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A M Fagan

Publications and source records attributed to A M Fagan.

34 records · Page 2Linked to original sources
PubMed1995

Non-TrkA-expressing small DRG neurons are lost in TrkA deficient mice.

Experiments over the past decade in which NGF/TrkA signaling has been abolished by antibodies or targeted gene mutations have shown that 70-85% of dorsal root ganglion (DRG) neurons require NGF for survival during development. There is consensus that many of the NGF-dependent neurons are small-diameter, peptidergic neurons subserving nociception. These neurons express the signaling receptor for NGF, TrkA. There is a major discrepancy, however, between the percentage of DRG neurons which require NGF for survival (70-85%) and percentage of DRG neurons expressing TrkA receptors (40-50%). The identity of these non-TrkA expressing, NGF-dependent neurons has not been established. A candidate group is a population of small DRG neurons with unmyelinated axons which bind BSI isolectins from the plant, Bandeiraea simplicifolia. We show here that most of these BSI-binding DRG neurons do not express TrkA in adult mice. However, in mutant mice in which NGF/TrkA signaling has been abolished by inactivation of the trkA gene, BSI-staining in the DRG and dorsal horn is completely eliminated. BSI-binding DRG cells are thus the first identified neuronal population in which cells do not express TrkA in maturity, but require NGF/TrkA signaling for survival during embryonic development. These neurons must either depend on NGF via a novel, indirect mechanism or alternatively, downregulate TrkA expression during development.

Animals↗
PubMed1994

Effects of brain-derived neurotrophic factor and nerve growth factor on remaining neurons in the lesioned nucleus basalis magnocellularis.

Rats received a unilateral lesion of the nucleus basalis magnocellularis (NBM) by infusion of ibotenic acid. Starting 2 weeks after the lesion, the animals were treated with nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) by intraparenchymal infusion of 3 micrograms per day for 4 weeks. Lesioned control animals received a similar amount of cytochrome c. The activity of choline acetyltransferase (ChAT) in the frontal neocortex was significantly reduced by the lesion (-39%). However, the intraparenchymal treatment with NGF or BDNF did not affect cortical ChAT activity. The number of p75 NGF receptor-immunoreactive neurons in the NBM was significantly decreased (-49%) by the lesion and was not affected by NGF or BDNF. The size of the remaining neurons was significantly increased by NGF (+32%), but not by BDNF (+12%). Similarly, in situ hybridization showed enhanced expression of the p75 NGF receptor following treatment with NGF, but not with BDNF. These results suggest that although BDNF occurs in the target area of cholinergic NBM neurons, its effects on these neurons are less pronounced than those of NGF.

Animals↗
PubMed1994

Mechanisms of sprouting in the adult central nervous system: cellular responses in areas of terminal degeneration and reinnervation in the rat hippocampus.

Neurons of the adult mammalian central nervous system are limited in their ability to regenerate in response to injury. In certain circumstances, however, such neurons can exhibit morphological plasticity (e.g. sprouting). Unilateral transection of the perforant path in the adult rat induces terminal degeneration of entorhinal axons within the molecular layer of the ipsilateral hippocampal dentate gyrus. Cholinergic (and other) afferents subsequently sprout within the denervated zone. We show that despite the breach in the blood-brain barrier at the site of the aspirative lesion, the barrier remains intact in the areas of terminal degeneration (and reinnervation), and peripheral monocytic macrophages do not infiltrate this area to participate in the degenerative and/or regenerative events. Perforant path transection does not induce expression of major histocompatibility antigens on reactive cells within the denervated zone, nor are T lymphocytes recruited to this area. T lymphocyte-deficient Nude rats exhibit normal cholinergic sprouting. Perforant path transection does induce rapid and robust proliferation of microglia, and astrocytes to a lesser extent, in areas undergoing terminal degeneration. Histological evaluation after antimitotic administration shows that this glial proliferation is not required for the subsequent neuronal sprouting events. These results show that the reparative process in this model system involves interactions between cells endogenous to the brain in a non-immune context. Knowledge of these cellular responses provides a framework from which to further investigate putative molecular signals involved in initiating the neuronal sprouting events. Discovering the cellular and molecular interactions taking place under sprouting conditions is likely to be critical for understanding the mechanisms of reactive neuronal growth and, furthermore, may provide insights as to why regeneration is so limited in the central nervous system.

Animals↗
PubMed1991

Intracerebral grafting of cultured autologous skin fibroblasts into the rat striatum: an assessment of graft size and ultrastructure.

