance on a simple memory task. These findings demonstrate that implantation of NGF-producing grafts to the lesion cavity allows axotomized septal cholinergic neurons to reinnervate the hippocampus, and that rats receiving these grafts show a partial recovery of function.

Animals↗
PubMed1995

Survival and differentiation of adult neuronal progenitor cells transplanted to the adult brain.

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 beta-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.

Animals↗
PubMed1995

Essential role of neocortical acetylcholine in spatial memory.

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.

Acetylcholine↗
PubMed1995

Bridging grafts and transient nerve growth factor infusions promote long-term central nervous system neuronal rescue and partial functional recovery.

Grafts of favorable axonal growth substrates were combined with transient nerve growth factor (NGF) infusions to promote morphological and functional recovery in the adult rat brain after lesions of the septohippocampal projection. Long-term septal cholinergic neuronal rescue and partial hippocampal reinnervation were achieved, resulting in partial functional recovery on a simple task assessing habituation but not on a more complex task assessing spatial reference memory. Control animals that received transient NGF infusions without axonal-growth-promoting grafts lacked behavioral recovery but also showed long-term septal neuronal rescue. These findings indicate that (i) partial recovery from central nervous system injury can be induced by both preventing host neuronal loss and promoting host axonal regrowth and (ii) long-term neuronal loss can be prevented with transient NGF infusions.

Acetylcholinesterase↗
PubMed1995

Brain-derived neurotrophic factor-transduced fibroblasts: production of BDNF and effects of grafting to the adult rat brain.

Local delivery of brain-derived neurotrophic factor (BDNF) by genetically modified cells provides the unique opportunity to examine the effects of BDNF on adult dopaminergic and cholinergic neurons in vivo. Primary rat fibroblasts were genetically engineered to produce BDNF. Conditioned media from BDNF-transduced fibroblasts supported embryonic chick dorsal root ganglion neurons as well as rat fetal mesencephalic neurons. BDNF-transduced fibroblasts grafted to the rat brain survived and showed continued mRNA production for at least 2 weeks. The effects of BDNF-transduced fibroblast grafts on the dopaminergic and cholinergic systems were then assessed. BDNF-transduced fibroblasts grafted into the normal intact substantia nigra induced sprouting of tyrosine hydroxylase- and neurofilament-immunoreactive fibers into the graft. Fibroblast grafts implanted into the normal intact striatum and midbrain as well as the 6-hydroxydopamine-lesioned brain did not induce sprouting of dopaminergic fibers; neither did they affect drug-induced rotational behavior. BDNF-transduced fibroblasts did, however, significantly increase the homovanillic acid/dopamine ratio when grafted into the normal midbrain. Following transection of the fimbriafornix, BDNF-transduced fibroblasts grafted into the septum were unable to rescue the septal cholinergic population, as did nerve growth factor-producing fibroblast grafts. Genetically modified fibroblast grafts may provide an effective, localized method of BDNF delivery in vivo to test biological effects of this factor on the central nervous system.

Animals↗
PubMed1995

Adrenal chromaffin cells transdifferentiate in response to basic fibroblast growth factor and show directed outgrowth to a nerve growth factor source in vivo.

Chromaffin cells exposed to basic fibroblast growth factor (bFGF) in vitro express characteristics of sympathetic neurons, extend neurites, and become dependent on nerve growth factor (NGF) for survival. We explored whether the growth factor responsiveness of chromaffin cells could be exploited to enhance the transdifferentiation, neurite outgrowth and functional efficacy of chromaffin cells implanted into rats with unilateral 6-hydroxydopamine lesions. Cografts of neonatal chromaffin cells and fibroblasts genetically modified to produce bFGF were placed into the dopamine-depleted striatum of adult rats. Either control-transfected or NGF-producing fibroblasts were then transplanted 1 mm distal to the cograft. Chromaffin cells transdifferentiated under the influence of bFGF, as indicated by the growth of neurites and the expression of neuron-specific proteins. Distal grafts of NGF-producing fibroblasts successfully induced chromaffin neurites to traverse through the host parenchyma to the NGF source. In the absence of NGF fibroblast grafts, neither neurite extension nor good, long-term survival of the chromaffin-derived neurons was observed. Assessments of apomorphine-induced rotational behavior 2- and 4-weeks postgrafting revealed no behavior improvements in any of the groups. These results indicate that localized sources of growth factors are effective in inducing the transdifferentiation of grafted chromaffin cells as well as the extension of chromaffin-derived neurites into the host parenchyma. Such chromaffin cell-derived neurons are, however, functionally ineffective in this rat model of Parkinson's disease. Whether the lack of behavioral improvement reflected the tropic growth of neurites to an inappropriate striatal region or the noradrenergic nature of the chromaffin cell-derived neurons remains to be clarified. Nonetheless, these results caution that promoting transdifferentiation and neurite extension from engrafted chromaffin cells may not be sufficient to achieve desired functional effects of such grafts.

