A major problem in neurobiology concerns the mechanisms by which damaged neurons may re-grow axons and form selective connections to restore function. We propose to test the role of migrating microglia in successful axonal regeneration that follows injury to the leech nervous system. Migration of microglia occurs promptly, accounts for the increase in cell numbers at the lesion, and appears influenced by nitric oxide synthase activity, which is rapidly up regulated at the lesion. Microglial migration is also affected by applied electric fields of a size consistent with injury currents we measure at the lesion. Evidently microglia deposit laminin, a component of the extracellular matrix that promotes axon growth. The leech is particularly advantageous for these studies because (1) its ganglia contain identifiable neurons capable of regenerating specific connections following axotomy, (2) individual microglia can be tracked and their movements charted minute by minute, and (3) adult and embryonic nervous systems can be manipulated and examined both in vivo and in vitro. Experiments that interfere with and block accumulation of microglia at injury sites will test the role of microglia in sprouting and regeneration. Immunocytochemistry has shown abundant laminin transiently in the embryonic leech nervous system along axon pathways. Following injury to the adult nervous system, laminin reappears (first in patches at the lesion, later in streaks) in advance of axons. Whether the microglia that migrate toward the site of the lesion produce the laminin, as in vitro, will be determined using antibodies and in situ hybridization with our riboprobes for laminin. We will determine whether the streaks of laminin, which may guide regenerating axons, mark the paths of migrating microglial cells; fluorescently labeled microglia will be tracked in living preparations using low-light video microscopy. Alterations of nitric oxide levels and its synthesis and of electric fields such as those generated by the lesion will determine the actions of nitric oxide and fields in regulating microglial migration. These studies will clarify the roles of microglia and of laminin in axonal regeneration following injury, and may suggest strategies for achieving equally successful axonal repair in the mammalian nervous system.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS037025-03
Application #
6393878
Study Section
Special Emphasis Panel (ZRG1-MDCN-7 (01))
Program Officer
Chiu, Arlene Y
Project Start
1999-07-18
Project End
2003-06-30
Budget Start
2001-07-01
Budget End
2002-06-30
Support Year
3
Fiscal Year
2001
Total Cost
$253,482
Indirect Cost
Name
University of Miami School of Medicine
Department
Physiology
Type
Schools of Medicine
DUNS #
City
Miami
State
FL
Country
United States
Zip Code
33146
Samuels, Stuart E; Lipitz, Jeffrey B; Wang, Junjie et al. (2013) Arachidonic acid closes innexin/pannexin channels and thereby inhibits microglia cell movement to a nerve injury. Dev Neurobiol 73:621-31
Duan, Yuanli; Sahley, Christie L; Muller, Kenneth J (2009) ATP and NO dually control migration of microglia to nerve lesions. Dev Neurobiol 69:60-72
Bao, Li; Samuels, Stuart; Locovei, Silviu et al. (2007) Innexins form two types of channels. FEBS Lett 581:5703-8
Ngu, Emmanuel Mbaku; Sahley, Christie L; Muller, Kenneth J (2007) Reduced axon sprouting after treatment that diminishes microglia accumulation at lesions in the leech CNS. J Comp Neurol 503:101-9
Kumar, S M; Porterfield, D M; Muller, K J et al. (2001) Nerve injury induces a rapid efflux of nitric oxide (NO) detected with a novel NO microsensor. J Neurosci 21:215-20
Chen, A; Kumar, S M; Sahley, C L et al. (2000) Nitric oxide influences injury-induced microglial migration and accumulation in the leech CNS. J Neurosci 20:1036-43