To identify a suitable donor cell population for gene therapy applications to the central nervous system, primary fibroblasts isolated from skin biopsies and maintained in culture are employed as autologous cells for intracerebral grafting within the adult rat striatum. Results from the present investigation reveal that cultured primary skin fibroblasts cease to proliferate once they reach confluence; these cells are thus contact inhibited in vitro. Following implantation within the striatum, the volume of the primary fibroblast grafts, stained immunohistochemically for fibronectin, does not differ significantly at 3 and 8 weeks. The graft size is dependent on the density of the cell suspension, but not dependent on either the number of passages the cells are taken through in culture prior to grafting or on the postoperative survival period. Ultrastructural evidence reveals that at 8 weeks the grafts are composed primarily of collagen and fibroblasts with rough endoplasmic reticulum and vesicles. Reactive astrocytic processes and phagocytic cells are also present in the grafts. The grafts are extensively vascularized with capillaries composed of nonfenestrated endothelium; intercellular junctions are evident at sites of apposition between endothelial cells. It is concluded that primary skin fibroblasts are able to survive for at least 8 weeks following intracerebral implantation and continue to synthesize collagen and fibronectin in vivo. Also, the grafts maintain a constant volume between 3 and 8 weeks, thereby indicating that primary skin fibroblasts do not produce tumors. Finally, dynamic host-to-graft interactions--including phagocytic migration, astrocytic hypertrophy and infiltration within the grafts, and angiogenesis--are features that constitute the structural integration of primary skin fibroblasts grafted within the adult rat central nervous system.

Animals↗
PubMed1991

Reactive synaptogenesis assessed by synaptophysin immunoreactivity is associated with GAP-43 in the dentate gyrus of the adult rat.

Reactive synaptogenesis and terminal proliferation are known to occur in the dentate gyrus of the rat hippocampus following removal of specific afferents. In the present study we have examined the relation of synaptophysin immunoreactivity to the immunohistochemical staining pattern of GAP-43, a putative marker of neuritic growth. Within the molecular layer of the normal dentate gyrus, synaptophysin immunolabeling shows a trilaminar pattern, with the inner and outer layers having the greatest density of staining. Within the first week following denervation, there was a significant decrease in the staining density in the outer two-thirds of the molecular layer, followed by a moderate recovery at 14 days and 80% recovery by 30 days. This pattern is consistent with the time course of denervation and reinnervation in this system as determined previously by electron microscopy. By comparison, the staining pattern for GAP-43 in the intact dentate gyrus showed the middle and outer thirds of the molecular layer to be less densely stained than the inner third. Within a week following deafferentation, the outer two-thirds of the molecular layer displayed decreased levels of GAP-43 immunoreactivity, followed by recovery to normal levels by 30 days. By 84 days postlesion, patterns of both synaptophysin and GAP-43 immunostaining reflected an increased width of the inner molecular layer. Laser confocal imaging of double-immunolabeled sections at 14 days postlesion showed a 370% increase in the number of GAP-43-positive terminals in the molecular layer as compared to unoperated controls. Many of these GAP 43-positive terminals were synaptophysin negative. We conclude that GAP-43 may play a role in the synaptic remodeling that occurs in the denervated rat hippocampus and that quantitative morphometry of synaptophysin immunolabeling accurately reflects the fate of presynaptic terminals in this model of degeneration and reinnervation.

Animals↗
PubMed1991

Ventriculo-pulmonary fistula. Case report, literature review and possible surgical approach to the infected LV suture line.

We describe a patient who developed a ventriculo-pulmonary fistula 2 years after resection of a left ventricular aneurysm, and mention the management of two further patients, one with a sinus, the other with a pseudo-aneurysm, both after left ventricular aneurysmectomy, to illustrate a possible surgical approach to a patient with a ventriculo-pulmonary fistula.

Female↗
PubMed1990

Cholinergic sprouting in the hippocampus: a proposed role for IL-1.

Damage to the entorhinal afferents (i.e., perforant path) to the hippocampal dentate gyrus leads to sprouting of the remaining intact septal cholinergic afferents within the denervated outer molecular layer. To investigate the cellular and molecular events which may contribute to this sprouting response, we describe the temporal sequence of cellular changes in the denervated zone prior to the observed neural reorganization. Rats were given perforant path (PP) transections and sacrificed at various time points following the lesion, on Days (D) 1, 2, 3, 4, 5, 6, and 30. Coronal sections at the level of the dorsal hippocampus were immunostained to localize microglia (OX-42), interleukin-1 (IL-1), and astroctytes (GFAP). We observed a rapid increase in the number of immunoreactive microglia in the denervated molecular layer within the first day following PP transection. Parallel sections show a concomitant increase in the number of IL-1-positive cells. Maximal reactive changes (i.e., hypertrophy and increase in number) in GFAP-positive astrocytes are not observed until D5. This time course of events suggests a role of microglia in astrocyte activation in vivo via production of IL-1 and offers support for a proposed hypothesis postulating a cascade of glial events which may lead to cholinergic sprouting following PP transection.

Animals↗
PubMed1989

Grafting genetically modified cells into the rat brain: characteristics of E. coli beta-galactosidase as a reporter gene.