Adrenal Medulla↗
PubMed1995

Regional differences in responsiveness of adult CNS axons to grafts of cells expressing human neurotrophin 3.

Neurotrophin 3 (NT3) belongs to the neurotrophin family, which also includes nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 4/5. NT3 mRNA is widely expressed in the rodent nervous system, but the physiological function of the native protein is still unclear. Genetically modified cell lines that produce physiological amounts of NT3 can provide a useful tool in the elucidation of the NT3 effects in the adult central nervous system (CNS). Genetically modified rat primary skin fibroblasts expressing and secreting human NT3 (hNT3) were prepared and characterized. In vitro, cell lines derived from different retroviral constructs expressed hNT3 mRNA, as determined by PCR and RNA blot analysis. Secretion of biologically active hNT3 was confirmed by specific elicitation of neurite outgrowth from cultured chick primary sympathetic and sensory neurons and from rat fetal locus coeruleus neurons in the presence of hNT3-producing cell conditioned media. In vivo, implanted fibroblasts survived well up to the maximal experimental time points of 6 weeks (brain) and 4 weeks (spinal cord) and continued to express hNT3 mRNA in vivo. As early as 2 weeks postgrafting, specific sprouting of host sensory neurites in response to hNT3-producing grafts was observed in the spinal cord. In contrast, hNT3-producing cerebral grafts did not induce a sprouting response different from that observed with control grafts. These findings establish the existence of a regionally different responsiveness of the CNS axons to local hNT3 overexpression.

Animals↗
PubMed1995

FGF-2-responsive neuronal progenitors reside in proliferative and quiescent regions of the adult rodent brain.

Neurogenesis is restricted to discrete germinal zones within the developing and the adult central nervous systems. With few exceptions, cells that migrate away from these zones and into the parenchyma no longer participate in the generation of new neurons. In this work, we have found that basic fibroblast growth factor is able to stimulate the proliferation of neuronal and glial progenitors isolated from the septum and striatum of adult rats. These progenitors are indistinguishable from those isolated from the adult hippocampus and subventricular zone, two regions that generate neurons well into adult life. Although a variety of cell types are initially isolated from each brain region, the progenitor-like cells from all four regions are capable of considerable proliferation and, with limited serial passage, can be cultured as enriched populations of immature cells that are capable of differentiating into mature glia and neurons following density arrest and growth factor withdrawal. The fact that cells isolated from the septum and striatum proliferate and have the ability to differentiate into neurons once they are removed from their local environment indicates that neurogenesis may be restricted to discrete areas of the developing and the adult brain by regional differences in regulatory signals rather than from an absence of progenitors capable of responding to neurogenic cues.

Animals↗
PubMed1995

Synaptic loss in cognitively impaired aged rats is ameliorated by chronic human nerve growth factor infusion.

In the present study, we assessed the synaptic changes in aged impaired and unimpaired rats, and the effect of exogenous human nerve growth factor administration on behavioral activity and synaptic density. Human nerve growth factor was administered into the rat ventricles with a cannula connected to an osmotic pump in adult, aged impaired and unimpaired rats. Behavioral performance was evaluated in the Morris water maze. Aged impaired rats had an 18 +/- 4% decrease in the number of synaptophysinimmunoreactive presynaptic terminals as compared to aged unimpaired rats. After a continuous four-week human nerve growth factor, the aged impaired rats displayed a significant 16 +/- 3% increase in the number of synaptophysin-immunoreactive presynaptic terminals in the frontal cortex, as compared to aged impaired rats treated with vehicle. This increase correlated with an improvement in water maze performance (r = -0.74, P < 0.001). Measurements of synaptophysin-immunoreactive presynaptic terminals in other cortical and subcortical regions did not show any statistically significant difference or correlations among the various groups. These results support the possibility that nerve growth factor mediates the induction of other trophic factors which, in turn, might potentially produce a sprouting response of non-cholinergic fibers that ameliorate the cognitive deficits in impaired, aged rats.

Aging↗
PubMed1995

Regeneration in the adult mammalian CNS: guided by development.

In the past year, the roles and mechanisms of molecules involved in cell survival (glial-derived neurotrophic growth factor), growth cone guidance (netrins and semaphorins), axonal outgrowth and sorting (neural cadherin, polysialylated neural cell adhesion molecules, and L1), and neuronal connectivity (cell adhesion molecules, dystroglycan, and agrin) have been described during development and, to a limited extent, in the mature CNS. Evidence is now emerging that some developmental events, such as the expression of polysialylated neural cell adhesion molecule and L1, are recapitulated during adult CNS regeneration. These results suggest new avenues to address more accurately the challenges of axonal regrowth in the adult mammalian CNS.

Animals↗
PubMed1995

Novel therapeutic directions for Parkinson's disease.

