Individual neurons in the leech can regenerate severed axons to reconnect with particular neurons that are their normal synaptic targets. In many animal species injured adult neurons may at first glance seem to revert to their developmental state, but there can be important differences between adult repair and embryonic development, including differences in synaptic function. Taking advantage of identifiable cells and cell types in the leech, the proposed project addresses the questions: (1) is axon sprouting controlled by certain cells and cellular interactions, (2) are particular molecules such as leech """"""""laminin"""""""" and surface markers on mechanosensory neurons associated with directed growth and repair, (3) do microglia play a critical role in regeneration, (4) can protein synthesis and transport in short axon systems, particularly during regeneration, be studied by injection of synthetic mRNA's, (5) how does cell structure determine synaptic function and connectivity, and (6) do mechanisms that produce successful repair recapitulate those that guide embryonic development? The methodology will include electrophysiological recording and intracellular injection of markers for subsequent light and electron microscopic examination. Growing axons and migrating cells labelled with fluorescent markers will be tracked in living preparations with the aid of low-light video enhancement. Properties of pathways and surfaces of particular cells that bind cell-specific ligands including monoclonal antibodies will be examined with electron microscopy. Identified neurons and axons will be injected with mRNA synthesized in vitro that codes for cytoplasmic and integral membrane proteins. Single cells will be killed with intracellular injection of proteases or focally lesioned with an argon laser and fluorescent dyes. 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 cells will be studied during development and compared with regeneration. Understanding mechanisms for development and 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 #
2R01NS020607-07
Application #
3401053
Study Section
Neurology B Subcommittee 1 (NEUB)
Project Start
1983-09-01
Project End
1992-07-31
Budget Start
1989-08-01
Budget End
1990-07-31
Support Year
7
Fiscal Year
1989
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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