Raymond D. Lund - US grants

Recent studies have identified pathways in the developing visual system which, as development proceeds, either disappear completely or become diminished in their area of origin or termination. In this proposal, we will investigate how some of these transient projections develop and the mechanisms whereby they are maintained or lost. Attention will be directed in part to the development of the corpus callosum of rats and tree shrews. We are interested to know how the projection becomes focussed in development at the 17/18(a) border and why after manipulations such as optic nerve or tract section, the pathway shows an abnormal distribution. It is hoped furthermore that by concentrating on the development of the 17/18 border region, it will be possible to approach the important issue of how the heterogeneities characteristic of the mature cortex are determined in development. Finally we hope by placing transplanted tissue along the course of pathways which normally disappear to maintain them, addiding credence to the view that the presence of an appropriate target region is an important requirement for preserving a projection. From these experiments, we hope to gain insight into factors which influence how the precise connections, forming the substrates of normal visual function, are established. In addition we hope to define certain conditions under which the normal developmental process may be disturbed.

The proposed work continues an investigation using embryonic retinal transplantation techniques in rodents to examine how functioning neural circuits, that form the substrates for vision, develop and can be modified in maturity. The connections made by retinal grafts will be examined in detail and correlated with functional responses. These responses will be recorded both physiologically and behaviorally (using the pupillary reflex and a conditioned suppression paradigm). Besides defining the optimal conditions for graft function, we plan to use the preparations for examining sprouting of graft connections after injury to the adult host visual system. Five interrelated studies are proposed. The first will examine the substrates of host pupillary reflex driven by photic stimulation of a retinal transplant; the second will correlate physiological responsiveness of the host brain to transplant stimulation and the anatomical correlates; the third will examine an adult sprouting situation; the fourth will study whether a retinal transplant can mediate a conditioned suppression response to light and the fifth study will use multiple transplants to create circuits. The work should provide fundamental understanding of the minimal substrates for visual function and further insight into the regenerative and plastic capacity of the visual system after damage either early in development or at maturity. It also explores transplantation strategies that might in time lead to ways of correcting visual deficits in humans.

An antibody has been identified to a cell surface protein, designated M6, which blocks neurite outgrowth in vitro. Studies on the developing optic nerve in vivo indicate that M6 is expressed only up to a certain critical period of development. The biological function in vitro and the pattern of expression in vivo suggested that by knowing more about the behavior of the antigen and its antibody, we would gain further insight into why optic axons stop growing during development and why they generally fail to regenerate after injury. Additional results collected over the past year confirm this expectation and indicate that a substantial investigation of the antigen and its antibody centered on the primary optic pathway is justified. This proposal focuses on three areas: (1) We wish to examine the hypothesis that the antigen is involved in vivo with the processes of axonal growth and cell migration. (2) We wish to use the antibody to arrest irreversibly both cell migration and axonal outgrowth as a tool for studying various interdependencies occurring during development and after injury. (3) We wish to examine how the context in which a neuron develops may regulate the expression of the M6 antigen and as a result modify neurite outgrowth and cell migration patterns. Nine individual experiments are proposed, each of which addresses one or more of the three areas raised. Collectively, they should provide insight into the behavior in vivo of an antigen which appears to regulate neurite extension by a molecular mechanism which is under investigation in parallel studies. They will also exploit the use of the antibody both as a probe and a label for investigating plasticity and regeneration of the visual system.

Two previous International Symposia on Neural Transplantation have been held, the first near Lund, Sweden in 1985 and the second in Rochester, New York in 1987. Funds are requested for travel and associated expenses for U.S. participants to attend a third symposium to be held in Cambridge, England, August 6-11, 1989. While the first meeting brought together for the first time those investigators involved in transplantation research, the second focused particularly on the application of implants to neurodegenerative diseases and was the springboard for a substantial commitment to examining whether adrenal medulla grafts might provide a suitable therapy for Parkinson's disease. The third meeting will have several missions. It will review clinical progress. It will examine the further development of suitable animal models for particular diseases. Most important, it will devote particular attention to the use of implants to understand fundamental mechanisms associated with development and regenerative growth of neural processes. Most important will be a consideration of the recent advances in cell and molecular biology (including the use of transformed cells as an alternative to the use of fetal tissue) and in neuroimmunology. The meeting will be structured to ensure a maximum of discussion time, a feature the organizing committee feels is necessary in this fast-growing field.

It is planned to limit the deleterious consequences of retinal dystrophy in RCS rats in transgenic rats with human rhodopsin mutation by introducing cells to the subretinal space. There are five specific aims. 1) To study efficacy of alternatives to fresh RPE cells in preventing photoreceptor degeneration resulting from a defect in the photoreceptors themselves or in the adjacent RPE. Immortalized human RPE cell lines and Schwann cells will be used as donor cells, transplanting them either to RCS rats or to transgenic rats with mutations in the rhodopsin gene causing a moderate rate of degeneration. 2) To examine how grafted cells settle in the subretinal space, how they interrelate with adjacent cells and how long they survive. 3) To examine how numbers and distribution of grafted cells correspond with the degree of photoreceptor rescue. 4) To examine how photoreceptor rescue correlates with spared central visual function. 5) To use grafted cells as vectors for introduced molecules. The purpose of the work is twofold. First, it will provide essential background data necessary in assessing the feasibility of developing a transplantation approach for patients with retinal degenerative diseases such as retinitis pigmentosa and age related macular degeneration. Second, it will also approach the basic biology of degeneration and repair, which in itself will provide insights into factors that may influence photoreceptor survival and perhaps obviate the need for transplantation as a potential therapy.

ABSTRACT NOT PROVIDED

ABSTRACT NOT PROVIDED