Individual neurons in the leech can regenerate severed axons to reconnect with particular neurons that are their normal synaptic targets. Repair occurs in stages, from initial sprouting of the injured axon and growth that may be along selected pathways to recognition of the target, synapse formation, and cessation of growth. The proposed project addresses the questions: (1) what cellular interactions and capabilities control sprouting, (2) which cells and extracellular elements along the pathway might stimulate or direct growth, (3) are inappropriate as well as appropriate contacts made, (4) how do the new synapses compare with the old in distribution and function, (5) why do axons stop growing, and (6) what features of axon growth and synapse formation during development are revived during regeneration? The methodology will include intracellular and extracellular electrophysiological recording and intracellular injection of markers for subsequent light and electron microscopic examination. Growth of axons, filled with fluorescent markers, will be tracked in living preparations, in some cases maintained in culture medium. Properties of pathways and surfaces of particular cells will be examined, using electron microscopy, with cell-specific ligands including monoclonal antibodies and with freeze-fracture. Single cells can be killed with intracellular injection of proteases or focally lesioned using dyes that produce photodynamic damage. The morphology of certain cells and the complex patterns of normal and regenerated synaptic contacts between them will be reconstructed with a computer. Growth of individual neurons will be studied during development and compared with regeneration. An understanding of the mechanisms for accurate regeneration in the leech central nervous system might suggest ways that nerve regeneration in higher animals including humans could be made more reliable and precise.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS020607-06
Application #
3401059
Study Section
Neurology B Subcommittee 1 (NEUB)
Project Start
1983-09-01
Project End
1989-07-31
Budget Start
1988-08-01
Budget End
1989-07-31
Support Year
6
Fiscal Year
1988
Total Cost
Indirect Cost
Name
University of Miami School of Medicine
Department
Type
Schools of Medicine
DUNS #
City
Miami
State
FL
Country
United States
Zip Code
33101
Sahley, C L; Modney, B K; Boulis, N M et al. (1994) The S cell: an interneuron essential for sensitization and full dishabituation of leech shortening. J Neurosci 14:6715-21
Masuda-Nakagawa, L M; Muller, K J; Nicholls, J G (1993) Axonal sprouting and laminin appearance after destruction of glial sheaths. Proc Natl Acad Sci U S A 90:4966-70
Gu, X N; Muller, K J; Young, S R (1991) Synaptic integration at a sensory-motor reflex in the leech. J Physiol 441:733-54
Muller, K J; Gu, X N (1991) Unequal competition between axons for neuronal targets. Philos Trans R Soc Lond B Biol Sci 331:315-22
Gu, X N (1991) Effect of conduction block at axon bifurcations on synaptic transmission to different postsynaptic neurones in the leech. J Physiol 441:755-78
Masuda-Nakagawa, L M; Muller, K J; Nicholls, J G (1990) Accumulation of laminin and microglial cells at sites of injury and regeneration in the central nervous system of the leech. Proc Biol Sci 241:201-6
McGlade-McCulloh, E; Muller, K J; Zipser, B (1990) Expression of surface glycoproteins early in leech neural development. J Comp Neurol 299:123-31
Gu, X N; Muller, K J (1990) Competitive interactions between neurons making axosomatic contacts in the leech. J Neurosci 10:3814-22
Gu, X N; Macagno, E R; Muller, K J (1989) Laser microbeam axotomy and conduction block show that electrical transmission at a central synapse is distributed at multiple contacts. J Neurobiol 20:422-34
McGlade-McCulloh, E; Morrissey, A M; Norona, F et al. (1989) Individual microglia move rapidly and directly to nerve lesions in the leech central nervous system. Proc Natl Acad Sci U S A 86:1093-7

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