1985 — 1996 |
Meyer, Ronald L |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Growth of Retinotectal Connections @ University of California Irvine
In adult goldfish, the regenerative growth of severed optic axons back to the optic tectum will be used as a model system for the normal development of selective axon connections. In following leads developed from our previous work, retina, tectum or optic pathways are to be variously altered surgically, and the response of regenerating fibers and the resulting retinotectal projection systematically measured. The methods include an eye-in-water electrophysiological recording technique for accurately mapping the terminal arborizations of optic fibers and various anatomical procedures in particular autoradiography and HRP backfilling. These methods will be applied toward further analysis of the following: (1) the inhomogeneities and asymmetries in the reorganized retinotectal projection which follows various retinal and tectal ablations, (2) the segregation of fibers which have been surgically deflected into the wrong, ispsilateral tectum from the optic fibers which normally innervate this tectum, (3) the disorderly projection that results when only a small number of fibers are permitted to innervate the tectum and (4) aberrations in the pathways taken by regenerating fibers. In addition, thymidine labelling and autoradiography as well as cell counting will be aimed at further study of (5) the continual addition of new cells to the retina and tectum of normal juvenile and adult goldfish.
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1989 — 1991 |
Meyer, Ronald L |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Retinal Explants From the Adult @ University of California Irvine
In adult mammals, severed optic axons, like most long projecting CNS axons, do not normally regenerate with the CNS so that axonal damage such as following spinal cord injury results in permanent deficits. However, it has recently been shown that optic fibers will regenerate when retina is placed in culture and that this regeneration is dramatically accelerated by prior optic nerve damage (Meyer & Miotke, 1987). This proposal will use such retinal explants from adult mice as a model to study the regenerative response of retinal fibers and to investigate cellular interactions and other factors that may be responsible for the lack of regeneration in the CNS. There are three major aims. The first is to optimize the culture conditions. Different gas mixtures, media, serum concentrations, additives, and methods of maintaining the explants will be explored. In addition, an attempt will be made to develop serum free culture conditions. The second aim will be to further characterize the regenerative response. The number of ganglion cells that survive at short and long culture periods will be counted. The effect of the time and position of the nerve injury prior to explanation will be explored. Elongation rate and growth distance will be measured for early and late explants. And the effect of explant size and shape will be explored. The third aim is to confront growing optic neurites with several conditions that may be relevant to their environment. These include pieces of optic nerve from adults or neonates, pieces of sciatic nerve and different substrates of extracellular matrix including laminin, collagen, and fibronectin.
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1994 — 1996 |
Meyer, Ronald L |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Retinal Explants @ University of California Irvine
During development, mammalian neurons can extend long axonal process, but with maturation, lose the capacity to express this growth within the central nervous system (CNS). Consequently, when severed, adult CNS axons fail to regenerate resulting in permanent dysfunction. Most recent work has focused on the possibility that glia mature so as to prevent the regeneration of CNS axons. In contrast, these proposed studies will explore the possibility that neurons themselves mature so as to become unable to grow within the CNS environment even though they retain considerable intrinsic capacity for growth. This possibility is supported by preliminary evidence showing that with maturation axons undergo several functional and molecular changes that likely compromise their ability to grow within a glial environment. - The proposed studies make extensive use of the in vitro retinal explant system developed in this laboratory to elicit regenerative growth of adult optic axons in tissue culture. This system will be used to compare the cellular function and molecular constitution of regenerating adult optic axons with growing embryonic axons. Three areas relevant to regeneration will be investigated. The first is cell surface molecules involved in the regulation neurite growth on astrocytes. Specifically, the presence and function of integrins, N-cadherin, N-CAM and Thy-1 will be compared in adult and embryonic optic fibers. The second area is intracellular molecules that are associated with and thought to be required for axons growth. One in particular, GAP-43, will be assayed for its expression in adult axons and for possible down-regulation by glia. The third area is cellular interactions between optic fibers and glia. The possibility will be tested that adult optic axons, in marked contrast to embryonic axons, are deficient in their ability to grow over astroglia in culture. Initial characterization of the basis of this differential interaction will be explored. These studies will identify differences between adult and embryonic growing axons that are important for understanding regenerative failure in the adult CNS and for developing future therapies for promoting axonal regeneration.