The utility of grafting genetically modified cells to the mammalian brain was examined using the E. coli beta-galactosidase gene (lacZ) as a reporter gene in retroviral infection. Following implantation of the infected cells to the brain, lacZ continued to be expressed in vivo and could be detected easily with enzyme histochemistry. However, beta-galactosidase-positive cells were also observed in control grafts which had not been infected with the virus. This false-positive staining was found to be endogenous lysosomal activity associated with macrophage infiltration presumably induced by the damage associated with grafting. The E. coli gene product was distinguished from cellular lysosomal beta-galactosidase by using immunohistochemical staining with an antibody specific for E. coli beta-galactosidase. With this antibody, retrovirus-infected cells could be distinguished in the brain, and no false positives were observed in non-infected cells. We conclude that E. coli beta-galactosidase is a useful reporter gene for determining the fate of implanted cells to the brain if appropriate caution is taken to distinguish it from cellular beta-galactosidase by immunocytochemical procedures.

Animals↗
PubMed1986

Learning sets, discrimination reversal, and hippocampal function.

Impairments of discrimination reversal are commonly found following lesions of the hippocampal system. In a recent experiment, however, acquisition of a reversed discrimination was actually facilitated, rather than impaired, by partial lesions of the fimbria-fornix (FFX), an extrinsic fiber connection to the hippocampus. That experiment differed from most previous reversal experiments in that the discriminative stimuli were olfactory rather than spatial or visual, and 3 discriminations were given prior to the reversal of the third discrimination, rather than a single discrimination. The present experiment was designed to determine the generality of the results obtained in the olfactory experiment. Rats with partial lesions of the FFX and operated controls were tested on a series of 3 Go, No-go spatial discriminations, a reversal of the third discrimination, and 4 subsequent discriminations, in that order. Control rats acquired a learning set in the first 3 discriminations, reaching criterion on the third discrimination in fewer trials than they took on the first discrimination. Their choice accuracy was not significantly affected by the reversal and discrimination performance reached an asymptotic level after the reversal. Rats with FFX lesions also acquired a learning set in the first 3 discriminations, but they consistently took longer than control rats to learn each of the 7 discriminations. These rats were especially impaired on the reversal. These results contrast markedly with those obtained when a similar procedure was used with olfactory discriminations. Identification of the variables responsible for these differences should help distinguish those behaviors that require hippocampal function from those that do not.

Acetylcholinesterase↗
PubMedDate not supplied

Purification and characterization of astrocyte-secreted apolipoprotein E and J-containing lipoproteins from wild-type and human apoE transgenic mice.

The varepsilon4 allele of apolipoprotein E (apoE) is a genetic risk factor for Alzheimer's disease (AD). In order to gain a better understanding of the molecular mechanisms by which apoE and possibly other apolipoproteins produced in the central nervous system (CNS) influence AD pathogenesis, we have purified and characterized the two most abundant apolipoproteins produced in the CNS, apoE and apoJ. We purified apoE and apoJ from primary cultures of mouse astrocytes, which were derived from transgenic mice expressing human apoE isoforms in the absence of mouse apoE. Utilizing antibody affinity columns, we were able to purify both human apoE3 and apoE4, as well as mouse apoJ-containing lipoproteins. Astrocyte-secreted human apoE was present in high density-like lipoproteins of three predominant sizes ranging from 8 to 15 nm in diameter. Mouse apoJ was in particles between 10 and 17 nm in diameter with a peak size range of approximately 11 nm. ApoE and apoJ were in distinct lipoproteins. Utilization of quick-freeze, deep-etch electron microscopy revealed the apoE particles were discs while the apoJ particles were smaller and more irregular in appearance. The lipid composition of apoE particles was very different from those containing apoJ. ApoE-particles contained a similar mass of apoE and lipid, with cholesterol and phospholipid being about equal in mass per particle. ApoJ-particles were relatively lipid poor (three parts protein, one part lipid), with phospholipids being much more abundant than cholesterol. Detailed characterization of phospholipid composition by electrospray ionization mass spectrometry analysis revealed ethanolamine glycerophospholipids to be the most abundant phospholipid present in both apoE and apoJ particles. Analysis of cerebrospinal fluid from apoE3 and apoE4 transgenic mice revealed that human and mouse apoE were in particles the same size as those secreted by astrocytes. Further use of physiological preparations of CNS-derived lipoproteins may allow for a detailed understanding of the role of these molecules in the normal brain and in diseases such as AD.

Animals↗
PubMedDate not supplied

Surviving home healthcare: one agency's experience.

Too often, home health agencies are narrow and territorial in their outlook. Ideas need to be sought, developed, and acted upon after all the risks have been weighed. If home health agencies don't manage themselves as businesses, then they will be out of business and not able to serve anyone.

Home Care Services↗