Problems associated with the long-term use of L-dopa to treat Parkinson's disease have prompted considerable interest in developing alternative therapeutic strategies for this disorder. Newer approaches have included dopamine-cell transplantation, genetic manipulation of striatal cells in situ and the localized administration of trophic factors to injured neurons in the substantia nigra. These studies not only offer promise for treating Parkinson's disease, but also provide insights into properties of the nigrostriatal system that may eventually help to prevent neuronal degeneration.

Adrenal Glands↗
PubMed1995

Basic fibroblast growth factor increases dopaminergic graft survival and function in a rat model of Parkinson's disease.

The clinical use of fetal neural grafts as an intracerebral source of dopamine for patients with Parkinson's disease has met with limited success. Since basic fibroblast growth factor (bFGF) enhances the survival and growth of dopaminergic neurons in vitro, we explored whether cells genetically modified to produce bFGF would improve the functional efficacy of dopaminergic neurons implanted into rats with experimental Parkinson's disease. Results show that bFGF-producing cells grafted together with fetal dopamine neurons have potent growth-promoting effects on the implanted neurons in vivo. Moreover, rats implanted with such co-grafts display the most pronounced behavioural improvements post-grafting. These findings not only provide insight into the function of bFGF in situ, but also suggest an approach for enhancing the survival and function of dopamine neurons grafted into the damaged brain.

Animals↗
PubMed1995

Retrovirus-mediated expression of an artificial beta-endorphin precursor in primary fibroblasts.

Peptides are of potential interest in the field of gene therapy but require modification by genetic engineering to facilitate their secretion. Amino terminal addition of a signal peptide is not always sufficient to achieve this goal, as found in this study for beta-endorphin. To overcome this problem, addition of the pre-pro-sequence of mouse nerve growth factor to beta-endorphin was tested. Retrovirus-mediated expression of a hybrid construct of the pre-pro-sequence of nerve growth factor and human beta-endorphin in primary fibroblasts resulted in the secretion of beta-endorphin immunoreactivity at a rate of 620 pg/h/10(6) cells. Analysis of the secreted beta-endorphin immunoreactivity with reverse-phase HPLC, immunoassays using three different antibodies, and an assay for the specific displacement of [3H][D-Ala2,N-MePhe4,Gly-ol5]enkephalin from mu-opioid receptors suggests that the pre-pro-sequence is cleaved off from the pre-pro-sequence/beta-endorphin construct prior to secretion, resulting in bona fide beta-endorphin. Transplantation of beta-endorphin-secreting cells into brain or spinal cord may provide a gene therapy approach for the treatment of chronic, opioid-sensitive pain states.

3T3 Cells↗
PubMed1995

Expression of biologically active basic fibroblast growth factor by genetically modified rat primary skin fibroblasts.

Basic fibroblast growth factor (FGF-2) is normally expressed as a cell-associated protein, and accordingly it is not clear how it exerts its action on target cells in vivo. It has been proposed that cells release, by death or other mechanisms, small amounts of FGF-2 that then acts in an autocrine manner. To address the question of whether it is necessary that FGF-2 remain cell associated or needs to be secreted from cells to have biological activity, we expressed the 18-kDa form of FGF-2 in primary fibroblasts as a cell-associated (FGF-2-B) or as a secreted (FGF-2-S) protein. FGF-2 protein is detected in cell lysates and membrane fractions of both cell types, whereas it is present in significant amounts only in the conditioned medium of FGF-2-S cells. No FGF-2 is detected in control (untransfected) cells. FGF-2-S cells also grow faster than the control of FGF-2-B cells. Yet, when evaluated for their ability to promote the survival of embryonic hippocampal neurons in vitro, both the cell types are active, establishing the activity of the transgene product. We conclude that FGF-2 is active when engineered to be expressed as a cell-associated form or secreted from cells.

Animals↗
PubMed1995

Isolation, characterization, and use of stem cells from the CNS.

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)

Adult↗
PubMed1995

Somatic gene transfer of NGF to the aged brain: behavioral and morphological amelioration.

Primary fibroblasts modified to secrete nerve growth factor (NGF) were implanted into the nucleus basalis magnocellularis (NBM) of aged memory impaired rats. The NGF-producing fibroblasts survived for 6 weeks following transplantation and continued expressing NGF mRNA through the duration of the experiment. A significant amelioration of the memory impairment and a significant increase in size and number of low-affinity NGF receptor (p75)-positive neurons in the basal forebrain were observed. Implantation of NGF-producing cells into normal young adult rats resulted in a transient but significant memory impairment and hypertrophy of low-affinity NGF receptor-positive neurons. These results show that naturally occurring age-related memory loss can be reversed by grafting cells engineered to secrete NGF directly to the NBM, and that either cholinergic hyper- or hypofunction may lead to cognitive impairments.

Aging↗