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2002 — 2004 |
Meyer, Ronald L |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Synaptic Homeostasis in the Visual System @ University of California Irvine
[unreadable] DESCRIPTION (provided by applicant): Recent theoretical and experimental work suggest that neurons need to regulate their total synaptic current and maintain an optimal activity level in order to remain responsive to continually variable input and function properly within their parent neural networks. The visual system is particularly remarkable in this regard in that it can maintain responsiveness over an enormous range of stimuli and under pathological conditions such as glaucoma where many elements of the network are damaged. How this homeostasis is maintained remains an important outstanding question. The present study is focused on a recently discovered phenomenon, Silenced Induced Potentiation (SIP), in the visual system of the goldfish. It is a large (80 percent) increase in optic synaptic efficiency that is induced by the loss of spontaneous activity in optic fibers. SIP occurs within minutes and is a strong candidate to be the first example of a rapid homeostatic response and one of the first to be seen in situ. [unreadable] [unreadable] In vivo studies on intact animals are proposed to further characterize and analyze this potentiation. These will examine its time course, longevity, localization and reversibility. Pharmacological methods will be used to analyze what transmitter systems might be responsible for regulating SIP and whether protein kinases and protein synthesis are required for its maintenance. The relationship between SIP and spontaneous postsynaptic activity will also be explored. [unreadable] [unreadable] These studies will document and analyze a new form of synaptic plasticity that may not only be important for normal function but might also underlie functional recovery following neuronal injury and disease.
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2003 — 2006 |
Meyer, Ronald L |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Reinnervation Following Sparse Regeneration @ University of California Irvine
DESCRIPTION (provided by applicant): When the optic nerve of an adult goldfish is severed, optic fibers will grow back to the optic tectum, their primary termination site, to reestablish optic connections. With time, the retinotopic precision of this regenerated projection becomes indistinguishable from normal. In adult mammals, optic and other CNS axons do not normally regenerate. However, efforts to promote regeneration have met with limited success. Regeneration past the injury zone, formation of connections and restoration of some function have been achieved. Unfortunately, the number of fibers that regenerate in mammals are relatively sparse. The consequences of having low numbers of regenerating fibers on their capacity to reform accurate connections is largely unknown. To explore this question, the present study asks how well optic fibers in the goldfish reform ordered connections when their number is greatly reduced. The approach will utilize a surgical method developed in this laboratory wherein a controlled number of fibers ranging from a few percent to 40-50 percent of retina will be redirected from one tectum into the opposite host tectum. The host tectum will be denervated of optic fibers by removing its contralateral eye at various times prior to this "deflection." The formation of the low density projection will be analyzed by anatomical, in vivo imaging and electrophysiological methods.
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2012 — 2013 |
Meyer, Ronald L |
R03Activity Code Description: To provide research support specifically limited in time and amount for studies in categorical program areas. Small grants provide flexibility for initiating studies which are generally for preliminary short-term projects and are non-renewable. |
In Vivo Imaging of Cns Neurons in the Adult Zebrafish @ University of California-Irvine
DESCRIPTION (provided by applicant): Animal models of human disease that exploit the power of genetics offer a powerful tool to understand and cure diseases. One of the most widely used genetic animal models is the zebrafish. However, its use has largely been restricted to the analysis of development. Relatively few studies have utilized the mature fish even though many human diseases occur after development. For neurological studies, it is important to be able to analyze neuronal function in vivo. Imaging and electrophysiological recording are the predominant methods to do so. Unfortunately, there are essentially no studies on genetically altered adult zebrafish using these methods. These proposed studies will develop the technology to enable in vivo imaging as well as electrophysiological recording from the brain of living adult zebrafish and provide initial results using in vivo imaging. There are 4 goals: 1) Develop a stereotactic style head holder to immobilize the cranium and protocols to maintain the fish for several hours. This will include electrophysiological recording of evoked unit activit in tectum to demonstrate stability and physiological viability. 2) Using available zebrafish lines, GFP labeled optic fibers or Kaede labeled neurons will be imaged in the tectum of adult fish through a cranial opening for several hours using a 2 photon laser scanning microscope. 3) Generate zebrafish that are transparent as adults that have fluorescent optic fibers or tectal neurons. 4) Image these transparent adult zebrafish through the closed cranium using 2 photon microscopy and revive these fish for second imaging session. This project will demonstrate the feasibility of studying real time structural plasticity in living adult zebrafish thereby opening u a new animal model for these studies. This new model can take advantage of a large genetic base, an extensive background of developmental studies and a system that is far less costly than mice. Since adult fish show robust recovery of function following CNS injuries, planned future work using this model to study plasticity may provide insight into understanding and stimulating recovery in the human following CNS injuries and diseases. PUBLIC HEALTH RELEVANCE: This project will develop the technology to look at individual nerve cells inside of the brain of living zebrafish. This will enable researchers to see how nerve cells respond to damaged and to use the power of genetics to understand the mechanisms of this response. This could lead to new treatments forbrain damage.
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